Nm23/NDP kinases in human male germ cells: role in spermiogenesis and sperm motility?

Nucleoside diphosphate (NDP) kinases, responsible for the synthesis of nucleoside triphosphates and produced by the nm23 genes, are involved in numerous regulatory processes associated with proliferation, development, and differentiation. Their possible role in providing the GTP/ATP required for sperm function is unknown. Testis biopsies and ejaculated sperm were examined by immunohistochemical and immunofluorescence microscopy using specific antibodies raised against Nm23-H5, specifically expressed in testis germinal cells and the ubiquitous NDP kinases A to D. Nm23-H5 was present in sperm extract, together with the ubiquitous A and B NDP kinases (but not the C and D isoforms) as shown by Western blotting. Nm23-H5 was located in the flagella of spermatids and spermatozoa, adjacent to the central pair and outer doublets of axonemal microtubules. High levels of NDP kinases A and B were observed at specific locations in postmeiotic germinal cells. NDP kinase A was transiently located in round spermatid nuclei and became asymmetrically distributed in the cytoplasm at the nuclear basal pole of elongating spermatids. The distribution of NDP kinase B was reminiscent of the microtubular structure of the manchette. In ejaculated spermatozoa, the proteins presented specific locations in the head and flagella. Nm23/NDP kinase isoforms may have specific functions in the phosphotransfer network involved in spermiogenesis and flagellar movement.

The cytosolic chaperonin CCT associates to cytoplasmic microtubular structures during mammalian spermiogenesis and to heterochromatin in germline and somatic cells

Spermiogenesis, the haploid phase of spermatogenesis, is characterised by a dramatic cytodifferentiation of spermatids. The two major steps, nuclear shaping and cytoplasmic reorganisation of the organelles, rely on an extensive remodelling of the microtubule cytoskeleton. Folding of alpha- and beta-tubulin is mediated by the cytoplasmic chaperonin containing TCP-1 (CCT), highly expressed in testis. We studied CCT cellular distribution throughout spermatogenesis by immunofluorescence and immunoelectron microscopy. We unveil two main cytoplasmic localisations for CCT: at the centrosome and at the microtubules of the manchette, a structure unique to male germ cells. Both structures are essential for spermatid differentiation and may require CCT function. Although CCT is essentially cytoplasmic, a few reports suggest that a subset may have a nuclear localisation. We demonstrate that in the nucleus of germline and somatic cells, part of CCT associates to heterochromatin. In interphase cells, CCT seems generally confined to constitutive heterochromatin. Nevertheless, in condensing nucleus of future spermatozoon, it is also associated with chromatin undergoing compaction. Finally, in fully-condensed mitotic chromosomes, CCT is located all along the chromosomes. Our finding that CCT is associated with constitutive heterochromatin and to compacting chromatin raises the possibility that it may be implicated in maintenance and remodelling of heterochromatin.

Glutamylated tubulin: diversity of expression and distribution of isoforms

Glutamylation of alpha and beta tubulin isotypes is a major posttranslational modification giving rise to diversified isoforms occurring mainly in neurotubules, centrioles, and axonemes. Monoglutamylated tubulin isoforms can be differentially recognized by two mAbs, B3 and GT335, which both recognize either polyglutamylated isoforms. In the present study, immunoelectron microscopy and immunofluorescence analyses were performed with these two mAbs to determine the expression and distribution of glutamylated tubulin isoforms in selected biological models whose tubulin isotypes are characterized. In mouse spermatozoa, microtubules of the flagellum contain polyglutamylated isoforms except in the tip where only monoglutamylated isoforms are detected. In spermatids, only a subset of manchette microtubules contain monoglutamylated tubulin isoforms. Cytoplasmic microtubules of Sertoli cells are monoglutamylated. Mitotic and meiotic spindles of germ cells are monoglutamylated whereas the HeLa cell mitotic spindle is polyglutamylated. Three models of axonemes are demonstrated as a function of the degree and extent of tubulin glutamylation. In lung ciliated cells, axonemes are uniformly polyglutamylated. In sea urchin sperm and Chlamydomonas, flagellar microtubules are polyglutamylated in their proximal part and monoglutamylated in their distal part. In Paramecium, cilia are bi- or monoglutamylated only at their base. In all cells, centrioles or basal bodies are polyglutamylated. These new data emphasize the importance of glutamylation in all types of microtubules and strengthen the hypothesis of its role in the regulation of the intracellular traffic and flagellar motility.

