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THE ANATOMICAL RECORD 254:508–520 (1999)
Postnatal Differentiation of the
Ductus Deferens, Tail of the
Epididymis, and Distal Body of the
Epididymis in Goats Occurs
Independently of Rete Testis Fluid
HARI O. GOYAL,1* CAROL S. WILLIAMS,1 MOHAMMED K. KHALIL,1
MADAN M. VIG,2 AND M.A. MALONEY3
1Department of Biomedical Sciences, Tuskegee University, Tuskegee, Alabama 36088
2Department of Clinical Sciences, Tuskegee University, Tuskegee, Alabama 36088
3Department of Agricultural Sciences, Tuskegee University, Tuskegee, Alabama 36088
ABSTRACT
Observations from extratesticular rete-ligated, mature goats indicated
that epithelial morphology in the tail of the epididymis can be maintained
without any input from testicular fluid (Goyal et al., Acta Anat., 1994;150:
127–135). Hence, the objective of this study was to determine whether the
tail of the epididymis and/or other regions of the male excurrent ducts can
differentiate prior to the appearance of lumen in the seminiferous tubules,
which is an indicator for the onset of seminiferous tubular fluid secretion.
Based on age and scrotal circumference (SC), 20 male goats were divided
into four groups of five animals each: 1–4 weeks (SC, 6.5–7.5 cm), 7–10
weeks (SC, 8.5–11.0 cm), 12–15 weeks (SC, 11.0–14.0 cm), and 15–25 weeks
(SC, 16.0–19.0 cm). Tissues were collected from the testis, six regions of the
epididymis (proximal, middle and distal head; proximal and distal body; and
tail), and the ductus deferens, and were processed for light and electron
microscopic examination. Changes in epithelial height and cytological
features associated with absorption (microvilli, pinocytotic and coated
vesicles) and protein secretion (RER, Golgi body) were used as markers for
differentiation. Differentiation of all of these features was comparable to
that observed in the 15–25-week-old animals in the ductus deferens by ⱖ1
week, in the tail of the epididymis by ⱖ7 weeks, in the distal body of the
epididymis by ⱖ12 weeks, and in the proximal body of the epididymis and all
three regions of the head of the epididymis by ⱖ15 weeks. Seminiferous
tubules developed lumens between 12 and 15 weeks. In conclusion, epithelial differentiation in the ductus deferens, tail of the epididymis, and distal
body of the epididymis follows a time-dependent, spatial, ascending order
and is achieved before lumen formation in the seminiferous tubules. Conversely,
epithelial differentiation in all three regions of the head and the proximal body of
the epididymis occurs simultaneously and after lumen formation in the seminiferous tubules. Anat Rec 254:508–520, 1999. r 1999 Wiley-Liss, Inc.
Key words: postnatal; epididymis; ductus deferens; differentiation
The mammalian epididymis is a long tube where sperm
acquire the potential to move in a forward direction and
fertilize ova (Bedford, 1975; Orgebin-Crist et al., 1975).
Grossly, the epididymis in most species can be divided into
three regions—head, body and tail—although further subdivisions have been described in virtually all species
(Glover and Nicander, 1971; Hamilton, 1975). While the
r 1999 WILEY-LISS, INC.
Grant sponsor: NIH; Grant number: MBRS-5-S06-GM08091;
Grant sponsor: USDA; Grant number: CSR-EES-ALX-TU-CTIF;
Grant sponsor: NIH; Grant number: RCMI-5-G12RRO3059–08.
