Evolution of Sertoli cell processes invading the cytoplasm of rat spermatids

Unique structures of organelles observed in primary spermatocytes after micro-injection of protein solutions such as immunoglobulin into the lumen of the seminiferous tubules in mice and rats

Unique membranous structures of intracytoplasmic organelle, sting of a stack of a few flat cisternae about 50 nm in thickness, were found in mouse and rat spermatocytes after micro-injection of immunoglobulin G into the lumina of the seminiferous tubules. Other proteins such as BSA and cytochrome c used in this study also induced the structures. In most cases, the stacks of cisternae were rolled up like cigars or cylinders. The structures varied in length and diameter, the largest one observed in this study being 10.7 μm in length. The structures did not appear when the testes were fixed just after micro-injection and were formed transiently: they were observed in the spermatocytes fixed between 1 and 4 h after injection. Cytochrome c, micro-injected as an inter-cellular tracer, was visualised by a diaminobenzidine reaction. As the reaction product was not contained in the cisternae of the unique structures, the lumen of the cisternae of the organelles was not continuous with the inter-cellular space. A flocculent material of low density was observed in the cisternae of the organelle. Similar material was observed in the lumina of solitary cisternae of the rough endoplasmic reticulum in the spermatocytes, suggesting that the structures derived from endoplasmic reticulum.

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.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: changes in spermatid organelles associated with development of spermatozoa

Spermiogenesis is a long process whereby haploid spermatids derived from the meiotic divisions of spermatocytes undergo metamorphosis into spermatozoa. It is subdivided into distinct steps with 19 being identified in rats, 16 in mouse and 8 in humans. Spermiogenesis extends over 22.7 days in rats and 21.6 days in humans. In this part, we review several key events that take place during the development of spermatids from a structural and functional point of view. During early spermiogenesis, the Golgi apparatus forms the acrosome, a lysosome-like membrane bound organelle involved in fertilization. The endoplasmic reticulum undergoes several topographical and structural modifications including the formation of the radial body and annulate lamellae. The chromatoid body is fully developed and undergoes structural and functional modifications at this time. It is suspected to be involved in RNA storing and processing. The shape of the spermatid head undergoes extensive structural changes that are species-specific, and the nuclear chromatin becomes compacted to accommodate the stream-lined appearance of the sperm head. Microtubules become organized to form a curtain or manchette that associates with spermatids at specific steps of their development. It is involved in maintenance of the sperm head shape and trafficking of proteins in the spermatid cytoplasm. During spermiogenesis, many genes/proteins have been implicated in the diverse dynamic events occurring at this time of development of germ cells and the absence of some of these have been shown to result in subfertility or infertility.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Ultrastructure and function of Sertoli cell processes in the Korean native goat

The ultrastructure of Sertoli cell in the testes of Korean native goats was investigated by scanning and transmission electron microscopy to elucidate the relationship between germ cell and Sertoli cell processes in the spermiogenetic cycle. Type-A Sertoli cells at stage V of the spermiogenetic cycle and type-B Sertoli cells at stage VII of the spermiogenetic cycle were used for analysis. Morphologically, the Sertoli cell processes were classified into sheet-like and slender cord-like processes. The sheet-like process originated solely from the Sertoli cell column while the slender cord-like process projected either from the Sertoli cell column or the sheet-like process. Periodic acid (PA)-thiocarbohydrazide (TCH)-silver protein (SP)-physical development (PD)-positive granules were found diffusively both in the sheet-like and slender cord-like processes near the round spermatid, whereas they had accumulated near the head of the elongated spermatid. The morphological variation and glucoconjugate histochemical reaction of the Sertoli cell processes reflect nourishment, movement and transformation of the spermatogenic cells in accordance with spermiogenesis.

