A new rat gene RT7 is specifically expressed during spermatogenesis

Haplo-deficiency of ODF1/HSPB10 in mouse sperm causes relaxation of head-to-tail linkage

The small heat shock protein ODF1/HSPB10 is essential for male fertility in mice. Targeted deletion of Odf1 resulted in acephalic sperm in homozygous mice of mixed background (C57BL/6J//129/Sv), whereas heterozygous animals are fully fertile. To further elucidate the function of ODF1, we generated incipient congenic mice with targeted deletion of Odf1 by successive backcrossing on the 129/Sv background. We observed that fecundity of heterozygous Odf1(+/-) male mice was severely reduced over backcross generations. However, neither aberrant sperm parameters nor sperm anomalies could be observed. Ultra-structural analyses of sperm from incipient congenic heterozygous Odf1(+/-) males of backcross generation N7 revealed no obvious pathological findings. However, we observed an enlargement of the distance between nuclear membrane and capitulum, indicating a weakening of the sperm head-to-tail coupling. Severe male subfertility provoked by haplo-deficiency of ODF1 is therefore most probably caused by impaired head-to-tail coupling that eventually might induce sperm decapitation on the specific conditions of in vivo fertilisation. As subfertility in haplo-deficient ODF1 male mice could not be diagnosed by semen analysis, it seems to be a paradigm for unexplained infertility that is a frequent diagnosis for male fertility impairment in humans.

A 5'-flanking region of gonadotropin-regulated testicular RNA helicase (GRTH/DDX25) gene directs its cell-specific androgen-regulated gene expression in testicular germ cells

Gonadotropin-regulated testicular RNA helicase (GRTH/Ddx25) is a posttranscriptional regulator of genes that are essential for spermatid elongation and completion of spermatogenesis. It also prevents Leydig cells (LCs) from gonadotropin overstimulation of androgen production. In transgenic (Tg) mice carrying deletions of the GRTH 5'-flanking regions, we previously demonstrated that the -1085 bp to ATG contains the elements for basal and androgen-induced LC-specific expression. No expression in germ cells (GCs) was found with sequences extended up to -3.6 kb. To define regulatory regions of GRTH required for expression in GC, Tg mice were generated with 5'-flanking sequence 6.4 kb (6.4 Kb-Tg) and/or deletion using green fluorescent protein (GFP) as reporter gene in the present study. GFP was expressed in all lines. Immunohistochemistry analysis showed that 6.4 Kb-Tg directed GFP expression in both GCs and LCs. Deletion of the sequence -205 bp to -3.6 kb (6.4 Kb/del-Tg) directs GFP expression only in meiotic and haploid GCs. This indicated that the distal region -6.4 kb/-3.6 kb is required for GRTH cell-specific expression in GC. Also, it inhibits the expression of GRTH in LC directed by the 205-bp promoter, an effect that is neutralized by the -3.6-kb/-205-bp sequence. Androgen receptor antagonist, flutamide treatment prevents GFP/GRTH expression in Tg lines, demonstrating in vivo direct and indirect effects of endogenous androgen on LCs and GCs, respectively. Our studies have generated and characterized Tg lines that can be used to define requirements for cell-specific expression of the GRTH gene and to further advance our knowledge on the regulation of GRTH by androgen in GCs.

The small heat shock protein ODF1/HSPB10 is essential for tight linkage of sperm head to tail and male fertility in mice

Sperm motility and hence male fertility strictly depends on proper development of the sperm tail and its tight anchorage to the head. The main protein of sperm tail outer dense fibers, ODF1/HSPB10, belongs to the family of small heat shock proteins that function as molecular chaperones. However, the impact of ODF1 on sperm tail formation and motility and on male fecundity is unknown. We therefore generated mutant mice in which the Odf1 gene was disrupted. Heterozygous mutant male mice are fertile while sperm motility is reduced, but Odf1-deficient male mice are infertile due to the detachment of the sperm head. Although headless tails are somehow motile, transmission electron microscopy revealed disturbed organization of the mitochondrial sheath, as well as of the outer dense fibers. Our results thus suggest that ODF1, besides being involved in the correct arrangement of mitochondrial sheath and outer dense fibers, is essential for rigid junction of sperm head and tail. Loss of function of ODF1, therefore, might account for some of the cases of human infertility with decapitated sperm heads. In addition, since sperm motility is already affected in heterozygous mice, impairment of ODF1 might even account for some cases of reduced fertility in male patients.

Gene trap mutation of murine outer dense fiber protein-2 gene can result in sperm tail abnormalities in mice with high percentage chimaerism

BACKGROUND

Outer dense fiber protein 2, Odf2, is a major component of the outer dense fibers, ODF, in the flagellum of spermatozoa. ODF are associated with microtubule doublets that form the axoneme. We recently demonstrated that tyrosine phosphorylation of Odf2 is important for sperm motility. In the course of a study of Odf2 using Odf2 mouse knockout lines we observed that males of a high percentage chimaerism, made using XL169 embryonic stem cells, were infertile, whereas mice of low-medium percentage chimaerism were fertile.

RESULTS

XL169 ES cells have a beta-geo gene trap cassette inserted in the Odf2 gene. To determine possible underlying mechanisms resulting in infertility we analyzed epididymal sperm and observed that >50% displayed bent tails. We next performed ultrastructural analyses on testis of high percentage XL169 chimaeric mice. This analysis showed that high percentage XL169 chimaeric mice produce elongating spermatids that miss one or more entire outer dense fibers in their midpiece and principal piece. In addition, we observed elongating spermatids that show thinning of outer dense fibers. No other obvious abnormalities or defects are present in elongating spermatids. Spermatozoa from the caput and cauda epididymis of XL169 mice of high percentage chimaerism show additional tail defects, including absence of one or more axonemal microtubule doublets and bent tails. Sperm with bent tails display abnormal motility.

CONCLUSIONS

Our results document the possible impact of loss of one Odf2 allele on sperm tail structure and function, resulting in a novel sperm tail phenotype.

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.