Differential distribution of glutamylated tubulin isoforms along the sea urchin sperm axoneme

Tubulin belongs to a highly conserved multigenic family, in which several gene products usually coexist in the same tissue or the same cell. Moreover, seven classes of post-translational modifications of these gene products lead to an amazing diversity of tubulin polypeptide chains, within the same cell type, whose physiological function remains elusive. Such diversity has been found in a very stable microtubular organelle, the sea urchin sperm flagellum, where some tubulin isoforms have been directly implicated in motility, whereas others may play a more structural role. In particular, polyglutamylated tubulin has been shown to be crucial for motility (Gagnon et al., 1996: J Cell Sci 109:1545 p). Here, we show with the GT335 antibody that polyglutamylated tubulin is distributed according to a decreasing gradient along the sea urchin sperm axoneme, since a semi-quantitative measurement of immunofluorescence intensity reveals that in its proximal half, the axoneme is sixfold more labeled than in its distal half. This gradient along the length of the axoneme is confirmed by immunogold labeling procedures which, in addition, demonstrate a uniform distribution of polyglutamylated tubulin among peripheral doublets and a lesser content in the central pair within a same section. Moreover, our data obtained with B3, an antibody that recognizes both mono- and poly-glutamylated tubulin, suggest that the number of glutamate residues in the lateral poly-glutamyl chain of tubulin varies along the whole length of the axoneme. These novel results coupled with those published earlier may be important to understand the role of polyglutamylation in flagellar motility.

Expression of glycylated tubulin during the differentiation of spermatozoa in mammals

Using quantitative immunogold analyses of tubulin isoforms we previously demonstrated a unique differential expression of glutamylated tubulin in the flagellum of mouse and man spermatozoa [Fouquet et al., 1997: Tissue Cell 29:573-583]. We have performed similar analyses for glycylated tubulin using two monoclonal antibodies, TAP 952 and AXO 49, directed to mono- and polyglycylated tubulin respectively. Glycylated tubulin was not found in centrioles and cytoplasmic microtubules (manchette) of germ cells. In mouse and man, axonemal tubulin was first monoglycylated and uniformly distributed in all doublets at all levels of the flagellum in elongating spermatids. In human mature spermatozoa axonemal microtubules were enriched in monoglycylated tubulin from the base to the tip of the flagellum. In mouse sperm flagellum a similar gradient of monoglycylated tubulin was also observed in addition to an opposite gradient of polyglycylated tubulin. In both species, monoglycylated tubulin labeling predominated in doublets 3-8 whereas glutamylated tubulin labeling [Fouquet et al., 1997] predominated in doublets 1-5-6. These differential labelings were suppressed after motility inhibition of mouse spermatozoa by sodium azide treatment and in non-motile human spermatozoa lacking dynein arms. The unique distribution of these tubulin isoforms and the known inhibition of motility induced by their specific antibodies are consistent with a complementary role of tubulin glycylation and glutamylation in the regulation of flagellar beating in mammalian spermatozoa.

Glutamylation of centriole and cytoplasmic tubulin in proliferating non-neuronal cells

We have examined the distribution of glutamylated tubulin in non-neuronal cell lines. A major part of centriole tubulin is highly modified on both the alpha- and beta-tubulin subunits, whereas a minor part of the cytoplasmic tubulin is slightly modified, on the beta-tubulin only. Furthermore, we observed that tubulin glutamylation varies during the cell cycle: an increase occurs during mitosis on both centriole and spindle microtubules. In the spindle, this increase appears more obvious on the pole-to-pole and kinetochore microtubules than on the astral microtubules. The cellular pattern and the temporal variation of this post-translational modification contrast with other previously described tubulin modifications. The functional significance of this distribution is discussed.

Composition and organization of tubulin isoforms reveals a variety of axonemal models

In the flagellum of mammalian spermatozoa, glutamylated and glycylated tubulin isoforms are detected according to longitudinal gradients and preferentially in axonemal doublets 1-5-6 and 3-8, respectively. This suggested a role for these tubulin isoforms in the regulation of flagellar beating. In the present work, using antibodies directed against various tubulin isoforms and quantitative immunogold analysis, we aimed at investigating whether the particular accessibility of tubulin isoforms in the mammalian sperm flagellum is restricted to this model of axoneme surrounded with periaxonemal structures or is also displayed in naked axonemes. In rodent lung ciliated cells, all studied tubulin isoforms are uniformly distributed in all axonemal microtubules with a unique deficiency of glutamylated tubulin in the transitional region. A similar distribution of tubulin isoforms is observed in cilia of Paramecium, except for a decreasing gradient of glutamylated tubulin labeling in the proximal part of axonemal microtubules. In the sea urchin sperm flagellum, predominant labeling of tyrosinated and detyrosinated tubulin in 1-5-6 and 3-8 doublets, respectively, were observed together with decreasing proximo-distal gradients of glutamylated and polyglycylated tubulin labeling and an increasing gradient of monoglycylated tubulin labeling. In flagella of Chlamydomonas, the glutamylated and glycylated tubulin isoforms are detected at low levels. Our results show a specific composition and organization of tubulin isoforms in different models of cilia and flagella, suggesting various models of functional organization and beating regulation of the axoneme.

