The major component of the rat sperm fibrous sheath is a phosphoprotein

Higher abundance of DLD protein in buffalo bull spermatozoa causes elevated ROS production leading to early sperm capacitation and reduction in fertilizing ability

BACKGROUD

Before fertilization, spermatozoa undergo a crucial maturation step called capacitation, which is a unique event regulates the sperm's ability for successful fertilization. The capacitation process takes place as the spermatozoa pass through the female reproductive tract (FRT). Dihydrolipoamide dehydrogenase (DLD) protein is a post-pyruvate metabolic enzyme, exhibiting reactive oxygen species (ROS) production which causes capacitation. Additionally, other vital functions of DLD in buffalo spermatozoa are hyperactivation and acrosome reaction. DLD produces the optimum amount of ROS required to induce capacitation process in FRT. Depending on physiological or pathophysiological conditions, DLD can either enhance or attenuate the production of reactive oxygen species (ROS). Aim of this study was to investigate whether changes in the production of ROS in sperm cells can impact their ability to fertilize by triggering the capacitation and acrosome reaction.

RESULTS

In this study, abundance of DLD protein was quantified between high (n = 5) and low fertile bull (n = 5) spermatozoa. It was found that compared to high-fertile (HF) bulls, low-fertile (LF) bulls exhibited significantly (P < 0.05) higher DLD abundances. Herein, we optimised the MICA concentration to inhibit DLD function, spermatozoa were treated with MICA in time (0, 1, 2, 3, 4, and 5 h) and concentrations (1, 2.5, 5, and 10 mmol/L) dependent manner. Maximum DLD inhibition was found to be at 4 h in 10 mmol/L MICA concentration, which was used for further experimentation in HF and LF. Based on DLD inhibition it was seen that LF bull spermatozoa exhibited significantly (P < 0.05) higher ROS production and acrosome reaction in comparison to the HF bull spermatozoa. The kinematic parameters of the spermatozoa such as percent total motility, velocity parameters (VCL, VSL, and VAP) and other parameters (BCF, STR, and LIN) were also decreased in MICA treated spermatozoa in comparison to the control (capacitated) spermatozoa.

CONCLUSIONS

The present study provides an initial evidence explaining the buffalo bull spermatozoa with higher DLD abundance undergo early capacitation, which subsequently reduces their capacity to fertilize.

CABYR binds to AKAP3 and Ropporin in the human sperm fibrous sheath

Calcium-binding tyrosine phosphorylation-regulated protein (CABYR) is a highly polymorphic calcium-binding tyrosine- and serine-/threonine-phosphorylated fibrous sheath (FS) protein involved in capacitation. A putative domain (amino acids 12-48) homologous to the regulatory subunit of type II cAMP-dependent protein kinase A (RII) dimerisation and A kinase-anchoring protein (AKAP)-binding domains of protein kinase A at the N-terminus suggests that CABYR may self-assemble and bind to AKAPs. Moreover, there is evidence that CABYR has limited interaction with AKAPs. However, further evidence and new relationships between CABYR and other FS proteins, including AKAPs, will be helpful in understanding the basic physiology of FS. In this study, a new strategy for co-immunoprecipitation of insoluble proteins, as well as the standard co-immunoprecipitation method in combination with mass spectrometry and western blot, was employed to explore the relationship between CABYR, AKAP3 and Ropporin. The results showed that AKAP3 was co-immunoprecipitated with CABYR by the anti-CABYR-A polyclonal antibody, and, conversely, CABYR was also co-immunoprecipitated with AKAP3 by the anti-AKAP3 polyclonal antibody. Another RII-like domain containing protein, Ropporin, was also co-immunoprecipitated with CABYR, indicating that Ropporin is one of CABYR's binding partners. The interactions between CABYR, AKAP3 and Ropporin were confirmed by yeast two-hybrid assays. Further analysis showed that CABYR not only binds to AKAP3 by its RII domain but binds to Ropporin through other regions besides the RII-like domain. This is the first demonstration that CABYR variants form a complex not only with the scaffolding protein AKAP3 but also with another RII-like domain-containing protein in the human sperm FS.

