Ultrastructural changes in the seminiferous epithelium of two seasonally reproducing bats (Mammalia: Chiroptera)

The Sertoli cells of the Cape horseshoe bat (Rhinolophus capensis) and Schreiber's long-fingered bat (Miniopterus schreibersii) undergo marked changes in ultrastructure related to stages in the spermatogenic cycle. The amount of lipid stored in the Sertoli cells varies annually and is at a maximum from just after spermiation to early in the following spermatogenic cycle. During spermatogenesis, the diameter of the lipid droplets decreases, reaching a minimum prior to spermiation. Sertoli cells exhibit a marked apicobasal differentiation, particularly in the vicinity of developing late spermatids, where the cytoplasm of the Sertoli cell is packed with smooth endoplasmic reticulum. The possible roles of lipid droplets and smooth endoplasmic reticulum. The possible roles of lipid droplets and smooth endoplasmic reticulum in steroidogenesis by Sertoli cells are discussed. Junctional complexes occur between Sertoli cells and spermatogonia, are apparently absent from between Sertoli cells and spermatocytes, and are restricted to the region of the developing acrosome in the spermatids. Annulate lamellae, which occur commonly in the developing germinal cells and less frequently in the Sertoli cells, may be associated with the production of microtubules, which are present in both spermatids and Sertoli cells.     

The ultrastructure of the Sertoli cell of the vervet monkey, Chlorocebus aethiops

The ultrastructure of the Sertoli cell of the vervet monkey was studied using both scanning and transmission electron microscopic techniques. SEM micrographs revealed perforated sleeve-like processes which encased mature elongated spermatids which are ready for spermiation. TEM micrographs showed a large Sertoli cell nucleus characterized by many lobes (4–5) and consisting of a homogenous nucleoplasm and a distinctive nucleolus. The nucleus occupies a significant portion of the basal region of the cell. The distribution of chromatin clearly shows high activity of these cells. Lipid droplets and free ribosomes are also found scattered throughout the cytoplasm. Well-developed Golgi apparatus is found in the basal region of the cell. There is phagocytic activity in the Sertoli cells as revealed by the presence of numerous phagosomes. Numerous mitochondria with well-developed tubular cristae are found on the basal side of the nucleus, whereas few mitochondria are located on the apical side of the nucleus. Distinct desmosomes are located between cells. A well-developed smooth endoplasmic reticulum and granular endoplasmic reticulum are frequently found in the cytoplasm of the Sertoli cells. The results of this investigation showed that Sertoli cells of the vervet monkey are almost similar to those of humans and show many similarities with other mammalian species.     

An ultrastructural study of the effect of a diabetogenic dose of alloxan on the secretory ameloblasts of the rat incisor

Sertoli cells of the ground squirrel (Spermophilus lateralis), a seasonal breeder, were examined by light and electron microscopy and their structure, particularly the organization of the cytoskeleton, was related to events that occur in the seminiferous epithelium during spermatogenesis. Among the events considered and described are the apical movement of elongate spermatids, withdrawal of residual cytoplasm from germ cells, transport of smooth endoplasmic reticulum (SER) between the base and apex of the Sertoli cells, and sperm release. These events are dramatically evident in this species because the seminiferous epithelium is thin, i.e., there are few germ cells, and both the germ cells and Sertoli cells are large. Sertoli cells of the ground squirrel have a remarkably well developed cytoskeleton. Microfilaments occur throughout the cell but are most evident in ectoplasmic specializations associated with junctions. Intermediate filaments occur around the nucleus, as a layer at the base of the cell, and adjacent to desmosome-like junctions with germ cells. Intermediate filaments, together with microtubules, are also abundant in regions of the cell involved with the transport of SER, in cytoplasm associated with elongate spermatids, and in processes that extend into the residual cytoplasm of germ cells. Our observations of ultrastructure are consistent with the hypothesis that Sertoli cell microtubules are involved with the movement of germ cells within the seminiferous epithelium, and further implicate these structures as possibly playing a role in the retraction of residual cytoplasm from germ cells and the intracellular transport of SER. The abundance and organization of intermediate filaments suggest that these cytoskeletal elements may also be involved with events that occur during spermatogenesis.     