Inhibition of tyrosine phosphorylation of sperm flagellar proteins, outer dense fiber protein-2 and tektin-2, is associated with impaired motility during capacitation of hamster spermatozoa

In mammals, acquisition of fertilization competence of spermatozoa is dependent on the phenomenon of sperm capacitation. One of the critical molecular events of sperm capacitation is protein tyrosine phosphorylation. In a previous study, we demonstrated that a specific epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor, tyrphostin-A47, inhibited hamster sperm capacitation, accompanied by a reduced sperm protein tyrosine phosphorylation. Interestingly, a high percentage of tyrphostin-A47-treated spermatozoa exhibited circular motility, which was associated with a distinct hypo-tyrosine phosphorylation of flagellar proteins, predominantly of Mr 45,000-60,000. In this study, we provide evidence on the localization of capacitation-associated tyrosine-phosphorylated proteins to the nonmembranous, structural components of the sperm flagellum. Consistent with this, we show their ultrastructural localization in the outer dense fiber, axoneme, and fibrous sheath of spermatozoa. Among hypo-tyrosine phosphorylated major proteins of tyrphostin-A47-treated spermatozoa, we identified the 45 kDa protein as outer dense fiber protein-2 and the 51 kDa protein as tektin-2, components of the sperm outer dense fiber and axoneme, respectively. This study shows functional association of hypo-tyrosine-phosphorylation status of outer dense fiber protein-2 and tektin-2 with impaired flagellar bending of spermatozoa, following inhibition of EGFR-tyrosine kinase, thereby showing the critical importance of flagellar protein tyrosine phosphorylation during capacitation and hyperactivation of hamster spermatozoa.

CABS1 is a novel calcium-binding protein specifically expressed in elongate spermatids of mice

Single intraperitoneal injection of busulfan at 20 mg/kg body weight to mature male mice induced the deletion of the spermatogenic cells, followed by the restoration of the spermatogenesis by the surviving undifferentiated spermatogonia. The changes of the protein contents in testis during these processes were analyzed by two-dimensional gel electrophoresis in order to identify the proteins expressed at the specific stages of spermatogenesis. An acidic protein that disappeared and recovered in the same time course as spermatids after the busulfan treatment was identified as CABS1 by mass spectrometry. It was found that CABS1 was specifically expressed in the elongate spermatids at steps 13 to 16 in stages I to VIII of the seminiferous epithelium cycle of the mouse, and then it localized to the principal piece of flagellum of the mature sperm in the cauda epididymis. We have found for the first time that CABS1 is a calcium-binding protein that binds calcium during the maturation in the epididymis.

Intramanchette transport during primate spermiogenesis: expression of dynein, myosin Va, motor recruiter myosin Va, VIIa-Rab27a/b interacting protein, and Rab27b in the manchette during human and monkey spermiogenesis

AIM

To show whether molecular motor dynein on a microtubule track, molecular motor myosin Va, motor recruiter myosin Va, VIIa-Rab27a/b interacting protein (MyRIP), and vesicle receptor Rab27b on an F-actin track were present during human and monkey spermiogenesis involving intramanchette transport (IMT).

METHODS

Spermiogenic cells were obtained from three men with obstructive azoospermia and normal adult cynomolgus monkey (Macaca fascicularis). Immunocytochemical detection and reverse transcription-polymerase chain reaction (RT-PCR) analysis of the proteins were carried out. Samples were analyzed by light microscope.

RESULTS

Using RT-PCR, we found that dynein, myosin Va, MyRIP and Rab27b were expressed in monkey testis. These proteins were localized to the manchette, as shown by immunofluorescence, particularly during human and monkey spermiogenesis.

CONCLUSION

We speculate that during primate spermiogenesis, those proteins that compose microtubule-based and actin-based vesicle transport systems are actually present in the manchette and might possibly be involved in intramanchette transport.

Nuclear regulator Pygo2 controls spermiogenesis and histone H3 acetylation

Mammalian spermiogenesis, a process where haploid male germ cells differentiate to become mature spermatozoa, entails dramatic morphological and biochemical changes including remodeling of the germ cell chromatin. Proteins that contain one or more plant homeodomain (PHD) fingers have been implicated in the regulation of chromatin structure and function. Pygopus 2 (Pygo2) belongs to a family of evolutionarily conserved PHD finger proteins thought to act as co-activators of Wnt signaling effector complexes composed of beta-catenin and LEF/TCF transcription factor. Here we analyze mice containing hypomorphic alleles of pygopus 2 (Pygo2 or mpygo2) and uncover a beta-catenin-independent involvement of the Pygo2 protein in spermiogenesis. Pygo2 is expressed in elongating spermatids at stages when chromatin remodeling occurs, and block of Pygo2 function leads to spermiogenesis arrest and consequent infertility. Analysis of spermiogenesis in Pygo2 mutants reveals reduced expression of select post-meiotic genes including protamines, transition protein 2, and H1fnt, all of which are required for germ cell chromatin condensation, and drastically altered pattern of histone H3 hyperacetylation. These findings suggest that Pygo2 is involved in the chromatin remodeling events that lead to nuclear compaction of male germ cells.

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.

Mammalian transcription in support of hybrid mRNA and protein synthesis in testis and lung

Post-transcriptional mechanisms including differential splicing expand the protein repertoire beyond that provided by the one gene-one protein model. Trans-splicing has been observed in mammalian systems but is low level (sometimes referred to as noise), and a contribution to hybrid protein expression is unclear. In the study of rat sperm tail proteins a cDNA, called 1038, was isolated representing a hybrid mRNA derived in part from the ornithine decarboxylase antizyme 3 (Oaz3) gene located on rat chromosome 2 fused to sequences encoded by a novel gene on chromosome 4. Cytoplasmic Oaz3 mRNA is completely testis specific. However, in several tissues Oaz3 is transcribed and contributes to hybrid 1038 mRNA synthesis, without concurrent Oaz3 mRNA synthesis. 1038 mRNA directs synthesis of a hybrid 14-kDa protein, part chromosome 2- and part chromosome 4-derived as shown in vitro and in transfected cells. Antisera that recognize a chromosome 4-encoded C-terminal peptide confirm the hybrid character of endogenous 14-kDa protein and its presence in sperm tail structures and 1038-positive tissue. Our data suggest that the testis-specific OAZ3 gene may be an example of a mammalian gene that in several tissues is transcribed to contribute to a hybrid mRNA and protein. This finding expands the repertoire of known mechanisms available to cells to generate proteome diversity.