Characterization and immunolocalization of beta-D-glucuronidase in mouse testicular germ cells and spermatozoa

Spermatozoa released from the seminiferous tubules are terminally differentiated cells with no known synthetic activity. Their components are synthesized in the spermatogenic cells during spermatogenesis. In this study, we report the characterization and immunolocalization of beta-glucuronidase in mouse testicular germ cells and spermatozoa. The enzyme is an exoglycohydrolase with dual localization, being present in lysosomes and endoplasmic reticulum of several mouse and rat tissues. The purified germ cell preparations (spermatocytes, round spermatids, and condensed/elongated spermatids) when assayed for beta-glucuronidase activity showed that the spermatocytes contained five times more enzyme activity per cell than the spermatids. Polyacrylamide gel electrophoresis, carried out under native and denaturing conditions, demonstrated that the germ cells express only the lysosomal form of the enzyme (pI 5.5-6.0) with a subunit molecular mass of 74 kDa. Immunocytochemical studies revealed a positive reaction in the Golgi membranes, Golgi-associated vesicles, and lysosomes of late spermatocytes (pachytene spermatocytes) and a stage-specific localization during spermiogenesis. The forming or formed acrosome of the elongated spermatids (stages 9-16) and epididymal spermatozoa was highly immunopositive. Comparison of immunoprecipitation curves and kinetic properties of the enzyme present in spermatocytes and spermatozoa revealed no major differences. Taken together, our results demonstrate that beta-glucuronidase activities present in the lysosomes of spermatocytes and the sperm acrosome are kinetically and immunologically similar.

Gamma-tubulin during the differentiation of spermatozoa in various mammals and man

The distribution of gamma-tubulin as a marker of microtubule organizing centres (MTOC) was studied during spermiogenesis in rodents and in rabbit, monkey and man. A polyclonal antibody directed against human gamma-tubulin was used both for indirect immunofluorescence (IIF) and post-embedding immunogold procedures. In all species, gamma-tubulin was detected in the proximal and distal centrioles of round spermatids. In elongating spermatids, gamma-tubulin was predominantly found in the pericentriolar material (PCM) of both centrioles and particularly around the adjunct of the proximal centriole. At this level, some labelling was also associated with manchette microtubules, but other parts of the manchette and the nuclear ring were never labelled. We propose a role for distal centriole gamma-tubulin in axoneme nucleation and centriolar adjunct gamma-tubulin in manchette nucleation. The disappearance of gamma-tubulin in mature spermatozoa indicates that sperm aster nucleation should be dependent on oocyte gamma-tubulin. Remnants of gamma-tubulin in some human spermatozoa suggest that paternal gamma-tubulin also could contribute to sperm aster formation.

Expression of tubulin isoforms during the differentiation of mammalian spermatozoa

Using the GT 335 mAb we have previously demonstrated a differential expression of glutamylated tubulin isoforms during spermatogenesis and in spermatooza of the mouse and human. Moreover, the proximodistal decrease of the immunolabeling and its predominance in doublets 1-5-6, corresponding to the plane of the flagellar wave, suggested that the glutamylated tubulin could be involved in a functional heterogeneity of microtubules in peripheral doublets of the sperm flagellum. In order to characterize further the importance of glutamylated tubulin in the sperm model, we analyzed tubulin isoforms by immunoblotting and quantitative immunogold, using antibodies to the C-terminal domain of both subunits including non-glutamylated and glutamylated epitopes. The unique differential immunolabeling of the glutamylated tubulin was confirmed with three mAbs 406-3, 392-2 and B3, in addition to GT 335. This differential labeling was interpreted as a differential accessibility of tubulin epitopes since it was greatly reduced in human spermatozoa lacking dynein arms and after motility inhibition of normal spermatozoa by azide pretreatment. We suggest that the glutamylated tubulin interacts with other axonemal and/or periaxonemal proteins which could be involved in flagellar beating and its regulation.

Glutamylated tubulin as a marker of microtubule heterogeneity in the human sperm flagellum

Four site-directed monoclonal antibodies (mAbs) to tubulin: DM1A and DM1B general anti-alpha and anti-beta tubulin, 6-11B-1 anti-acetylated alpha tubulin and GT335 anti-glutamylated alpha and beta tubulin were used to study the distribution of tubulin isoforms in the human sperm flagellum. Since indirect immunofluorescence (IIF) did not give reliable results, a quantitative study of the immunogold labelling of the flagellum was performed at five levels: the mid-piece, three successive regions of the principal piece and the terminal piece. A uniform labelling was observed with DM1A, DM1B and 6-11B-1 mAbs. In contrast, the labelling of glutamylated tubulin detected with GT335 mAb decreased from the middle piece to the terminal piece both for peripheral doublets and the central pair. The changes in labelling of peripheral doublets were related to the pattern of outer dense fibre (ODF) changes. Thus doublets 1-5-6, associated with the largest number of ODF, were the most heavily labelled. This predominant labelling corresponded to the plane of flagellar beating suggesting a functional heterogeneity of peripheral doublets.

