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Erythropoiesis in the yolk sac of the bat Tadarida brasiliensis cynocephala.

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Erythropoiesis in the Yolk Sac of the Bat
Tadarida brasiliensis cynocephala
Cell Biology Program, Stanford Research Institute,
Menlo Park, California 94025
The process of erythropoiesis and vasculogenesis in the yolk sac
of the bat (Tadarida brasiliensis cynocephala) has been studied through the use
of both light and electron microscopy. Stem cells arise from the leading edge of
the migrating splanchnic mesoderm and transform into primitive erythroblasts.
Differentiation involves either contact or association with the endodermal cells,
since all erythropoietic activity occurs on the endodermal side of the expanding
vascular bed, and many of the cells are in close apposition to the lateral or basal
plasma membranes of the endodermal cells. Endodermal cells also phagocytize
developing primitive erythroblasts during the later stage of the process when
erythropoiesis is subsiding in the yolk sac.
Cells destined to become the endothelium of the expanding vascular bed also
arise from the leading edge of the migrating splanchnic mesoderm. Their process
of differentiation involves the development of cytoplasmic extensions that may
surround a group of differentiating erythroblasts, enclosing them in the newly
formed lumen of the blood vessel. The cytoplasmic extensions make contact and
develop junctional complexes with similar processes from other cells to complete
the lumen of the lengthening vascular bed.
Cells of the granulocyte series or megakaryocytes are not observed in the yolk
sac of the bat as has been described in certain other species.
Erythropoiesis occurs first in the yolk
sac of all amniote embryos, followed by formation in the liver, spleen, and finally
bone marrow (Yoffey, '71). Several papers
have been published which indicate that
during morphogenesis three different, electrophoretically distinguishable types of hemoglobin are produced (embryonic, fetal,
and adult) in humans (Huehns et al.,'64)
and cattle (Kleihauer et al., '66). Krantz
and Jacobson ('70) and Ingram ('72)
showed that primitive nucleated erythrocytes formed in the yolk sac synthesize
mainly Hb-Gower-1 ( ~ 4 )and
, - 2 (a2 ~ 2 )
while hepatic erythroid cells synthesize
Hb-F ( a 2 y2) and Hb-A ( a 2 p2). The proportion of Hb-A increases as the hematopoietic process shifts from the hepatic to
the myeloid site,
A review by Barker ('67) showed that
embryonic and adult hemoglobins are also
found in a wide variety of species, including the tadpole, chick, duckling, mouse
and elephant. Embryonic hemoglobins are
apparently formed exclusively by the yolk
ANAT. REC., 186: 525-552.
sac in conjunction with the formation of
primitive nucleated erythrocytes by that
organ (Kleihauer et al., '66; Barker, '68),
whereas adult hemoglobins first appear
when formation of erythrocytes shifts from
the yolk sac to the liver (Barker, '68;
Kovach et al.,'67; Craig and Russell, '64).
Ultrastructural descriptions of erythropoiesis in the avian yolk sac have been published by Mato et al. ('64), Edmonds ('64,
'66), and Miura and Wilt ('70). In addition, similar studies on several mammalian
species have appeared in the literature, in, cluding those on the guinea pig (Sorenson,
'61), mouse (Kovach et al., '67; Haar and
Ackerman, '71a,b), and human (Fukuda,
'73). In general, erythropoiesis in the yolk
sac of the bat parallels that described for
other species, but there are also specific differences which have been given special attention below.
Received Oct. 17, ' 7 5 . Accepted June 8 , '76.
1 This investigation was supported by the National
Institutes of Health, Child Health and Human Development Grant 03391-02.
Previous publications from this laboratory described the development of the three
main sequential placental relationships in
Tadarida, and specific attention was given
to the differentiation of the yolk sac endoderm (Stephens and Easterbrook, '68, '69,
'71) and mesoderm (Stephens and Cabral,
'71a). The purpose of this study was to describe observations, both at the light and
electron microscope levels, of the process of
erythropoiesis in the yolk sac.
In Tadarida the endodermal cells are established through a process of delamination from the inner cell mass and proliferation to form a complete lining of the trophoblastic vesicle creating a bilaminar
omphalopleure. At first the yolk sac consists of a single layer of squamous endodermal cells. Subsequently the mesoderm
migrates into the space between the endoderm and the trophoblast. This event is accompanied by a wave of erythropoiesis that
proceeds around the circumference of the
trophoblastic vesicle.
