Genetic control of mitosis, meiosis and cellular differentiation during mammalian spermatogenesis

Gametogenesis in both the male and female mammal represents a specialized and highly regulated series of cell cycle events, involving both mitosis and meiosis as well as subsequent differentiation. Recent advances in our understanding of the genetic control of the eukaryotic cell cycle have underscored the evolutionarily-conserved nature of these regulatory processes. However, most of the data have been obtained from yeast model systems and mammalian cell lines. Furthermore, most of the observations focus on regulation of mitotic cell cycles. In the present paper: (i) aspects of gametogenesis in mammals that represent unique cell-cycle control points are highlighted; (ii) current knowledge on the regulation of the germ cell cycle, in the context of what is known in yeast and other model eukaryotic systems, is summarized; and (iii) strategies that can be used to identify additional cell cycle regulating genes are outlined.

Homeotic transformation of cervical vertebrae in Hoxa-4 mutant mice

Hoxa-4 (previously known as Hox-1.4) is a mouse homeobox-containing gene that is expressed in the presumptive hindbrain and spinal cord, prevertebrae, and other tissues during embryogenesis. To understand the role of Hoxa-4 during development, we generated Hoxa-4 mutant mice. Homozygous mutants were viable and fertile. Analysis of neonatal skeletons revealed the development of ribs on the seventh cervical vertebra at variable penetrance and expressivity. A low frequency of alterations in sternal morphogenesis was also observed. In addition, we analyzed the skeletons of transgenic mice that overexpress Hoxa-4 and found that the formation of the small rib anlagen that often develop on the seventh cervical vertebra was suppressed. Analysis of adult homozygous mutant skeletons revealed that the dorsal process normally associated with the second cervical vertebra was also found on the third cervical vertebra. These results demonstrate that Hoxa-4 plays a role in conferring positional information along the anteroposterior axis to specify the identity of the third and the seventh cervical vertebrae.

Second locus for Hirschsprung disease/Waardenburg syndrome in a large Mennonite kindred

We have studied a large Mennonite kindred in which 20 members were affected with Hirschsprung disease (HSCR), 5 of whom had one or more manifestations of Waardenburg syndrome (WS) type II (WS2). Eleven additional relatives had signs of WS2 without HSCR. Since HSCR and WS2 each represent perturbations of neural crest migration/differentiation, this large pedigree with apparent cosegregation of HSCR and WS2 offered an opportunity to search for linkage between these loci, candidate genes, and random DNA markers, particularly in view of recent discoveries of genes for Waardenburg syndrome type I (WS1) and Hirschsprung disease (c-ret). We have examined the following possible linked markers in 69 relatives in this family: the c-ret gene (HSCR); the human PAX3 gene (HuP2) on chromosome 2q (WS1) and placental alkaline phosphatase (ALPP) on chromosome 2q (linked to WS1); argininosuccinate synthetase (ASS) on chromosome 9q, close to ABO blood groups which have shown weak linkage to WS; and the beta 1 GABA receptor gene (GABARB1) on chromosome 4q13-11, close to c-kit, deletions of which cause piebaldism. Linkage between any of these loci and HSCR/WS in this kindred was excluded, demonstrating that there is at least one further locus for HSCR other than c-ret.

[Genetic control of cellular differentiation and proliferation during gametogenesis in mammals]

Understanding the genetic program that controls the regulation of cells progressing through the mitotic and meiotic cell cycles, whether in response to growth factors, other extracellular signals, or intrinsic programs, is critical to problems in infertility and in gonadal neoplasias. In this study, we present a consideration of important stages of cell cycle control in mammalian germ cells and data illustrating the experimental approaches that can be used to determine the pattern of such genes which may be involved in these events.

Proenkephalin gene expression in testicular interstitial cells is down-regulated coincident with the appearance of pachytene spermatocytes

Two distinct forms of proenkephalin messenger RNA (mRNA) are present in the murine testis, a family of 1.7 kilobases (kb), germ cell-specific transcripts and a 1.45-kb form that is also found in somatic tissues. In situ hybridization and molecular analysis of purified spermatogenic cell types were used to characterize the cellular localization of these different transcripts during development of the mouse testis. Both forms of proenkephalin mRNA were observed in isolated germ cells by RNA gel-blot analysis, but in distinct developmental patterns; the 1.7-kb transcripts were present in cells undergoing meiosis and spermiogenesis, whereas the 1.45-kb mRNA was detected primarily in type B spermatogonia. In contrast, in situ hybridization analysis did not detect significant amounts of the 1.45-kb transcript in any spermatogenic cell type. Using transcript-specific probes, distinct patterns of developmental expression were evident for the two mRNAs. The 1.45-kb transcript was the only form detected in the prepubertal testis, where it was localized mainly in interstitial cells. In contrast, the 1.7-kb transcripts were the major mRNAs observed in the adult testis and were localized to spermatogenic cells. A transition from the prepubertal to the adult pattern occurred on or about postnatal day 21, when proenkephalin-expressing pachytene spermatocytes begin to populate the seminiferous tubules. In situ hybridization analysis further demonstrated that proenkephalin gene expression in mutant (at/at) mice, which lack germ cells, was identical to that observed in the early prepubertal testis. These results suggest that the 1.45-kb proenkephalin mRNA is developmentally down-regulated in mouse interstitial cells and that this process requires ongoing spermatogenesis.