Intermediate filaments in Sertoli cells

Using immunohistochemical techniques both at light and electron microscopic levels, the arrangement and distribution of intermediate filaments in Sertoli cells of normal testis (in rat and human), during pre- and postnatal development (in rabbit, rat, and mouse) and under experimental and pathological conditions (human, rat), have been studied and related to the pertinent literature. Intermediate filaments are centered around the nucleus, where they apparently terminate in the nuclear envelope providing a perinuclear stable core area. From this area they radiate to the plasma membranes; apically often a close association with microtubules is seen. Basally, direct contacts of the filaments with focal adhesions occur, while the relationship to the different junctions of Sertoli cells is only incompletely elucidated. In the rat (not in human) a group of filaments is closely associated with the ectoplasmic specializations surrounding the head of elongating spermatids. Both in rat and human, changes in cell shape during the spermatogenic cycle are associated with a redistribution of intermediate filaments. As inferred from in vitro studies reported in the literature, these changes are at least partly hormone-dependent (vimentin phosphorylation subsequent to FSH stimulation) and influenced by local factors (basal lamina, germ cells). Intermediate filaments, therefore, are suggested to be involved in the hormone-dependent mechanical integration of exogenous and endogenous cell shaping forces. They permit a cycle-dependent compartmentation of the Sertoli cell into a perinuclear stable zone and a peripheral trafficking zone with fluctuating shape. The latter is important with respect to the germ cell-supporting surface of the cell which seems to limit the spermatogenetic potential of the male gonad.

The Sertoli cell membrane body in the skink

The structure of the Sertoli cell and its physical relationship with the germ cells was studied in laboratory maintained skinks, Eumeces laticeps (Schneider) in January, and September, corresponding to the periods of prenuptial and postnuptial spermatogenesis respectively. Light micrographs obtained using 1 micron thick plastic sections, show the Sertoli cell to have a large polymorphic nucleus located in the basal portion of the cell, and a darkly staining juxtanuclear body. In ultrathin sections, this body consists of a complex array of thin, electron dense membranous structures resembling the endoplasmic reticulum. The lumina of these membranous channels appear empty. Between the channels, there are structures that resemble the expanded cisternae of the endoplasmic reticulum. In some sections, these dilated cisternae are confluent with the channels, indicating that the channels and the cisternae are parts of the same structure. Three organelles, namely, mitochondria, lysosomes and microfilaments are found among the elements of the membrane body. There is no structural modification of the channels where they come in contact with mitochondria, but they are dilated in proximity to lysosomes. In some sections bundles of microfilaments are clearly visible within the diamond shaped region of contact between two channels, suggesting that these organelles are involved in structural or functional organization of the membrane body.

Spermiation and sperm maturation in the marmoset

The scanning and transmission electron microscopes were used to examine the processes of spermiation and sperm maturation in the marmoset. We observe that the heads of late spermatids are embedded in the apical aspect of the large sleeve-like columnar portion of Sertoli cells. As spermiogenesis progresses, spermatids become associated with numerous small apical Sertoli cell extensions. These finger-like processes undergo a sequence of changes during spermiation. Spermatozoa from the caput, corpus, and cauda epididymides were examined. In caput epididymis of marmoset, the apical segment of the spermatozoa extends well beyond the rostral edge of the nucleus and folds back on itself. In sagittal sections, the acrosome exhibits a distinct hook shape. In the corpus, the distinctive hook-shaped apical segment of the acrosome is observed in some spermatozoa, but the apical extension is significantly smaller or projects out only slightly beyond the nucleus. In cauda epididymis, the extension is absent. A similar acrosomal hook has been reported in the pigtailed monkey, which is an Old World species. We suggest that changes in acrosome structure during sperm maturation may be fairly widespread among primates.

Changes in endoplasmic reticulum during spermiogenesis in the mouse

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 micron-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.