Light microscope sections, 1 micron
thick, were cut from the same blocks as
those used for electron microscopy. These
sections were placed on glass slides and
stained with a 1% solution of toluidine
blue in 1% borax for observation and correlative study.
Implantation in Tadarida is central and
superficial; endodermal cells delaminate
from the inner cell mass and proliferate to
form a lining of the trophoblastic vesicle
(figs. 1, 4). Mesoderm from the primitive
streak area spreads laterally between the
trophoblast and the newly formed endoderm (figs. 2, 3, 5). Concomitant with the
spreading of the mesoderm is the transformation of the endoderm from a squamoustype epithelium to one that is columnar
(cf. fig. 1 with figs. 2, 3; see also Stephens
and Easterbrook, '71). An interstitial space
exists between the endoderm and the cytotrophoblast prior to the migration of the
mesoderm into this area. This space conMATERIALS AND METHODS
tains only a few irregular cytoplasmic exThe animals used in this study were col- tensions from the endoderm and a wispy
lected in the vicinity of Gainsville and Tal- Aocculent material (figs. 1 , 2 , 4 , 5 ) . A baselahassee, Florida. Of the 125 specimens ment lamina covers the cytotrophoblast
collected throughout the gestation period, (figs. 4, 5 ) , but the endodermal cells do
from early March through the middle of not possess a similar lamina. Together with
June, several animals were in the proper the advancing edge of the mesoderm, cytostage of gestation (the neural groove stage) plasmic spherules appear in close proximto study the process of erythropoiesis in the ity to the endodermal cells (figs. 3, 5-8).
yolk sac. Details of the collection proce- At the electron microscope level, these
dures, shipment of the animals, and prep- spherules are observed to contain a variaration of the tissue have been previously able population of cytoplasmic compopublished (Stephens and Easterbrook, '71; nents. Some contain a mixture of organStephens, '69 ).
elles including ribosomes, endoplasmic reTissues were fixed for 45 minutes in 1% ticulum, and mitochondria (figs. 6-43>,
OsO, buffered to a pH of 7.4 with Veronal while others appear to be more restrictive
acetate, or for two hours in 3% glutaralde- in their contents, possessing only small
hyde buffered to a pH of 7.4 with cacodyl- cytoplasmic vesicles and small dense bodate. After fixation in glutaraldehyde, the ies (fig. 6, inset fig. 6). The size of the
tissue was washed repeatedly in cacodylate spheruIes is also variable (figs. 3, 5-8). The
buffer for two hours and then post-fixed in spherules stain intensely with toluidine
1% OsO,. All tissues were dehydrated in a blue (fig. 3 ) and may become closely asgraded series of ethanol and subsequently sociated with or surrounded by the basal
embedded in Maraglas. Sections were cut plasma membrane and cytoplasm of the
on a Porter-Blum MT2 ultramicrotome, endodermal cells (figs. 7, 8). Between
placed on uncoated grids, and stained with these spherules and the migrating mesolead citrate (Reynolds, ' 6 3 ) before observa- derm is a substantial layer of a loose floction with a Philips 200 electron micro- culent substance with characteristics and
density similar to those of a basement lam-
ina, but it does not follow the contours of
the basal plasma membrane of the endoderm and is less well defined than a typical
basement lamina (figs. 5, 6).
The migrating mesodermal cells are
elongate in appearance (figs. 2, 3, 5 ) and
possess a sparse population of cytoplasmic
organelles (fig. 5 ) . Stem cells arising from
the mesodermal layer adjacent to the endoderm transform into angioblasts, or "primitive erythroblasts," becoming ovoid to
spherical in shape (figs. 3, 9, 10). The
cytoplasm of these angioblasts becomes
"condensed and contains a large oval nucleus with a prominent nucleolus (figs. 3,9,
l o ) , a modest population of mitochondria,
a Golgi complex, very little endoplasmic
reticulum and a large number of free ribosomes (fig. 9 ) . At &st only a few of these
cells are evident; they do not appear to be
organized into cords (fig, 10) as they are
in the chick and mouse. The tissue space
between the endoderm and mesoderm becomes larger and is filled with erythropoietic cells in various stages of differentiation (figs. 11, 14). The nuclei of the differentiating cells become condensed and stain
more intensely with toluidine blue as maturation continues (fig. 11). Some of the
newly formed angioblasts and primitive
erythroblasts are in close association with
the endodermal cells (figs. 12-14). Frequently cytoplasmic extensions from the
endodermal cells extend almost completely
around differentiating angioblasts (fig. 13),
primitive erythroblasts (fig. 14), or polychromatic erythroblasts (fig. 16). During
the early maturation process, ribosomes
become aggregated into polyribosomal
groups, and coated vesicles may be observed along the plasma membrane of polychromatic erythroblasts (fig. 15).