Distribution of the microtubule-dependent motors cytoplasmic dynein and kinesin in rat testis.

To examine the possible role of microtubule-based transport in testicular function, we used immunofluorescent techniques to study the presence and localization of the microtubule mechanoenzymes cytoplasmic dynein (a slow-growing end-directed motor) and kinesin (a fast-growing end-directed motor) within rat testis. Cytoplasmic dynein immunofluorescence was observed in Sertoli cells during all stages of spermatogenesis, with a peak in apical cytoplasm during stages IX-XIV. Cytoplasmic dynein immunofluorescence was also localized within Sertoli cells to steps 9-14 (stages IX-XIV) germ cell-associated ectoplasmic specializations. In germ cells, cytoplasmic dynein immunofluorescence was observed in manchettes of steps 15-17 (stages I-IV) spermatids, and small, hollow circular structures were seen in the cytoplasm of step 17 and step 18 spermatids during stages V and VI. Kinesin immunofluorescence was observed in manchettes of steps 10-18 spermatids (stages X-VI). The stage-dependent apical Sertoli cell cytoplasmic dynein immunofluorescence, in conjunction with the previously reported orientation of Sertoli cell microtubules (slow-growing ends toward the lumen) and peak secretion of androgen-binding protein and transferrin, is consistent with the hypothesis that cytoplasmic dynein is involved in Sertoli cell protein transport and secretion. Further, the localization of cytoplasmic dynein and kinesin to manchettes is consistent with current hypotheses concerning manchette function.     

Ultrastructure of germ cells, the Leydig cells, and Sertoli cells during spermatogenesis in Boleophthalmus pectinirostris (Teleostei, Perciformes, Gobiidae)

The ultrastructures of germ cells, Leydig cells, and Sertoli cells during spermatogenesis in male Boleophthalmus pectinirostris were investigated by electron microscopic observations. During the period of maturation divisions, well-developed Leydig cells have three major morphological characteristics: a vesicular nucleus, mitochondria with tubular cristae, and a number of smooth endoplasmic reticulum. Based on cytoplasmic features, it appears that Leydig cells are responsible for the synthesis of male sex steroids. Although no clear evidence of steroidogenesis was found in the Sertoli cells, they were found to perform a phagocytic function in the seminiferous lobules. Most Sertoli cells contain granules thought to represent deposited glycogen or lipid but there is no indication of a transfer of nutrients to the spermatids. During the period of germ cell degeneration, several characteristics of phagocytosis appear in the cytoplasm of the Sertoli cells. In particular, it is assumed that the Sertoli cells are involved in the degeneration and resorption of undischarged spermatids after spermiation. No acrosome of the sperm is formed. The structure of the spermatozoon in B. pectinirostris is very similar and closely resembles to those of suborder Gobioidei (perciform type teleosts). The flagellum or sperm tail shows the typical 9+2 array of microtubules.     

Changes in endoplasmic reticulum during spermiogenesis in the mouse

Summary Changes in the endoplasmic reticulum of mouse spermatids during spermiogenesis were examined by scanning electron microscopy, applying the OsO₄-DMSO-OsO₄ method, which permits 3-dimensional observation of cell organelles. At the same time, the endoplasmic reticulum was stained selectively by the Ur-Pb-Cu method, and 0.5 m-thick sections were prepared for observation by transmission electron microscopy. The results demonstrated stereoscopically the mode of disappearance of the endoplasmic reticulum. In spermatids of the early maturation phase, the endoplasmic reticulum was of uniform diameter, branched and anastomosed, forming a complicated three-dimensional network throughout the cytoplasm. A two-dimensional net was also noted to have formed just beneath the plasma membrane and about Sertoli cell processes invaginating the spermatid cytoplasm. As spermiogenesis progressed, the spread-out endoplasmic reticulum gradually aggregated to form a condensed, glomerulus-like structure consisting of a very thin endoplasmic reticulum connected to the surrounding endoplasmic reticulum. This structure corresponds to the so-called radial body. Thus, the endoplasmic reticulum may aggregate, condense, be transformed into a radial body, and be removed from the cytoplasm. The two-dimensional endoplasmic reticulum-net, just beneath the plasma membrane and surrounding processes of Sertoli cells, disappeared in spaces where the three-dimensional endoplasmic reticulum network was scarce. Both the two-dimensional endoplasmic reticulum-net structure and the three-dimensional endoplasmic reticulum network disappeared at the same time, indicating that they may be closely related.     