Regulation of M-phase promoting factor activity during development of mouse male germ cells

While the role of M-phase promoting factor (MPF) in controlling meiosis in oocytes has been well documented, very little is known about its function in male germ cells. Previous studies have localized transcripts for cyclin B1, the regulatory subunit of MPF, in male germ cells, with highest levels in postmeiotic, early round spermatids and much reduced levels in the meiotically dividing pachytene spermatocytes. The present study describes the localization of the regulatory and the catalytic subunits of MPF, CycB1 and Cdc2, respectively, to specific cell types within the testis. Immunoblotting revealed that both CycB1 and Cdc2 were present at highest levels in pachytene spermatocytes, with lower levels observed in the postmeiotic compartment. To assay for MPF activity, kinase complexes were isolated from lysates of testicular cells using p13suc1 agarose and antibodies directed against Cdc2 and CycB1. Activity of these kinase complexes was analyzed using histone H1 as an exogenous substrate. Cdc2 and CycB1-associated kinase activities were localized to the meiotically dividing pachytene spermatocytes, but not to postmeiotic spermatids.

Expression of proliferating cell nuclear antigen in the mouse germ line and surrounding somatic cells suggests both proliferation-dependent and -independent modes of function

The distribution of proliferating cell nuclear antigen (PCNA) in specific somatic and germ cells of the adult mouse ovary and testis was assessed using immunocytochemical staining and immunoblot analysis and was correlated with cellular proliferation and differentiation. In the adult ovary, immunocytochemical staining for PCNA within follicular cells varied depending on the stage of follicular growth. Since PCNA staining has proven to be a useful indicator of cells involved in DNA synthesis and repair, the pattern of PCNA staining in the ovary was compared to previous studies which used tritiated thymidine labeling as a marker for DNA synthesis. In the testis, PCNA was detected in the mitotically proliferating spermatogonia, but not in spermatocytes which had just entered meiosis. PCNA staining was again observed in spermatogenic cells in later stages of meiotic prophase, in particular zygotene and pachytene spermatocytes. As these cells are undergoing meiotic recombination, the presence of PCNA in these meiotic prophase cells could reflect a second function of PCNA, that of DNA excision repair.

Sequence and expression of a cDNA encoding the mouse homologue of the rat ribosomal protein L28

A cDNA encoding the mouse homologue of the rat ribosomal protein L28 was isolated from an adult mouse total testis cDNA library. The L28 cDNA contained a single long open reading frame and exhibited a high degree of conservation to rat L28 at both the nucleotide and amino-acid levels. Northern blot hybridization analysis detected a single transcript in embryo, placenta and adult tissues.

Developmentally regulated expression during gametogenesis of the murine gene meg1 suggests a role in meiosis

Previous studies have shown that in adult male mice, expression of the meg1 gene is restricted to meiotic and early postmeiotic testicular germ cells. We have now analyzed the expression of meg1 during postnatal testicular development and the comparable meiotic stages in the female. The 0.75 kb transcript for meg1 begins to accumulate in testes at d8-9 of postnatal (pn) development, coincident with the entry of germ cells into meiosis, and is expressed most abundantly at pn d14 and subsequent stages, when the spermatocytes have entered pachytene. In situ hybridization analysis shows that meg1 is expressed at very low levels in leptotene cells and increases as the cells progress through zygotene and pachytene stages. In the embryonic ovary, meg1 is not detected until after day 15 of gestation when the cells have entered the pachytene stage of meiosis I. In situ hybridization analysis suggests that meg1 transcripts are expressed at higher levels in degenerating rather than in healthy pachytene stage oocytes; meg1 is not expressed in any cells of the adult ovary, regardless of the stage of follicular development. These results suggest that meg1 is indeed a meiosis-associated gene in both male and female germ cells through the pachytene stage of meiosis I and appears to exhibit sex-specific differences in its expression thereafter.

Identification and characterization of the developmentally regulated pattern of expression in the testis of a mouse gene exhibiting similarity to the family of phosphodiesterases

A cDNA for a rat brain phosphodiesterase (PDE) was used to screen a mouse testis library to identify the murine PDEs which are expressed in this tissue. A clone of 981 bp, p4-6, was isolated and shown to exhibit limited identity at the amino acid level to the rat brain PDE (20%). The putative protein encoded by clone p4-6 also contains multiple potential modification sites, for phosphorylation, myristylation, and glycosylation, many of which are located at positions similar to those found for rat brain PDE. The gene identified by p4-6 yields 3 transcripts, an abundant 1.9 kb transcript, and less abundant transcripts of 3.8 and 6.7 kb. Of the nine tissues examined in this study, the expression of the corresponding gene was limited to the adult mouse testis. Furthermore, the expression in the testis was most abundant in the germ cell lineage, although low levels were detected in somatic cells of the testis as well. Analysis of RNA from testes at different stages of development suggested that the p4-6 gene is most abundantly expressed in germ cells that have completed the meiotic divisions.