In contrast to the rapidly dividing and
more densely staining erythrocytic series
of cells, a small number of cells also derived from mesoderm and located in the
same tissue space beneath the endoderm
retain an elongate nucleus and stain less
intensely (fig. 11). The cytoplasm of these
cells becomes attenuated, and they are destined to become the endothelium of the enlarging vitelline circulation (figs. 11, 14,
17, 18). The cytoplasmic extensions may
make contact with erythroblasts (fig. 17)
or may form junctional complexes with the
cytoplasmic processes from similar cells
producing the endothelium of a new capillary (fig. 18). The primitive erythrocytes
may be formed outside the lumen and
must then enter the vessel via the process
of diapedesis.
As the wave of erythropoiesis progresses
around the outer surface of the yolk sac
and the new capillary bed is established,
some of the primitive erythroblasts remain
in close association with the endodermal
cells (figs. 19, 20). Perhaps it should be
mentioned here again that a basement lamina is not present beneath the endodermal
cells, and numerous erythroblasts migrate
in between the lateral walls of endodermal
cells, Some of the polychromatic erythroblasts become phagocytized and degraded
by the endodermal cells (figs. 20, 22),
while others (figs. 20, 22) remain in close
contact with the plasma membrane of the
.endodermal cells but eventually migrate into the adjacent capillaries.
Circulating nucleated erythroblasts stain
intensely with toluidine blue (fig. 20) and
assume variable shapes while in circulation
(fig. 21). They possess a nucleus, a sparse
population of small mitochondria, and, frequently, dense bodies that apparently represent accumulations of ferritin (fig. 21).
The establishment of the vitelline circulation completes the yolk sac placenta which
includes the mesothelium, the trophoblastic
tissues, and maternal blood vessels of the
uterine wall (fig. 19).
The development of the yolk sac and the
degree to which it becomes vascularized
have been described for a number of species in the order Chiroptera at the light microscope level. Implantation varies from
family to family and affects the extent to
which the yolk sac becomes vascularized.
Some aspects of this process have been described for several families: i.e., Phyllostomedae (Hamlett, '34, '35), Vespertilionidae (Wimsatt, '44, '45, '49; Branca, '23;
Gerard, ' 2 8 ) , Desrnodontidae (Wimsatt,
'54), E,mballonuridae (Gopalakrishna, '58),
Hipposidaridae (Karirn, '72), Noctilionidae
(Anderson and Wimsatt, ' 5 3 ) , and Molossidae (Stephens, '62). To our knowledge,
however, the ultrastructural changes related to the establishment and differentiation of the various components of this
interesting organ in the bat have been described for only one species, Tadarida brasiliensis cynocephala (Stephens and Easterbrook, '68, '69, '71; Stephens and Cabral,
'71a). In these earlier studies, an attempt
was made to describe the histological and
ultrastructural changes that accompany
the differentiation and function of the endoderm (Stephens and Easterbrook, '71)
and mesothelium (Stephens and Cabral,
'71a) and to discuss their potential significance in the prolonged gestational period
of the bat. The structural changes observed
suggest that the functional role of the
yolk sac is continually changing (Stephens
and Easterbrook, '71; Stephens and Cabral,
The current study was undertaken to extend our earlier work through a detailed
description of the structural components
involved in erythropoiesis and vasculogenesis of the vitelline circulation in the same
It has been noted in earlier histological
studies on the yolk sac of the bat that the
endoderm, which is originally squamous,
begins to hypertrophy as the splanchnic
mesoderm migrates in between the two layers of the omphalopleure. Ultrastructural
studies on Tadarida (Stephens and Easterbrook, '71) as well as other mammals
(Haar and Ackerman, '71a; Padykula et
al., '66; Deren et al., '66a,b; Larsen, '63)
have shown that the apical mechanism for
absorption develops in the endodermal cells
as they differentiate from squamous to
columnar shape. Thus, the establishment
of the vascular system of the yolk sac is
concomitant with the development of the
absorptive mechanism of the endodermal
cells. It also appears noteworthy that by
this time the trophoblast has penetrated
deeply into the maternal endometrium and
surrounds many of the superficial maternal blood vessels. Therefore, nutrients absorbed by the trophoblast as a result of the
breakdown of maternal tissue or absorbed
from the maternal blood vessels could be
transported to the embryo via the newly
forming vitelline circulation. Taken together these tissues constitute the transient
yolk sac placenta. Later in gestation when
the yolk sac becomes separated from the
uterine wall, an absorptive apparatus is
also developed in the mesothelial cells facing the exocoelom (Stephens and Cabral,
'71a), and it is postulated that the vitelline
circulation continues to play an important
role through the transportation of material
selectively absorbed from both the cavity
of the yolk sac and the exocoelom.