Effect of the microtubule disrupting agents,colchicine and vinblastine,on seminiferous tubule structure in the rat

Injections of colchicine or vinblastine were given intratesticularly and rats sacrificed 6 and 12 hr later. Colchicine and vinblastine produced identical morphological patterns of response in the seminiferous tubules resulting in arrest of germcell mitoses and meioses and a rapid depletion of the microtubules normally found within the Sertoli cell. Sloughing of cells into the lumen of seminiferous tubules was the most prominent feature noted. Germ cells and portions of the apical Sertoli cells were frequently sloughed together where they remained in close association. Usually germ cells and associated Sertoli cell fragments were cleaved from the wall of the seminiferous tubule at a level between dissimilar generations of germ cells, e.g. between spermatocytes and spermatids. This selective sloughing probably occurred as the result of the support normally provided by intercellular bridges which link clones of like germ cell types. Sequential steps in the process leading to sloughing of Sertoli-germ cell associations could be inferred from observations made in plastic 1 μm sections. Cell sloughing at 12 hr post-injection was generally more extensive. It was frequently noted that germ cells and the apical portions of Sertoli cells had been extruded to the level of the most adluminal tight junctions forming the blood-testis barrier. It was concluded that disruption of Sertoli microtubules was responsible for sloughing of Sertoli fragments and associated germ cells, and that the cytoskeletal support of the Sertoli cell was, at least in part, dependent upon the integrity of Sertoli microtubules. The Sertoli cell could not round-up after loss of its cytoskeletal support, due to the numerous attachment devices known to link it with various apically positioned germ cells. Thus, the cell was severed at some point along its delicate apical processes, as the consequence of forces produced by the ‘rounding-up’ process. Long-term sacrifice after vinblastine or colchicine treatment allowed the Sertoli cells to regain microtubules and long processes but not their typical configuration. Spermatogenesis remained severely impaired.     

Spermiogenesis in Xenopus laevis: from late spermatids to spermatozoa

Spermatogenesis is a complex morphogenetic process in which microfilaments and microtubules have been shown to play an important role. The last steps of Xenopus spermatogenesis, i.e., the corkscrew shaping of the sperm head, have been followed to study actin and microtubule distribution by conventional and immunoelectron microscopy. During sperm head morphogenesis, actin is absent in the elongating spermatids, but it is present in the Sertoli cells where results localized at the periphery of their cytoplasm that surrounds the developing germ cells. Sertoli cell actin and microtubules may assist the elongation and the shaping of the spermatids and function in maintaining the Sertoli-spermatid association.     