*Correspondence to: H.O. Goyal, Department of Biomedical
Sciences, School of Veterinary Medicine, Tuskegee University,
Tuskegee, AL 36088. E-mail: goyalho@acd.tusk.edu
Received 19 September 1998; Accepted 18 November 1998
POSTNATAL DIFFERENTIATION OF THE EPIDIDYMIS
TABLE 1. Age, scrotal circumference (SC),
and status of the seminiferous epithelium
of animals used in the study
Age
(weeks)
SC
(cm)
Status of the
seminiferous epithelium
I
1
6.5
I
I
I
I
II
II
II
II
II
1
1
3
4
7
8
8
9
10
7.0
7.5
7.0
7.5
9.0
9.0
8.5
10.0
11.0
III
12
11.0
III
12
11.5
III
13
12.5
III
III
14
15
12.0
14.0
IV
15
16.0
IV
19
16.5
IV
IV
IV
21
23
25
18.5
17.5
19.0
Sertoli cells and gonocytes,
lumen absent
Same as above
Same as above
Same as above
Same as above
Same as above
Same as above
Same as above
Same as above
Occasional spermatocytes,
lumen absent
Spermatocytes more frequent,
lumen absent
Same as above, but lumen present in some tubules
Spermatocytes and lumens
present in most tubules
Same as above
Round spermatids, few elongated spermatids
Spermatogenesis established
in most tubules
Spermatogenesis established
in all tubules
Same as above
Same as above
Same as above
Group
head and body are involved in sperm maturation, the tail
is associated with sperm storage (Glover and Nicander,
1971; Cooper, 1986).
Androgens play many important roles in the epididymis,
including prenatal and postnatal differentiation, absorption of testicular fluid, maturation of sperm, and secretion
of proteins (Brooks, 1987; Robaire and Hermo, 1988;
Hinton and Palladino, 1995). Experiments involving orchidectomy, testosterone substitution, and ligation of the
efferent ductules or extratesticular rete indicate regionspecific, differential epididymal responses to androgen
deprivation in adult animals (Fawcett and Hoffer, 1979;
Abe and Takano, 1989a,b; Robaire and Viger, 1995).
Whereas the structure of the tail of the epididymis can be
Fig. 1. Approximate boundaries of different regions of the epididymis
in adult goats. Regions I, II, and III constitute the proximal, middle, and
distal head, respectively; regions IVa and IVb, the proximal and distal
body, respectively; and region V, the tail. ED, efferent ductules; DD,
ductus deferens.
Fig. 2. Epididymides from a 4-week-old goat. The head (h), body (b),
and tail (t) regions are identified. Arrowheads demarcate the boundary
between the descending and ascending limbs of the head. Note that the
tail of the epididymis is as large as or larger than the head of the
epididymis at this stage. 3⫻.
Fig. 3. A longitudinal section of the descending limb of the head of the
epididymis at 1 week. Arrows demarcate the boundary between the
efferent ductules (ED) and the epididymis (EP). Note that except for a few
epididymal tubules located at its distal end, the entire descending limb is
occupied by the efferent ductules. Epididymal tubules, compared to the
efferent ductules, have a thicker muscle coat and a larger luminal
diameter. 31⫻.
509
maintained with circulating androgens alone, that of the
head of the epididymis is dependent upon luminal androgens and/or other factors present in the rete testis fluid
(Fawcett and Hoffer, 1979; Goyal et al., 1994). These
results raise a hypothesis that the tail of the epididymis
and/or other regions of the male reproductive tract may
postnatally mature in the absence of rete testis fluid.
To test the hypothesis, we propose to study postnatal
light and electron microscopic differentiation of different
regions of the male reproductive tract in goats and determine which regions complete their differentiation prior to
510
GOYAL ET AL.
and the rat ductus deferens (Francavilla et. al., 1987).
Similar studies in large animals are few and limited to
light microscopic observations of the epididymis in pigs
(Wrobel and Fallenbacher, 1974), buffaloes (Goyal and
Dhingra, 1975), and rams (Nilnophakoon, 1978).
In the present study, goats are used as an experimental
animal model for large species because, morphologically,
the reproductive tract of male goats, rams, and bulls is
essentially similar (Amann, 1987; Goyal, 1985; Goyal and
Williams, 1991). Among these three species, male goats are
preferred because, they, unlike rams, are non-seasonal
(Skalet et al., 1988) and, unlike bulls, are inexpensive and
easier to handle for surgical maneuvers.
MATERIALS AND METHODS
Animals
Twenty Nubian bucks, 1 to 25 weeks of age and with 6.5
to 19.0 cm of SC, were divided into four groups of five
animals each, depending upon the age and SC of animals
(Table 1). All animals were kept in a covered shelter,
allowed to walk freely, and given hay and water (except
1–8-week-old kids, which were bottle-fed milk) ad libitum.
A general management schedule for deworming and disease prevention was followed.