Comparison of recently published accounts of vasculogenesis and erythropoiesis
in the mouse (Haar and Ackerman, '71a),
chick (Edmonds, '66), guinea pig (Sorenson, '61), and human (Fukuda, '73) with
those of Tadarida reveals several dissimilarities, although the general nature of maturation of the nucleated erythrocytes is
similar in all cases. In Tadarida distinct
angioblastic cords do not develop as reported in the mouse and chick; rather, the
process of erythropoiesis advances as a
single wave of activity, following the lateral spread of the mesoderm between the
two layers of the bilaminar omphalopleure.
At first the mesodermal cells appear spindle-shaped but in rapid succession a few
of the cells located toward the endoderm
begin to change their morphological appearance, and the cytoplasm commences to
"round up." Cytoplasmic spherules are observed in close proximity to the endoderma1 cells, both preceding angioblast formation and concurrent with erythroblast
differentiation. To date, we have been unable to unequivocally determine the source
of these spherules, although an analysis of
the data leads us to the conclusion that
they probably arise from forming angioblasts and differentiating erythroblasts, although an origin from the endodermal cells
cannot be completely ruled out at this time.
The presence of these cytoplasmic droplets is apparently unique as they have not
been reported during erythropoiesis in
other species. Rapid division of the newly
formed primitive erythroblasts produces an
accumulation of differentiating primitive
blood cells and, as the wave of activity
moves forward, new capillaries are also
formed by cells of a mesodermal origin.
The maturing primitive erythroblasts in
the wake of the advancing wave may differentiate within the lumen of the forming
blood vessels or enter the developing circulatory system from the tissue space be-
neath the endoderm. The expanding vascular bed assists in establishing the yolk sac
placenta, the first of three distinctly different vascularized placental forms that develop in Tadarida (Stephens and Cabral,
’71b, ’72; Stephens, ’69).
Close association between the developing
primitive erythroblasts and endodermal
cells has previously been noted in humans
by Fukuda (’75). He stated that these
“primordial blood cells seem to require contact with the endodermal epithelium for
their differentiation, although the origin
and way of emigration into the endodermal
layer is uncertain” (p. 211). The relationship between endodermal cells and developing erythroblasts was described as being
similar to that observed between hepatocytes and erythroid cells in the liver during hematopoiesis (Fukuda and Sato, ’71;
Fukuda, ’73) and it is perhaps noteworthy
that both the hepatocytes and the endodermal cells of the yolk sac are derived from
the endoderm of the primitive gut. In a
study of hematopoiesis in the guinea pig
yolk sac, Sorenson (’61) discusses two
functions for the macrophages found in
the yolk sac. One of these functions is
“nurturing” erythroblasts, while the other
is “digesting erythroblasts.” The role of a
“nurse cell” for macrophages has also been
described by Bessis and Breton-Gorius (’57,
’59) in human bone marrow. It is clear
that in Tadarida, many of the differentiating erythroblasts are observed in very close
proximity to the basal and lateral membranes of the endodermal cell. This relationship might be explained through a concept of cellular crowding that results from
rapid cellular division of the primitive
erythroblasts, but this does not appear to
be a satisfactory or complete explanation.