Interrelationships between Sertoli cells and germ cells in the Syrian hamster

The interrelationships of the Sertoli cells and germ cells in the Syrian hamster were examined using the electron microscope. Demosome-like junctions were observed attaching Sertoli cells to spermatogonia and spermatocytes. In the region of the junctions dense plaques lay on the cytoplasmic surfaces of the plasmalemma of the opposing cells. Sertoli cell cytoplasmic filaments converged in the area of the junctions and inserted into the subsurface densities. Filaments were not observed associated with the subsurface densities of the germ cells. In the region of the junctions a 15...20 nm gap, filled with an attenuate amorphous substance, separated the plasmalemmata. Another attachment device termed "junctional specialization" occurred between Sertoli cells, and preleptotene spermatocytes and all successive developmental steps in the germ cell line in the hamster. The junctional specializations consisted of a mantel of Sertoli cell cytoplasmic filament lying subjacent to the Sertoli cell plasmalemma and an opposed cisterna of the endoplasmic reticulum. In stages VII-VIII preleptotene supermatocytes were observed in transit from the basal compartment to the adluminal compartment. While Sertoli-Sertoli junctions adluminal to the spermatocytes remained intact, typical Sertoli-Sertoli junctions formed between opposed Sertoli cell processes basal to the spermatocytes. It is proposed that, during the passage of spermatocytes in to the adluminal compartment, junctional specializations associated with preleptotene spermatocytes in the basal compartment migrate basal to the spermatocytes and contribute to formation of Sertoli-Sertoli junctions. Treatment of seminiferous tubules with hypertonic media was used to demonstrate that the junctional specializations function in cell-to-cell adhesion. Data indicated that these junctions function to retain the developing spermatids within the seminiferous epithelijm until the time of spermiation. At spermination the junctional specializations disappear and the spermatids drift off into the tubule lumen.     

Ultrastructural localization of phosphatases in the testes of the domestic fowl: Acid phosphatase and thiamine pyrophosphatase

Summary ACPase and TPPase activity has been examined in the germinal epithelium of the testes in the domestic fowl. ACPase activity in spermatogonia and spermatocytes was confined to the Golgi complex. In spermatids ACPase activity was seen in the endoplasmic reticulum and nuclear envelope in the phase I and especially in the phase II (the elongating phase). This activity gradually decreased during the next phase III, and had disappeared in the final phase IV. The membrane body showed ACPase reaction in the small peripheral vacuoles and cisternal structures surrounding large central vacuoles. ACPase was also present in vesicles surrounding the developing tail. Late spermatids showed an abundance of autophagic vacuoles which had a complex array of ACPase positive delimiting membranes. In Sertoli cells ACPase activity was predominant in the lysosomes. TPPase activity was seen in the cisternae of the Golgi complex in spermatogonia and spermatocytes. In spermatids activity was present in the endoplasmic reticulum during the phase II, but it is lost in later stages. The smaller vacuoles and cisternal structures in the membrane body also showed reaction products. According to the present results it is thought likely that the smaller vacuoles and cisternal structures of the membrane body are of endoplasmic reticulum origin. The autophagic vacuoles in spermatids and the lysosomes of Sertoli cells are considered responsible for the degradation of residual bodies cast off by spermatids.     

Molecular cloning and localization of a CEACAM2 isoform,CEACAM2‐L,expressed in spermatids in mouse testis

Carcinoembryonic antigen (CEA) family, a subgroup of the immunoglobulin (Ig) superfamily, is divided into two sub‐families: the CEA‐related cell adhesion molecules (CEACAM) and the pregnancy‐specific glycoproteins. The isoform CEACAM2 is expressed in mouse testis; in this study, we identified a novel isoform of Ceacam2, Ceacam2‐Long (Ceacam2‐L). CEACAM2‐L is different from CEACAM2 in that it has much longer cytoplasmic tail region. Ceacam2‐L starts to appear faintly in mouse testis after 3 weeks of postnatal development, and its expression level increased after 5 weeks. Immunoblot analysis confirmed the expression of CEACAM2‐L in the seminiferous epithelium of mouse testis. Immunohistochemical data showed that CEACAM2‐L was not observed on spermatogonia, spermatocytes, round spermatids, or Sertoli cells, but was seen at the plasma membrane of elongating spermatids in contact with extended cytoplasmic processes of Sertoli cells. CEACAM2‐L was not detected at the head region of elongating spermatids, where the apical ectoplasmic specialization is constructed. These data suggest that CEACAM2‐L might be a novel adhesion molecule contributing to cell‐to‐cell adhesion between elongating spermatids and Sertoli cells within the seminiferous epithelium. Mol. Reprod. Dev. 79: 843–852, 2012. © 2012 Wiley Periodicals, Inc.     