Structural abnormalities associated with congenital megacolon in transgenic mice that overexpress the Hoxa-4 gene

Congenital megacolon develops in transgenic mice that overexpress the homeobox-containing gene, Hoxa-4. The current study was done to identify abnormalities of the terminal colon that might account for the phenotype. The terminal bowel of transgenic mice was compared with that of control and lethal spotted (ls/ls) mice, a strain in which megacolon also develops. The terminal colon of the transgenic mice contained fewer ganglia than that of controls, but was hypoganglionic, rather than aganglionic like that of ls/ls mice. The neurons present in the adult transgenic colon were significantly increased in size and a subset of very large neurons (> 40 microns in maximum diameter) were observed. Electron microscopic studies of young adult transgenic mice revealed that the ganglia and nerves of the myenteric plexus had the ultrastructure of extraenteric peripheral nerve rather than that of the enteric nervous system (ENS). The myenteric ganglia in the transgenic animals contained Schwann cells associated with a basal lamina that enveloped axons completely and individually, instead of glia. Although collagen is excluded from the ganglia and thin nerve fibers of the normal ENS, a collagen-containing endoneurium surrounded each of the axon-Schwann cell units of the abnormal nerve fibers of the transgenic colon. Some of the neurons of the transgenic mice were located in these nerve bundles rather than in ganglia. There were also smooth muscle abnormalities in the terminal bowel of the transgenic mice. Wide gaps were present in the longitudinal muscle of the transgenic mice; these gaps contained ganglia that were in contact with the adventitia. These longitudinal smooth muscle cells were more irregular than those of controls and they contained fewer puncta adherens; moreover, a larger proportion of the volume of the cytoplasm of transgenic smooth muscle cells was occupied by organelles. Finally, an extensive thickening and reduplication of the basal lamina surrounding the smooth muscle cells of the muscularis mucosa was observed in the transgenic colon and resembled that found in ls/ls mice. These data suggest that both smooth muscle and the innervation of the terminal bowel of neonatal Hoxa-4 transgenic mice are structurally abnormal. Although some of the abnormalities seen in Hoxa-4 transgenic mice are similar to those which arise in ls/ls mice, the two conditions are not identical. In both animals, the data are consistent with the hypothesis that the defects arise as a result of a defective interaction between the precursors of enteric neurons and smooth muscle.

Protein product of the somatic-type transcript of the Hoxa-4 (Hox-1.4) gene binds to homeobox consensus binding sites in its promoter and intron

The murine Hoxa-4 gene encodes a protein with a homeodomain closely related to those produced by the Antennapedia-like class of Drosophila genes. Drosophila homeodomain proteins can function as transcription factors, binding to several specific DNA sequences. One sequence that is frequently encountered contains a core ATTA motif within a larger consensus sequence, such as CAATTAA. The in vitro synthesized protein product of Hoxa-4 was shown to bind to a subset of restriction fragments of the Hoxa-4 gene itself as determined by gel retardation experiments. Direct examination of the sequences of the fragments bound by Hoxa-4 protein revealed the presence of four regions containing the core ATTA motif. Two regions contained sequences of the CAATTAA class and were located approximately 1 kb upstream from the putative somatic Hoxa-4 promoter and within the intron. Two additional binding sites containing the consensus target sequence involved in autoregulation of Drosophila Deformed gene were identified: one immediately downstream of the putative embryonic transcription start site and one within the intron, respectively. Specific binding of the in vitro produced Hoxa-4 protein to oligonucleotides corresponding to these sequences was observed in gel retardation assays. The same results were obtained with Hoxa-4 protein produced in a Baculovirus expression system. Experiments using oligonucleotides containing base substitutions in positions 1, 3, 4, and 5 in the sequence CAATTAA showed severely reduced binding. The use of truncated mutant Hoxa-4 proteins in gel retardation assays and in transient co-transfection experiments revealed that the intact homeodomain was required for the binding. These results also suggested that the Hoxa-4 gene has the potential to auto-regulate its expression by interacting with the homeodomain binding sites present in the promoter as well as in the intron.

Differential expression of the proto-oncogenes c-abl and c-mos in developing mouse germ cells

C-abl and c-mos, two proto-oncogenes with unique patterns of expression in gonadal tissues, were examined by in situ hybridization with respect to their expression in the germ line. C-abl transcripts were observed to be most abundant in late round spermatids and elongating spermatids. C-mos transcripts were also expressed in round spermatids, but at much reduced levels compared to the levels of c-abl. C-abl mRNAs were also detected in mouse oocytes which have entered the growth phase. This temporal specificity of accumulation of c-abl transcripts was similar to that observed for c-mos, which also accumulates in growing and fully grown oocytes (follicle stages 4-6). Quantitative evaluation suggested that c-abl mRNA levels in oocytes are at least an order of magnitude lower than those of c-mos transcripts.

Members of the raf gene family exhibit segment-specific patterns of expression in mouse epididymis

The proto-oncogene c-raf-1 and the related genes A-raf and B-raf encode serine/threonine protein kinases thought to be involved in regulating gene expression by acting as part of second-messenger signaling pathways within the cell. Among the tissues in which A-raf and c-raf-1 have been shown to be expressed was mouse epididymis. The present studies were undertaken to determine if the raf family genes exhibited specificity in their pattern of expression that might be indicative of specific function in the epididymis. Northern and in situ hybridization analyses demonstrated that c-raf-1 mRNA was expressed as a 3.1 kb transcript at uniform levels throughout the length of the epididymis in all types of epididymal epithelial cells. Neither the germ cell-specific testicular transcripts nor the somatic transcripts of B-raf were detected by either Northern or in situ hybridization analysis in any region of the epididymis. A-raf, expressed as two transcripts of 2.6 and 4.3 kb, was the only gene examined which exhibited a segment-specific pattern of expression, being highest in the principal epithelial cells of the proximal caput epididymis and decreasing progressively in more distal regions of the tubule. These studies indicate that each raf gene exhibits a characteristic pattern of expression in the epididymis; A-raf in particular may play a unique regulatory role in the regionalized functions of the epididymis.