Tissues and Fixation
Fig. 4. A comparison of regional differences in mean measurements
for the epithelial height (EH), luminal diameter (LD), and tubular diameter
(TD) among different age groups. Notable observations are significant
(P ⱕ 0.05) increases in EH, LD, and TD in the tail (V) of the epididymis
between groups I and II; significant (P ⱕ 0.05) increases in EH and LD in
the distal body (IVb) of the epididymis between groups II and III; and
significant (P ⱕ 0.05) increases in EH, LD, and TD in the proximal head (I),
middle head (II), distal head (III), and proximal body (IVa) of the
epididymis between groups III and IV.
lumen formation in the seminiferous tubules, an indicator
for the onset of seminiferous tubular fluid secretion.
Studies involving temporal differentiation of the male
reproductive tract at the light and/or electron microscopic
levels have concentrated mainly in laboratory animals,
including the rat epididymis (Reid, 1959; Leeson and
Leeson, 1964; Flickinger, 1969; Sun and Flickinger, 1979;
Francavilla et. al., 1987), the mouse epididymis (Takano,
1980; Abou-Haila and Fain-Maurel, 1985; Taggart et al.,
1993), the rabbit epididymis (Leeson and Leeson, 1970),
Tissues were collected from the testis, six regions of the
epididymis (proximal, middle and distal head; proximal
and distal body; and tail), and the ductus deferens under
general anesthesia (Fig. 1). Tissues from one side of the
animal were perfusion-fixed with Bouin’s fluid, and those
from the other side were either immersion-fixed or perfusion-fixed (two animals in each group) with 5% glutaraldehyde in 0.2 M s-collidine buffer at pH 7.4. Since it was
difficult at the gross level to distinguish between the
proximal head of the epididymis and the efferent ductules
in young animals, the entire descending limb of the head of
the epididymis was collected (note: efferent ductules are
located in the descending limb). Tissues were further fixed
in Bouin’s fluid for 24 hr using slow agitation. They were
cleared of Bouin’s fluid overnight in 70% alcohol, dehydrated in alcohol, cleared in xylene, and embedded in
paraffin. Sections at 5–6 µm thickness were collected and
stained with hematoxylin and eosin or periodic acid-Schiff
(PAS).
Fig. 5. A–F: Light micrographs of paraffin sections from the proximal
head (A), middle head (B), distal head (C), proximal body (D), distal body
(E), and tail (F) of the epididymis in group I animals. Epithelium is
undifferentiated and contains only principal cells (p) in all regions, except
in the tail of the epididymis where lymphocytes were also occasionally
observed (not shown here). A–F, 360⫻.
Fig. 6. A: A low power electron micrograph of the epithelium from the
distal head of the epididymis at one week. Principal cells (p) are the only
cell type present in the epithelium. Most cell organelles, except for some
ribosomes and mitochondria, are poorly developed. Lucent areas (stars)
containing myelin-like figures may have resulted from a fixation artifact. B:
A high power electron micrograph from the apical area of principal cells.
Note the presence of a few, short microvilli, but endocytotic features, such
as, pinocytotic vesicles and canaliculi are absent. C: Light micrograph of a
semithin section of the epithelium from an area similar to that shown in A.
D: An electron micrograph showing a junctional complex, zonula occludens (ZO), zonula adherens (ZA), and desmosome (DE), between two
principal cells in the epithelium of the middle head of the epididymis at 1
week. A, 7,400⫻; B, 17,800⫻; C, 720⫻; D, 15,500⫻.
POSTNATAL DIFFERENTIATION OF THE EPIDIDYMIS
Figures 5 and 6.
511
512
GOYAL ET AL.
Figures 7 and 8.
POSTNATAL DIFFERENTIATION OF THE EPIDIDYMIS
In the case of glutaraldehyde fixation, 1-mm thick tissue
slices from six regions of the epididymis and the ductus
deferens were fixed (or further fixed in the case of perfusion fixation) with 5% glutaraldehyde in 0.2 M s-collidine
buffer for 3–6 hr, postfixed with 2% osmium tetroxide in
0.2 M s-collidine buffer, dehydrated in ethanol, cleared in
propylene oxide, and embedded in Epon. Sections 1 µm
thick were stained with 1% toluidine blue in 1% borax and
examined with a light microscope. Ultrathin sections
exhibiting silver to gold colors were stained with uranyl
acetate and lead citrate and examined with a Philips 201
electron microscope at 60 kV.