CABYR isoforms expressed in late steps of spermiogenesis bind with AKAPs and ropporin in mouse sperm fibrous sheath

BACKGROUND

CABYR is a polymorphic calcium-binding protein of the sperm fibrous sheath (FS) which gene contains two coding regions (CR-A and CR-B) and is tyrosine as well as serine/threonine phosphorylated during in vitro sperm capacitation. Thus far, the detailed information on CABYR protein expression in mouse spermatogenesis is lacking. Moreover, because of the complexity of this polymorphic protein, there are no data on how CABYR isoforms associate and assemble into the FS.

METHODS

The capacity of mouse CABYR isoforms to associate into dimers and oligomers, and the relationships between CABYR and other FS proteins were studied by gel electrophoresis, Western blotting, immunofluorescence, immunoprecipitation and yeast two-hybrid analyses.

RESULTS

The predominant form of mouse CABYR in the FS is an 80 kDa variant that contains only CABYR-A encoded by coding region A. CABYR isoforms form dimers by combining the 80 kDa CABYR-A-only variant with the 50 kDa variant that contains both CABYR-A and CABYR-B encoded by full length or truncated coding region A and B. It is proposed that this step is followed by the formation of larger oligomers, which then participate in the formation of the supramolecular structure of the FS in mouse sperm. The initial expression of CABYR occurs in the cytoplasm of spermatids at step 11 of spermiogenesis and increases progressively during steps 12-15. CABYR protein gradually migrates into the sperm flagellum and localizes to the FS of the principal piece during steps 15-16. Deletion of the CABYR RII domain abolished the interaction between CABYR and AKAP3/AKAP4 but did not abolish the interaction between CABYR and ropporin suggesting that CABYR binds to AKAP3/AKAP4 by its RII domain but binds to ropporin through another as yet undefined region.

CONCLUSIONS

CABYR expresses at the late stage of spermiogenesis and its isoforms oligomerize and bind with AKAPs and ropporin. These interactions strongly suggest that CABYR participates in the assembly of complexes in the FS, which may be related to calcium signaling.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

Rat Spag5 associates in somatic cells with endoplasmic reticulum and microtubules but in spermatozoa with outer dense fibers

The leucine zipper motif has been identified as an important and specific interaction motif used by various sperm tail proteins that localize to the outer dense fibers. We had found that rat Odf1, a major integral ODF protein, utilizes its leucine zipper to associate with Odf2, another major ODF protein, Spag4 which localizes to the interface between ODF and axonemal microtubule doublets, and Spag5. The rat Spag5 sequence indicated a close relationship with human Astrin, a microtubule-binding spindle protein suggesting that Spag5, like Spag4, may associate with the sperm tail axoneme. RT PCR assays indicated expression of Spag5 in various tissues and in somatic cells Spag5 localizes to endoplasmic reticulum and microtubules, as expected for an Astrin orthologue. MT binding was confirmed both in vivo and in in vitro MT-binding assays: somatic cells contain a 58 kDa MT-associated Spag5 protein. Western blotting assays of rat somatic cells and male germ cells at different stages of development using anti-Spag5 antibodies demonstrated that the protein expression pattern changes during spermatogenesis and that sperm tails contain a 58 kDa Spag5 protein. Use of affinity-purified anti-Spag5 antibodies in immuno electron microscopy shows that in rat elongated spermatids and epididymal sperm the Spag5 protein associates with ODF, but not with the axonemal MTs. This observation is in contrast to that for the other Odf1-binding, MT-binding protein Spag4, which is present between ODF and axoneme. Our data demonstrate that Spag5 has different localization in somatic versus male germ cells suggesting the possibility of different function.