Isolation of the murine cyclin B2 cDNA and characterization of the lineage and temporal specificity of expression of the B1 and B2 cyclins during oogenesis, spermatogenesis and early embryogenesis

A cDNA encoding the murine cyclin B2 (cycB2) was isolated from an adult mouse testis cDNA library as part of studies designed to identify cyclins involved in murine germ cell development. This cycB2 cDNA was then used to examine the pattern of cycB2 expression during male and female germ cell development and in early embryogenesis, and to compare this expression with the previously characterized expression of cycB1. A single 1.7 kb cycB2 transcript was detected by northern blot hybridization analysis of total RNA isolated from midgestation embryos and various adult tissues. Northern blot and in situ hybridization analyses revealed that cycB2 expression in the testis was most abundant in the germ cells, specifically in pachytene spermatocytes. This is in contrast to the highest levels of expression of cycB1 being present in early spermatids. In situ analysis of the ovary revealed cycB2 transcripts in both germ cells and somatic cells, specifically in the oocytes and granulosa cells of growing and mature follicles. The pattern of cycB1 and cycB2 expression in ovulated and fertilized eggs was also examined. While the steady state level of cycB1 and cycB2 signal remained constant in oocytes and ovulated eggs, signal of both appeared to decrease following fertilization. In addition, both cycB1 and cycB2 transcripts were detected in the cells of the inner cell mass and the trophectoderm of the blastocyst. These results demonstrate that there are lineage- and developmental-specific differences in the pattern of the B cyclins in mammalian germ cells, in contrast to the co-expression of B cyclins in the early conceptus.

Developmental and cell lineage specificity of raf family gene expression in mouse testis

The proto-oncogene c-raf-1 and the related genes A-raf and B-raf encode serine/threonine protein kinases thought to be involved in regulating gene expression by transducing extracellular signals into the cell. All three raf family genes have been shown previously to be expressed in mouse testis. Northern and in situ hybridization analyses with probes specific for each gene demonstrated that c-raf-1 mRNA is ubiquitously expressed in both somatic and germ cells as a 3.1-kb transcript. Additionally, the levels of c-raf-1 expression are developmentally regulated in the germ cells, exhibiting highest expression in early pachytene spermatocytes and decreasing progressively through later stages. A-raf is expressed predominantly in the somatic compartment as two transcripts of 2.6 and 4.3 kb. A-raf expression in Leydig cells appears to be elevated in testes undergoing spermatogenesis. In contrast, B-raf is expressed as two major transcripts of 4.0 and 2.6 kb, with the 4.0-kb transcript first expressed at low levels in pachytene spermatocytes and the more abundant 2.6-kb transcript restricted to post-meiotic spermatids. These studies indicate that each raf gene exhibits a characteristic, limited pattern of expression and suggests that the different forms may play a unique regulatory role in androgen production and/or spermatogenesis.

Sequences 5′ of the homeobox of the Hox-1.4 gene direct tissue-specific expression of lacZ during mouse development

The murine homeobox-containing gene Hox-1.4 is expressed in restricted patterns during embryogenesis and in male germ cells. To begin identification of the cis-acting elements regulating this expression, transgenic mice were generated carrying a chimeric construct that contained approx. 4 kb of 5′ flanking sequence and approx. 1 kb of structural gene, fused in frame to the E. coli lacZ gene. This construct directed expression of the resulting Hox-1.4, beta-galactosidase fusion protein in a pattern that reproduced virtually the complete embryonic and adult sites of expression of the endogenous gene. Embryonic expression of the fusion protein was first detected in mesoderm at day 8.0 of gestation (E 8.0). Between gestational ages E 8.5 to E 12.5, beta-gal expression was observed in the somites, the lateral walls of the posterior myelencephalon, the dorsal region and ventral wall of the spinal cord, spinal ganglia and prevertebrae and their surrounding mesenchyme, between presumptive ribs, as well as in mesenchymal layers in the lung, kidney and portions of the gut. Expression was also noted in the pancreas and in the supporting cells and sheath around subsets of peripheral nerves, sites that had not been detected previously. Adult expression was observed in testes, specifically in meiotic and post-meiotic male germ cells. In contrast, transgenic mice carrying 5′ deletions of the construct which leave approx. 1.2 kb or approx. 2.0 kb of Hox-1.4 sequence 5′ to the embryonic promoter, did not exhibit beta-gal staining. These deletion experiments defined at least one cis-acting control element necessary for the expression of the Hox-1.4 gene to a 2 kb region located 2 to 4 kb 5′ of the embryonic transcription start site.

Conservation and divergence of patterns of expression and lineage-specific transcripts in orthologues and paralogues of the mouse Hox-1.4 gene

A possible correlation between the structural organization of homeobox-containing genes and their cell-specific expression was examined in studies determining similarities and differences in the expression patterns of orthologues and paralogues of the murine Hox-1.4 gene. We first compared the expression pattern of members of the Hox-1.4 subfamily, Hox-2.6 and Hox-4.2, in the adult mouse testis. Although these three evolutionarily related genes exhibited similar anterior limits of expression in the embryonic central nervous system, their cellular specificity of expression was very different in the adult testis. Hox-1.4 was abundantly expressed only in the germ cells; Hox-2.6 was expressed at very low levels in both spermatogenic cells and somatic cells; and Hox-4.2 transcripts appeared to be restricted to the somatic cells. We next analyzed the expression of several of the Hox-1.4 orthologues in the mouse testis to determine if other members of the Hox-1 cluster are involved in the male germ cell differentiation pathway. We showed that the two adjacent genes of Hox-1.4, Hox-1.3 and Hox-1.5, are expressed in the germ line but at lower levels. Further, both Hox-1.3 and Hox-1.4 produced unique, germ line-specific transcripts as compared to other adult tissues and the Day 12.5 embryo.

