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The structure of cytoplasmic bridges in dividing spermatocytes of the rooster.

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The Structure of Cytoplasmic Bridges in Dividing
Spermatocytes of the Rooster'
Department of Anatomy, University of Washington, Seattle, Washington
It is known from studies with the electron microscope that there may exist cytoplasmic connections between spermatogenic or epithelial cells (Burgos and Fawcett, '55; Fawcett and Burgos, '56 and
Fawcett, Ito and Slautterback, '59) resulting from incomplete or delayed cytoplasmic partitioning following nuclear division.
The significance of persistent cytoplasmic
connections has been discussed by Fawcett and his collaborators.
Recently lamellar systems of cytoplasmic
membranes in dividing spermatogenic cells
of Drosophila virilis have been studied by
Ito ('60). However, he has not dealt in detail with cytoplasmic connections during
meiosis in this species.
This paper describes newly discovered
membranous systems associated with cytoplasmic bridges at specific stages of meiosis
in the rooster.
Rooster testes were cut into slices about
5 mm in thickness with a razor blade. The
slices were fixed in cold 10% acrolein
(Luft, '59) buffered with s-collidine (Bennett and Luft, '59) for one hour and then
rinsed with the buffer solution for a short
time. The slices were cut into smaller
pieces, which were then placed in 1%
buffered osmium tetroxide solution for one
hour at room temperature. This fixation
method wrought more satisfactory results
with this tissue than did the usual fixation
with buffered osmium tetroxide solution
alone. After dehydration through a series
of graded ethanols, the materials were immersed in propylene oxide for 30 minutes
and embedded in epoxy resin mixture according to the method of Luft ('61). Sections were cut with glass knives on a
Porter-Blum microtome and picked up on
grids coated with carbon films. Sections
were stained with uranyl acetate (Watson,
'58a) or lead hydroxide (Watson, '58b) and
examined with an RCA-2C electron microscope fitted with a specially stabilized
power supply.
Thicker sections were stained with iron
hematoxylin and examined with a light
An unusual type of cytoplasmic bridge
can be noted during the telophase of both
meiotic divisions in the rooster. Examples
are illustrated in figures 1 to 4. Such
bridges join secondary spermatocytes or
spermatids. Within the bridges, numerous
elongated profiles of membranous cisternae
are seen oriented at approximately right
angles to the original spindle axis. Cisternae situated near the center of the
bridges appear flat in section, while those
further from the center appear to curve
away from the plane of cleavage of the
cells. Membranes of the cisternae have
not been observed to be continuous with
the plasma membrane of cells in this region (see fig. 3 ) . The cytoplasm between
cisternae appears to be denser than the intracisternal substance and to be contjnuous with the cytoplasmic matrix. The
widths of the 3paces between cisternae
seem to be more constant (about 250 A )
than the widths lof the cisternae themselves
(about 300 to 500 A). The curved cisternae
located away from the center of the bridge
appear to be coiitinuous with smooth surfaced components of the endoplasmic reticulum distributed in the cytoplasm (fig.
4 ) . Some of the cisternae do not extend
completely across the bridge at the center.
In such circumstances the matrix between
cisternae is seen as expanded spaces conThis study was supported in part by grant
B-401 from the National Institutes of Health,
U. S. Public Health Service, Department of
Health, Education and Welfare.
taining dense particles similar to those "mid-bodies'' (Flemming, 1891) . It has
originally described by Palade ('55) (fig. been reported that in some instances,
3 ) . Figure 4 shows a bridge cut through the spindle breaks down into a densely
near the edge. The cisternal profiles ap- staining granule which persists for a conpear to be oriented regularly at right angles siderable time and forms a connection beto the original spindle axis. These profiles tween daughter cells. This is called the
are interpreted as representing sections spindle remnant (see Wilson, '25). Burgos
through oriented cisternae shaped like flat and Fawcett ('55) have described cytodiscs or curved saucers or bowls nested to- plasmic bridges between spermatids of the
gether in the constricted region of cyto- cat, and Fawcett et al. ('59) have conplasm constituting the intercellular bridge. sidered cytoplasmic bridges to be imporThe plasma membrane at the constricted tant in synchronous cell division.
region of these bridges connecting dividing
In the telophase of meiotic divisions in
cells is denser and thicker than in other re- grasshopper spermatocytes, elongated migions over the cells (figs. 2 to 4). These spe- tochondria have been observed in the concialized regions of the plasma membrane stricted region of the cytoplasm (Tahmisresemble those of cytoplasmic bridges of ian, Powers and Devine, '56). Yasuzumi,
interkinetic stages in this material (fig. 6 ) Ishida, Nakano and Yamamoto ('60) also
and of other cells (Burgos and Fawcett, described morphological changes in the mi'55; Fawcett and Burgos, '56; Fawcett et tochondria and endoplasmic reticulum of
insect and molluscan spermatocytes in
al., '59).