Structure of mammalian spermatozoa in respect to viability, fertility and cryopreservation

Morphological assessment of spermatozoa has a long history and it is generally accepted that specific morphologic structural deviations correlate with male sub- and infertility. Although many different and also new methods are used in semen analysis, light microscopy is still used for routine morphological evaluation. This paper gives an overview about the detailed structure of physiological mammalian spermatozoa as well as the most common morphological deviations in correlation to fertility. This should be the basis for explanation of problems resulting from semen cryopreservation. General aspects of semen cryopreservation should be regarded before to facilitate the understanding of methods and mechanisms.

Multiple glycolytic enzymes are tightly bound to the fibrous sheath of mouse spermatozoa

The fibrous sheath is a cytoskeletal structure located in the principal piece of mammalian sperm flagella. Previous studies showed that glyceraldehyde 3-phosphate dehydrogenase, spermatogenic (GAPDHS), a germ cell-specific glycolytic isozyme that is required for sperm motility, is tightly bound to the fibrous sheath. To determine if other glycolytic enzymes are also bound to this cytoskeletal structure, we isolated highly purified fibrous sheath preparations from mouse epididymal sperm using a sequential extraction procedure. The isolated fibrous sheaths retain typical ultrastructural features and exhibit little contamination by axonemal or outer dense fiber proteins in Western blot analyses. Proteomic analysis using peptide-mass fingerprinting and MS/MS peptide fragment ion matching identified GAPDHS and two additional glycolytic enzyme subunits, the A isoform of aldolase 1 (ALDOA) and lactate dehydrogenase A (LDHA), in isolated fibrous sheaths. The presence of glycolytic enzymes in the fibrous sheath was also examined by Western blotting. In addition to GAPDHS, ALDOA, and LDHA, this method determined that pyruvate kinase is also tightly bound to the fibrous sheath. These data support a role for the fibrous sheath as a scaffold for anchoring multiple glycolytic enzymes along the length of the flagellum to provide a localized source of ATP that is essential for sperm motility.

Novel Tyrosine-Phosphorylated Post-Pyruvate Metabolic Enzyme, Dihydrolipoamide Dehydrogenase, Involved in Capacitation of Hamster Spermatozoa1

Capacitation is a process that confers fertilizing ability to spermatozoa and this critical event occurs in the development of mammalian spermatozoa during their transit through the female reproductive tract and precedes fertilization. Because spermatozoa are relatively silent in transcription and translation, posttranslational modifications perform the regulatory functions in these cells during capacitation. In this report, we identify a candidate protein, dihydrolipoamide dehydrogenase, which is a post-pyruvate metabolic enzyme, exhibiting tyrosine phosphorylation during hamster spermatozoal capacitation. This is the first report showing dihydrolipoamide dehydrogenase as a phosphoprotein. The cDNA sequence of hamster testes dihydrolipoamide dehydrogenase does not show any variation from the already reported mammalian dihydrolipoamide dehydrogenases. Downregulation of the activity of the hamster spermatozoal enzyme by its specific inhibitor, 5-methoxyindole-2-carboxylic acid, blocks acrosome reaction completely and hyperactivation partially, confirming the role of dihydrolipoamide dehydrogenase in hamster spermatozoal capacitation. We also delineate the temporal involvement of glucose and pyruvate-lactate, showing that the former is required in the earlier stages and the latter for the later stages of hamster spermatozoal capacitation. The essentiality of pyruvate-lactate during hyperactivation and acrosome reaction necessitates the involvement of the post-pyruvate-lactate enzyme, dihydrolipoamide dehydrogenase.