Easy access to the space between the lateral membranes of the endodermal cells is
made possible because there is no basement lamina covering their basal aspect.
However, the close proximity of the plasma
membrane of the two cell types appears to
indicate a more specific relationship, and
the possibility of an exchange of nutrients
or other materials, such as iron, required
for their differentiation cannot be ruled
out. In Tadarida the endodermal cells have
also been observed to be erythrophagocytic
in that a number of primitive polychro-
matic erythroblasts have been observed
within the cytoplasm of the endodermal
cells in various stages of degradation.
Therefore, it appears possible that in different species different cell types may serve as
both the source of nutrients for normal differentiation of developing erythroblasts
and at the same time phagocytize and destroy other erythrocytes for reasons that
are still unknown.
Blood formation in the yolk sac of the
bat appears to be limited to the production
of primitive nucleated erythrocytes. To
date, we have not observed the presence of
granulocytes or primitive meg akaryocy tes
as reported by Fukuda (’73) and Bloom
and Bartelmez (’40) in the human yolk
sac. Megakaryocytes were also observed by
Sorenson (’61) in guinea pigs but he did
not observe the presence of granulocytes.
Granulocytes were reported in the rabbit
(Maximow, ’09) and rat (Block, ’46).
The fact that hemocytoblast activity in
the yolk sacs of various species apparently
does not result in the establishment of
either a granulocytic series or megakaryocytes appears to argue against the totipotent concept of the monophyletic theory
and possibly strengthens the view of a polyphyletic scheeme of blood cell formation.
Clearly, the stem cells are all mesenchymal
in origin, but our ability to distinguish the
difference among stem cells on a morphological basis in this case may be limited.
Anderson, J. W., and W. A. Wimsatt 1953 The
fetal membranes and placentation of the tropical American noctilionid bat, Dirias albiventer
minor. Anat. Rec., 11 7: 573-574.
Barker, J. E. 1967 Hemoglobin Production in
Embryonic Mouse Liver and Yolk Sac. Ph.D.
thesis, University of Wisconsin, Madison.
1968 Development of the mouse hematopoietic system. I. Types of hemoglobin produced in embryonic yolk sac and liver. Devel.
Biol., 18: 14-29.
Bessis, M., and J. Breton-Gorius 1957 Etude au
microscope electronique des granulations ferrugineuses des erythrocytes normaux et pathologiques. Rev. Hemat., 12: 43.
1959 Ferritin and ferruginous micelles
in normal erythroblasts and hypochromic hypersideremic anemia. Blood, 14: 423.
Block, M. 1946 A n experimental analysis of
hematopoiesis in the rat yolk sac. Anat. Rec.,
96: 289.
Bloom, W., and G. Bartelmez 1940 Hemato-
poiesis i n young human embryos. Am. J. Anat.,
67: 21.
Branca, A. 1923 Recherches sur la vesicule
ombilicale. 11. La vesicule ombilicale des cheiropthres. Arch. d. Biol., 33: 517-604.
Craig, M. L., and E. S. Russell 1964 A developmental change in hemoglobins correlated with
an embryonic red cell population in the mouse.
Devel. Biol., 10: 191-201.
Deren, J. J., H. A. Padykula and T. H. Wilson
1966a Development of structure and function
in the mammalian yolk sac. 11. Vitamin Bt2 u p
take by the rabbit yolk sac. Devel. Biol., 13:
1966b Development of structure and
function in the mammalian yolk sac. 111. The
development of amino acid transport by rabbit
yolk sac. Devel. Biol., 13: 370- 384.
Edmonds, R. H. 1964 Areas of attachment between developing blood cells. J. Ultrastruct.
Res., 11: 577-580.
1966 Electron microscopy of erythropoiesis in the avian yolk sac. Anat. Rec., 154:
Fukuda, T. 1973 Fetal hemopoiesis. I. Electron
microscopic studies on human yolk sac hemopoiesis. Virchows Arch. Abt. B. Zellpath., 14:
Fukuda, T., and H. Sat0 1971 Desmosomes,
cilia, and peculiar structures of membranes in
erythroblasts of human fetal liver. Virchows
Arch. Abt. B., 7: 309-313.