This special arrangement of cisternae at telophase. None of these workers has deintercellular bridges has been observed scribed spindle fibers in the constricted reonly in relation with meiotic divisions. In gion of cytoplasm at telophase in spermasome cases such special cytoplasmic togenic cells. However, resorbing spindle
bridges have been observed also in the fibers have been noted in intercellular
metaphase of the second meiotic division bridges between cnidoblasts of Hydra
(fig. 5), though this picture does not show (Fawcett et al., '59). The cisternae associthe two secondary spermatocytes at meta- ated with these cytoplasmic bridges of
phase joined completely by this bridge. rooster spermatocytes appear completely
The bridge is, however, similar to that unrelated to spindle fibers.
shown in figures 2 to 4.
Although many details of the formation
No indications of spindle fibers have of these bridges on the rooster spermatobeen observed in these cytoplasmic bridges. genic cells are not yet known, one can
The spindle fibers, however, are clearly dis- speculate on the mode of their formation.
cernible as dense tubule-like structures at As the cytoplasm becomes constricted at
metaphase (fig. 5) and anaphase.
the equa.tor during telophase and in the
Cisternae are no longer closely associ- cytoplasmic bridge which formed after the
ated with the bridges during interkinetic division, cisternae distributed in the cytostages in this species. At such times the plasm may orient themselves parallel to
bridges appear to be similar to those de- each other at right angles to the spindle
scribed in other species (fig. 6 ) (Burgos axis in the region of the constriction. This
and Fawcett, '55; Fawcett and Burgos, '56; special arrangement of cisternae is seen in
the bridges only in dividing stages. These
Fawcett et al., '59).
In thicker sections stained with iron membranous cisternae are observed in the
hematoxylin for light microscopy a dense cytoplasm of the meiotic cells (fig. 2) and
body is observed in the constricted region probably would correspond to the lamellar
of meiotic division (fig. 1, arrows). This systems of membranes which have been
is interpreted as representing an intercellu- observed in the cytoplasm of dividing sperlar bridge with associated cisternae
matogenic cells of Drosophila (Ito, '60).
The membranous discs in the cytoplasm
of the bridge may serve as a temporary barLight microscopists have described stain- rier between two daughter cells. These
able granules on the spindle of dividing discs are no longer observed after the telocells at telophase. These have been termed phase in the cytoplasmic bridge area (fig.
6 ) , nor are they found after two daughter
cells have separated completely.
It is not known whether the cytoplasmic
bridge described above is confined to the
meiotic divisions or is characteristic of
other cell divisions. This bridge seems to
characterize one stage of meiotic division
in the rooster.
The structure of the cytoplasmic bridges
in dividing spermatocytes of the rooster is
observed with the electron microscope. A
number of membranous disc-like cisternae
are seen in the cytoplasm of the bridge at
specific stages of meiosis. The formation
and significance of these cisternae are discussed.
The author wishes to acknowledge the
encouragement and suggestions of Professor H. Stanley Bennett in the course of this
study and during the preparation of the
manuscript. He further wishes to express
his appreciation to other members of the
Anatomy Department, School of Medicine,
University of Washington, for advice on
this study.
Bennett, H. S . , and J. H. Luft 1959 s-Collidine
as a basis for buffering furatives. J. Biophys.
Biochem. Cytol., 6: 113-114.
Burgos, M. H., and D. W. Fawcett 1955 Studies on the fine structure of the mammalian
testis. I. Differentiation of the spermatids in
the cat (Felis dornestica). Ibid., I: 287-300.
Fawcett, D. W., and M. H. Burgos 1956 Observations on the CJ tomorphosis of the germinal
and interstitial cells of the human testis. In:
A Ciba Foundation Colloquia on Aging. G . E.
W. Wollstenholme and E. C. P. Millar, eds.
Little, Brown and Co., Boston, vol. 2, pp. 86-96.
Fawcett, D. W., S. ]to and D. Slautterback 1959
The occurrence of intercellular bridges in
groups of cells exhibiting synchronous differentiation. J. Biophys. Biochem. Cytol., 5: 453460.