Molecular cloning and characterization of a complementary DNA encoding sperm tail protein SHIPPO 1

Formation of the tail in developing sperm is a complex process involving the organization of the axoneme, transport of periaxonemal proteins from the cytoplasm to the tail, and assembly of the outer dense fibers and fibrous sheath. Although detailed morphological descriptions of these events are available, the molecular mechanisms remain to be fully elucidated. We have isolated a new gene, named shippo 1, from a haploid germ cell-specific cDNA library of mouse testis, and also its human orthologue (h-shippo 1). The isolated cDNA is 1.2 kilobases long, carrying a 762-base pair open reading frame that encodes SHIPPO 1, a sperm protein predicted to consist of 254 amino acids. The amino acid sequence includes 6 Pro-Gly-Pro repeats, which are also present in the human orthologue protein (hSHIPPO 1) as well as in 2 other newly reported proteins of Drosophila melanogaster. Transcription of shippo 1 is exclusively observed in haploid germ cells. Antibody raised against SHIPPO 1 identified a testis-specific M(r) 32 x 10(-3) band in Western blot analysis. The protein was further localized in the flagella of the elongated spermatids and along the entire length of the tail in mature sperm. SHIPPO 1 in sperm is resistant to treatment with nonionic detergents and coextracted with the cytoskeletal core proteins of the mouse sperm tail.

CABYR, a novel calcium-binding tyrosine phosphorylation-regulated fibrous sheath protein involved in capacitation

To reach fertilization competence, sperm undergo an incompletely understood series of morphological and molecular maturational processes, termed capacitation, involving, among other processes, protein tyrosine phosphorylation and increased intracellular calcium. Hyperactivated motility and an ability to undergo the acrosome reaction serve as physiological end points to assess successful capacitation. We report here that acidic (pI 4.0) 86-kDa isoforms of a novel, polymorphic, testis-specific protein, designated calcium-binding tyrosine phosphorylation-regulated protein (CABYR), were tyrosine phosphorylated during in vitro capacitation and bound (45)Ca on 2D gels. Acidic 86-kDa calcium-binding forms of CABYR increased during in vitro capacitation, and calcium binding to these acidic forms was abolished by dephosphorylation with alkaline phosphatase. Six variants of CABYR containing two coding regions (CR-A and CR-B) were cloned from human testis cDNA libraries, including five variants with alternative splice deletions. A motif homologous to the RII dimerization domain of PK-A was present in the N-terminus of CR-A in four CABYR variants. A single putative EF handlike motif was noted in CR-A at aas 197-209, while seven potential tyrosine phosphorylation-like sites were noted in CR-A and four in CR-B. Pro-X-X-Pro (PXXP) modules were identified in the N- and C-termini of CR-A and CR-B. CABYR localizes to the principal piece of the human sperm flagellum in association with the fibrous sheath and is the first demonstration of a sperm protein that gains calcium-binding capacity when phosphorylated during capacitation.

Identification of the major tyrosine phosphorylated protein of capacitated hamster spermatozoa as a homologue of mammalian sperm a kinase anchoring protein

The molecular basis of mammalian sperm capacitation is unique in that, it is associated with a protein kinase A (PKA) dependent upregulation of protein tyrosine phosphorylation. Therefore, PKA activity during capacitation would be crucial for the downstream events of protein tyrosine phosphorylation, and mechanisms may exist to ensure that PKA phosphorylates its specific substrate. This could be achieved by bringing PKA close to its substrate, a function normally carried out by an A-kinase anchoring protein (AKAP). We showed previously that cauda epididymidal spermatozoa of hamster undergo a capacitation-dependent increase in protein tyrosine phosphorylation. In the present study, evidence is provided that two major tyrosine phosphorylated proteins of molecular weight 97 and 83 kDa are the hamster homologues of mouse pro-AKAP82 and AKAP82, and have been designated as hamster pro-AKAP83 and AKAP83 respectively. Hamster AKAP83 resembled the mouse AKAP82 with respect to its molecular weight, pI (pH 5-5.5) and cDNA and amino acid sequences. Sequence analysis indicated that the primary structure of pro-AKAP83 was highly conserved and exhibited 91% identity with mouse and rat AKAP82. Further, the functional domains, namely the region involved in binding the regulatory subunit of PKA and the proteolytic cleavage site between pro-AKAP83 and AKAP83, were identical with that observed in rat and mouse pro-AKAP82 and AKAP82. Immunoblot analysis using polyclonal hamster anti-AKAP83 antibodies indicated that AKAP83 was present both in caput and cauda epididymidal spermatozoa. The antibody also identified the pro-AKAP82 and AKAP82 in mouse caput and cauda epididymidal spermatozoa. Immunofluorescence studies indicated that AKAP83 in hamster spermatozoa was localized along the length of principal piece of the tail. It was also demonstrated that hamster pro-AKAP83/AKAP83 gene expression was testis specific and was not expressed in other organs in either sex. This is the first report implicating AKAP in capacitation in rodents.