Gerard, P. 1928 Contribution a l'btude morphologique de la vesicule ombilicale chez les Cheiropthres (Vesperugo noctula, Schreib ) Arch. d.
Biol., 38: 203-217.
Gopalakrishna, A. 1958 Foetal membranes in
some Indian microchiroptera. J. Morph., 102:
Haar, J. L., and G. A. Ackerman 1971a A
phase and electron microscopic study of vasculogenesis and erythropoiesis i n the yolk sac of
the mouse. Anat. Rec., 170: 199-224.
1971b Ultrastructural changes i n the
mouse yolk sac associated with the initiation
of vitelline circulation. Anat. Rec., 170: 437456.
Hamlett, G. W. D. 1934 Implantation of embryonalhiillen bei zwei siidamerikanischen Fledermausen. Anat. Anz., 79: 146-149.
1935 Notes o n the embryology of a
phyllostomid bat. Am. J. Anat., 56: 327-353.
Huehns, E. R., N. Dance, G. H. Beaven, F. Heght
and A. G. Motulsky 1964 Human embryonic
hemoglobins. Cold Springs Harbor Symposium.
Quantative Biol., 29: 327-332.
Ingram, V. M. 1972 Embryonic red cell formation. Nature (London), 235: 338-339.
Karim, K. B. 1972 Foetal membranes and placentation i n the Indian leaf-nosed bat, Hipposidaros fulvus fulvus (Gray). Proc. Ind. Acad.
Sci., 76: 71-78.
Kleihauer, E., E. Brauchle and G. Brandt 1966
Ontogeny of cattle haemoglobin. Nature, 212:
Kovach, J. S., P. A. Marks, E. S. Russell and
H. Epler 1967 Erythroid cell development in
fetal mice: Ultrastructural characteristics and
hemoglobin synthesis. J. Mol. Biol., 25: 131142.
Krantz, S. B., and L. 0. Jacobson 1970 Erythropoieten and Regulation of Erythropoiesis.
Chicago University Press, Chicago-London.
Larsen, J. F. 1963 Histology and fine structure
of the avascular and vascular yolk-sac placentae and the obplacental giant cells in the rabbit. Am. J. Anat., 112: 269-283.
Mato, M., E. Aikawa and K. Kishi 1964 Some
observations on interstice between mesoderm
i n the area vasculosa of chick blastoderm. Exp.
Cell Res., 35: 426-428.
Maximow, A. A. 1909 Untersuchungen uber
blut und bindegewebe. I. Die friihesten entwicklungsstadien der blut und bindegewebzellen bein saugetierembryo, bis zum anfang
der blutbildung i n der leber. Arch. Miks. Anat.,
73: 444-561.
Miura, Y.,and F. H. Wilt 1970 The formation
of blood islands in dissociated-reaggregated
chick embryo yolk sac cells. Exptl. Cell Res., 59:
Padykula, H. A., J. J. Deren and T. H. Wilson
1966 Developmental morphology and vitamin
BIZ uptake of the rat yolk sac. Devel. Biol.,
13: 311-348.
Reynolds, E. S. 1963 The use of lead citrate
at high pH as an electron-opaque stain in electron microscopy. J. Cell Biol., 17: 208-212.
Sorenson, G. D. 1961 A n electron microscopic
study of hematopoiesis i n the yolk sac. Lab.
Invest., 10: 178-193.
Stephens, R. J. 1962 Histology and histochemistry of the placenta and fetal membranes i n
the bat (Tadarida brasiliensis cynocephala).
Am. J. Anat., 1 1 1 : 259-286.
1969 The development and fine structure of the allantoic placental barrier in the
bat, Tadarida bmsiliensis cynocephala. J. U1trastruct. Res., 28: 371-398.
Stephens, R. J., and L. J. Cabral 1971a Cytological differentiation of the mesothelial cells
of the yolk sac of the bat, Tadarida brasiliensis
cynocephala. Anat. Rec., 171: 293-312.
1971b Direct contribution of the cytotrophoblast to the syncytiotrophoblast in the
diffuse labyrinthine endotheliochorial placenta
of the bat. Anat. Rec., 169: 243-252.