HSP86 and HSP84 exhibit cellular specificity of expression and co-precipitate with an HSP70 family member in the murine testis

This study extends to the protein level our previous observations, which had established the stage and cellular specificity of expression of hsp86 and hsp84 in the murine testis in the absence of exogenous stress. Immunoblot analysis was used to demonstrate that HSP86 protein was present throughout testicular development and that its levels increased with the appearance of differentiating germ cells. HSP86 was most abundant in the germ cell population and was present at significantly lower levels in the somatic cells. By contrast, the HSP84 protein was detected in the somatic cells of the testis rather than in germ cells. The steady-state levels of HSP86 and HSP84 paralleled the pattern of the expression of their respective mRNAs, suggesting that regulation at the level of translation was not a major mechanism controlling hsp90 gene expression in testicular cells. Immunoprecipitation analysis revealed that a 70-kDa protein coprecipitated with the HSP86/HSP84 proteins in testicular homogenates. This protein was identified as an HSP70 family member by immunoblot analysis, suggesting that HSP70 and HSP90 family members interact in testicular cells.

Identification of a mouse B-type cyclin which exhibits developmentally regulated expression in the germ line

To begin to examine the function of cyclins in mammalian germ cells, we have screened an adult mouse testis cDNA library for the presence of B-type cyclins. We have isolated cDNAs that encode a murine B-type cyclin, which has been designated cycB1. cycB1 was shown to be expressed in several adult tissues and in the midgestation mouse embryo. In the adult tissues, the highest levels of cycB1 transcripts were seen in the testis and ovary, which contain germ cells at various stages of differentiation. The major transcripts corresponding to cycB1 are 1.7 and 2.5 kb, with the 1.7 kb species being the predominant testicular transcript and the 2.5 kb species more abundant in the ovary. Examination of cDNAs corresponding to the 2.5 kb and 1.7 kb mRNAs revealed that these transcripts encode identical proteins, differing only in the polyadenylation signal used and therefore in the length of their 3' untranslated regions. Northern blot and in situ hybridization analyses revealed that the predominant sites of cycB1 expression in the testis and ovary were in the germinal compartment, particularly in early round spermatids in the testis and growing oocytes in the ovary. Thus cycB1 is expressed in both meiotic and postmeiotic cells. This pattern of cycB1 expression further suggests that cycB1 may have different functions in the two cell types, only one of which correlates with progression of the cell cycle.

Identification and characterization of the regulated pattern of expression of a novel mouse gene, meg1, during the meiotic cell cycle

The gene designated meg1 (meiosis expressed gene) is a new mouse gene identified during a search for mammalian genes potentially involved in meiotic processes. Two classes of complementary DNAs were isolated from an adult mouse testis complementary DNA library, which shared the same 3' end including the entire putative coding region but differed in their 5' ends. Only one of these complementary DNA classes appeared to correspond to the very abundant 0.75-kilobase testicular transcript of meg1. Sequence analysis predicts a 10.8-kilodalton protein which is highly charged and lysine rich. It is also relatively rich in potential phosphoacceptor amino acids (approximately 17%), several of which are located in phosphorylation consensus sequences. The pattern of expression of meg1 was studied utilizing a combined Northern blot and in situ hybridization analysis. Of the adult tissues examined, meg1 transcripts were detected exclusively in testis. Analysis of mRNA from testes of two germ cell deficient mutant strains did not reveal significant levels of meg1 transcripts. Analysis of RNA from enriched populations of spermatogenic cells from adult testes and localization by in situ hybridization revealed that meg1 transcripts are most abundant in pachytene spermatocytes. These results suggest a role for meg1 during germ cell differentiation, possibly during meiotic prophase.

Zfp-37, a new murine zinc finger encoding gene, is expressed in a developmentally regulated pattern in the male germ line

To begin to examine the function in the mouse testis of genes containing the zinc finger motif, we have screened an adult mouse total testis cDNA library with probes to a conserved region of zinc fingers. We have isolated cDNAs for a new murine zinc finger encoding gene that has been designated Zfp-37. Northern blot hybridization analysis revealed Zfp-37 transcripts at high levels in the testis, the only adult tissue in which Zfp-37 expression was observed. Zfp-37 was also expressed at lower levels in the mid-gestation embryo and placenta. The major testicular transcripts are 2.3 and 2.6 kb. A 4.0 kb transcript was detected at lower levels in the testis as well as in embryo and placenta. Northern blot and in situ hybridization analysis revealed that expression of Zfp-37 was most abundant in germ cells which have completed meiosis and are undergoing the complex morphogenetic changes of spermiogenesis. The pattern of expression of Zfp-37 and the presence of the zinc finger domain suggest that Zfp-37 may have a role in regulating spermiogenesis.

Stage and lineage-regulated expression of two hsp90 transcripts during mouse germ cell differentiation and embryogenesis

The expression of members of the heat shock protein 90 (hsp90) gene family during testicular and embryonic development was investigated. Two different hsp90 transcripts were detected in RNA from mouse testis, approximately 3.2 kb and 2.9 kb in size, and were shown to exhibit cellular and developmental stage specificity of expression. The larger, more abundant transcript was expressed at high levels in the germinal compartment of the testis, particularly in germ cells in meiotic prophase. The smaller hsp90 transcript was expressed predominantly in the somatic compartment of the testis. Expression of the two hsp90 transcripts was observed in testes of other species, suggesting an important role for hsp90 in mammalian testicular function. In addition, expression of both hsp90 transcripts was detected in the embryonic and extra-embryonic compartments of mid-gestation embryos.