Tdrd1/Mtr-1, a tudor-related gene, is essential for male germ-cell differentiation and nuage/germinal granule formation in mice

Embryonic patterning and germ-cell specification in mice are regulative and depend on zygotic gene activities. However, there are mouse homologues of Drosophila maternal effect genes, including vasa and tudor, that function in posterior and germ-cell determination. We report here that a targeted mutation in Tudor domain containing 1/mouse tudor repeat 1 (Tdrd1/Mtr-1), a tudor-related gene in mice, leads to male sterility because of postnatal spermatogenic defects. TDRD1/MTR-1 predominantly localizes to nuage/germinal granules, an evolutionarily conserved structure in the germ line, and its intracellular localization is downstream of mouse vasa homologue/DEAD box polypeptide 4 (Mvh/Ddx4), similar to Drosophila vasa-tudor. Tdrd1/Mtr-1 mutants lack, and Mvh/Ddx4 mutants show, strong reduction of intermitochondrial cement, a form of nuage in both male and female germ cells, whereas chromatoid bodies, another specialized form of nuage in spermatogenic cells, are observed in Tdrd1/Mtr-1 mutants. Hence, intermitochondrial cement is not a direct prerequisite for oocyte development and fertility in mice, indicating differing requirements for nuage and/or its components between male and female germ cells. The result also proposes that chromatoid bodies likely have an origin independent of or additional to intermitochondrial cement. The analogy between Mvh-Tdrd1 in mouse spermatogenic cells and vasa-tudor in Drosophila oocytes suggests that this molecular pathway retains an essential role(s) that functions in divergent species and in different stages/sexes of the germ line.

Rat kinesin light chain 3 associates with spermatid mitochondria

We recently discovered that in rat spermatids, kinesin light chain KLC3 can associate with outer dense fibers, major sperm tail components, and accumulates in the sperm midpiece. Here, we show that mitochondria isolated from rat-elongating spermatids have bound KLC3. Immunoelectron microscopy indicates that the association of KLC3 with mitochondria coincides with the stage in spermatogenesis when mitochondria move from the plasma membrane to the developing midpiece. KLC3 is able to bind in vitro to mitochondria from spermatids as well as somatic cells employing a conserved kinesin light chain motif, the tetratrico-peptide repeats. Expression of KLC3 in fibroblasts results in formation of large KLC3 clusters close to the nucleus, which also contain mitochondria: no other organelles were present in these clusters. Mitochondria are not present in KLC3 clusters after deletion of KLC3's tetratrico-peptide repeats. Our results indicate that the rat spermatid kinesin light chain KLC3 can associate with mitochondria.

Cloning and developmental analysis of murid spermatid-specific thioredoxin-2 (SPTRX-2), a novel sperm fibrous sheath protein and autoantigen

Thioredoxins compose a growing family of proteins that participate in different cellular processes via redox-mediated reactions. We report here the cloning, developmental expression, and location of murid Sptrx-2. Mouse and rat SPTRX-2 proteins display a high homology to their human ortholog in the thioredoxin and NDP kinase domains, and the coding genes are located at syntenic positions. Northern blotting and in situ hybridization confirmed the testis-specific expression of murine Sptrx-2 mRNA, mostly in round spermatids. Immunohistochemical analysis of the 19 steps of rat spermiogenesis showed that SPTRX-2 expression becomes prominent in the cytoplasmic lobe of step 15-18 spermatids and diminishes in step 19 just before spermiation. However, in the spermatid tail, SPTRX-2 immunoreactivity increased from step 15 to 19 and was confined to the principal piece. By immunogold electron microscopy, SPTRX-2 was first detected scattered throughout the cytoplasm of the axoneme in step 14-15 spermatids, but began to be incorporated by step 16 into the fibrous sheath (FS). During steps 17-18, the labeling increased over the ribs and columns of the assembled FS. It peaked in step 19 and remained in the FS of epididymal spermatozoa. Immunoblots of isolated FS obtained from spermatozoa confirmed that SPTRX-2 is an integral component of the FS and a post-obstruction autoantigen in vasectomized rats. Our data indicate that SPTRX-2 incorporation into the FS lags well behind FS assembly, suggesting it is required during the final stages of sperm tail maturation in the testis and/or epididymis, where extensive disulfide bonding of FS proteins occurs.

Acroplaxome, an F-actin-keratin-containing plate, anchors the acrosome to the nucleus during shaping of the spermatid head

Nuclear shaping is a critical event during sperm development as demonstrated by the incidence of male infertility associated with abnormal sperm ad shaping. Herein, we demonstrate that mouse and rat spermatids assemble in the subacrosomal space a cytoskeletal scaffold containing F-actin and Sak57, a keratin ortholog. The cytoskeletal plate, designated acroplaxome, anchors the developing acrosome to the nuclear envelope. The acroplaxome consists of a marginal ring containing keratin 5 10-nm-thick filaments and F-actin. The ring is closely associated with the leading edge of the acrosome and to the nuclear envelope during the elongation of the spermatid head. Anchorage of the acroplaxome to the gradually shaping nucleus is not disrupted by hypotonic treatment and brief Triton X-100 extraction. By examining spermiogenesis in the azh mutant mouse, characterized by abnormal spermatid/sperm head shaping, we have determined that a deformity of the spermatid nucleus is restricted to the acroplaxome region. These findings lead to the suggestion that the acroplaxome nucleates an F-actin-keratin-containing assembly with the purpose of stabilizing and anchoring the developing acrosome during spermatid nuclear elongation. The acroplaxome may also provide a mechanical planar scaffold modulating external clutching forces generated by a stack of Sertoli cell F-actin-containing hoops encircling the elongating spermatid nucleus.