Comparative immunogold analysis of tubulin isoforms in the mouse sperm flagellum: unique distribution of glutamylated tubulin

The distribution of different tubulin isoforms in the mouse sperm flagellum was studied using four site-directed antibodies to tubulin: DM1A and DM1B general anti alpha and beta-tubulin, 6-11B-1 anti-acetylated alpha-tubulin, and GT335 anti-glutamylated alpha and beta-tubulin. Quantitative immunogold analyses were performed on five regions of the flagellum: the middle piece, three successive regions of the principal piece, and the terminal piece. A uniform labeling was observed with DM1A and DM1B along the entire flagellum both for peripheral doublets and the central pair. Similar results were obtained with 6-11B-1 directed to acetylated alpha-tubulin, an N-terminal-modified tubulin isoform. In contrast, the labeling for glutamylated alpha and beta-tubulin, C-terminal modified isoforms, was not uniform. The highest intensity was found in the middle piece and the terminal piece. The labeling which decreased significantly both for peripheral doublets and central pair along the principal piece was considered as a loss of glutamylated tubulin accessibility. From the middle piece to the end of the principal piece, this labeling was predominant in doublets 1-5-6, corresponding to the plane of the flagellar wave. However, the labeling for doublets 2-3-4-7-8-9 was heterogeneous, showing an increasing asymmetry. These results suggest that in the mammalian sperm cell model, the glutamylated tubulin might be involved in a functional heterogeneity among peripheral doublets of the flagellum.

Differential distribution of glutamylated tubulin in the flagellum of mouse spermatozoa

Using a monoclonal antibody (GT 335) we previously demonstrated that glutamylation is a predominant posttranslational modification of alpha and beta tubulin isoforms in the axoneme of mouse spermatozoa (Fouquet et al., Cell Motil. Cytoskel. 27, 49, 1994). However, we noted that the staining intensity and/or distribution of glutamylated tubulin were not identical using either indirect immunofluorescence (IIF) or immunoelectron microscopy. To test this discrepancy various permeabilization procedures were performed for IIF: methanol or acetone alone or in combination, including freezing pretreatment and with or without paraformaldehyde fixation. Each procedure gave a particular labeling of sperm axoneme. The diversity of axoneme labeling in mouse spermatids and spermatozoa appeared dependent both on the absence or presence of periaxonemal sheaths and permeabilization procedures. For comparison with IIF and to avoid problematic premeabilization treatments a quantitative postembedding immunogold approach was preferred. In these conditions the labeling predominated in the middle piece of the sperm flagellum and decreased progressively in the principal piece. However, the labeling of the terminal piece was similar to that of the middle piece. These results suggested a differential glutamylated tubulin distribution along the axoneme of the mouse sperm flagellum.

Differential distribution of glutamylated tubulin during spermatogenesis in mammalian testis

The distribution of glutamylated tubulin has been analyzed in mammalian testis using the specific mAb GT335 by immunoelectron microscopy and immunoblotting. In spermatozoa of various species, immunogold labeling showed the presence of glutamylated tubulin in all of the microtubules of axoneme and centrioles, whereas the microtubule network of the spermatid manchette was unlabeled. In earlier germ cells, centriole was the only microtubule structure to be labeled. A similar distribution was observed using the anti-acetylated tubulin antibody (6-11B-1), confirming previous results of Hermo et al. [Anat. Rec. 229:31-50, 1991]. However, among testicular somatic cells, microtubules of some Sertoli cell branches were not acetylated but glutamylated. 2-D PAGE of mouse and hamster sperm extracts showed a high level of alpha and beta-tubulin heterogeneity, comparable to that found in brain. Immunoblotting with GT335 revealed a large amount of glutamylated tubulin resolved into numerous alpha as well as beta-tubulin isoforms. This suggests that the major testis-specific tubulin isotypes (m alpha 3/7 and m beta 3) are also glutamylatable. These results show a subcellular sorting of posttranslationally modified tubulin isoforms in spermatids, glutamylation being associated with the most stable microtubule structures.

The cytoskeleton of mammalian spermatozoa

The mammalian spermatozoa are endowed with a unique cytoskeleton which consists both of ubiquitous and specific proteins, some of them arising from gene haploid transcription. In the head, a dense perinuclear layer is made of basic proteins (calicin, cylicin, etc) associated with calmodulin and actin remnants. In the flagellum, the axonemal microtubules are mainly composed of glutamylated tubulin isoforms; the periaxonemal outer dense fibers and fibrous sheath are considered as related cytoskeletal structures on the basis of some common polypeptides.