Mechanism for the removal of residual cytoplasm from spermatids during mouse spermiogenesis

During spermiogenesis, cytoplasmic processes of Sertoli cells invade spermatid cytoplasm to form a canal complex (Sakai et al., 1988). Thin tubules are formed from the canal complex and intertwine with each other to give rise to the "mixed body." In the present study, analysis of the changes undergone by the intertwining thin tubules indicated that they contribute to the removal of cell organelles from spermatid cytoplasm. Intertwining thin tubules were first detected at step 13. By step 15, their number had greatly increased. In the present study, the membranes of the intertwining thin tubules were clearly observed to be continuous with the spermatid plasma membranes. Thus, the mixed body possibly may be formed as a long pit of the spermatid plasma membrane situated close to the invading Sertoli cell process. With the progress of spermiogenesis, the lumens of the intertwining thin tubules gradually became swollen, and the intertwining swollen tubules fused with each other so that the spermatid cytoplasm enclosed by the intertwining swollen tubules isolated into fragments. This fragmented cytoplasm, which contained a large amount of endoplasmic reticulum, became spherical. Small branches of the invading Sertoli cell processes entered into the lumens of the intertwining swollen tubules and occupied their interior to the point that, finally, they completely engulfed the fragmented spermatid cytoplasm. Because the invading Sertoli cell processes were continuous with Sertoli cell bodies surrounding a spermatid at this step, it is possible for the fragmented cytoplasm to be transported into the latter by way of the invading Sertoli cell processes.

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%.

Endocytic origin for periaxonemal vesicles along the flagellum during mouse spermiogenesis

In mouse spermatogenesis, formation of the flagellum is associated with the presence of numerous periaxonemal vesicles. These are present in the cytoplasmic portion, limited by the deep invagination of the plasma membrane surrounding the axoneme; the number and size of these vesicles varies during spermiogenesis. The vesicles appear at step 10 in young spermatids and increase in number and size until step 14; they then rapidly decrease and disappear at step 16. Cationic ferritin (CF), an endocytic marker, directly injected in the lumen of the seminiferous tubules, labels periaxonemal vesicles, 1 hour after the injection, showing their endocytic origin. Some vesicles are membrane invaginations, still in continuity with the extracellular space, whereas others probably come from a phagocytic mechanism. The CF also shows that some vesicles flow along the axoneme and they accumulate in small cytoplasmic extensions before disappearing. All these complex endocytic phenomena go on to form certain components of the flagellum.

Changes in the distribution of microtubules and intermediate filaments in mammalian Sertoli cells during spermatogenesis

We have studied the distribution of microtubules and intermediate filaments in mammalian Sertoli cells during spermatogenesis. The arrangement of microtubules was determined, by indirect immunofluorescence, in ground squirrel testes that were 1) fixed, mechanically fragmented, and attached to polylysine-coated slides, and 2) fixed, embedded in polyethylene glycol, and sectioned. Intermediate filament patterns were determined, also by indirect immunofluorescence, in sections of unfixed rat testis. Results from these studies were confirmed and extended using electron microscopy. Microtubules first become evident in lateral processes that embrace round spermatids. When spermatids elongate and become situated in apical crypts of Sertoli cells, the microtubules become oriented parallel to the long axis of Sertoli cells and surround the crypts. As spermatids mature and acquire a saucer shape, apical microtubules progressively concentrate in Sertoli cell regions adjacent to the acrosome and eventually form discrete C-shaped structures that disappear during spermiation. Intermediate filaments in rat Sertoli cells are centered around the nucleus. From perinuclear regions, filaments extend toward desmosome-like junctions with early spermatogenic cells and into the apical cytoplasm where they have a transient association with crypts containing elongate spermatids. Filaments amongst crypts are most evident in early stages of the spermatogenic cycle when apical crypts are situated deep within the epithelium. They become less evident and eventually disappear as spermatids assume a more apical position. Our fluorescence studies and ultrastructural analyses indicate that the association of intermediate filaments with crypts is specific to regions adjacent to the dorsal or convex aspect of spermatid heads. In these regions, approximately 8 to 12 uniformly aligned filaments are intimately associated with actin filaments in ectoplasmic specializations surrounding the crypts. We conclude that, like actin, the distribution of microtubules and intermediate filaments changes in Sertoli cells during spermatogenesis. The distribution of microtubules correlates with the irregular columnar shape of Sertoli cells. We suspect that the apically situated intermediate filaments may play a role in anchoring or positioning Sertoli cell crypts deep within the epithelium during the early stages of the spermatogenic cycle.