Ropporin, a sperm-specific binding protein of rhophilin, that is localized in the fibrous sheath of sperm flagella

The small GTPase Rho; functions as a molecular switch that regulates various cellular processes such as cell adhesion, motility, gene expression and cytokinesis. We previously isolated several putative Rho; targets including rhophilin which bound selectively to the GTP-bound form of Rho;. Rhophilin is expressed highly in testis and is localized specifically in sperm flagella. The presence of a PDZ domain at the carboxy terminus of rhophilin suggested that rhophilin works as an adaptor molecule. To test this hypothesis, we employed a yeast two hybrid system using the rhophilin PDZ domain as a bait, and screened a mouse testis cDNA library. We isolated several positive clones containing the same insert. The open reading frame of the cDNA encoded a novel protein of 212 amino acids designated as ropporin from a Japanese word ‘oppo’ (the tail). The amino-terminal 40 amino acid sequence of ropporin showed high homology to that of the regulatory subunit of type II cAMP-dependent protein kinase, which is involved in dimerization and binding to A-kinase anchoring proteins. Consistently, a yeast two hybrid assay and gel filtration of recombinant ropporin indicated that ropporin dimerizes through this domain. Deletion analysis indicated that the carboxy-terminal four amino acids are essential for binding of ropporin to rhophilin, and ropporin and RhoV14 coprecipitated in the presence of rhophilin in vitro. Northern blot analysis showed that ropporin is exclusively expressed in testis, and induced at the late stage of spermatogenesis. This induction paralleled that of rhophilin. Immunocytochemistry using anti-ropporin antibody showed that ropporin is localized in the principal piece and the end piece of sperm flagella. Electronmicroscopy revealed that ropporin is mostly localized in the inner surface of the fibrous sheath while rhophilin is present in the outer surface of the outer dense fiber. These results suggest that rhophilin and ropporin may form a complex in sperm flagella.

Conservation and function of a bovine sperm A-kinase anchor protein homologous to mouse AKAP82

Protein kinase A regulates sperm motility through the cAMP-dependent phosphorylation of proteins. One mechanism to direct the activity of the kinase is to localize it near its protein substrates through the use of anchoring proteins. A-Kinase anchoring proteins (AKAPs) act by binding the type II regulatory subunit of protein kinase A and tethering it to a cellular organelle or cytoskeletal element. We showed previously that mAKAP82, the major protein of the fibrous sheath of the mouse sperm flagellum, is an AKAP. The available evidence indicates that protein kinase A is compartmentalized to the fibrous sheath by binding mAKAP82. To characterize AKAP82 in bovine sperm, a testicular cDNA library was constructed and used to isolate a clone encoding bAKAP82, the bovine homologue. Sequence analysis showed that the primary structure of bAKAP82 was highly conserved. In particular, the amino acid sequence corresponding to the region of mAKAP82 responsible for binding the regulatory subunit of protein kinase A was identical in the bull. Bovine AKAP82 was present in both epididymal and ejaculated sperm and was localized to the entire principal piece of the flagellum, the region in which the fibrous sheath is located. Finally, bAKAP82 bound the regulatory subunit of protein kinase A. These data support the idea that bAKAP82 functions as an anchoring protein for the subcellular localization of protein kinase A in the flagellum.