Association of spectrin with manchette microtubules in mammalian spermatids

In hamster and mouse spermatozoa a spectrin immunogold labeling was found under the plasma membrane in the principal piece of the flagellum. During spermatid differentiation, the spectrin labeling was associated with the manchette, a transient microtubular network involved in nuclear shaping and organelle translocation.

Spectrin and ankyrin like proteins in spermatids and spermatozoa of the hamster and some other mammals

The presence of spectrin and ankyrin-like proteins was investigated during the differentiation and maturation of spermatozoa in mammalian species which have previously been studied for actin and calmodulin. These actin-binding proteins were characterized by immunoblotting and localized by immunoelectron microscopy. Neither spectrin nor ankyrin could be detected in the F-actin rich subacrosomal layer of spermatids in any species. In hamster and mouse maturing spermatids and spermatozoa, spectrin was mainly evidenced around the fibrous sheath of the flagellum whereas ankyrin was detected only in the neck. In rabbit spermatozoa, spectrin was evidenced in the outermost cytoplasmic layer of the post-acrosomal region and a light ankyrin labeling appeared in the neck. In rat, monkey and human sperm cells, these 2 proteins were not demonstrated. These results showed that as for actin there was no uniform pattern of distribution of spectrin and ankyrin among the 6 species studied.

Species-specific localization of actin in mammalian spermatozoa: fact or artifact?

Actin has been characterized and localized in sperm cells of many mammals. Nevertheless, the reported localizations obtained by different methods and/or antibodies varied from species to species and even for the same species. To clarify the question, sperm actin distribution was reinvestigated under uniform technical conditions. Immunogold post-embedding procedures were performed using a polyclonal and two monoclonal antibodies of known specificity to localize actin in spermatids and spermatozoa of rabbit, mouse, rat, monkey, and human. In these species, actin (F-actin) was detected with the three antibodies between the nucleus and the acrosome of round and elongating spermatids. Species-specific changes occurred in maturing spermatids. In the rabbit, actin labeling decreased and disappeared from the tip to the base of the subacrosomal layer. In testicular and epididymal spermatozoa actin was detected only with a monoclonal antibody (Amersham) successively in the neck, postacrosomal area, and subacrosomal bulges. In mouse late spermatids a transitory labeling of the neck was detected only with the polyclonal antiactin. In testicular and epididymal spermatozoa an actin labeling was observed in the principal piece of the tail. In rat, monkey, and human sperm cells actin remained undetected. These results suggest that there is a redistribution of actin in late spermatids and spermatozoa which is a species-specific process but not an artifact of methodological origin. Thus, a function for actin in sperm, if any, remains to be demonstrated.

Perinuclear cytoskeleton of acrosome-less spermatids in the blind sterile mutant mouse

The perinuclear cytoskeleton of mammalian spermatids is thought to play a major role in nucleus-acrosome association and in shape changes of the head during spermiogenesis. To test these hypotheses acrosome-less spermatids in blind-sterile mutant mice were investigated for the development of the subacrosomal layer. Immunogold procedures were used for the detection of actin and calmodulin. In addition to various other abnormalities many acrosome-less round and elongating spermatids developed a subacrosomal layer with an actin and calmodulin distribution similar to that observed in normal spermatids. However, in mutant elongating spermatids the apical part of the nucleus was truncated and/or folded. The expected elongation and shaping of the nucleus only occurred in its caudal part associated with an hypertrophied and somewhat ectopic manchette. These abnormalities and those previously observed in mutant and experimental models indicated that the subacrosomal layer may form independently of the acrosome. It is suggested that the subacrosomal filamentous actin is a transitory scaffolding which might be involved in the assemblage of other proteins of the perinuclear cytoskeleton. However, by itself, this layer is not sufficient to ensure a normal shaping of the nucleus. Acrosome-nucleus interactions mediated by the subacrosomal layer seem necessary to shape the cranial spermatid head. The manchette appears to be involved only in the caudal nuclear shaping.

Sperm actin and calmodulin during fertilization in the hamster: an immune electron microscopic study

The distribution of actin and CaM in hamster spermatozoa was examined during the early events of fertilization using postembedding immunogold procedures. Actin was immunolocalized with a polyclonal antibody and two monoclonal antibodies. CaM was immunodetected with a polyclonal antibody. In epididymal sperm, actin labeling was found solely in the principal piece of the flagellum. CaM labeling was observed in the postacrosomal lamina, subacrosomal ring, and tip of the perforatorium. These distributions were not modified after capacitation and acrosome reaction. During the successive steps of sperm-egg fusion actin remained undetected in the sperm head whereas its location did not change in the flagellum. CaM distribution remained unmodified until the sperm head begins to decondense. At later stages of sperm head decondensation the postacrosomal lamina and its CaM labeling disappeared, whereas gold particles were still detected in the subacrosomal layer. The predominant location of actin into the egg cortex, particularly the microvillus-free area was confirmed. Except for the CaM labeling of the meiotic spindle, no special CaM location could be found throughout the egg. Thus, in hamster, a role for sperm actin in sperm-egg fusion appears unlikely. In contrast the CaM present in the Ca(2+)-rich postacrosomal lamina could be involved in the regulation of egg activation.