Dynamic changes in Sertoli cell processes invading spermatid cytoplasm during mouse spermiogenesis

Studies using thick sections stained by ATPase cytochemistry and scanning electron microscopy were carried out to determine three-dimensional ultrastructural alterations in Sertoli cell processes invading neighboring spermatids during mouse spermiogenesis. Sertoli cell processes start invading spermatid cytoplasm at the acrosomal phase of development and undergo considerable change at the maturation phase of development. At step 14, these processes elongate and begin to branch in the spermatid cytoplasm, and by step 15, they extend in various directions to form a complex of canals that the authors have designated the canal complex. The present observations also clarify that the complicated canal complex undergoes regional modification. At the late stages of maturation, the endoplasmic reticulum has gathered with other cell organelles to form aggregates of endoplasmic reticulum in the vicinity of which invading Sertoli cell processes extensively ramify further into thin tubules that intertwine with each other to form a region of thin tubules. In thin sections, each such region was a complex, consisting of small vesicles and endoplasmic reticulum, and corresponded to what has been defined as a mixed body by Morales and Clermont (Anat. Rec., 203:233-244, 1982). During the course of the formation of the region, the invading Sertoli cell processes are continuous at all times with the cell body of the surrounding Sertoli cell.

The ultrastructural effects of di-n-pentyl phthalate on the testis of the mature rat

A sequential morphological study has been carried out to examine the ultrastructural effects of di-n-pentyl phthalate (DPP) on the mature rat testis. A single oral dose of 2.2 g DPP/kg body wt was administered, and testes, perfuse-fixed 3-48 hr after dosing, were examined by transmission electron microscopy. By 3 hr, rarefaction of the basal Sertoli cell cytoplasm was seen and the basal plasma membranes separating adjacent Sertoli cells were thrown into a series of convoluted profiles with the appearance of interdigitating cell processes. The subjacent ectoplasmic specializations that normally face these membranes were disrupted, and by 12 hr the inter-Sertoli junctions showed numerous membrane discontinuities. The lateral processes of Sertoli cell cytoplasm, which separate germ cells, showed retraction and fragmentation, resulting in direct contact between adjacent germ cells or the isolation of germ cells unapposed by Sertoli cell plasma membrane. In addition, the ectoplasmic specializations associated with Sertoli-spermatid and Sertoli-pachytene spermatocyte junctions were often disrupted or absent. The mitochondria in the Sertoli cells were enlarged and, in some tubules, increased in number. The changes seen were restricted to tubules in the successive stages XI-XIV, I, and II of the spermatogenic cycle. Elongating spermatids (steps 12-15) showed cytoplasmic condensation and vacuolation by 12 hr and were necrotic by 24 hr. A small proportion of zygotene and early pachytene spermatocytes showed necrosis by 24 hr after dosing. By 48 hr, the cytoplasmic rarefaction and convoluted plasma membranes had regressed and ectroplasmic specializations had reformed along Sertoli-Sertoli junctions.

Glycoprotein synthesis in the Golgi apparatus of spermatids during spermiogenesis of the rat