Spermatid nuclear and sperm periaxonemal anomalies in the mouse Ube2b null mutant

Ube2b (yeast Ubc2b/Rad6 homolog) null mice were described previously. Ube2b encodes the murine ubiquitin conjugating enzyme mHR6B. Ube2b(-/-) mice were shown to present male infertility and their sperm head shape anomalies suggested that Ube2b may be involved in the replacement of nuclear proteins during spermatid chromatin condensation. Apoptosis of spermatocytes suggested additional targets of Ube2b during spermatogenesis. Consistently, we found Ube2b transcription in both meiotic and postmeiotic stages by in situ hybridization. Immuno-electron microscopy revealed that transition proteins 1 and 2, protamines 1 and 2, and actin appear normally distributed during morphogenesis of Ube2b(-/-) spermatid heads. Surprisingly, electron microscopy revealed a particular sperm flagellum phenotype characterized by an abnormal distribution of periaxonemal structures. Flagellar anomalies of Ube2b null mice were previously described in infertile men indicating a possible genetic pathway for flagellar periaxonemal assembly in human.

Protein phosphatase 1cgamma is required in germ cells in murine testis

The protein phosphatase 1cgamma (PP1cgamma) gene is required for spermatogenesis. Males homozygous for a null mutation are sterile, and display both germ cell and Sertoli cell defects. As these two cell types are physically and functionally intimately connected in the testis, the question arises as to whether the primary site of PP1cgamma action is in Sertoli cells, germ cells, or both. We generated chimeric males by embryo aggregation to test whether wild type Sertoli cells are capable of rescuing mutant germ cells. To distinguish between the desired XY-XY chimeras and uninformative XX-XY chimeras, we designed an adaptation of the single nucleotide primer extension (SNuPE) assay. None of the XY-XY chimeras sired pups derived from mutant germ cells, indicating that the protein is required in germ cells for production of functional sperm. Analysis of a chimeric testis revealed intermediate phenotypes when compared with PP1cgamma-/- testes, suggestive of cell nonautonomous effects. We conclude that PP1cgamma is required in a cell autonomous fashion in germ cells. There may be an additional cell nonautonomous role played by this gene in testes, possibly mediated by defective signaling between germ cells and Sertoli cells.

Association of kinesin light chain with outer dense fibers in a microtubule-independent fashion

Conventional kinesin I motor molecules are heterotetramers consisting of two kinesin light chains (KLCs) and two kinesin heavy chains. The interaction between the heavy and light chains is mediated by the KLC heptad repeat (HR), a leucine zipper-like motif. Kinesins bind to microtubules and are involved in various cellular functions, including transport and cell division. We recently isolated a novel KLC gene, klc3. klc3 is the only known KLC expressed in post-meiotic male germ cells. A monoclonal anti-KLC3 antibody was developed that, in immunoelectron microscopy, detects KLC3 protein associated with outer dense fibers (ODFs), unique structural components of sperm tails. No significant binding of KLC3 with microtubules was observed with this monoclonal antibody. In vitro experiments showed that KLC3-ODF binding occurred in the absence of kinesin heavy chains or microtubules and required the KLC3 HR. ODF1, a major ODF protein, was identified as the KLC3 binding partner. The ODF1 leucine zipper and the KLC3 HR mediated the interaction. These results identify and characterize a novel interaction between a KLC and a non-microtubule macromolecular structure and suggest that KLC3 could play a microtubule-independent role during formation of sperm tails.

Novel RING finger protein OIP1 binds to conserved amino acid repeats in sperm tail protein ODF1

Outer dense fibers (ODFs) and the fibrous sheath (FS) are unique structures of the mammalian sperm tail. Recently, progress has been made in the molecular cloning of ODF and FS proteins, and because of this, questions addressing the morphogenesis and underlying protein network that make up sperm tail structures and their function can now be addressed. Using the N-terminal leucine zipper motif of the major ODF protein ODF1, we had previously isolated interacting proteins Odf2, Spag4, and Spag5. We report here a yeast two-hybrid strategy to isolate a novel rat testicular protein, OIP1, that binds to the evolutionarily conserved Cys-Gly-Pro repeats in the C-terminus of ODF1. OIP1 is expressed in round spermatids as well as in spermatocytes and several somatic tissues, albeit at a lower level. No expression was detectable in epididymis, heart, and smooth muscle. OIP1 protein localizes to the sperm tail in a pattern expected for an ODF1-interacting protein. OIP1 belongs to the family of RING finger proteins of the H2 subclass. Deletion of the putative RING motif significantly decreased binding to ODF1. Genomic analysis of rat Oip1 and Oip1 homologs indicates that Oip1 is highly conserved. Oip1 is subject to differential splicing and alternative polyadenylation events. It is interesting that Oip1 mRNAs have been reported that lack the exon encoding the putative RING finger.

Developmental expression of spermatid-specific thioredoxin-1 protein: transient association to the longitudinal columns of the fibrous sheath during sperm tail formation

The mammalian sperm tail presents a complex organization in which a number of additional structures, namely outer dense fibers and fibrous sheath, surround the central axoneme and are thought to regulate flagellar motility. We have previously described a novel member of the thioredoxin family of proteins with a spermatid specific expression pattern, spermatid-specific thioredoxin-1 (Sptrx-1). We report here the developmental analysis of Sptrx-1 expression during murine spermiogenesis. Immunocytochemical analysis of Sptrx-1 through the different steps of spermiogenesis in rat seminiferous tubule sections showed that its expression begins at step 9, gets progressively stronger until steps 14-16 (where a peak is reached), and then diminishes in steps 17 and 18 until practically no immunolabeling is detected in step 19 spermatid. During its transient expression in spermiogenesis, Sptrx-1 is most concentrated in the periaxonemal compartment of the tail of the elongating spermatid, except in the very last steps (steps 17-19), when periaxonemal labeling disappears and a residual buildup of Sptrx-1 occurs in the shrinking cytoplasmic lobe. Electron microscopic analysis by immunogold labeling pinpointed the localization of Sptrx-1 to the assembling longitudinal columns of the fibrous sheath, whereas the forming ribs of the fibrous sheath were unlabeled. Immunoblotting of isolated fibrous sheath and tails obtained from epididymal or ejaculated sperm of rat and human confirmed our immunocytochemical observation: Sptrx-1 is no longer a component of the mature fibrous sheath. To our knowledge, this is the first report of a protein that specifically associates to the fibrous sheath during development but does not become a permanent structural component. The expression pattern of Sptrx-1 during rat spermiogenesis suggests that it could be part of a nucleation center for the formation of the longitudinal columns and transverse ribs that bridge the latter.