Ultrastructure of spermiogenesis in the American alligator,Alligator mississippiensis (Reptilia,Crocodylia, Alligatoridae)

Testicular samples were collected to describe the ultrastructure of spermiogenisis in Alligator mississipiensis (American Alligator). Spermiogenesis commences with an acrosome vesicle forming from Golgi transport vesicles. An acrosome granule forms during vesicle contact with the nucleus, and remains posterior until mid to late elongation when it diffuses uniformly throughout the acrosomal lumen. The nucleus has uniform diffuse chromatin with small indices of heterochromatin, and the condensation of DNA is granular. The subacrosome space develops early, enlarges during elongation, and accumulates a thick layer of dark staining granules. Once the acrosome has completed its development, the nucleus of the early elongating spermatid becomes associated with the cell membrane flattening the acrosome vesicle on the apical surface of the nucleus, which aids in the migration of the acrosomal shoulders laterally. One endonuclear canal is present where the perforatorium resides. A prominent longitudinal manchette is associated with the nuclei of late elongating spermatids, and less numerous circular microtubules are observed close to the acrosome complex. The microtubule doublets of the midpiece axoneme are surrounded by a layer of dense staining granular material. The mitochondria of the midpiece abut the proximal centriole resulting in a very short neck region, and possess tubular cristae internally and concentric layers of cristae superficially. A fibrous sheath surrounds only the axoneme of the principal piece. Characters not previously described during spermiogenesis in any other amniote are observed and include (1) an endoplasmic reticulum cap during early acrosome development, (2) a concentric ring of endoplasmic reticulum around the nucleus of early to middle elongating spermatids, (3) a band of endoplasmic reticulum around the acrosome complex of late developing elongate spermatids, and (4) midpiece mitochondria that have both tubular and concentric layers of cristae. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Fine structural changes in Sertoli and Leydig cells during the reproductive cycle of the ground squirrel, Citellus lateralis

During spermatogenesis in sexually mature ground squirrels Leydig and Sertoli cells were morphologically well differentiated. For Leydig cells the most prominent organelles were lipid droplets, mitochondria with tubulo-vesicular cristae and abundant agranular reticulum organized as a mass of anastomosing tubules. These morphological criteria suggest that the Leydig cells were steroidogenically active. Sertoli cells exhibited a topographical distribution of certain organelles with basal regions containing stacks of granular reticulum, and large areas of agranular reticulum. The cytoplasm surrounding maturing germ cells contained numerous microtubules, and an adluminal layer of spermatids at a certain stage of spermiogenesis became enveloped by Sertoli cytoplasm containing an enormous proliferation of agranular reticulum. The presence of these organelles in Sertoli cells suggests that during spermatogenesis they are active in the synthesis of proteins and steroids. In particular the mass of agranular reticulum surrounding late stage spermatids indicates that steroids may be required for spermatid maturation and/or spermiation. By contrast Leydig and Sertoli cells observed during testicular regression, when only spermatogonia remain in the seminiferous tubules, had undergone structural changes. Leydig cells were still numerous and large with abundant agranular reticulum that was now organized as a loose assemblage of single unbranched tubules. Sertoli cells were drastically reduced in both cytoplasmic volume and content of organelles.     

Membranes and calcium sequestration during spermiogenesis in the cotton seed bug (Dysdercus intermedius: Heteroptera)

Summary By use of osmium ferricyanide (OsFeCN) staining the fate of cytoplasmic membranes was followed during spermiogenesis in the cotton seed bug (Dysdercus intermedius). During early spermiogenesis interzonal lamellae of endoplasmic reticulum become aggregated as a stack of membranes traversing the entire cell body from the nucleus to the cytoplasmic bridge connecting neighbouring spermatids. Cisternae of endoplasmic reticulum ensheath the acroblast from which vesicles of different sizes are pinched off into the cytoplasm. The oxalate method was used to show that acroblast and associated vesicles are calcium-sequestering sites in spermatids. Membrane profiles with dense calcium oxalate precipitate derived from the acroblast form an uninterrupted membranous sheath at the apical side of the nucleus where the proacrosome will be attached. With further development of the spermatids, the vesicles derived from the acroblast also participate in forming a calciumsequestering sheath enveloping the axoneme and the mitochondrial nebenkern derivatives.     