Histoquantitative Observations
Using a computer-assisted image analysis system, histoquantitative data were collected from six regions of the
epididymis. Five intermittent sections from each region of
each animal were examined. Five tubules with a round
profile from each section were randomly analyzed for
epithelial height, luminal diameter, and tubular diameter
(basal lamina to basal lamina, smooth muscle cells were
not included). The data were analyzed by two-way analysis
of variance for evidence of significant differences among
age groups (P ⱕ 0.05).
RESULTS
Testis
Developmental changes in the seminiferous epithelium
of the goat testis are briefly described here for the purpose
of comparison with those of the epididymis and the ductus
deferens. Seminiferous epithelium contained only Sertoli
cells and gonocytes from 1 to 9 weeks (SC, ⱕ10.0 cm).
Primary spermatocytes were occasionally found at 10
weeks (SC, 11.0 cm), but were frequently encountered at
ⱖ13 weeks (SC, ⱖ12.5 cm). Seminiferous epithelium containing all germ cell lineages was present at ⱖ19 weeks
(SC, ⱖ16.5 cm). The lumen was seen in some seminiferous
tubules at 12 weeks (SC, 11.5 cm) and in almost all tubules
at 15 weeks (SC, 14.0 cm).
Epididymis
Group 1 (1–4 weeks; SC, 6.5–7.5 cm). The epididymis at week 1 was distinguished into head, body, and tail
regions. The head consisted of a descending limb and an
ascending limb, and lay over the dorso-caudal border of the
testis. The body was a thin thread-like structure attached
Fig. 7. A–C: Light micrographs of paraffin sections from the proximal
head (A), proximal body (B), and tail (C) regions of the epididymis in group
II animals. Whereas the epithelium is undifferentiated in the head and
body, it is differentiated in the tail of the epididymis and contains both
principal (p) and basal (b) cells. Note significantly taller epithelium in the
tail than in other regions. A–C, 360⫻
Fig. 8. A–C: Electron micrographs of epithelial cells from the tail of the
epididymis at 8 weeks. A: Apical portions of principal cells containing
absorptive features including stereocilia (S), pinocytotic and coated
vesicles (arrows), and subapical vacuoles (v). Supranuclear (B) and
infranuclear (C) portions of principal cells (p) containing protein synthetic
organelles, such as, the Golgi cisternae (G), rough endoplasmic reticulum
(arrowhead), and small, dense granules (arrow). The latter are especially
abundant near the basal lamina. Basal cell, (b); blood capillary, (bc).
Inset: Light micrograph of a semithin section of epithelium from an area
similar to that shown in these electron micrographs. A,B, 10,500⫻; C,
8,000⫻; inset, 330⫻.
513
on the caudo-medial border of the testis. The tail was a
large promontory-like structure attached on the ventromedial border of the testis (Fig. 2). Except for a few
epididymal tubular cross-sections located at the distal end,
the entire descending limb of the head was occupied by the
efferent ductules (Fig. 3).
The epididymis in 1–4-week-old goats showed distinct
morphometric differences along the length. The epithelial
height was significantly taller in the body and tail than in
the head (19–22 µm vs. 12–14 µm). The luminal and
tubular diameters were significantly greater in the tail
than in the body or the head (65 µm vs. 31–44 µm, 102 µm
vs. 64–74 µm, respectively). However, neither parameter
differed among different regions of the head or the body
(Fig. 4).
Except for morphometric differences noted above, epithelial morphology was similar throughout the length of the
epididymis (Fig. 5). Simple columnar epithelium contained
principal cells in all regions except in the tail of the
epididymis where intraepithelial lymphocytes/macrophages were also occasionally encountered. Basal and
apical epithelial cells were absent in all regions. Principal
cells contained an oval, heterochromatic nucleus that
occupied most of the cell cytoplasm. Except for free ribosomes/polysomes, organelles associated with protein synthesis such as RER and Golgi cisternae were poorly
developed. Similarly, except for a few short, irregular
apical microvilli, organelles associated with fluid absorption such as canaliculi, pinocytotic and coated vesicles, and
subapical vacuoles were scarce (Fig. 6A,B). The junctional
complex between two adjacent principal cells was differentiated (Fig. 6C).