Localization of calmodulin in perinuclear structures of spermatids and spermatozoa: a comparison of six mammalian species

The distribution of Calmodulin was examined during spermiogenesis and sperm epididymal maturation in rabbit, hamster, mouse, rat, monkey, and human. An affinity-purified antibody to Calmodulin was used to characterize this protein in sperm extracts by immunoblot analysis. Post-embedding immunogold procedures were used to localize Calmodulin at the ultrastructural level. The pattern of Calmodulin distribution was similar in the six species studied. A diffuse labeling was observed in round spermatids. Gold particles accumulated first in the subacrosomal layer of elongating spermatids. The perinuclear ring was also labeled. During the maturation phase of spermatids, Calmodulin labeling extended to the postacrosomal sheath. Dramatic changes occurred at spermiation so that in testicular sperm Calmodulin immunostaining was predominant in the postacrosomal sheath. Some labeling was still detected in restricted areas of the subacrosomal layer. This feature varied from species to species. Calmodulin location did not change during sperm epididymal maturation. A role for Calmodulin in the control of manchette development and regulation of subacrosomal actin aggregation state during spermiogenesis is proposed. The unique location of Calmodulin in the postacrosomal sheath of all species that have been studied in this work, together with the known presence of calcium in this area suggest a pivotal role for Calmodulin in sperm-egg fusion process.

Immunoelectron microscopic distribution of actin in hamster spermatids and epididymal, capacitated and acrosome-reacted spermatozoa

The distribution of actin in hamster sperm cells was studied during spermiogenesis, epididymal transit, in vitro capacitation and acrosome reaction by immunogold procedures using a polyclonal and two monoclonal antiactin antibodies. A predominant actin labeling (F-actin) was detected in the subacrosomal space of spermatids. Actin labeling was also observed under the plasma membrane of intercellular bridges and along the outer acrosomal membrane. In late spermatids there was both F-actin depolymerization and a loss of actin immunolabeling, thus suggesting a dispersion of G-actin monomers. No obvious labeling was evidenced in residual bodies. This pattern was observed with the three antiactin probes. In contrast, an actin labeling reappeared over the fibrous sheath of the flagellum in epididymal spermatozoa but only when the polyclonal antibody was used. Only one single actin reactive band was detected by immunoblotting of sperm extracts. Since the sperm tails were NBD phallacidin negative they were considered to contain either G-actin or actin oligomers rather than bundles of actin filaments. It is suggested that G-actin originating in the head of late spermatids was redistributed to the flagellum of epidymal spermatozoa. No further changes were noted after capacitation and acrosome reaction thus indicating no apparent effect on actin polymerization and distribution.

Immunogold distribution of actin during spermiogenesis in the normal rabbit and after experimental cryptorchidism

Immunogold procedures for actin detection were used in combination with experimental cryptorchidism in the rabbit as a model to shed more light on the function of subacrosomal actin during spermiogenesis. In the normal testis, actin was localized in the perinuclear substance (PNS) from round spermatid onward but it was not detected in late spermatids. Actin labeling in each type of spermatid was essentially unmodified after 24 hr of cryptorchidism. However, among relevant immediate and delayed effects, discontinuous acrosomes overlying a continuous PNS with normal actin labeling were noted. Nuclear invaginations were seen in combination with subacrosomal dilatations; at this site actin labeling was found only in the PNS closely apposed to the nuclear envelope. In subacrosomal areas lacking PNS, actin labeling also was lacking. These results suggest that the subacrosomal actin (F-actin) is a component of the PNS that is tightly bound to the nuclear envelope rather than the overlying inner acrosomal membrane. Therefore, a function for the subacrosomal actin either in anchoring the acrosome to the nucleus or in capping the inner acrosomal membrane appears unlikely. The data rather suggest a capping function for the nuclear membrane during spermiogenesis.