Actin-related intercellular adhesion junctions in the germinal compartment of the testis in the hagfish (Eptatretus stouti) and lamprey (Lampetra tridentatus)

The germinal epithelium of male vertebrates consists of Sertoli cells and spermatogenic cells. Intercellular junctions formed by Sertoli cells assume critical roles in the normal functions of this epithelium. While Sertoli cell junctions have been well characterized in mammals, similar junctions in nonmammalian vertebrates have received little attention. We examined the intercellular junctions found within the germinal epithelium of the hagfish (Eptatretus stouti) and lamprey (Lampetra tridentatus). Ultrastructurally, Sertoli cells were seen to form filament-associated junctions in both species. Adjacent Sertoli cells formed microfilament-related junctions near their apices. Filaments of these junctions were arranged in loose networks and were not associated with cisterns of endoplasmic reticulum. In fixed, frozen sections of hagfish testis, similar areas labeled with rhodamine phalloidin, indicating the filament type is actin. In the lamprey, desmosomes were observed immediately below the microfilament-related junctions. In appearance and location, the Sertoli cell junctions observed in these species resembled those of the typical junctional complex of other epithelial cell types. No junctions were observed between Sertoli cells and elongating spermatids. In the hagfish, but not the lamprey, an additional zone of microfilaments occurred near the base of Sertoli cells in areas of association with the basal lamina. Our observations are consistent with the proposal that the unique forms of intercellular attachment found in the testes of higher vertebrates evolved from a typical epithelial form of intercellular junction.     

Cytoplasmic microtubules and fungal morphogenesis: ultrastructural effects of methyl benzimidazole-2-ylcarbamate determined by freeze- substitution of hyphal tip cells

The effects of methyl benzimidazole-2-ylcarbamate (MBC), one of only a few agents that are active against microtubules of fungi, were analyzed at the ultrastructural level in freeze-substituted hyphal tip cells of Fusarium acuminatum. Nontreated and control cells had numerous microtubules throughout. After just 10 min of exposure to MBC, almost no cytoplasmic microtubules were present, except near spindle pole bodies. After 45 min of exposure to MBC, no microtubules were present in hyphal tip cells, but they were present in the relatively quiescent subapical cells. These observations suggested that there are different rates of turnover for cytoplasmic microtubules in apical and subapical cells and for microtubules near spindle pole bodies and that MBC acts by inhibiting microtubules assembly. A statistical analysis of the distribution of intracytoplasmic vesicles in thick sections of cells treated with MBC, D2O or MBC + D2O was obtained by use of a high- voltage electron microscope. More than 50% of the vesicles in the apical 30 micrometers of control cells were found to lie within 2 micrometers of the tip cell apex. MBC treatment caused this vesicle distribution to become uniform, resulting in a substantial increase in the number of vesicles in subapical regions. The reduction in the number of cytoplasmic microtubules, induced by MBC, apparently inhibited intracellular transport of these vesicles and rendered random the longitudinal orientation of mitochondria. In most cases, D2O appeared capable of preventing these MBC-effects through stabilization of microtubules. These observations support the "vesicle hypothesis" of tip growth and establish a transport role for cytoplasmic microtubules in fungal morphogenesis.     

