Mouse testes contain two size classes of actin mRNA that are differentially expressed during spermatogenesis

Identification and validation of mouse sperm proteins correlated with epididymal maturation

Sperm need to mature in the epididymis to become capable of fertilization. To understand the molecular mechanisms of mouse sperm maturation, we conducted a proteomic analysis using saturation dye labeling to identify proteins of caput and cauda epididymal sperm that exhibited differences in amounts or positions on two-dimensional gels. Of eight caput epididymal sperm-differential proteins, three were molecular chaperones and three were structural proteins. Of nine cauda epididymal sperm-differential proteins, six were enzymes of energy metabolism. To validate these proteins as markers of epididymal maturation, immunoblotting and immunofluorescence analyses were performed. During epididymal transit, heat shock protein 2 was eliminated with the cytoplasmic droplet and smooth muscle γ-actin exhibited reduced fluorescence from the anterior acrosome while the signal intensity of aldolase A increased, especially in the principal piece. Besides these changes, we observed protein spots, such as glutathione S-transferase mu 5 and the E2 component of pyruvate dehydrogenase complex, shifting to more basic isoelectric points, suggesting post-translational changes such dephosphorylation occur during epididymal maturation. We conclude that most caput epididymal sperm-differential proteins contribute to the functional modification of sperm structures and that many cauda epididymal sperm-differential proteins are involved in ATP production that promotes sperm functions such as motility.

Expression patterns of SP1 and SP3 during mouse spermatogenesis: SP1 down-regulation correlates with two successive promoter changes and translationally compromised transcripts

Because of their prominent roles in regulation of gene expression, it is important to understand how levels of Krüpple-like transcription factors SP1 and SP3 change in germ cells during spermatogenesis. Using immunological techniques, we found that both factors decreased sharply during meiosis. SP3 declined during the leptotene-to-pachytene transition, whereas SP1 fell somewhat later, as spermatocytes progressed beyond the early pachytene stage. SP3 reappeared for a period in round spermatids. For Sp1, the transition to the pachytene stage is accompanied by loss of the normal, 8.2-kb mRNA and appearance of a prevalent, 8.8-kb variant, which has not been well characterized. We have now shown that this pachytene-specific transcript contains a long, unspliced sequence from the first intron and that this sequence inhibits expression of a reporter, probably because of its many short open-reading frames. A second testis-specific Sp1 transcript in spermatids of 2.4 kb also has been reported previously. Like the 8.8-kb variant, it is compromised translationally. We have confirmed by Northern blotting that the 8.8-, 8.2-, and 2.4-kb variants account for the major testis Sp1 transcripts. Thus, the unexpected decline of SP1 protein in the face of continuing Sp1 transcription is explained, in large part, by poor translation of both novel testis transcripts. As part of this work, we also identified five additional, minor Sp1 cap sites by 5' rapid amplification of cDNA ends, including a trans-spliced RNA originating from the Glcci1 gene.

Transcription in haploid male germ cells

Major modifications in chromatin organization occur in spermatid nuclei, resulting in a high degree of DNA packaging within the spermatozoon head. However, before arrest of transcription during midspermiogenesis, high levels of mRNA are found in round spermatids. Some transcripts are the product of genes expressed ubiquitously, whereas some are generated from male germ cell-specific gene homologs of somatic cell genes. Others are transcript variants derived from genes with expression regulated in a testis-specific fashion. The haploid genome of spermatids also initiates the transcription of testis-specific genes. Various general transcription factors, distinct promoter elements, and specific transcription factors are involved in transcriptional regulation. After meiosis, spermatids are genetically but not phenotypically different, because of transcript and protein sharing through cytoplasmic bridges connecting spermatids of the same generation. Interestingly, different types of mRNAs accumulate in the sperm cell nucleus, raising the question of their origin and of a possible role after fertilization.

Chromosome synapsis defects and sexually dimorphic meiotic progression in mice lacking Spo11

Spo11, a protein first identified in yeast, is thought to generate the chromosome breaks that initiate meiotic recombination. We now report that disruption of mouse Spo11 leads to severe gonadal abnormalities from defective meiosis. Spermatocytes suffer apoptotic death during early prophase; oocytes reach the diplotene/dictyate stage in nearly normal numbers, but most die soon after birth. Consistent with a conserved function in initiating meiotic recombination, Dmc1/Rad51 focus formation is abolished. Spo11(-/-) meiocytes also display homologous chromosome synapsis defects, similar to fungi but distinct from flies and nematodes. We propose that recombination initiation precedes and is required for normal synapsis in mammals. Our results also support the view that mammalian checkpoint responses to meiotic recombination and/or synapsis defects are sexually dimorphic.