Group II (7–10 weeks; SC, 8.5–11.0 cm). Mean
measurements for epithelial height and luminal and tubular diameter did not differ from group I in any region of the
head or the body of the epididymis. However, all of these
parameters more than doubled in the tail of the epididymis
(51 µm vs. 22 µm, 115 µm vs. 52 µm, 212 µm vs. 94 µm,
respectively) (Fig. 4).
Epithelial morphology at the light or electron microscopic level did not differ from group I in any region of the
head or the body (Fig. 7). Principal cells were the only cell
type encountered in the epithelium, and cell organelles
associated with protein synthesis and/or fluid absorption
were poorly developed. Conversely, epithelium in the tail
of the epididymis was differentiated. It was pseudostratified and contained principal cells, basal cells and intraepithelial lymphocytes/macrophages. Principal cells were the
predominant cell type and developed cytological features
suggestive of fluid absorption and protein synthesis (Fig.
8). Basal cells were characterized by a relatively large,
slightly indented nucleus and a few vacuoles in the
cytoplasm. Intraepithelial lymphocytes were characterized by a heterochromatic nucleus and a pale cytoplasm
with few organelles.
Group III (12–15 weeks; SC, 11–14 cm). Compared
to the previous group, epithelial height and luminal and
tubular diameter did not change within any region of the
head of the epididymis or in the proximal body of the
epididymis, but epithelial height and tubular diameter
almost doubled in the distal segment of the body (55 µm vs.
22 µm, 173 µm vs. 94 µm, respectively). None of the
parameters differed from group II in the tail of the
epididymis (Fig. 4).
514
GOYAL ET AL.
Figures 9 and 10.
POSTNATAL DIFFERENTIATION OF THE EPIDIDYMIS
Epithelial morphology in different regions of the head as
well as in the proximal body was still undifferentiated, but
that of the distal body was differentiated (Fig. 9). Morphological features associated with differentiation were similar to those observed for the tail of the epididymis in the
previous group. Epithelium changed from simple columnar to pseudostratified and contained principal cells, basal
cells, and intraepithelial lymphocytes or macrophages.
Principal cells acquired cytological features reflective of
absorptive and protein synthetic activities. Cisternae of
RER containing pale proteinaceous material were especially large in the Golgi area and in the infranuclear
cytoplasm (Fig.10). Basal cells and intraepithelial lymphocytes presented a morphology which was similar to that
described above in the tail of the epididymis.
Group IV (15–25 weeks; SC, 16.0–19.0 cm). Between group III and group IV, all three regions of the head
as well as the proximal body of the epididymis underwent
a tremendous increase in epithelial height (160–230%),
luminal diameter (49–155%), and tubular diameter (130–
190%). However, all of these parameters, except statistically insignificant reduction in epithelial height in the tail
of the epididymis, showed modest, but statistically significant, increases in the distal body and the tail (Fig. 4).
Epithelium in all three regions of the head of the
epididymis presented a differentiated morphology (Fig.
11), although the degree of differentiation in the proximal
head somewhat varied among individual animals within
the group. For example, epithelial height was lower and
more uniform in younger animals (15 and 19 weeks) than
in older animals (21, 23, and 25 weeks). Regardless of the
region of the head, the epithelium was pseudostratified
and contained principal cells, basal cells, apical cells, and
intraepithelial lymphocytes. At the light microscopic level,
the proximal head was characterized by a stellate lumen
and by a pale Golgi area in the supranuclear region of
principal cells. The middle head and distal head were
morphologically similar and possessed an even lumen
lined with principal cells which contained vacuoles in the
cytoplasm.
At the ultrastructural level, principal cells of all three
regions of the head of the epididymis contained a well
developed endocytotic apparatus in the apical cytoplasm; a
large Golgi complex consisting of concentrically arranged
cisternae in the supranuclear cytoplasm; small, flat cisternae of SER distributed throughout the cytoplasm; and long
Fig. 9. A–C: Light micrographs of paraffin sections from the proximal
head (A), proximal body (B), and distal body (C) of the epididymis in group
III animals. Whereas epithelium is still undifferentiated in all three regions
of the head and in the proximal body, it is differentiated in the distal body.