Cell lineage specificity of expression of the murine transforming growth factor beta 3 and transforming growth factor beta 1 genes

We have cloned a murine transforming growth factor (TGF) beta 3 complementary (cDNA) from normal tissue by low stringency screening of a testicular cDNA library with a TGF beta 1 probe. The coding domain of this TGF beta 3 cDNA agrees completely with the sequence reported for the TGF beta 3 cDNA isolated from the AKR-2B cell line, but the testicular clone uses a distinct and unusual polyadenylation signal resulting in an altered 3' untranslated domain. Northern blot hybridization analysis of gonadal tissues showed that both TGF beta 3 and TGF beta 1 mRNAs are detectable in the mouse testis and ovary. A detailed analysis of TGF beta 3 and TGF beta 1 gene expression in normal and germ cell-deficient male mice showed that the somatic cell compartment of the mouse testis expresses the usual-sized transcripts for both genes. However, a smaller (1.8-kilobase) TGF beta 1 mRNA is expressed selectively in male germ cells, and expression of this transcript was constitutive throughout the spermatogenic stages examined. This result demonstrates a new pattern of TGF beta 1 gene expression, consistent with cell lineage-specific transcriptional regulation during spermatogenesis.

Characterization and inducibility of hsp 70 proteins in the male mouse germ line

The properties and inducibility of the heat shock protein 70 (hsp 70) gene products were examined during differentiation of mouse testicular cells by one and two-dimensional gel electrophoresis and immunoblotting. Low levels of the 72- and 73-kD heat shock proteins normally found in mouse cell lines were detected in the mouse testis. A novel isoform with a relative molecular mass of 73 kD (called 73T) was also observed, in the presence or absence of heat shock. 73T was shown to be produced by germ cells since it was not detected in testes from mutant mice devoid of germ cells. Furthermore, 73T was found only in adult mouse testicular cells, not in testes from animals that lack meiotic germ cells. 73T was synthesized in enriched cell populations of both meiotic prophase and postmeiotic cells, but was not inducible by in vitro heat shock. In the adult testis, low levels of the bona fide 72-kD heat-inducible (hsp72) were induced in response to elevated temperatures. In contrast, in testes from animals in which only somatic cells and premeiotic germ cells were present, there was a substantial induction of hsp 72. It is suggested that hsp 72 is inducible in the somatic compartment and possibly in the premeiotic germ cells, but not in germ cells which have entered meiosis and which are expressing members of the hsp 70 gene family in a developmentally regulated fashion.

Identification of an IL-4-inducible gene expressed in differentiating lymphocytes and male germ cells

Interleukin 4 (IL-4) is a cytokine that is involved in the differentiation of B and T lymphocytes. In this report, we describe the identification of a novel gene, N.52, which was cloned from the murine pre-B cell line R8205 grown in the presence of IL-4 for 48 hr. Although N.52 expression is detectable at low levels in unstimulated R8205 cells, the level of N.52 dramatically increases after only 4 hr exposure to IL-4 and remains at a high level up to 48 hr. Although N.52 expression is low or absent in normal spleen B and T cells, its expression can be induced by the differentiation signals delivered by LPS in B cells and by Con A in T-cell hybrids. While N.52 mRNA is absent in all highly differentiated organs, it is detectable in stem cell harboring lymphoid tissues such as bone marrow, fetal liver, and thymus. Furthermore, N.52 mRNA is expressed at strikingly high levels in the testis, specifically in differentiating male germ cells. It is induced by differentiation signals triggered by the combination of cyclic AMP and retinoic acid in teratocarcinoma F9 cells. Taken together, these data suggest that N.52 is a developmentally regulated gene whose expression in cells of the immune and reproductive systems may be controlled by stimuli that induce differentiation.

P150c-abl is detected in mouse male germ cells by an in vitro kinase assay and is associated with stage-specific phosphoproteins in haploid cells

We have utilized c-abl antibodies and an in vitro kinase assay to identify the protein products of the c-abl gene in mouse testis. Although the testis contains high levels of a unique c-abl mRNA, along with lower amounts of two c-abl mRNAs common to somatic cells, we detected only a single polypeptide of approximately 150 kd, indistinguishable by our methods from P150c-abl observed in murine tissues and cell lines. P150c-abl was also detected in enriched populations of germ cells, including late stage spermatids which contain the highest levels of the novel c-abl transcript. In mature testis, and specifically in late spermatids, P150c-abl co-precipitated with phosphoproteins of approximately 74 kd which were labeled during the in vitro kinase assay. These proteins were phosphorylated predominantly on serine and their phosphopeptide maps differed from that of P150c-abl. The P74 phosphoproteins were not found in association with P150c-abl in germ cells at earlier developmental stages, nor in other tissues or cell lines examined.