Expression of green fluorescent protein under beta-actin promoter in living spermatogenic cells of the mouse: stage-specific regulation by FSH

Spermatogenic cells from a mouse strain expressing enhanced green fluorescent protein (EGFP) under chicken beta-actin promoter were studied under living conditions to analyse stage- and cell-specific expression and hormonal regulation of the transgene. The isolated seminiferous tubules were examined by transillumination and the live cell squashes by phase contrast and fluorescence microscopy. FSH effects were measured in whole seminiferous tubules comparing stages I-VI, VII-VIII and IX-XII of the cycle. Beta-actin was highly expressed in spermatogonia, but almost no expression was found at early meiosis (leptotene spermatocytes). A gradual increase in translation of beta-actin was found during later stages of meiosis and early spermiogenesis, with a maximum in elongating spermatids. FSH increased the translation of beta-actin after 4 h and 24 h of incubation at stages I-VI, after 24 h at stages VII-VIII but not at stages IX-XII of the cycle. The results support the view that beta-actin plays a role in the nuclear elongation of spermatids and that its expression is regulated by FSH in a stage-specific fashion. Techniques used in this study give us new insight to study temporal and hormonal regulation of gene products in living spermatogenic cells.

Analysis of expression and function of topoisomerase I and II during meiosis in male mice

Topoisomerases are nuclear enzymes that remove torsional stress in DNA. Their function is important for replication, transcription, chromosome condensation, and chromosome segregation during mitosis and meiosis. The goal of this work is to analyze both expression and function of topoisomerases during the meiotic stages of mammalian spermatogenesis. The patterns of expression of topoisomerase I and topoisomerase II alpha genes were followed on Northern blots of RNA from testes of mice of different ages and from specific germ cell populations. The transcript of the topoisomerase I gene was highest in somatic cells of the testis and in the mitotically proliferating spermatogonia and meiotic prophase spermatocytes, with the level of transcript decreasing dramatically in postmeiotic spermatids. In contrast, the levels of topoisomerase II alpha transcript were negligible in germ-cell free testes and highest in late meiotic prophase cells and round spermatids. Enzyme activity for both topoisomerase I and topoisomerase II was detected in both pachytene spermatocytes and in round spermatids; topoisomerase II exhibited a higher level of activity in meiotic spermatocytes than in round spermatids. In cultured cells, camptothecin, an inhibitor of topoisomerase I, caused some abnormalities of paired meiotic homologs, but did not inhibit the transition to metaphase. In contrast, teniposide and ICRF-193, inhibitors of topoisomerase II, dramatically inhibited the formation of metaphase chromosomes in cells induced to progress from prophase to metaphase. However, the disassembly of the synaptonemal complex was not inhibited, indicating that this process could be uncoupled from condensation of chromatin to form chromosomes. These studies constitute evidence for a functional requirement for topoisomerase II activity in the transition from meiotic prophase to meiotic metaphase I in mammalian spermatocytes.

In postmeiotic male germ cells poly (A) shortening accompanies translation of mRNA encoding gamma enteric actin but not cytoplasmic beta and gamma actin mRNAs

In the mammalian testis the cytoplasmic beta and gamma actins are expressed in all stages of germ-cell differentiation, whereas gamma enteric actin is expressed in germ cells solely in postmeiotic stages. Northern blot analysis of mouse testicular RNAs reveals actin mRNAs of about 2.1, 1.5, and 1.4 kB. The 2.1-kB mRNAs encode the cytoplasmic beta and gamma actins, whereas the two faster-migrating actin mRNAs encode gamma enteric actin. When postmitochondrial mouse testis extracts are fractionated by sucrose gradient centrifugation, the 1.5-kB gamma enteric actin mRNA is primarily found in the nonpolysomal fraction, whereas the 1.4-kB gamma enteric actin is polysomal. When the poly (A) tails are removed, the nonpolysomal and polysomal gamma enteric actin mRNAs both migrate at 1.3 kB, indicating that the difference in electrophoretic mobilities of the two gamma enteric actin mRNAs is caused by poly (A) length differences. The nonpolysomal and polysomal forms of the cytoplasmic beta and gamma actins show similar electrophoretic mobilities before and after deadenylation. Sequence comparison of the 3' untranslated region of the mouse gamma enteric actin to the 3' untranslated regions of other testicular mRNAs that undergo partial deadenylation reveals three highly-conserved sequence elements. These data demonstrate that the poly (A) shortening of polysomal mRNAs previously seen only with testis-specific mRNAs that are stored as mRNPs also occurs with mRNAs of widely-expressed genes that are expressed in postmeiotic male germ cells. The mRNAs all contain specific conserved sequence elements in their 3' untranslated regions.