Note in the distal body the presence of both principal (p) and basal (b)
epithelial cells, and significantly taller epithelium than in other regions.
A–C, 360⫻.
Fig. 10. A–C: Electron micrographs of epithelial cells from the distal
body of the epididymis at twelve weeks. Principal cells show an abundance of organelles associated with absorption in the apical portions (A)
and those associated with protein synthesis, such as, the Golgi cisternae
(G) and rough endoplasmic reticulum in the supranuclear (B) and
infranuclear portions (C). Note the distension of RER with a proteinaceous
material (arrows). A basal cell (b) with few cell organelles lies next to the
basal lamina. Inset: Light micrograph of a semithin section of the
epithelium showing principal (p) and basal (b) cells from an area similar to
that shown in these electron micrographs. A,B, 10,500⫻; C, 8,000⫻;
inset, 330⫻.
515
flat or slightly distended RER cisternae in the infranuclear
cytoplasm and on the lateral aspect of the Golgi body (Fig.
12).
Apical cells were few in number, interspersed among
principal cells, and extended from the lumen of the tubule
to the basal lamina. They were characterized by an apical
position of the nucleus, a convex luminal border that was
free of microvilli, and mitochondrial aggregation in the
apical cytoplasm (Fig. 12D). Basal cells and intraepithelial
lymphocytes were morphologically similar to those present
in the distal body or the tail of the epididymis.
The proximal body, like the head of the epididymis,
acquired differentiation in this age group and was morphologically similar to the distal body. Both regions of the body
were characterized by a tall, irregular epithelium that
accounted for the stellate shape of the lumen (Fig. 11C).
The pseudostratified epithelium contained principal cells,
basal cells and intraepithelial lymphocytes, but apical
cells were not encountered. Principal cells in the proximal
body acquired absorptive and protein synthetic organelles,
similar to those acquired by principal cells of the distal
body in group III animals. Basal cells formed a continuous
row near the basal lamina and possessed ultrastructural
features similar to those described previously in other
regions of the epididymis.
The epithelium of the tail of the epididymis was as
differentiated as noted in earlier groups except that the
epithelial height was slightly lower.
Ductus Deferens
Groups I–IV (1–25 weeks; SC, 6.5–19.0 cm). Unlike
the epididymis, the epithelium in the ductus deferens was
differentiated at week 1. The pseudostratified epithelium
was very tall, actually taller than at week 25 (65 ⫾14 µm
vs. 32 ⫾ 8 µm), and contained principal cells, basal cells,
and intraepithelial lymphocytes/macrophages (Fig. 13).
Basal cells formed a row of nuclei near the basal lamina,
and were characterized at the ultrastructural level by
empty-appearing vacuoles in the cytoplasm. Principal cells
exhibited absorptive features including microvilli, canaliculi, and pinocytotic/coated vesicles, and protein synthesizing features including a stack of Golgi cisternae, RER
cisternae, and small, dense granules. The latter were
mainly seen near the basal lamina (Fig. 14).
DISCUSSION
This is the first study in large animals that describes
postnatal spatial and temporal differentiation at the light
and electron microscopic levels in different regions of the
epididymis and in the ductus deferens. Based on morphological differences, the epididymis in adult, 2–3-year-old
goats was divided into five regions: proximal head, middle
head, distal head, body, and tail (Goyal and Williams,
1991). Regardless of the region, the epithelium contained
principal cells and basal cells, and principal cells of all
regions contained cytological features reflective of an
absorptive function (microvilli, canaliculi, pinocytotic and
coated vesicles, and subapical vacuoles) and a protein
synthetic function (RER and Golgi bodies) (Goyal and
Williams, 1991). Using the presence of both principal and
basal cells in the epithelium and the presence of both
absorptive and protein synthetic features in principal cells
as criteria for differentiation, epithelium can be classified
as differentiated in the ductus deferens by ⱖ1 week, in the
516
GOYAL ET AL.