Transgenic mice overexpressing the mouse homoeobox-containing gene Hox-1.4 exhibit abnormal gut development

The mouse homoeobox-containing genes exhibit temporally and spatially specific patterns of expression in embryonic and adult tissues and are thought to be important in regulation of development and cellular differentiation, perhaps by mechanisms analogous to homoeotic genes in Drosophila melanogaster. There has been no direct demonstration that expression of these mammalian genes can affect developmental processes, however. Hox-1.4, like other mouse homoeobox-containing genes, has been shown to be expressed in specific regions of the mid-gestation embryo, but is unique in that its highest level of expression in the adult animal is restricted to developing male germ cells. We have introduced a construct carrying the mouse Hox-1.4 gene into the germ line of mice to begin to identify the cis-acting elements required for proper expression and to assess the consequences of increasing Hox-1.4 gene expression. The construct was designed to produce normal Hox-1.4 protein from transcripts that are distinguishable from the products of the endogenous gene. The integrated transgene seemed to exhibit the appropriate tissue specificity of expression, but transcript levels were elevated in certain tissues, particularly the embryonic gut. This overexpression correlated with changes in the normal developmental program of the gut, resulting in an inherited abnormal phenotype known as megacolon.

Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

A unique member of the mouse HSP70 gene family has been isolated and characterized with respect to its DNA sequence organization and expression. The gene contains extensive similarity to a heat shock-inducible HSP70 gene within the coding region but diverges in both 3' and 5' nontranslated regions. The gene does not yield transcripts in response to heat shock in mouse L cells. Rather, the gene appears to be activated uniquely in the male germ line. Analysis of RNA from different developmental stages and from enriched populations of spermatogenic cells revealed that this gene is expressed during the prophase stage of meiosis. A transcript different in size from the major heat-inducible mouse transcripts is most abundant in meiotic prophase spermatocytes and decreases in abundance in postmeiotic stages of spermatogenesis. This pattern of expression is distinct from that observed for another member of this gene family, which was previously shown to be expressed abundantly in postmeiotic germ cells. These observations suggest that specific HSP70 gene family members play distinct roles in the differentiation of the germ cell lineage in mammals.

Evidence for the involvement of the proto-oncogene c-mos in mammalian meiotic maturation and possibly very early embryogenesis

The c-mos proto-oncogene exists as a maternal mRNA in mammalian oocytes, in that it has been shown to accumulate in mouse oocytes during the growth phase and to be present at high levels in fully grown oocytes. The function of c-mos during the subsequent development of the oocytes and embryos was examined by determining the fate of the oocyte c-mos mRNAs by in situ hybridization and Northern blot hybridization analysis. A substantial decrease in the levels of c-mos transcripts was observed in oocytes undergoing meiotic maturation. By the two-cell stage, levels of c-mos transcripts dropped to below the limits of detection using in situ hybridization. c-mos transcripts remained undectable through the blastocyst stage of embryogenesis. Analysis of meiotic maturation in vitro permitted finer temporal resolution of the initial drop in c-mos levels. Between approximately 7 and 17 h of culture, the amount of c-mos mRNA fell to 18-43% of the levels found in the fully grown oocyte. This interval corresponds to the progression of meiotic maturation from metaphase I to metaphase II. Our in vivo studies showed that ovulation per se is not the stimulus for the drop in c-mos transcript levels, since preovulatory metaphase II oocytes exhibited this decline to a degree comparable to that of ovulated metaphase II oocytes. The development specificity of c-mos transcript levels suggests a role of this putative serine kinase in the meiotic maturation of mammalian germ cells.

Translational regulation of the novel haploid-specific transcripts for the c-abl proto-oncogene and a member of the 70 kDa heat-shock protein gene family in the male germ line

Expression of the c-abl proto-oncogene in the mouse testis is characterized by the production of a unique 4.7-kb transcript present in germ cells that have entered the haploid phase of spermatogenesis. A similar developmental stage specificity of expression is observed for a member of the 70-kDa heat-shock protein (hsp 70) gene family. A unique-sized hsp 70 transcript (T-hsp 70) is produced in haploid spermatids and is stable throughout spermatogenesis. In the present study, we examined the regulation of expression of these genes by examining their association with polyribosomes. The germ cell-specific c-abl and T-hsp 70 mRNA variants were both associated with the polysomal fractions of mouse testis cells, suggesting that they are functional mRNAs. However, both c-abl and T-hsp 70 mRNAs were also found in the ribonucleoprotein particle fractions. The distribution of these mRNAs in both the polysomal and nonpolysomal fractions is comparable to that seen for the mRNA of protamine-1, a gene whose expression in the testis is known to be regulated at the level of translation. In contrast, transcripts from the beta-tubulin gene were seen predominantly in the polyribosomal fractions. These findings suggest that translation of the novel c-abl and T-hsp 70 transcripts is confined to subpopulations of testicular cells.

Differential expression of the c-abl proto-oncogene and the homeo box-containing gene Hox 1.4 during mouse spermatogenesis

Mammalian spermatogenesis is a complex developmental process. Spermatozoa, like ova, are uniquely capable of supporting embryonic development. Our approach to understanding this process is to identify genes whose developmental pattern of expression suggests that they may play a role in spermatogenesis. Experiments on the cellular oncogene c-abl and the homeo box-containing gene Hox-1.4 indicate that these genes may be important for male germ cell development. Both genes produce testis-specific transcripts that are present in particular cellular populations of the adult testis. Their developmental specificity, however, is different: c-abl is haploid-specific, whereas Hox-1.4 is expressed in the germ cells as soon as they have entered meiosis. Future studies will focus on examining the protein products of these genes and their function in testicular cells.