Targeted disruption of the testicular SPAG5/deepest protein does not affect spermatogenesis or fertility

In an effort to define the molecular basis for morphogenesis of major sperm tail structures, including outer dense fibers, we recently cloned the Spag5 gene by virtue of its strong and specific leucine-zipper-mediated interaction with Odf1, the 27-kDa major outer dense fiber protein. Spag5 is expressed during meiosis and in round spermatids and is similar, if not identical, to Deepest, a putative spindle pole protein. Here we report the disruption of the Spag5 gene by homologous recombination. Spag5-null mice lack Spag5 mRNA and protein. However, male mice are viable and fertile. Analysis of the process of spermatogenesis and sperm produced in Spag5-null mice did not reveal a major phenotype as a consequence of the knockout event. This result suggests that if Spag5 plays a role in spermatogenesis it is likely compensated for by unknown proteins.

Bypassing natural sperm selection during fertilization: the azh mutant offspring experience and the alternative of spermiogenesis in vitro

Molecular aspects of spermiogenesis can be studied using mouse mutants and spermatids developed in vitro. The azh/azh mutant is an attractive model system because structural abnormalities in the sperm head and the ectopic position of the manchette are associated with tail bending and looping. Spermatids, developing an axoneme in vitro and capable of cell motility, offer the possibility of the dynamic analysis of tail development. Offspring generated by intracytoplasmic injection of azh/azh sperm heads into normal mouse oocytes complement the mouse mutant approach. A central question of sperm tail development is the role of the manchette, a transient microtubular structure assembled soon after the organization of the axoneme. The fractionation of intact manchettes by gradient centrifugation has enabled a biochemical analysis of constitutive tubulin isotypes and transiently associated proteins. For example, keratins Sak57, Odf1, and Odf2 are initially stored in the manchette before being sorted to the outer dense fibers and fibrous sheath of the developing spermatid tail. Additional proteins associated with the manchette include two proteases, the 26S proteasome and N-arginine convertase (both sorted to the developing spermatid tail), a spermatid perinuclear RNA binding protein, Spag4, an Odf1-binding protein, and type 4 cAMP-specific phosphodiesterase D. Keratin 9 and delta-tubulin are two proteins found in the perinuclear ring of the manchette, the insertion site of the microtubular mantle. Available data indicate that the manchette is a highly dynamic structure providing microtubular tracks to structural proteins participating in the sperm tail development.

Transcriptional regulation of spermiogenesis: insights from the study of the gene encoding the acrosomal protein SP-10

Spermiogenesis is the terminal differentiation process of the male germ cell during which haploid spermatids acquire unique structures such as the acrosome and flagellum and undergo extensive cellular reorganization. Although well described morphologically, the molecular mechanisms underlying spermiogenesis are not well understood. The SP-10 gene, which codes for the acrosomal protein SP-10, has been well characterized in mice and men. This single copy gene is localized to syntenic regions of chromosomes 9 and 11 in mouse and human, respectively. The SP-10 gene is testis-specific, and is transcribed and translated in round spermatids. The differentiation marker SP-10 serves as a useful model to address questions regarding the regulation of round spermatid-specific gene transcription and acrosome biogenesis. This paper defines the temporal pattern of SP-10 gene expression during spermiogenesis and reviews the work done on analysis of the SP-10 promoter. Transgenic mice demonstrated that either the -408/+28 or the -266/+28 region of the SP-10 promoter could drive round spermatid-specific expression of a GFP reporter gene whereas the -91/+28 region lacked promoter activity. The transgene expression mimicked the spatial and temporal patterns of expression of the endogenous SP-10 gene. Surprisingly, none of the transgenic lines showed expression of GFP in tissues other than testis. Given the complexity of eukaryotic transcriptional regulation, the fact that a short 294-bp promoter is capable of conferring developmental stage- and cell type-specific transcription of a gene is intriguing and paradoxical.

Molecular cloning of Odf3 encoding a novel coiled-coil protein of sperm tail outer dense fibers

The outer dense fibers (ODF) are the main cytoskeletal structures of the sperm tail found in animals with internal fecundation. They consist of at least 14 polypeptides from which only a few are identified due to difficulties in isolation of the protein components. Here we report the isolation and molecular characterization of Odf3, encoding a novel protein of rat sperm ODF. Odf3 is transcribed in testes and more specifically in spermatids but it is also expressed in epididymides and brain suggesting a possible involvement in building of the cellular cytoskeleton. Odf3 encodes a putative protein of approximately 110 kDa. Secondary structure predictions indicated that ODF3 is a coiled-coil protein. The identification of coiled-coil proteins as constituents of outer dense fibers reveals a model for ODF formation.