Figures 11 and 12.
POSTNATAL DIFFERENTIATION OF THE EPIDIDYMIS
tail of the epididymis by ⱖ7 weeks, in the distal body of the
epididymis by ⱖ12 weeks, and in the proximal body and all
three regions of the head of the epididymis by ⱖ15 weeks.
From the above data, one can conclude that postnatal
epithelial differentiation in the male reproductive tract of
goats begins in the ductus deferens and then ascends in a
time-dependent manner toward the tail, the distal body,
and finally the proximal body and all three regions of the
head of the epididymis. An ascending pattern of differentiation is also reported in the male reproductive tract of rats
(Francavilla et al., 1987), rabbits (Gaddum, 1964), bulls
(Abdel-Raouf, 1960), pigs (Wrobel and Fallenbacher, 1974),
and rams (Nilnophakoon, 1978). According to the latter
study, epithelium in the epididymis of lambs acquired
mature-like characteristics in the distal cauda at 6 weeks,
proximal cauda at 10 weeks, distal body at 12 weeks,
proximal body at 15 weeks, and head at 18 weeks. In
contrast to the above reports, a descending mode of
differentiation is reported in the male tract of brown
marsupial mice (Taggart et al., 1993), rats (Reid, 1959;
Sun and Flickinger, 1979), rabbits (Leeson and Leeson,
1970), and rhesus monkeys (Alexander, 1972). Reasons for
differences in the mode of differentiation could be speciesrelated, but are hard to explain between studies within the
same species.
The significance of androgens in prenatal and postnatal
differentiation of the male reproductive tract is well established in all species studied to date (Robaire and Hermo,
1988; Robaire and Viger, 1995). However, regional differences observed in the timing of postnatal differentiation of
the male reproductive tract in goats suggest a differential
androgen regulation. Observations that the ductus deferens, tail of the epididymis and distal body of the epididymis differentiated prior to the onset of lumen formation in
the seminiferous tubules (12–15 weeks, an indicator for
the beginning of seminiferous tubular fluid production)
suggest that differentiation of all these regions does not
require luminal androgens or other components of the rete
testis fluid, but may require circulating androgens. The
latter possibility is supported by many previous reports in
the literature. For example, 1) epithelium in the tail of the
epididymis was taller in infantile lambs than in adult
lambs (Carreau et al., 1984); 2) testosterone replacement
restored epithelial height and volume density of epithelium to the control level in the tail of the epididymis of
orchidectomized goats (Goyal et al., 1994); 3) the tail
region of the epididymis maintained its normal structure
in rete fluid-deprived epididymides of bulls (Gustaffson,
Fig. 11. A–C: Light micrographs of paraffin sections from the proximal
head (A), distal head (B), and proximal body (C) of the epididymis in group
IV animals. Epithelium in all regions presents a differentiated morphology
and contains both principal (p)and basal (b) cells. A–C, 360⫻.
Fig. 12. A–C: Electron micrographs of epithelial cells from the proximal head of the epididymis at 19 weeks. Notable observations in principal
cells (p) include the presence of endocytotic components in the apical
portions (A) and rough endoplasmic reticulum (arrows) and Golgi cisternae (G) in the supranuclear (B) and infranuclear (C) portions. Inset: Light
micrograph of a semithin section of the epithelium from an area similar to
that shown in these electron micrographs. Principal cells in other regions
of the epididymis possessed similar cytological features and, therefore,
are not shown. D: An electron micrograph of the apical cell. Note the
absence of microvilli at the luminal border and an aggregation of
mitochondria in the apical cytoplasm. A, 10,500⫻; B, 13,300⫻; C,
8,000⫻; D, 5,500⫻; inset, 330⫻
517
1966) and rats (Fawcett and Hoffer, 1979); and 4) castration and androgen replacement did not affect protein
synthesis ability of the body and tail regions of the rabbit
epididymis (Jones et al., 1981).