Comparison of LR white resin, Lowicryl K4M and Epon postembedding procedures for immunogold staining of actin in the testis

The efficiency of various postembedding procedures for actin immunogold detection was compared using testicular tissue as a model. Whatever the fixative, testes embedded in LR White resin or in Lowicryl K4M showed few differences as regard ultrastructural preservation and gave similar actin antigenicity preservation. A purified polyclonal antibody (IgG) and a monoclonal antibody (IgM) visualized with gold secondary antibody yielded high labeling intensity whereas the IgG-protein-A gold association was less efficient. Crude antisera gave a low specific staining/background ratio. Samples of testes, fixed in different conditions, were also embedded in Epon, omitting propylene oxide and lowering polymerization temperature to 40 degrees-50 degrees C. This slight modification improved ultrastructural preservation which was better than with hydrophilic resins, as well as made possible immunogold detection of actin though antigenicity preservation was lesser than with these resins. Thus, in Epon embedded samples actin labeling, using IgG antiactin-gold secondary antibody, was similar to that observed after hydrophilic resin-protein-A gold procedures. In addition to actin labeling of various somatic cells it was confirmed that actin is a consistent component of the subacrosomal space of spermatids during the greater part of spermiogenesis in rat.

Immunogold distribution of actin during spermiogenesis in the rat, hamster, monkey, and human

The localization of actin during spermiogenesis in the rat, hamster, monkey, and human was examined at the ultrastructural level using postembedding immunogold methods. Results revealed a similar pattern of actin distribution in these four species, although the staining intensity was higher in rodent spermatids than in those obtained from primates. Gold particles were first detected in the nascent subacrosomal space of round spermatids. This subacrosomal labeling extended as the acrosome spread over the nucleus during the elongation phase, remained unchanged during the first steps of the maturation phase, and disappeared completely before spermiation. Thus, using antiactin probes (present results) and other specific probes, actin appears to be a consistent component of the subacrosomal layer of spermatids during the greater part of spermiogenesis in many mammals.

Ultrastructural analysis of a local regulation of Leydig cells in the adult monkey (Macaca fascicularis) and rat

Peritubular Leydig cells located in interstitial areas surrounded by tubules at nearly the same stage of spermatogenesis were analysed. Low-power electron micrographs were used for measurement of cell profile area and higher magnification views provided volume density of SER, Golgi stacks, mitochondria, and lipids. In the adult monkey, no cyclic changes were found in Leydig cells in their size or in the volume density of their organelles. In the adult rat (63 days of age), a comparison limited to stage VII-VIII and stage XI-XII peritubular Leydig cells demonstrated a significantly higher SER content (P less than 0.01) in the former, but no other differences. The study of subadult rats (45 days of age) showed that the full development of spermatogenesis was required to detect significant changes in Leydig cell SER content. The present results provide morphological evidence for an intratesticular control of the Leydig cells of the rat but not for those of the monkey.

Mitotic activity in monkey and rat Leydig cells

The testes of the monkey, Macaca fascicularis, from birth to adulthood and of rats from puberty to adulthood were examined by both light and electron microscopy to estimate the mitotic activity of the Leydig cells. In monkeys, mitotic activity was measurable only in neonates: 2.3% in Leydig cells and 0.4% in fibroblast-like cells. From measurements of 3H-thymidine incorporation, mature Leydig cells were labeled in neonates (2%) and adult animals (1%). The labeling indices were significantly increased with increasing time after isotope exposure, and some pairs of labeled cells were found. In prepubertal (28 days of age) and pubertal (45 days of age) rats, mitotic indices were 2 and 0.2%, respectively, in the Leydig cells and 0.4 and 0.1% in fibroblast-like and myoid cells, respectively. Mitoses were not detected in postpubertal rats at 63 days of age. Taken together, these results demonstrate the self-renewal ability of mature Leydig cells during normal development.

Renewal of spermatogonia in the monkey (Macaca fascicularis)

Populations of different types of spermatogonia and their mitotic activity were analyzed in the monkey Macaca fascicularis: 3 adults aged 5-6 yr and 3 young aged 2-3 mo. Two young and two adult monkeys received injections of 3H-thymidine for radioautographic study of the relationships between Type A spermatogonia: dark Type A (Ad), pale Type A (Ap) and transition Type A (At). In the adult the number of Ad and At spermatogonia did not change significantly throughout the seminiferous epithelium cycle. The number of Ap spermatogonia doubled at Stage VII, and half divided at Stage IX to give rise to B1 spermatogonia. The durations of the seminiferous epithelium cycle and spermatogenesis were estimated as 10.5 days and 42 days respectively. In the young and adult monkeys, some Ap spermatogonia and a lesser number of At spermatogonia were labeled one h after injection of precursor. At longer intervals after injection, the number of labeled At spermatogonia increased significantly, and some Ad as well as Ap spermatogonia were also labeled. These results indicate that Ap spermatogonia are renewal stem cells, and Ad spermatogonia are reserve stem cells. The differences in labeling after isotope exposure suggest that Ap cells may give rise successively to At and Ad cells.