Association of histone H4 genes with the mammalian testis-specific H1t histone gene

Mouse and human H4 genes associated with the testis-specific H1t gene were isolated from genomic libraries and were sequenced. The deduced amino acid sequences are identical to other mouse or human H4 histones, but the genes differ significantly in their nucleotide sequences. Both the human and the mouse genes are located on the same DNA strand compared with the H1t gene. In contrast to this identical transcriptional orientation of H1t and its neighboring H4 gene in mouse and man, an H4 gene with the opposite orientation has been described in the vicinity of the rat H1t gene. Northern blot analysis of RNA from testicular cells separated by centrifugal elutriation, S1 nuclease mapping, and reverse transcriptase polymerase chain reaction (RT-PCR) amplification show that both the murine and human H4 genes, like the H1t gene, are expressed in testicular cells, whereas the H4 genes, in contrast to the H1t gene, are expressed in nontesticular human and mouse cell culture cells.

Low-affinity nerve growth factor receptor is expressed during testicular morphogenesis and in germ cells at specific stages of spermatogenesis

Nerve growth factor (NGF) is essential for neuronal development and differentiation. Recent reports have shown that its low-affinity receptor (LNGFR) is expressed and developmentally regulated in a broad range of embryonic and adult tissues outside the nervous system, although the functions of the receptor in such tissues remain unknown. Recently, NGF and LNGFR have been detected in adult mouse, rat, and human testis. The results of the present work demonstrate that LNGFR is expressed much before the onset of spermatogenesis in both mouse and rat testis. In situ hybridization shows that the mRNA for LNGFR is expressed in the peritubular cells of the embryonic mouse testis. Immunohistochemical analysis of the rat testis shows LNGFR-expressing cells to be scattered in the intertubular compartment in the embryonic testis, and to become organized in a cellular layer that surrounds myoid cells of the seminiferous tubules during postnatal development. Furthermore, in peripuberal and adult mouse and rat testis we have identified the expression of an abundant and shorter mRNA of 3.2 kb that cross hybridizes to the low-affinity NGF receptor transcript (3.7 kb). This shorter mRNA species, which appears at the beginning of spermatogenesis in the adult, has been identified by in situ hybridization and by Northern blot with RNA isolated from homogeneous populations of meiotic germ cells to be expressed by pachytene spermatocytes and round spermatids. Our results suggest a complex developmental role for LNGFR during testicular morphogenesis and identify the expression, at specific stages of spermatogenesis, of a new germ cell-specific transcript homologous to the receptor RNA.

Characterization of male meiotic germ cell-specific antigen (Meg 1) by monoclonal antibody TRA 369 in mice

We have identified a male meiotic germ cell-specific antigen (Meg 1) with monoclonal antibody (mAb) TRA 369 in mice. The Meg 1 antigen was strongly expressed in specific steps of meiotic germ cells from pachytene spermatocyte to early spermatid, and not in other germ cells or somatic cells. Immunohistochemical examination revealed that the antigen was localized to the cytoplasm and was not distributed in the nucleus or on the cell surface. This antigen was demonstrated to have a molecular weight of 93 kDa and an isoelectric point of 5.2 by Western blotting. This molecule was first detected in the testis of 13-day-old mouse when pachytene spermatocytes first appeared. Thus this is a differentiation-specific antigen in male meiotic germ cells, and mAb TRA 369 is a useful tool to study the regulation of germ cell differentiation and to define germ cell development in a molecular level.

A silencer-like cis element for the testis-specific phosphoglycerate-kinase-2-encoding gene

Phosphoglycerate kinase (PGK), a glycolytic enzyme, possesses two isozymes: somatic-type PGK-1 and testis-specific PGK-2, encoded by distinct genes. Tissue-specific expression of the two PGK-encoding genes (Pgk) seems to be transcriptionally controlled, since tissue distribution of the mRNAs coincides well with that of the proteins. In the present study, we determined the cis-acting DNA elements that regulate the transcription of mouse Pgk-2. A transient expression assay of DNAs having various portions of the Pgk-2 upstream region linked to the chloramphenicol acetyltransferase (CAT)-encoding gene (cat) was performed using mouse cell lines that exclusively express Pgk-1. A substantial increase in cat expression was observed when the region between nucleotides (nt) -1404 and -685, relative to the most distal transcription start point at nt +1, was lost. This cis-acting region appeared to function as a silencer, since it repressed cat expression independently of either orientation to or distance from the Pgk-2 promoter. Moreover, the cis element inhibited Pgk-2 transcription with no effect on Pgk-1 transcription in a cell-free system using nuclear extracts of rat liver. These results suggest that a silencer-like negative cis element is responsible, at least partly, for tissue-specific transcription of Pgk-2.