Testicular protein Spag5 has similarity to mitotic spindle protein Deepest and binds outer dense fiber protein Odf1

Outer dense fibers (ODF) and the fibrous sheath (FS) are major cytoskeletal structures in the mammalian sperm tail. The molecular mechanisms underlying their morphogenesis along the axoneme or their function are poorly understood. Recently, we reported the cloning and characterization of Odf2, a major ODF protein, and Spag4, an axoneme-binding protein, by virtue of their strong interaction with Odf1, the 27 kDa major ODF protein. We proposed a crucial role for leucine zippers in molecular interactions during sperm tail morphogenesis. Here we report the cloning and characterization of a novel gene, Spag5, which encodes a 200 kDa testicular protein that interacts strongly with Odf1. Spag5 is transcribed and translated in pachytene spermatocytes and spermatids. It bears 73% similarity with the mitotic spindle protein Deepest of unknown function. We identified two putative leucine zippers in the C-terminal part of the Spag5 protein, the downstream one of which is involved in interaction with Odf1. Interestingly, these motifs are present in Deepest. These results highlight the importance of the leucine zipper in sperm tail protein interactions. Mol. Reprod. Dev. 59: 410-416, 2001.

Spermatid manchette: plugging proteins to zero into the sperm tail

Spermiogenesis pursues three major objectives: (1) The safeguard of the male genome within the confines of a compact nucleus. (2) The accumulation of enzymes in the acrosome of be released at fertilization. (3) The development of a sperm propelling tail consisting of an axoneme surrounded by a scaffold of keratin-containing outer dense fibers and a fibrous sheath. Recent experimental data indicate that three keratins-Sak57, 0df1 and 0df2-and other proteins (the 26S proteasome and the 0df1-binding protein Spag4) are temporarily stored in the manchette before being sorted to the developing sperm tail. These findings support a general model for the manchette as an ephemeral structure timely developed and strategically positioned to provide a transient storage to both structural and signaling proteins. Some of the proteins are later sorted to the developing tail; others may participate in the reciprocal nuclear-cytoplasmic signaling pathways as the gene activity of the male genome gradually becomes silent. Mol. Reprod. Dev. 59: 347-349, 2001.

Outer dense fiber proteins are dominant postobstruction autoantigens in adult Lewis rats

Obstruction of the male reproductive tract commonly results in generation of antisperm autoantibodies. However, only a few of the sperm autoantigens recognized by these antibodies have been characterized. To identify postobstruction rat sperm autoantigens, sperm proteins were separated by two-dimensional(2-D) gel electrophoresis. Spots corresponding to proteins that were stained by at least 50% of postvasectomy rat sera on 2-D Western blots were removed from polyacrylamide gels and microsequenced by tandem mass spectrometry. From a total of 21 spots, 12 contained peptides that matched solely to either of two outer dense fiber proteins, odf1 or odf2. Six additional spots contained peptides comprising odf1 or odf2 and were accompanied by peptides representing other proteins. Only three spots lacked outer dense fiber peptides but did contain sequences of other known proteins. The results indicate that the outer dense fiber proteins odf1 and odf2 are dominant postobstruction autoantigens because they were detected in the majority of the immunoreactive protein spots examined. Possible explanations for this observation include the abundance of outer dense fiber proteins in spermatozoa, slow solubility, which may provide a sustained supply of antigen, and testis-specific expression during spermiogenesis.

Spag4, a novel sperm protein, binds outer dense-fiber protein Odf1 and localizes to microtubules of manchette and axoneme

Outer dense fibers are structures unique to the sperm tail. No definite function for these fibers has been found, but they may play a role in motility and provide elastic recoil. Their composition had been described before, but only two of the fiber proteins, Odf1 and Odf2, are cloned. We cloned Odf2 by virtue of its functional and specific interaction with Odf1, which, we show, is mediated by a leucine zipper. Further work demonstrated that the 84-kDa Odf2 protein localizes to both the cortex and the medulla of the fibers, whereas the 27-kDa Odf1 protein is present only in the medulla. Here we report the cloning and characterization of a new Odf1-interacting protein, Spag4. Spag4 mRNA is spermatid specific, and the 49-kDa Spag4 protein complexes specifically with Odf1, but not Odf2, mediated by a leucine zipper. It also self-associates. In contrast to Odf1 and Odf2, Spag4 protein localizes to two microtubule-containing spermatid structures. Spag4 is detectable in the transient manchette and it is associated with the axoneme in elongating spermatids and epididymal sperm. Our data suggest a role for Spag4 in protein localization to two major sperm tail structures.

Testis-specific TTF-D binds to single-stranded DNA in the c-mos and Odf1 promoters and activates Odf1

We recently identified testis-specific nuclear factor binding sites in the testis-specific promoters of the c-mos gene and the Odf1 gene, which are 80% identical. Here we characterize a testis-specific nuclear factor, TTF-D, which is able to complex with both binding sites and stimulates Odf1 promoter activity. TTF-D is detectable in mouse testis as early as day 11 postpartum and contains three peptides of 22, 25, and 35 kDa in size. Surprisingly, TTF-D binds specifically to its cognate double-stranded DNA binding site as well as to its single-stranded DNA binding site. Both double-stranded and single-stranded binding site oligonucleotide DNA can specifically repress Odf1 promoter activity. Our results suggest that TTF-D is involved in positive transcription regulation of a pre-meiotic and a post-meiotic gene in the testis.

Mouse Odf2 cDNAs consist of evolutionary conserved as well as highly variable sequences and encode outer dense fiber proteins of the sperm tail

The outer dense fibers (ODF) of the mammalian sperm tail comprise a unique, specialized, and very prominent structure, consisting of nine fibers surrounding the axoneme. The ODF may play an important but as yet undefined role in sperm morphology, integrity and function. Study of the ODF is hampered by insufficient knowledge of their protein composition and the genetic regulation of their synthesis. We report here on the characterization of cDNAs encoding the Odf2 proteins of outer dense fibers of mouse sperm. We isolated two cDNA clones with variable 5' regions. Variability in sequence is restricted to specific regions in the N-terminal part of the encoded proteins, whereas the C-terminal part is highly conserved in Odf2 proteins both between species and within a species. This variability is confirmed at the protein level. The outer dense fibers could be detected immunologically in total sperm tails allowing a direct comparison of their length in relation to the length of the sperm tail. Odf2 transcripts could be demonstrated in testicular RNA and are restricted to germ cells. The start of transcription is in step 5 spermatids of tubular stage V and the RNA could be detected in the cytoplasm of differentiating spermatids in all subsequent tubular stages.