1972 The diffuse labyrinthine endotheliodichorial placenta of the free-tail bat: A light
and electron microscopic study. Anat. Rec., 172:
Stephens, R. J., and N. Easterbrook 1968 Development of the cytoplasmic membranous organelle i n tne endodermal cells of the yolk
sac of the bat, Tadarida brasiliensis cynocephala. J. Ultrastruct. Res., 24: 239-248.
1969 A new cytoplasmic organelle related to both lipid and glycogen storage materials i n the yolk sac of the bat, Tadaridn
brasiliensis cynocephala. Am. J. Anat., 124:
1971 Ultrastxuctural differentiation of
the endodermal cells of the yolk sac of the bat,
Tadarida brasiliensis cynocephala. Anat. Rec.,
169: 207-240.
Wimsatt, W. A. 1944 A n analysis of implantation in the bat, Myotis lucifugus lucifugus.
Am. J. Anat., 74: 355411.
1945 The placentation of a vespertilionid bat, Myotis Zucifugus Zucifugus. Am. J.
Anat., 77: 1-51.
1949 Cytochemical observations on the
fetal membranes and placenta of the bat, Myotis
lucifugus lucifugus. Am. J. Anat., 84: 63-142.
- 1954 The fetal membranes and placen-
tation of the tropical American vampire bat,
Desmodus rotundus murinus. Acta Anat., 2 1 :
Yoffey, J. M. 1971 Fetal and neonatal erythropoiesis: The stem cell problem in the fetus.
Israel J. Med. Sci., 7: 825-833.
This light micrograph shows the bilaminar omphalopleure consisting of the cytotrophoblast (CT) and endoderm ( E ) just before migration of the mesoderm into
the space between these two tissues. Cavity of the yolk sac (CY). x 555.
The migrating mesoderm ( M ) can be observed here between the endoderm ( E )
and cytotrophoblast (CT). At first the mesodermal cells are elongate and undifferentiated. The syncytial trophoblast (ST) has penetrated into the uterine wall and
has surrounded the maternal capillaries (MC). X 5 5 5 .
The mesodermal cells i n the tissue space (TS) to the right of the e n d d e r m ( E )
are in stages of differentiation. The oval cell with the prominent nucleolus just
below the center of the micrograph has the characteristics of a primitive erythroblast (PE), and the two cells directly above are mesodermal stem cells (SC) in
the process of transforming into erythroblasts. The layer of mesodermal cells
( M ) toward the trophoblast ( T ) at the extreme right will become the mesothelial
layer of the yolk sac. Small, densely staining cytoplasmic spherules can be observed immediately beneath the endoderm (arrows). x 1,250.
An electron micrograph, at low magnification, shows the squamous endoderm
( E ) separated from the cytotrophoblast (CT) by a tissue space (TS) into which
the mesoderm will migrate. A single cytoplasmic spherule (arrow) is present
within the space. A basement lamina ( B L ) is closely associated with the cytotrophoblast but the endoderm does not possess a basement lamina. Flocculent material ( F M ) ; cavity of the yolk sac (CY). x 9,940.
Robert J. Stephens and Linda J. Cabral-Anderson
Undifferentiated mesodermal cells ( M ) are shown here migrating
into the space between the cndoderin ( E ) and the cytotrophoblast
(CT). Cytoplasmic spherules ( C S ) and a flocculent material ( F M ) are
present immediately beneath the endoderm. Basement lamina (BL).
x 14,400.
Robert J. Stephens and Linda J. Cabral-Anderson
These electron micrographs are included to show thc variable nature
of the cytoplasmic spherules and their relationship to the endoderm
( E ) . Several spherules are present in figure 6 that are immediately
beneath the endoderm. The size distribution is substantial, and the
cytoplasmic organelles that each contains are also variable. The
inset (fig. 6 ) contains a spherule that possesses a n accumulation
of small vesicles and small dense bodies. A spherule is partially surrounded by the endodermal cytoplasm i n figure 7 and completely
surrounded in figure 8. Flocculent material ( F M ) . x 24,600;
x 22,700; x 22,700; inset x 23,700.
Robert J. Stephens and Linda J. Cabral-Anderson
The typical characteristics of a primitive erythroblast are shown i n
this figure. The oval cell contains a prominent oval nucleus, a
sparse population of mitochondria (Mi), a Golgi complex ( G )
with adjacent centriole ( C ) , very little rough endoplasmic reticulum, and a high population of free ribosomes. Endoderm ( E ) .