The expression pattern of the pyruvate dehydrogenase E1 alpha subunit genes during spermatogenesis in adult mouse

The expression patterns of the testis-specific and somatic forms of the pyruvate dehydrogenase (PDH) E1 alpha subunit genes were examined in adult mouse testis by in situ hybridization with specific cDNA probes and by immunostaining. A considerable increase in the mRNA level of the testis-specific PDH E1 alpha gene was observed in spermatocytes at the pachytene stage. The expression gradually decreased in spermatids as spermiogenesis progressed (especially after step 11) and it was not detectable in residual bodies. Transcripts of the testis-specific PDH E1 alpha gene were not identified in nongerminal Leydig and Sertoli cells. In contrast, the expression of the somatic form of the PDH E1 alpha gene was detected in spermatogonia, Leydig cells, and Sertoli cells at a low level. Transcripts of the somatic form of the PDH E1 alpha gene were not identified in other types of germ cells in adult mouse testis. Immunostaining with a PDH E1 alpha-specific antibody showed that the synthesis of PDH E1 alpha protein was dramatically increased in primary spermatocytes and that PDH E1 alpha protein existed abundantly in pachytene spermatocytes. The amount of PDH E1 alpha protein remained at a high level throughout spermiogenesis; however, it declined remarkably in epididymal spermatozoa. Leydig cells, Sertoli cells, and spermatogonia had low levels of PDH E1 alpha protein. These results suggest that (1) the transcription switch from the somatic form of the PDH E1 alpha gene to the testis-specific PDH E1 alpha gene occurs during the first meiotic prophase of spermatogenesis in adult mouse testis, and (2) PDH E1 alpha protein coded for by the testis-specific PDH E1 alpha gene is involved in the development of spermatogenic cells especially at stages after first meiotic prophase until the end of spermiogenesis in the testis.

Identification of the gene for the developmentally expressed 70 kDa heat-shock protein (P70) of mouse spermatogenic cells

Mouse spermatogenic cells synthesize a 70-kDa protein (P70) closely related to the major heat-shock protein (hsp70) of mammalian cells (R. L. Allen, D. A. O'Brien, and E. M. Eddy, Mol. Cell. Biol. 8, 828-832, 1988). Expression of P70 is developmentally regulated while hsp70 is induced in response to stress, suggesting that P70 is the product of a unique member of the Hsp70 multigene family transcribed in spermatogenic cells. A strong candidate for this gene was the Hsp70.2 gene (Z. F. Zakeri, D. J. Wolgemuth, and C. R. Hunt, Mol. Cell. Biol. 8, 2925-2932, 1988). A DNA segment from the 5' region of Hsp70.2 hybridized to a 2.7-kb transcript with a temporal pattern of expression in mouse spermatogenic cells similar to the P70 protein. We used a polyclonal antiserum generated against a synthetic peptide predicted from the Hsp70.2 sequence to characterize its protein product and to isolate cDNA clones from a pachytene spermatocyte expression library. The antiserum reacted specifically with meiotic and postmeiotic spermatogenic cells on sections of mouse testis. It recognized the P70 protein on Western blots of two-dimensional gels and did not bind to other heat-shock proteins of spermatogenic or somatic cells. The cDNAs hybridized to a 2.7-kb mRNA that was abundant in unstressed pachytene spermatocytes and round spermatids but was not detected in other cell types. Two cDNAs were sequenced and found to be 99% homologous to the 3' end of the Hsp70.2 gene. These data strongly supported the hypothesis that P70 is the expressed product of the Hsp70.2 gene in mouse spermatogenic cells.

Distribution of actin isoforms within cells of the seminiferous epithelium of the rat testis: evidence for a muscle form of actin in spermatids

Recently, a cDNA that coded for an enteric smooth muscle gamma-actin (SMGA) that was expressed in post-meiotic mouse testicular cells was identified. To determine the cellular location(s) of the protein encoded by this cDNA, this SMGA was probed for by immunocytochemistry in the cells of the seminiferous epithelium with two different monoclonal antibodies (Mabs), B4 and HUC 1-1, known to be muscle actin selective. As a control, we also examined the immunoreactivity of a third Mab, C4, that reacts with all non-muscle and muscle vertebrate isoactins. Using light and electron microscopy, a progressive increase in immunolabeling was observed with the muscle selective HUC 1-1 Mab over a loose actin filamentous network distributed throughout the cytoplasm of steps 4-16 spermatids. Thereafter, the labeling decreased such that at step 17 spermatids, only cytoplasmic labeling in the tail of the spermatids was observed. No labeling of this network was noted with the C4 or B4 Mabs. However, myoid cells enveloping seminiferous tubules and smooth muscle cells of interstitial blood vessels demonstrated comparable intense labeling with each of the three Mabs. The C4 Mab intensely labeled actin filaments of the Sertoli-Sertoli and Sertoli-spermatid ectoplasmic specializations. Also well labeled were numerous actin filaments found in the apical Sertoli cell processes encapsulating the heads of late step 19 spermatids at stage VII of the cycle of the seminiferous epithelium. In addition, actin filamentous bundles enveloping tubulobulbar complexes of the late spermatids within the Sertoli cell apical processes were intensely labeled. The actin filaments in the Sertoli apical processes and surrounding the tubulobulbar complexes were also strongly immunolabeled with the HUC 1-1 Mab. The C4 Mab but not the B4 or HUC 1-1 Mabs, recognized actin in the subacrosomal space of steps 4-18 spermatids. This study suggests that there are muscle isoforms of actin within the cytoplasm of developing spermatids and within apical processes of Sertoli cells.