Assembly of AKAP82, a protein kinase A anchor protein, into the fibrous sheath of mouse sperm

The assembly of the mammalian sperm flagellum is a complex developmental event requiring the sequential activation of genes encoding the component parts and the coordinated assembly of these proteins during the differentiation of the haploid spermatid. In this study, the mechanism underlying the assembly of the fibrous sheath surrounding the axoneme was examined. The subject of the study was the major fibrous sheath protein of the mouse sperm flagellum, AKAP82, a member of the A Kinase Anchor Protein (AKAP) family of polypeptides that bind the regulatory (RII) subunit of protein kinase A (PK-A). Immunoelectron microscopy demonstrated that AKAP82 is present throughout the transverse ribs and longitudinal columns of the fibrous sheath. Since AKAP82 is initially synthesized as a precursor (pro-AKAP82) during spermiogenesis, an antiserum was raised against a peptide from the processed region of pro-AKAP82 (M(r) 97,000). In immunoblotting experiments, the antibody detected pro-AKAP82 in condensing spermatids but not in epididymal sperm. In addition, two other immunoreactive proteins of M(r) 109,000 (p109) and M(r) 26,000 (p26, representing the "pro" domain of the precursor) were present in epididymal sperm. Alkaline phosphatase treatment of epididymal sperm proteins demonstrated that p109 was a phosphorylated form of pro-AKAP82 that remained in sperm. By immunofluorescence, pro-AKAP82 was localized to the entire length of the principal piece in testicular sperm, while in epididymal sperm p109 and p26 were present only in the proximal portion of the principal piece. Pro-AKAP82 was solubilized when germ cells were extracted with Triton X-100. However, in sperm, both AKAP82 and p109 were almost totally resistant to these extraction conditions and remained in the particulate fraction even after extraction with Triton and dithiothreitol. Similar to pro-AKAP82, the RII subunit of PK-A was present in the Triton X-100-soluble fraction of developing germ cells. In sperm, much of the RII also became particulate, consistent with the hypothesis that AKAP82 anchors RII in the flagellum. These data indicate that pro-AKAP82 is synthesized in the cell body, transported down the axoneme to its site of assembly in the fibrous sheath, and then proteolytically clipped to form mature AKAP82.

Immunochemical characterization of a human sperm fibrous sheath protein, its developmental expression pattern, and morphogenetic relationships with actin

Among the monoclonal antibodies (MAbs) prepared against human sperm extracts, MAb 4F7 was found to be specific to the human and Macaca fascicularis sperm cytoskeletal fibrous sheath (FS). In Western blotting, MAb 4F7 stains a doublet of polypeptides of about M(r) 95 x 10(3) in extracts of human sperm cells. These polypeptides are not recognized by the KL1 anti-cytokeratin MAb, nor by the MAbs known to bind to the carboxy terminal (IFA) and to the amino terminal (ME101) rod domain of intermediate filaments. Sequential extraction procedures shows that the FS polypeptides recognized by MAb 4F7 are exposed after treatment with 8 M urea 4F7 immunoreactivity is lost after treatment with high ionic solutions (NaCl; KCl, Kl). Immunogold electron microscopy reveals that this protein is present throughout the FS. This FS antigenic determinant first accumulates in an FS proximal body in late spermatids, then in granules extending distally along the flagellum. Staining of spermatozoa with flagellar dysgenesis reveals that this FS protein colocalizes with actin no matter what the location of their abnormal assembly. These data suggest that the transient microtubule-like spindle-shaped body of as yet unknown function could be involved in FS protein deposition and that the assembly of the FS and actin could be under the control of some common morphogenetical factor(s). MAb 4F7 should allow further investigations of this peri-axonemal structure in both normal and pathological conditions.