Sertoli cell ectoplasmic specializations in the seminiferous epithelium of the testosterone-suppressed adult rat

The Sertoli cell ectoplasmic specialization is a unique junctional structure involved in the interaction between elongating spermatids and Sertoli cells. We have previously shown that suppression of testicular testosterone in adult rats by low-dose testosterone and estradiol (TE) treatment causes the premature detachment of step 8 round spermatids from the Sertoli cell. Because these detaching round spermatids would normally associate with the Sertoli cell via the ectoplasmic specialization, we hypothesized that ectoplasmic specializations would be absent in the seminiferous epithelium of TE-treated rats, and the lack of this junction would cause round spermatids to detach. In this study, we investigated Sertoli cell ectoplasmic specializations in normal and TE-treated rat testis using electron microscopy and localization of known ectoplasmic specialization-associated proteins (espin, actin, and vinculin) by immunocytochemistry and confocal microscopy. In TE-treated rats where round spermatid detachment was occurring, ectoplasmic specializations of normal morphology were observed opposite the remaining step 8 spermatids in the epithelium and, importantly, in the adluminal Sertoli cell cytoplasm during and after round spermatid detachment. When higher doses of testosterone were administered to promote the reattachment of all step 8 round spermatids, newly elongating spermatids associated with ectoplasmic specialization proteins within 2 days. We concluded that the Sertoli cell ectoplasmic specialization structure is qualitatively normal in TE-treated rats, and thus the absence of this structure is unlikely to be the cause of round spermatid detachment. We suggest that defects in adhesion molecules between round spermatids and Sertoli cells are likely to be involved in the testosterone-dependent detachment of round spermatids from the seminiferous epithelium.     

Membranous tubes in pseudoscorpion spermiogenesis

The highly complicated differentiation of the spermatid in the pseudoscorpion Diplotemnus sp. is accomplished without the presence of microtubules. Instead membranous tubes measuring approximately 50 nm in diameter and closely associated with endoplasmic reticulum are found from early to mid spermatids. The lumen of the tube is devoid of electron dense contents but a fluffy material is attached to the cytoplasmic side. They run straight or slightly bent and are in open connection with the cell membrane. First appearing near the cell bridge of the interconnected spermatids they form a bundle in the longitudinal axis during a transitory phase of elongation. When the cell rounds off again the tubules together with the endoplasmic reticulum disappear. The arrangement of the tubes and their presence during abortive elongation of the spermatid suggest a supportive function commonly attributed to microtubules. Moreover, the open connection with the cell membrane and their close association with the endoplasmic reticulum may indicate their participation also in transport.     

Spermiogenesis in the bullfrog (Rana catesbeiana): a study of cytoplasmic events including cell volume changes and cytoplasmic elimination

The process by which spermatid cytoplasmic volume is reduced and cytoplasm eliminated during spermiogenesis was investigated in the bullfrog Rana catesbeiana. At early phases of spermiogenesis, newly formed, rounded spermatids were found within spermatocysts. As acrosomal development, nuclear elongation, and chromatin condensation occurred, spermatid nuclei became eccentric within the cell. A cytoplasmic lobe formed from the caudal spermatid head and flagellum and extended toward the seminiferous tubule lumen. The cytoplasmic lobe underwent progressive condensation whereby most of its cytoplasm became extremely electron dense and contrasted sharply with numerous electron-translucent vesicles contained therein. At the completion of spermiogenesis, many spermatids with their highly condensed cytoplasm still attached were released from their Sertoli cell into the lumen of the seminiferous tubule. There was no evidence of the phagocytosis of residual bodies by Sertoli cells. Because spermatozoa are normally retained in the testis in winter and are not released until the following breeding season, sperm were induced to traverse the duct system with a single injection of hCG. Some spermatids remained attached to their cytoplasm during the sojourn through the testicular and kidney ducts; however, by the time the sperm reached the Wolffian duct, separation had occurred. The discarded cytoplasmic lobe (residual body) appeared to be degraded with the epithelium of the Wolffian duct. It was determined that the volume of the spermatid was reduced by 87% during spermiogenesis through a nuclear volume decrease of 76% and cytoplasmic volume decrease of 95.3%.