Expression of the mRNA for the ligand of c-kit in mouse Sertoli cells

The expression of the mRNA for SLF (the c-kit ligand), a product of the "steel" locus, has been investigated in postnatal mouse testis and homogeneous populations of testicular cells. The message was found expressed in postnatal mouse testis but not in germ cells. Studies on primary mouse Sertoli cell cultures from 18 day old mice show that Sertoli cells are the site of SLF mRNA expression in the seminiferous tubules. Treatment of Sertoli cell cultures with cAMP analogs led to a significant increase in the SLF mRNA levels.

Several testis-expressed genes in the mouse t-complex have expression differences between wild-type and t-mutant mice

The t-complex of the mouse occupies the proximal half of chromosome 17 and contains genes which have profound effects on spermatogenesis. Mutations of several loci in the t-complex appear to interact to cause male sterility or transmission ratio distortion (TRD). By cDNA screening or chromosomal walking we have identified seven genes, which are expressed in the germ cells of testis and map to various regions of the t-complex. These genes were named t-complex testis-expressed (Tctex) genes. An analysis of their expression patterns in testes from +/+, +/t, and t/t mice was done by in situ hybridization and by northern blotting. Six genes begin to be expressed at the pachytene stage: Three of them are more abundant at pachytene stage, while three others are more abundant at postmeiotic stages. One gene is expressed at all the stages of spermatogenesis. Interestingly, four Tctex genes show differences in the amount of transcript between wild-type and t-mutant testes. The chromosomal location and expression pattern imply that Tctex genes might be candidate genes for sterility or TRD.

Detection of secreted and temporarily inducible heat shock responsive proteins in mouse testicular tissue

Temperature-induced effects on the synthesis of murine testicular proteins were investigated by one- and two-dimensional SDS polyacrylamide gel electrophoresis. Newly synthesized proteins were monitored by incorporation of 35S-methionine and autoradiography. Three heat shock responsive proteins, which are differently affected by elevated temperatures, are described. These proteins represent special examples for how testicular cells respond to environmental stress. One of these proteins, HSl36, is synthesized and secreted at 38 degrees C, whereas at lower, scrotal temperatures it is not detectable. HSlD74 protein is synthesized at elevated temperatures, but only in prepuberal testis, not in adult. Synthesis of the third example, HSR28, is decreased within the seminiferous tubules, but only in those regions which bear cell associations of the elongation stage. These results indicate that the use of DNA probes of the 'heat shock'-gene family might not be sufficient to describe the molecular reasons for impaired spermatogenesis following hyperthermia.

Acrosin biosynthesis in meiotic and postmeiotic spermatogenic cells

It has been widely accepted that mammalian sperm acrosin is first synthesized only in the postmeiotic stages of spermatogenic cells. In this study, we carried out Northern blot analysis of RNAs prepared from purified populations of mouse spermatogenic cells. The acrosin mRNA was obviously found in meiotic pachytene spermatocytes, and the mRNA content markedly increased in postmeiotic round spermatids. Also, the acrosin mRNA in pachytene spermatocytes was functionally associated with polysomes. These results provide evidence that acrosin biosynthesis is already started in meiotic cells and continues through the early stages of spermiogenesis.

Quantitative changes in cytoskeletal beta- and gamma-actin mRNAs and apparent absence of sarcomeric actin gene transcripts in early mouse embryos

Actin is known to be synthesized both during oogenesis and in cleavage-stage embryos in mice. Cytoskeletal beta-actin appears to be the major component, followed by gamma-actin, but the synthesis of alpha-actin has also been inferred from protein electrophoretic patterns. We have studied the expression of cytoskeletal (beta- and gamma-) and sarcomeric (alpha-cardiac and alpha-skeletal) actin genes at the level of the individual mRNAs in blot hybridization experiments using isoform-specific RNA probes. The results show that there are about 2 x 10(4) beta-actin mRNA molecules in the fully grown oocyte; this number drops to about one-half in the egg and less than one-tenth in the late two-cell embryo but increases rapidly during cleavage to about 3 x 10(5) molecules in the late blastocyst. The amount of gamma-actin mRNA is similar to that of beta-actin in oocytes and eggs but only about 40% as much in late blastocysts, indicating a differential accumulation of these mRNAs during cleavage. The developmental pattern of beta- and gamma-actin mRNA provides a striking example of the transition from maternal to embryonic control that occurs at the two-cell stage and involves the elimination of most or all of the maternal actin mRNA. There was no detectable alpha-cardiac or alpha-skeletal mRNA (i.e., less than 1,000 molecules per embryo) at any stage from oocyte to late blastocyst, suggesting that the sarcomeric actin genes are silent during preimplantation development.