X 21,800.
10,11 The rapid increase in blood elements between the endoderm ( E )
and mesothelium ( M ) can be observed i n these two micrographs.
Note that the vitelline capillaries have not fully differentiated at
this time. However, certain cells in figure 11 contain elongate
nuclei and stain less intensely with toluidine blue. These cells are
identified as precursors to the endothelium (EC). The primitive
erythroblasts (PE) i n figure 10 have large oval nuclei with proniinent nucleoli and a “rounded up” cytoplaFm. The differentiating
erythroblasts i n figure 11 possess a more condensed nucleus that
is spherical and stains more densely. Endoderm ( E ) . Cellular
trophoblast (CT). x 555; x 555.
Robert J. Stephens and Linda J. Cabral-Anderson
12, 13
Mesenchymal cells are shown here i n stages of differentiation
progressing toward a primitive erythroblast. Note that the cytoplasm of the cell located i n the center of figure 12 has the
characteristics of primitive erythroblast but it has not “rounded
up” yet. Figure 13 shows a similar cell i n close apposition to the
endoderm ( E ) that has begun to take on the typical oval shape.
The intimate relationship with the endoderm indicatcs that the
endoderm may play a significant role i n the process of differentiation. x 12,000; x 14,400.
Robert J. Stephens and Linda J. Cabral-Anderson
This electron micrograph at low magnification shows the endoderm
( E ) and a number of erythroblasts, all of which are i n a similar stage
of early differentiation. Note that some of the cells are in close association with the endoderm. Endothelial cell ( E C ) . x 4,370.
Robert J. Stephens and Linda J. Cabral-Anderson
15, 16 As the primitive erythroblasts differentiate toward polychromatic
erythroblasts, the cytoplasm becomes more electron dense, presuniably from the amount of hemoglobin present. Polyribosomal
aggregations become prominent (fig. 15). The cytoplasmic organelles are reduced in number; however, coated vesicles may be
observed along the plasma membrane. Eventually the nucleus
and cytoplasm become similar in electron density (fig. 16). Again,
they are frequently observed i n close relationship with the endoderni ( E ) . x 27,300; x 18,200.
Robert J. Stephens and Linda J. Cabral-Anderson
17, 18
Differentiating endothelial cells ( E C ) send out cytoplasmic extensions that may make contact with primitive erythroblasts ( P E )
(arrows: fig. 17), or they may contact extensions from other endothelial cells and form junctional complexes (arrows: fig. 18) to
lengthen the lumen of the developing vitelline circulation (fig. 18).
X 4,000; x 6,700.
Robert J. Stephens and Linda J. Cabral-Anderson
A rich vitelline vascular bed (VV) is established in close apposition to the cellular ( C T ) and syncytial trophoblasts (ST) i n the
wake of the wave of erythropoiesis that advances around the circumference of the trophoblastic vesicle. At this time the yolk sac,
together with the trophoblastic tissues and the maternal uterine
blood vessels ( M C ) constitute the transitory yolk sac placenta.
Some mature, densely staining primitive erythrocytes ( E C ) remain i n close apposition to the endodcrm ( E ) . These soon disappear, either through migration into the blood vessels, or occasionally they are phagocytized by the endoderm (arrows: fig. 20).
The circulating primitive erythrocytes can be observed in the
lumen of the blood vessels. x 555; x 1,250.
The circulating nucleated erythroblasts assume a variety of shapes.
They contain an oval nucleus and a sparse population of mitochondria. Small dense bodies representing accumulations of ferritin (arrows) may also be observed in the cytoplasm. The inset
at the lower left shows the ferritin accumulation at higher magnification. x 7,700. Inset x 116,500.
Robert J. Stephens and Linda J. Cabral-Anderson
The columnar endoderm ( E ) i s shown i n this electron micrograph
with a phagocytized disintegrating erythroblast (PDE) in the apical
cytoplasm of one of the endodermal cells. Polychromatic erythroblasts
can be seen between the lateral membranes of adjacent endodermal
cells. x 14,400.
Robert J . Stephens and Linda J. Cabral-Anderson
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bat, tadarida, cynocephala, sac, erythropoiesis, brasiliensis, yolk
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