Developmental expression of the 84-kDa ODF sperm protein: localization to both the cortex and medulla of outer dense fibers and to the connecting piece

Outer dense fibers (ODF) are specialized cytoskeletal elements of the mammalian sperm tail which are composed of several prominent proteins. We previously reported the isolation of a cDNA (111-450) encoding a putative 84-kDa ODF protein. Here we demonstrate by independent cDNA isolations and by translational/immunoprecipitation of testicular mRNAs using anti-ODF 84 antibodies that 111-450 cDNA encodes the 84-kDa protein. We then analyzed the testicular expression of the ODF 84 mRNA and protein. Riboprobes generated from the clones recognized four testicular-specific transcripts of 1.6, 2.2, 2.4, and 2.8 kb in both rat and bull of which the immunoprecipitable product of the 2.4-kb mRNA comigrates with ODF 84 protein. Developmental Northerns indicated that the 2.2- and 2.4-kb mRNAs are first transcribed during meiotic prophase while the other two species are first expressed in round spermatids. The levels of all the transcripts steadily increased up to elongated spermatids. Immunocytochemistry revealed that the anti-84 reactive ODF proteins were synthesized and assembled in the cytoplasm of elongated spermatids (steps 9-18) with peak activity occurring in step 16 of spermiogenesis. Immunogold labeling was selective to the assembling ODF and connecting piece of the tail and to granulated bodies of the cytoplasmic lobe. Both the striated collar and capitulum of the connecting piece were immunolabeled as well as the basal plate of the implantation fossa. A combination of pre- and postembedding immunogold labeling provided evidence that the 84-kDa ODF protein is localized to both the cortex and medulla of the ODF in contrast to the sole medullary localization of the major 27-kDa ODF protein. Thus the 84-kDa ODF protein, encoded by the 2.4 transcript, is translationally regulated, packaged after synthesis into granulated bodies, assembled in a proximal to distal direction along the axoneme and may interact by means of leucine zippers specifically with the 27-kDa ODF protein during assembly. Its localization to both the cortex and medulla of the ODF, as opposed to exclusive medullary localization of the 27-kDa ODF protein, and the presence of two leucine zippers, only one of which interacts with the 27-kDa ODF, suggests that it could act as a link between proteins of the two regions of the ODF.

Identification of a rat testis-specific gene encoding a potential rat outer dense fibre protein

Screening of a rat testis expression library with an antiserum specific for an outer dense fibre (ODF) has led to the identification of a gene encoding for a putative protein previously unknown as a component of the sperm tail. This gene has been designated tpx-1 by virtue of its homology with the mouse and human gene of the same name (79 and 73%, respectively). The tpx-1-like gene encoded a 1.6-kb mRNA and a 243-amino-acid protein that had significant homology with members of the cysteine-rich secretory protein (CRISP) family and partial homology with several venom/allergen proteins from both plants and insects. During rat spermatogenesis, the tpx-1-like transcript was first detected by in situ hybridization in low levels in late pachytene spermatocytes. Low but detectable levels of expression continued up to step 5 round spermatids, after which expression levels increased dramatically to a maximum in step 11-12 spermatids. Progressively decreasing levels of expression were detected in up to step 17 elongating spermatids. Testicular somatic cells did not contain detectable tpx-1-like transcript. This pattern of expression is consistent with published data on the development of the ODF in spermatogenesis and, when taken together with a comparison of the predicted amino acid sequence of tpx-1 with the amino acid analysis of a 29-kDa rat ODF protein, suggests that the tpx-1-like gene may encode for this protein.

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.

Cell interactions in testis development: overexpression of c-mos in spermatocytes leads to increased germ cell proliferation

Possible functions of the c-mos proto-oncogene during spermatogenesis were investigated through perturbations of its expression in transgenic mice. Two promoters, one from the pre-meiotic male germ cell-specific mouse phosphoglycerate kinase 2 gene, and the other from the post-meiotic male germ cell-specific rat RT7 gene were used to direct expression of c-mos. Northern blot analysis of testis RNA from transgenic PGK-c-mos mice indicated elevated levels of c-mos RNA in spermatocytes and spermatids compared to controls. No transgene expression was detected in any other tissue examined, suggesting that the mouse PGK2 promoter, like the previously used human PGK2 promoter, confers correct cell-specific expression onto c-mos. The promoter from a newly characterized rat gene, RT7, was shown to direct expression specific to post-meiotic spermatids. Transgenic mice carrying an RT7-lacZ construct displayed immunoreactive bacterial beta-galactosidase as well as enzyme activity in round spermatids. The cellular specificity for beta-galactosidase expression observed in RT7-lacZ transgenic animals was in agreement with endogenous RT7 transcript expression. Northern blot analysis of testis RNA of RT7-c-mos transgenic mice showed elevated levels of c-mos in spermatids, but not in other cells or tissues examined. Western blot analysis demonstrated elevated levels of p43c-mos in spermatids of both PGK-c-mos and RT7-c-mos transgenic animals, but only PGK-c-mos transgenics had increased p43c-mos levels in spermatocytes. Both RT7-c-mos and PGK-c-mos transgenic mice are fertile and show no tendency toward transformation. RT7-c-mos mice have no discernible phenotype associated with the c-mos overexpression in spermatids. However, PGK-c-mos transgenic males exhibited a significant increase in germ cell number, as determined by cell counts using total germ cells and germ cells fractionated by centrifugal elutriation. Because mitotic divisions of germ cells occur prior to PGK-c-mos transgene expression, our observations suggest that c-mos overexpression in spermatocytes causes an alteration in cell-cell interactions.