Stage-specific expression of the lactate dehydrogenase-X gene in adult and developing mouse testes

Lactate dehydrogenase-X (LDH-X), a glycolytic enzyme found only in mammalian testes and spermatozoa, is encoded by a single gene (Ldh-x) in the mouse haploid genome. Several studies have demonstrated that LDH-X is associated with germ cells at specific stages of development. We have examined the expression of the Ldh-x gene during mouse spermatogenesis and testis maturation using in situ mRNA hybridization and immunocytochemistry. The results showed that transcription and translation of the Ldh-x gene are initiated at the pachytene stage of germ cell differentiation. However, although the amount of LDH-X protein increased as the germ cells progressed to maturation, its mRNA level was greatly decreased. These observations were confirmed by Northern analysis of total RNA derived from fractionated spermatogenic cells and developing testes. Furthermore, Northern studies also indicated two sizes of Ldh-x transcripts among different populations of spermatogenic cells in mature mouse testis.

Stage-specific localization of cytoskeletal actin mRNA in murine seminiferous tubules and intestinal epithelia as demonstrated by in-situ hybridization

In-situ hybridization experiments have been performed using isoactin (beta and gamma)-specific riboprobes in various tissues of the rat and mouse. Distribution of the grains of actin mRNAs for both beta and gamma types was similar throughout sections of the rat testis. Although both mRNAs were evenly distributed in the seminiferous tubule, extremely heavy labeling was observed in about 10% of the seminiferous tubules that could be identified as stage XII of spermatogenesis. At high magnification, grains of the mRNA were found in the cytoplasm of elongating spermatids and in the Sertoli cell cytoplasm at the adluminal side. Much higher density of the grains of mRNA was observed in the neck region of the spermatids at stage XII. Thus, the dense distribution of cytoskeletal actin mRNAs is stage-specific in the tubule during spermatogenesis in the rat. The high expression of both beta and gamma actin mRNAs was also observed in the epithelial cells of the intestinal crypts.

Molecular analyses of gene expression during sea star spermatogenesis

We have investigated actin gene expression during the annual spermatogenic cycle of Pisaster ochraceus by Northern blot analyses of testes RNAs pooled from defined spermatogenic stages. Specific probes for cytoplasmic (Cy) and muscle (M) actin gene products detect 2.3 and 2.1 kb transcripts, respectively. In addition, actin-coding sequence probes detect a third, much larger (3.5 kb) transcript designated FAT. Preliminary sequence analyses of two cDNAs representing portions of the FAT transcript show over 90% homology to Pisaster Cy actin at the amino acid level but only 80% nucleotide identity. The expression patterns of these three transcripts, plus two spermiogenic indicator transcripts (H3 histone and beta-tubulin), were determined over the cycle. The Cy transcript is seen at all stages but is ten- to 100-fold higher early in the cycle when mitotic activity predominates. The M transcript appears at the onset of gonadal growth and is maintained at constant levels through spermatogenesis consistent with the expansion of the muscular sheath surrounding the testes. The FAT, H3 histone, and beta-tubulin transcripts reach their highest levels in ripe testes when spermiogenic activity is maximal. The homology of the FAT transcript to actin, and its pattern of expression, suggest the hypothesis that this transcript may encode acrosomal actin.

The protein encoded by a murine male germ cell-specific transcript is a putative ATP-dependent RNA helicase

The murine PL10 cDNA corresponds to a transcript expressed only in the male germ line. Its expression is developmentally regulated, with high levels of transcripts being present during the meiotic and haploid stages of spermatogenesis. The deduced protein is shown to be highly homologous to the murine translation initiation factor eIF-4A and to other proteins that are also homologous to eIF-4A, including the Drosophila protein vasa. By consensus sequence conservation and comparison of secondary structure predictions, putative mononucleotide binding and DNA/RNA binding domains are proposed to be shared by all these proteins. Taken together, these results suggest a helicase function for PL10 protein similar to that of eIF-4A and suggests its possible role in a key step of the spermatogenic process. The possible significance of the similarity between the PL10 protein and the protein product of the maternal effect gene vasa is also discussed.