Interactional cloning of the 84-kDa major outer dense fiber protein Odf84. Leucine zippers mediate associations of Odf84 and Odf27

The study of mammalian sperm tail outer dense fibers (ODF), a structure of unknown function, is hampered by the insoluble nature of ODF proteins and the availability of only one cloned component, Odf27. We report here the first use of the Odf27 leucine zipper as bait in a yeast two-hybrid screen to isolate a novel testis-specific protein whose interaction with Odf27 depends critically on the Odf27 leucine zipper. We find that the novel gene, 111-450, encodes a product that localizes to ODF as determined by fluorescence microscopy and immunoelectron microscopy and that the gene 111-450 product is identical to the major ODF protein, Odf84. Interestingly, Odf84 contains two C-terminal leucine zippers, and we demonstrate that all leucine residues in the upstream leucine zipper are required for interaction with Odf27, demonstrating the strategic validity of our approach. The use of the yeast screening approach to isolate leucine zipper containing proteins should be useful in other systems, and our findings have implications for ODF structural models.

Identification of a 53-kDa antigen in the fibrous sheath of avian spermatozoa

The intracellular fibrous sheath that surrounds the proximal part of the sperm flagellar axoneme in non-passerine birds is structurally different from that of mammals. We raised a monoclonal antibody against the fibrous sheath of cockerel spermatozoa by in vitro immunisation. Indirect immunofluorescence and immunogold labelling showed that the antibody bound specifically to the fibrous sheath. It also labelled the fibrous sheath in quail spermatozoa. In both species the antibody bound an antigen that had a molecular weight of about 53 kDa. In tissue sections from adult cockerel testis the antigen was located in spermatids and spermatozoa with little cross-reactivity with the basal region of the seminiferous epithelium or interstitial tissue. The antibody may prove to be a useful tool in studies of avian spermiogenesis.

Biogenesis of specialized cytoskeletal elements of rat spermatozoa

Our results on the formation of the ODF and perforatorium are diagrammatically summarized in Figures 30 and 31. The developmental expression of proteins making up these two cytoskeletal elements differs in timing, duration and intracellular localization. The ODF proteins are synthesized exclusively during the latter part of spermiogenesis, well after transcriptional activity in the haploid germ cell nucleus has ended. This implies that these major integral proteins of the tail are translationally regulated and that mechanisms must exist for the storage and eventual release of the mRNAs encoding these proteins. The perforatorial proteins, on the other hand, begin to be synthesized during the meiotic prophase reaching a peak of production in early spermiogenesis just before the initiation of the condensation of the spermatid's nucleus, at which time RNA synthesis stops. Another major difference between ODF and perforatorial protein production is that there seems to be a coordinated activity between the synthesis and the assembly of the ODF proteins, whereas there appears to be an almost 25 day delay between the initial meiotic synthesis and final condensation of perforatorial proteins in the subacrosomal space at the end of spermiogenesis. As for the intracellular localization of ODF and perforatorial proteins both have unprecedented distributions. The ODF proteins appear to be concentrated in a particular type of granular body which is especially abundant in the elongated spermatid at the time of peak ODF assembly. The perforatorial proteins, on the other hand, appear to be concentrated in the nuclei of pachytene spermatocytes and round spermatids until their displacement into the cytoplasm during nuclear condensation. Both forms of localization suggest a storage role for these proteins uniquely adapted by the spermatid to regulate the assemblies of the respective cytoskeletal elements.

Physiology and pathophysiology of the human spermatozoon: the role of electron microscopy

In this article, the major contributions of electron microscopy to the present understanding of the physiology and pathophysiology of the human spermatozoon are reviewed. The ultrastructural organization of sperm organelles playing a significant role for cell function and, therefore, for the reproductive process is described. Also, the major abnormalities and defects of the various organellar systems and how they impair the reproductive function and/or the viability of the cell are reviewed.