Molecular cloning and developmental expression of an mRNA encoding the 27 kDa outer dense fiber protein of rat spermatozoa

We have isolated a cDNA (ODF27), encoding the major 27 kDa protein of rat sperm outer dense fibers (ODF), by screening a testicular lambda-gt11 phage cDNA library with an affinity-purified anti-27 kDa ODF polyclonal antibody. A cyanogen bromide derived internal amino acid (a.a.) sequence of the 27 kDa ODF protein was identical to an internal region of the deduced a.a. sequence of this cDNA. The cDNA encodes a protein with a high proportion of a repetitive motif, Cys-Gly-Pro, at the carboxy-terminal end, reminiscent of the testis-specific Mst(3)CGP proteins of Drosophila melanogaster (Schäfer et al., 1993. Mol Cell Biol 13:1708-1718). Nick translation probes of the ODF27 cDNA recognized two complementary mRNAs of 1.2 and 1.5 kb in the rat testis. Developmental Northern blot analysis revealed that these mRNAs are first transcribed in round spermatids. In situ hybridization confirmed the haploid expression of these transcripts and demonstrated that they are found in the cytoplasm of spermatids throughout most of the duration of spermiogenesis. They reach a peak in steps 8-10 of spermiogenesis at the time transcription ceases, remain at high levels from steps 11 to 15, and diminish in steps 16-18 at the time ODF protein synthesis and assembly are shown to be maximum. The translation of these transcripts, therefore, appears to be post-transcriptionally controlled. A literature and NCBl database search revealed that the nucleotide sequence of the 027 cDNA is homologous to the rat gene RT7 (Van Der Hoorn et al., 1990. Dev Biol 142:147-154) and to the rat testis-specific cDNA rts 5/1 (Burfeind and Hoyer-Fender, 1991. Dev Biol 148:195-204), which encodes a 27 kDa polypeptide.

Identification of conserved potential regulatory sequences of the protamine-encoding P1 genes from ten different mammals

In order to detect regulatory conserved DNA elements within the protamine 1-encoding gene (P1) promoter, we have sequenced this region from the rat, guinea pig, gorilla, orangutan, anubis baboon and red monkey P1 genes and compared it to the homologous human, bull, boar and mouse nucleotide (nt) sequences. We demonstrate the presence of a consensus sequence, HSMCYTCAYAAT (Prot1C: protamine 1 consensus), from nt position -64 to position -53 in all P1 genes whose promoter sequences are now known. We also show that sequences similar to Prot1C are found in the promoter region of other testis-specific genes, such as the transition protein 1-encoding gene promoter which is thought to have derived from the P1 genes. The relevance of this conserved element in the expression of P1 genes is strongly supported by the recent demonstration of a mouse testis trans-acting factor [Tet-1; Tamura et al., J. Biol. Chem. 267 (1992) 4327-4332] which binds and matches in the mouse the first 11 bp of the corresponding consensus Prot1C sequence reported here. Another highly conserved element (TGTGAGG) has been identified 20 +/- 3 nt upstream from Prot1C. This sequence forms a perfect palindrome with the central 7 nt of Prot1C and is absent in the homologous region of other genes. Further upstream, at positions -113 to -132, a third highly conserved region is present (MATGCCCATATWTGGRCAYG) which is similar to the c-fos SRE (serum-response element) and contains the central core common to all SREs. This element has not been found in the homologous region of other sperm-specific genes.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure and chromosomal assignment of a gene encoding the major protein of rat sperm outer dense fibres

Outer dense fibres are located on the outside of the axoneme in the midpiece and principal piece of the mammalian sperm tail and may help to maintain the passive elastic structures and elastic recoil of the sperm tail. Here we describe the isolation and genomic organization of a rat gene encoding a cysteine-proline-rich outer dense fibre protein. The cDNA sequence of rts 5/1 and its expression pattern have already been published [Burfeind, P. & Hoyer-Fender, S. (1991) Dev. Biol. 148, 195-204]. There exist two different genes in the rat genome, rts 5/1 major and rts 5/1 minor. Rts 5/1 major consists of two exons interrupted by one intron of about 3.8 kb. Exon 1 and rts 5/1 minor contains a deletion of 120 bp, without destroying the open reading frame, which is flanked by short direct repeats, 15 bp in length. The first two nucleotides of the intronic sequence were identified as GA and, therefore, do not agree with the donor consensus sequence. From the analysis of mouse x rat cell hybrids, the rts 5/1 major gene has been assigned to chromosome 7. By immunoblotting and immunocytochemistry, it was demonstrated that the isolated gene encodes a major protein of rat sperm outer dense fibres.

Analysis of the expression of a large number of novel genes isolated from mouse prepubertal testis

The analysis of genes expressed in a restricted temporal and spatial manner during spermatogenesis has given insights into different gene-regulatory mechanisms active in germ cells. However, very few genes have so far been described that are predominantly active in spermatogonia and the early meiotic cell types of testis. To isolate a battery of such genes, more than 100 different mRNA molecules were isolated from a mouse prepubertal testicular cDNA library, and their expression patterns in different tissues analyzed. Thirty mRNAs, 26 of them previously not described in the literature, were found to be predominantly expressed in mouse testis. A detailed analysis of their expression patterns identified a number of mRNA molecules differentially expressed in testicular cell types, including both germ cells and somatic cell types. Characterization of these mRNAs also revealed five distinct temporal phases of gene expression during prepubertal germ cell development. Three different genes, mainly active in the spermatogonial and the early meiotic cell types of testis, were isolated and will be used to characterize further stage-specific gene expression during germ cell differentiation.

Factors involved in regulation of the RT7 promoter in a male germ cell-derived in vitro transcription system

We recently cloned and characterized a rat male germ cell-specific gene, RT7. The RT7 promoter contains a TATA box as well as sequences with homology to binding sites for a number of transcription factors. To investigate the regulation of the RT7 promoter we developed an active in vitro transcription system derived from rat seminiferous epithelium, which, in contrast to total testis, consists mostly of male germ cells. Also, DNase I footprinting analysis and gel retardation experiments were performed to analyze RT7 promoter-protein interaction. The experiments demonstrate that nuclear extracts prepared from rat male germ cells support in vitro transcription and that the RT7 promoter is positively regulated by a testis-specific transcription factor, TTF-D, by a factor similar to the transcription factor CREB, and by a nuclear factor that binds immediately upstream of the RT7 transcription start site.