Expression of a novel histone 2B during mouse spermiogenesis

During mammalian spermiogenesis transitional proteins and protamines replace histones on the DNA as the chromatin condenses. While previous studies suggested that histone genes are inactive postmeiotically, we have shown both by steady-state RNA analysis and nuclear run-off transcription assays that histone 2b (H2b) transcription occurs in mouse round spermatids. In addition, a novel H2b cDNA clone has been isolated from an adult mouse testes cDNA library. The sequence of this cDNA clone predicts a protein that is extremely similar to other mouse H2b proteins, except at the carboxyl-terminus where the testes H2b contains an additional 12 amino acids, seven of which are hydrophobic. In contrast to the replication-dependent histone mRNAs, the 3' untranslated region of this cDNA contains the poly(A) addition sequence (AAUAAA) upstream of a poly(A) tract. Furthermore, the conserved hairpin structure immediately upstream of replication-dependent histone mRNA termini is not present. Northern blot analysis of RNA from embryonic, ovarian, spermatogenic, and a variety of somatic tissues reveals that this novel H2b transcript is spermatid specific. The H2b mRNA is in polyribosomes isolated from spermatogenic cells, strongly suggesting that it is translated during spermiogenesis.

Changes in polyadenylation of lactate dehydrogenase-X mRNA during spermatogenesis in mice

The expression of the mRNA for mouse testicular lactate dehydrogenase (LDH-X) was examined by RNA:cDNA hybridization in situ in the testis and by Northern analyses of meiotic and postmeiotic spermatogenic cell populations. Silver grains accumulated in cells inside the second layer from the periphery of the seminiferous tubule, confirming previous findings that LDH-X mRNA first appears in the spermatocyte and continues to accumulate until the late spermatid stage. Northern analyses showed that meiotic and postmeiotic cells contained 1.2 and 1.3 kb classes of hybridizing mRNA, respectively. RNase H digestion of oligo (dT)-hybridized RNA and poly(U)-Sepharose column chromatography with differential elution by formamide revealed that the difference in size of the two classes of mRNAs was due to the poly(A) tail length of the LDH-X mRNA. When the distribution of the LDH-X mRNA was examined across polysome gradients, both mRNAs were partially associated with polysomes. These results suggest that the changes in the polyadenylation of LDH-X mRNA were associated with the meiotic division during spermatogenesis in the mouse. They raise the possibility that the stable accumulation of the LDH-X mRNAs in the postmeiotic cells is enhanced by poly(A) tails of increased length.

Spatial and temporal expression of cell surface galactosyltransferase during mouse spermatogenesis and epididymal maturation

We have previously shown that sperm-egg recognition in the mouse is mediated by the binding of galactosyltransferase (GalTase) on the sperm surface to its appropriate glycoside substrate in the egg zona pellucida [L. C. Lopez, E. M. Bayna, D. Litoff, N. L. Shaper, J. H. Shaper, and B. D. Shur (1985) J. Cell Biol. 101, 1501-1510]. In the present study, we have defined the spatial and temporal expression of surface GalTase during spermatogenesis and epididymal maturation. Purified populations of spermatogenic cells were isolated by unit gravity sedimentation, and surface GalTase expression was determined by indirect immunofluorescence and by direct enzymatic assay. GalTase is present on the surface of all spermatogenic cells assayed. During differentiation, there is a progressive redistribution of GalTase from an initially diffuse and uniform localization on the surface of primary spermatocytes to a restricted plasma membrane domain overlying the dorsal aspect of the mature acrosome. This apparent redistribution of surface GalTase was confirmed by direct enzymatic assays, which show that surface GalTase activity, normalized per cell, remains relatively constant throughout spermatogenesis, despite a drastic reduction in cell surface area. When normalized to the relevant cell surface area, the GalTase concentration per square micrometer increases 77-fold from pachytene spermatocytes to cauda epididymal sperm. Cell surface GalTase is thought to be a cytoskeletally associated transmembrane protein [N. L. Shaper, P. L. Mann, and J. H. Shaper (1985) J. Cell Biochem. 28, 229-239]; consequently we examined whether cytoskeletal components may be involved in the redistribution of GalTase during spermatogenesis. beta-Tubulin, monomeric actin, and filamentous actin were found to be present during spermatogenesis, as assayed by indirect immunofluorescence and by Western immunoblotting. alpha-Actinin and vinculin were not detectable under these conditions and served as negative controls. During spermatogenesis, the distribution of tubulin coincides with the appearance of the mitotic spindle, flagellum, and manchette. On the other hand, the distribution of filamentous actin coincides with surface GalTase, suggesting that actin-containing microfilaments may participate in the redistribution of surface GalTase during spermatogenesis.