During steps 1-7 of spermiogenesis the Golgi apparatus contributes to the formation of the acrosomic system which develops at the surface of the nucleus. Later, in step 8, the Golgi apparatus detaches from the acrosome and remains suspended in the elongated cytoplasm until it degenerates during step 16. Using 3H-fucose as a tracer and the radioautographic technique, we observed that the Golgi apparatus incorporates the tracer and delivers the labeled glycoproteins to the developing acrosomic system during steps 1-7 of spermiogenesis, to multivesicular bodies during steps 1-9, and to the remaining cytoplasm and plasma membrane during steps 1-15. Throughout these steps of spermiogenesis the Golgi apparatus does not show major changes in structure; it is composed of a cortex made up of connected stacks of saccules and a medulla showing a loose aggregate of vesicular profiles. Glycoprotein synthesis in this Golgi apparatus, before and after it contributes lysosomal glycoproteins to the growing acrosomic system, was quantitatively assessed in electron microscope EM radioautographs of tissue sections from animals sacrificed at 1, 4, 8, and 24 h of 3H-fucose injection. The incorporation of the labeled sugar was found to remain quantitatively similar during steps 1-15 of spermiogenesis, and therefore, no shift in glycoprotein synthesis took place following separation of the Golgi apparatus from the acrosomic system. Throughout these steps, fucose molecules are first incorporated in the cortex of the organelle and subsequently transported to the medulla, where they temporarily accumulate before being delivered, depending on the step of spermiogenesis, to the acrosomic system, to the multivesicular bodies, and also, presumably, to the plasma membrane.

Ultracytochemical and biochemical evidence for guanylate cyclase in guinea pig testis

Guanylate cyclase activity has been studied biochemically and cytochemically in guinea pig testis. The results of the biochemical assays indicate an equal distribution of this enzyme between the soluble and particulate fractions, which have a different sensitivity to adenosine triphosphate. The cytochemical results demonstrate that the reaction product of guanylate cyclase is detectable in the interstitial capillary endothelial cells and, in the seminiferous epithelium, mainly at the level of the adjacent surfaces of Sertoli and germ cells of the intermediate and adluminal compartments. Guanylate cyclase activity appears at the level of pachytene spermatocytes and persists throughout subsequent stages of development. The distribution in the seminiferous epithelium seems to indicate that guanylate cyclase is involved in the interrelationships between Sertoli and germ cells during gamete differentiation.

Ultrastructure of Sertoli-cell penetrating processes found in germ cells of the golden-mantled ground squirrel (spermophilus lateralis)

We have studied the ultrastructure of Sertoli-cell processes that extend into developing germ cells of the ground squirrel (Spermophilus lateralis). In other mammals it is speculated that these processes anchor germ cells to the seminiferous epithelium and transfer materials between Sertoli and germ cells. In the ground squirrel, Sertoli-cell projections first appear in round spermatids and consist of regions containing numerous mitochondria and intermediate filaments together with areas composed mainly of a fine filamentous matrix. Also present are what may be desmosomelike junctions with adjacent germ cells. During spermatogenesis, numerous changes in the penetrating processes and their internal composition occur. Especially significant are those occurring during the movement of residual cytoplasm basally over spermatid heads: some Sertoli-cell processes contain microtubules, mitochondria, and vesicular elements, but also present are regions that lack organelles and appear simply as thin lamellae of cytoplasm that line cavernous invaginations of the germ cell. Coated vesicles and pits are present in processes and adjacent germ-cell regions at all stages of spermatogenesis. Our observations are consistent with the suggestions that Sertoli-cell processes have an attachment function and that they also may facilitate the movement of residual cytoplasm into the epithelium. Further, they indicate that these structures might be involved with receptor-mediated edocytosis.

Cytochemical study on the distribution of adenylate cyclase in guinea pig testis

The distribution of adenylate cyclase in testis, by means of a specific substrate adenylyl-imidodiphosphate (AMP-PNP), has been determined. Membrane-associated reaction products, indicative of adenylate cyclase activity, are localized by a complete cytochemical medium (containing 10 mM NaF) at the level of the basal compartment of the seminiferous epithelium, on the basal surface of Sertoli cells, and on adjacent plasma membranes of Sertoli cells and spermatogonial cells. At the level of the adluminal compartment, reaction products were found on adjacent plasma membranes of Sertoli cells and early or elongated spermatids. Adenylate cyclase reaction products are detectable by a basal incubation medium (without 10 mM NaF) only in the adluminal compartment on the spermatid plasma membranes.