Renewal of Leydig cells in the neonatal and adult monkey: a radioautographic study

The populations of interstitial cells in the testis of three 2-3 month old monkeys and of three 5-6 years old adults (Macaca fascicularis) were analyzed: percentage, mitotic index and labeling index after 3H-thymidine injection. In the young monkey and the adult well differentiated Leydig cells incorporate the precursor as fibroblast-like cells. This demonstrates their ability of renewal.

Relationships between Leydig cell morphometry and plasma testosterone during postnatal development of the monkey, Macaca fascicularis

In neonates (0 to 3-4 months), the testis contained a mean number of 4.6 X 10(6) Leydig cells representing 4.2 % of its volume; Leydig cell cytoplasm contained 10.2 % of SER. In infants (up to 45 months), Leydig cells regressed but their number increased; their volume density did not change. Leydig cell cytoplasmic volume (454 microns3 ), which was about 2.5-fold less than in neonates (1 119 microns3 ) or adults (1 170 microns3 ), contained only 8.7% of SER. During meiosis stage (38-52 months). Leydig cell numbers and volume density did not vary but the cells reached a maximal size and an amount of SER comparable with that at birth was measured. When spermatogenesis was complete, the Leydig cells represented no more than 0.8% of testis volume, but their number and SER content were significantly increased. Except for a significant decrease when spermatogenesis was completed, Leydig cell lipid content did not change during development, and the volume density of mitochondria did not vary. The mean level of plasma testosterone was 2 ng/ml in neonates and 0.4 ng/ml in infants; it increased to 3 ng/ml during onset of meiosis and reached 10 ng/ml in adults. The profile of testosterone was positively and significantly correlated with the total volume and total number of Leydig cells (P less than 0.01 and P less than 0.02, respectively) and with changes in their cytoplasmic volume (P less than 0.001). Moreover, plasma testosterone levels were positively and significantly correlated with changes in Leydig cell SER content i.e. SER volume density and mean absolute volume per cell (P less than 0.001), total SER in the whole testis (P less than 0.01).

Morphometry of fetal Leydig cells in the monkey (Macaca fascicularis), correlation with plasma testosterone

The evolution of Leydig cells in Macaca fascicularis fetuses was followed throughout gestation (50-150 d) by morphometric procedures (volume densities of: cells, SER, mitochondria and lipid droplets). Testosterone from umbilical artery plasma was radioimmunoassayed starting on day 57. After predifferentiation and differentiation phases, Leydig cells entered the maturity phase (57-66 d), they occupied 19% of testicular volume, SER and lipid droplets represented 19% and 5% respectively of cytoplasmic volume. Then Leydig cells regressed dramatically (involution phase I: 66-83 d), their volume density decreased to 8%, that of SER to 12% whereas lipids doubled. Leydig cell volume density diminished to 5% during the second half of gestation (involution phase II), but their ultrastructure was not significantly altered. High plasma testosterone level (2.4 ng/ml) was observed during the maturity phase of Leydig cells, decline of testosterone occurred during involution phases I and II (1.13 and 0.58 ng/ml respectively). Its was shown that from day 57 to the end of fetal development the evolution of the plasma testosterone level correlated with the Leydig cell volume density and the SER volume density.

A comparative study of the development of the fetal testis and ovary in the monkey (Macaca fascicularis)

The gonadal development of the Macaca fascicularis fetus was studied between 37 and 118 days on serial semi-thin and thin sections. The testis and the ovary began to differentiate at the same age (37 days); the definitive architecture of the testis was acquired at 43 days, while a cortex and a medulla did not form in the ovary until 55 to 60 days. In spite of the time-lag and the divergent development, the testis and the ovary evidenced three comparable stages; the main event of these stages was the centrifugal role of the mesonephros. The first stage (37-43 days) included the centrifugal and antero-posterior differentiation of the sex cord anlages from the mesonephric mesenchyme in contact with the proximal loops of the anterior tubules (for a detailed study see Dang and Fouquet, 1979). From 43 days (second stage), a remainder of the mesonephric mesenchymal blastema of the gonad supplied the rete system. The mesonephric tubules fused secondarily with that system which was connected to the sex cords. Whereas in the testis, the rete blastema did not play a direct role in organizing testicular structures, but only in forming excretory pathways, in the ovary, it invaded the medulla (whose initial sex cords degenerated) and penetrated to the ovigerous cords of the cortex. The rete ovarii blastema was probably the major source of periovocyte cells. The third stage included the differentiation of a steroidogenic interstitial tissue (from 50 days in the testis; at about 60 days in the ovary) and is further involution; these processes were similar in both sexes. Observation of the fine structure showed the development of the male and female gonocytes to be the same; the prespermatogonia and the oogonia could be characterized by the formation of nuclear vacuoles. The Sertoli cells and the periovogonial cells showed the same features.