In situ localization of mRNAs coding for mouse testicular structural genes

In situ hybridization histochemistry has been used to localize mRNA transcripts of five nuclear and cytoplasmic structural genes in the mouse testis. The mRNAs for three nuclear structural proteins involved in chromatin transformation during spermatogenesis (the two protamine variants of the mouse and one of the testis-specific proteins) are restricted solely to postmeiotic germ cells. In contrast, mRNAs for two other structural proteins, actin and alpha tubulin, are detected throughout spermatogenesis. Although present in premeiotic, meiotic, and postmeiotic cell types, the mRNA levels of actin and alpha tubulin differ considerably during spermiogenesis, the haploid phase of spermatogenesis. Actin mRNA levels decrease markedly as the male gamete differentiates during spermiogenesis whereas alpha-tubulin mRNAs are equally abundant in the haploid round and elongating spermatids.

Expression of the proto-oncogene int-1 is restricted to postmeiotic male germ cells and the neural tube of mid-gestational embryos

The int-1 proto-oncogene is transcriptionally activated in mammary tumors by mouse mammary tumor virus insertion mutations and is normally expressed only in adult mouse testes and mid-gestational embryos. We have used anatomical dissection of embryos, germ-cell fractionation, peripuberal expression studies, and spermatogenesis mutants to identify more precisely the tissues and cells that contain int-1 RNA. In the testis, int-1 RNA is detected only in postmeiotic germ cells undergoing differentiation from round spermatids into mature spermatozoa. In embryos 11-15 days after conception, expression of the gene is restricted to the developing central nervous system in regions of the neural tube other than the telencephalon. Our findings suggest that int-1 mediates developmental events at these two sites.

Identification and quantification of actin isoforms in vertebrate cells and tissues

The cytoskeletal protein actin exists in vertebrates as six different isoforms, which are difficult to identify conclusively because of a high degree (greater than 90%) of overall sequence homology. We have used IEF immunoblotting in combination with a panel of isoform-specific and -selective antibodies to analyze the actin isoform composition of nine tissues from adult rat. In three nonmuscle tissues (lung, spleen, and testis), we detected a previously unreported isoform that we identified as smooth muscle alpha. The IEF immunoblot technique was also used to quantify the proportions of the isoforms expressed in these nine rat tissues.

Evolution and development of the outer acrosomal membrane (OAM) and evidence that acrosin-inhibitors are proteins of the OAM

An antiserum to the purified porcine outer acrosomal membrane (OAM) was raised in rabbits and the IgG fraction isolated by ammonium sulphate precipitation and ion exchange chromatography. The antibodies reacted exclusively with the acrosomal cap of the sperm head as revealed by indirect immunofluorescence. In addition they cross-reacted not only with the acrosomal part of the spermatozoa of all mammalian species tested (bull, horse, rabbit, rat, mouse, hamster, mole, antelope, monkey, man) but also with the spermatozoa of the cock (Class: birds) and the rainbow trout (Class: fish). All the species exhibited similar development of the acrosomal cap during spermatogenesis, with the appearance of the immunofluorescent stain in early round spermatids. In the mole the localization of the acrosome in elongated testicular spermatids differed from that in all other species: Instead of prominent fluorescence over the apical part of the sperm an equatorial belt was formed. The cross-reactivity of the anti-boar OAM antibody with the acrosomes of different vertebrate species at the morphological level was supported by the results of Western blotting experiments with purified boar OAM proteins and the SDS-extractable proteins of bull and human spermatozoa, respectively. Using anti-OAM antibodies and antibodies against the acrosin inhibitors I and II described recently by Tschesche et al. (1982), in absorption and Western blotting experiments, it was demonstrated that the acrosin inhibitor proteins are integrated in the outer acrosomal membrane.

Evidence for haploid expression of mouse testicular genes

Hybridization of RNA blots of total testicular RNA from prepuberal and sexually mature CD1 mice with several mouse testicular cDNA probes reveals that the mRNA encoding the two mouse protamines, an actin sequence of 1.5 kb, and a post-meiotically expressed 620 nucleotide mRNA are first detected in the testes of mice 22 days of age. These experiments and other studies analysing RNA preparations from isolated populations of testicular cell types with cDNA probes [1, 2] demonstrate that haploid gene expression occurs in the mammalian testis.

Transforming growth factor type beta regulation of actin mRNA

Stimulation of quiescent cultures of AKR-2B cells with transforming growth factor type beta (TGF beta) resulted in a transitory increase in actin cytoplasmic poly(A) + RNA. Levels of actin mRNA peaked approximately 4-8 hours subsequent to TGF beta addition and approached basal levels by 24 hours. The accumulation of actin transcripts was dose dependent and insensitive to inhibitors of protein synthesis; 1-3 ng/ml TGF beta induced maximal actin gene expression. Actin isotype-specific probes demonstrated that both beta- and gamma-cytoplasmic actins are induced by TGF beta.