Flemming, W. 1891 Neue Beitrage zur Kenntniss der Zelle. I. Theil., Arch. Mikr. Anat.,
37: 685-751.
Ito, S. 1960 The lamellar systems of cytoplasmic membranes i n dividing spermatogenic cells
of D?-osophila uirilis. J. Biophys. Biochem.
Cytol., 7: 43344'2.
Luft, J. H. 1959 The use of acrolein as a fixative for light and electron microscopy. Anat.
Rec., 133: 305.
1961 Improvements in epoxy resin embedding methods. J. Biophys. Biochem. Cytol.,
9: 409414.
Palade, G. E. 1955 A small particulate component of the cytoplasm. Ibid., I : 59-68.
Tahmisian, T. N., E. L. Powers and R. L. Devine
1956 Light and electron microscope studies of
morphological changes of the mitochondria during spermatogenesis in the grasshopper. Ibid.,
2: ( SUPPI.) 325-330.
W,atson, M. L. 1958a Staining of tissue sections for electron microscopy with heavy metals. Ibid., 4: 475478.
1958b Staining of tissue sections for
electron microscopy with heavy metals. 11. Applications of solutions containing lead and barium. Ibid., 4: 72,7-729.
Wilson, E. B. 1925 The Cell in Development
and Heredity, 3rd ed. Macmillan Company,
New York.
Yasuzumi, G . , H. Ishida, S. Nakano and H. Yamamot0 1960 SpermatogCnese des animaux r6velCe par le microscope Clectronique. IX.
atude a u microscope Clectronique de la t6lophase des spermatocytes de Cipangopaludina
malleata et Gelastonhinus bicoler de Haan avec
des remarques sur les Nebenkerns. J. Ultrastructure Res., 2: 484494.
All figures represent micrographs of sections of rooster testis fixed i n acrolein followed by
osmium tetroxide, and embedded in epoxy resin.
Light micrograph of a section about 1.5 ,u thick, showing two dense bodies (arrows) between three spermatocytes in the first meiotic division. These bodies appear to correspond to the cytoplasmic bridges of electron micrographs in figures 2 to 6. Chromosomes
(Ch) are seen. Many cross-sectioned nuclei of mature spermatids are seen in the upper
part of this picture, Stained with iron hematoxylin. X 2500.
Electron micrograph showing daughter spermatocytes at telophase of the first meiotic
division. Mitochondria ( M ) , endoplasmic reticulum ( E ) and chromatin material (Ch)
without a nuclear membrane are seen. A special cytoplasmic continuity between spermatocytes is observed in the area indicated by the arrow. A number of parallel membranes are seen in this area. Stained with uranyl acetate. X 6000.
Toshio Nagano
Electron micrograph showing a special intercellular or cytoplasmic bridge between two
daughter spermatids (Sp) at telophase in second meiotic division. A number of cisternae are oriented approximately parallel to the plane of division. The spaces between
the cisternae are denser than the inside of the cisternae. In this section one can see
that some cisternae do not appear to extend completely across the bridge. Expanded
spaces between cisternae contain a few Palade’s particles. The cisternae are similar in
profile to the smooth surfaced endoplasmic reticulum ( E ) . The plasma membrane is
thickened in the constricted region (arrow). Stained with uranyl acetate. X 48,000.
Electron micrograph showing a cytoplasmic bridge connecting two meiotic cells at telophase of the second meiotic division. The bridge is cut in a slightly oblique plane near
the edge. Some cisternae associated with the bridge are continuous with the smooth surfaced endoplasmic reticulum (E). Stained with lead hydroxide. X 54,000.
Metaphase of the second meiotic division. One can see the cisternae associated with the
cytoplasmic bridge (lower right) joining two cells. The spindle fibers ( S ) , chromosome
(Ch) and endoplasmic reticulum ( E ) are seen. Stained with lead hydroxide. X 30,000.
Electron micrograph showing a cytoplasmic bridge between two spermatids at resting
stage. Elongate cisternae associated with the bridge are absent at this stage. The endoplasmic reticulum (E), centriole (C), multivesicular bodies ( V ) , nucleus of the spermatid ( N ) , thickened plasma membrane and the cytoplasm of Sertoli cell ( X ) are seen.
Stained with lead hydroxide. X 32,000.
Toshio Nagano
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cytoplasmic, structure, dividing, rooster, bridge, spermatocytes
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