It is also possible that the ductus deferens, tail of the
epididymis, and distal body of the epididymis require a
lower concentration of androgens (or have a lower threshold) for maintaining their structure since differentiation in
these organs is completed at an early age when blood
testosterone concentration is low and rete testis fluid is
lacking in the epididymal lumen. In this context, it should
be noted that testosterone level in blood is low at infancy
and/or prepuberty and rises with the onset of puberty in
domestic animals including bulls (Rawlings et al., 1972;
Lacroix et al., 1977; Amann, 1983), rams (Lee et al., 1976;
Olster and Foster, 1986), boars (FlorCruz and Lapwood,
1978), and goats (Chakarborty et al., 1989; Ahmed et al.,
1996; Coleman et al., 1998). The latter authors conducted
a longitudinal study in Nubian kids and reported that
mean plasma testosterone concentration increased over
time from 0.37 ⫾ 0.18 ng/ml at 1 month to 2.21 ⫾ 0.18
ng/ml at 6 months, with significant increases occurring
between 1 and 2 months and 4 and 6 months.
In contrast to the differentiation of the ductus deferens,
tail of the epididymis, and distal body of the epididymis,
that of the proximal body and all three regions of the head
of the epididymis occurred soon after the appearance of
lumen in the seminiferous tubules, suggesting a role for
the rete testis fluid in their differentiation. These observations are in agreement with those of previous reports in
that 1) epithelial height in the proximal head of the lamb
epididymis increased by threefold between prepubertal
and pubertal stage (Carreau et al., 1984); 2) deprivation of
the rete fluid caused appreciable degenerative changes in
the head of the epididymis of rats (Fawcett and Hoffer,
1979), bulls (Gustaffson, 1966) and goats (Goyal et al.,
1994); 3) hypophysectomy caused significant changes in
the head of the boar epididymis (Morat et al., 1980); 4)
ligation of the efferent ductules caused changes in protein
profiles only in the proximal segment of the mouse epididymis (Holland et al., 1992); and 5) castration and testosterone treatment or ligation of the efferent ductules significantly reduced the protein synthesis ability of the initial
segment of the rabbit epididymis (Jones et al., 1981).
Of different components of the rete testis fluid, androgens and androgen binding protein (ABP) are considered
important in regulating the structure and function of the
head of the epididymis (Robaire and Hermo, 1988). It is
suggested that ABP secreted by Sertoli cells serves to
transport androgen to the epididymis and thus helps in
maintaining a high concentration of androgen surrounding the epithelial cells, especially in the head of the
epididymis (Pelliniemi et al., 1981; Bardin et al., 1994).
Principal cells in the epithelium lining the proximal part of
the head of the epididymis are shown to endocytose ABP,
which can deliver androgen into the cell where it can
activate cell-specific gene expressions (Attramadal et al.,
1981; Veeramachaneni and Amann, 1991; Hermo et al.,
1998).
In conclusion, postnatal differentiation of the ductus
deferens, tail of the epididymis, and distal body of the
epididymis follows a time-dependent, ascending order and
is achieved prior to lumen formation in the seminiferous
tubules. Conversely, that of the proximal body and all
518
GOYAL ET AL.
Figures 13 and 14.
POSTNATAL DIFFERENTIATION OF THE EPIDIDYMIS
Fig. 13. A–C: Light micrographs of paraffin sections from the ductus
deferens at 3 weeks (A) (group I), 13 weeks (B) (group III), and 19 weeks
(C) (group IV). Unlike the epididymis, the epithelium of the ductus
deferens in group I animals is differentiated and contains both principal (p)
and basal (b) cells. Note a significant reduction in epithelial height
between group III and group IV. A–C, 360⫻.
Fig. 14. A–C: Electron micrographs of epithelial cells from he ductus
deferens at three weeks. Note in principal cells (p) the prevalence of
endocytotic features in the apical cytoplasm (A), Golgi cisternae (G) in the
supranuclear cytoplasm (B), and mitochondria and small, dense granules
(arrow) in the infranuclear cytoplasm (C). b, Basal cells. Inset: Light
micrograph of a semithin section of the epithelium from an area similar to
that shown in these electron micrographs. A,B, 10,500⫻; C, 8,000⫻;
inset, 330⫻.
three regions of the head of the epididymis occurs simultaneously and after lumen formation.
ACKNOWLEDGMENTS
We thank V. Ingram and T. Martin for providing technical assistance, and S. M. Bryant for typing the manuscript.
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