Differential expression of the mouse homeobox-containing gene Hox-1.4 during male germ cell differentiation and embryonic development

Hox-1.4 is a mouse homeobox-containing gene (initially identified as HBT-1), whose expression appears to be testis-specific in the adult animal. Examination of Hox-1.4 transcripts in RNA from testes of mutant mice deficient in germ cells confirms that Hox-1.4 expression within the testis is germ cell-specific. Enriched populations of spermatogenic cells were used to localize the expression of Hox-1.4 specifically to germ cells that have entered into and progressed beyond the meiotic prophase stage of differentiation and to demonstrate the presence of two different size Hox-1.4 transcripts. Examination of RNA from teratocarcinoma cell cultures and mouse embryos at 10.5-16.5 days of gestation demonstrated the presence of several Hox-1.4 transcripts, which are larger than those present in germ cells. In the midgestation fetus, Hox-1.4 expression is most abundant in the spinal cord.

Distinct developmental patterns of c-mos protooncogene expression in female and male mouse germ cells

The protooncogene c-mos is expressed in murine reproductive tissues, producing transcripts of 1.7 and 1.4 kilobases in testis and ovary, respectively. In situ hybridization analysis of c-mos expression in histological sections of mouse ovaries revealed that oocytes are the predominant if not exclusive source of c-mos transcripts. c-mos transcripts accumulate in growing oocytes, increasing 40- to 90-fold during oocyte and follicular development. c-mos transcripts were also detected in male germ cells and are most abundant after the cells have entered the haploid stage of spermatogenesis. This developmentally regulated pattern of c-mos expression in oocytes and spermatogenic cells suggests that the c-mos gene product may have a function in normal germ-cell differentiation or early embryogenesis.

Differential expression in murine somatic and germinal tissues of transcripts homologous to an abundant embryonal-carcinoma-cell mRNA

EC1, a clone from a cDNA library of embryonal-carcinoma (EC) cells, was used to study the expression of the gene(s) homologous to this sequence in murine germ cells and somatic tissues. Northern-blot analysis was used to determine the size and relative abundance of ECl transcripts in EC cells, ovary, testis, liver, spleen, brain, thymus, and bone marrow. The stage-specific expression of EC1-related transcripts in meiotic cells was examined in enriched populations of testicular cells (meiotic prophase spermatocytes, early and late spermatids, and residual bodies). All tissues and cells examined contained mRNAs of approximately 1.3 and approximately 3.6 kb which were homologous to EC1. In RNA from liver and thymus, a faint, lower-molecular-weight transcript of 0.75 kb was seen. A unique pattern of expression was observed in male germ cells. In cells that had completed meiosis, two additional transcripts of 1.0 and 4.4 kb were visualized, as well as high levels of expression of the 1.3- and 3.6-kb species. Only the 1.3- and 3.6-kb transcripts were detected in ovarian RNAs. The high level and stage specificity of expression of EC1-related mRNAs in germ cells suggest that this gene may be important in meiosis or in germ-cell maturation.

Chromatin decondensation and DNA synthesis in human sperm activated in vitro by using Xenopus laevis egg extracts

An in vitro sperm activation system was used to study nuclear swelling-chromatin decondensation and DNA synthesis; processes that occur in vivo following fertilization. Lysolecithin-permeabilized human sperm were incubated in Xenopus laevis egg extract and examined by using phase-contrast light microscopy, electron microscopy, and autoradiography. During a 3-hour incubation, the activated sperm nuclear chromatin underwent a decondensation-recondensation cycle during which DNA was synthesized. This also occurred when egg extract was given a 3-hour preincubation before the addition of the sperm, suggesting that the factor(s) required for initiating the decondensation-recondensation cycle is associated with the sperm. Because both nuclear swelling and DNA synthesis were found to be reproducible and quantifiable, we studied the effect of various agents on the two processes, characterizing the critical component(s) in the egg extract that induces these events. EGTA was found to have no effect on the induced nuclear swelling or DNA synthesis that occurs in the activated sperm. Freezing and thawing the extract or treating the extract with aphidicolin also had no effect on subsequent nuclear swelling; however, the DNA synthesis activity was blocked. Sperm incubated in extract treated with alkaline phosphatase (AP) had both nuclear swelling and DNA synthesis blocked. However, if the sperm were pretreated with DTT, and then incubated with the AP-treated extract, only the DNA synthesis activity of the extract was blocked. When the extract was treated with serine protease inhibitors (PMSF, soybean trypsin inhibitor, or alpha-2-macroglobulin), nuclear swelling occurred; however, DNA synthesis was blocked. These data suggest that phosphoproteins are involved in one or more of the activation events and that a serine protease(s) is involved in the synthesis of DNA.

Developmental-stage-specific expression of the hsp70 gene family during differentiation of the mammalian male germ line

Mouse somatic tissues contain low levels of transcripts homologous to the heat shock-inducible and cognate members of the heat shock protein 70 (hsp70) gene family. An abundant, unique sized hsp70 mRNA of 2.7 kilobases (kb) is present in testes in the absence of exogenous stress. Its expression is restricted to germ cells and is developmentally regulated. The 2.7-kb transcript first appears during the haploid phase of spermatogenesis and is stable throughout the morphogenic stages of spermiogenesis. A 2.7-kb hsp70 mRNA is present in rat and human testes. These observations suggest that a member of the hsp70 gene family plays a role in the development of the mammalian male germ cell lineage.

Expression of the proopiomelanocortin gene is developmentally regulated and affected by germ cells in the male mouse reproductive system

Proopiomelanocortin (POMC), a major pituitary product, is also present in the adult mouse testis. We have shown previously that POMC mRNAs are most abundant in a subpopulation of Leydig cells associated with tubules in specific stages of the cycle of the seminiferous epithelium. In the present study, we examined the expression of the gene encoding POMC during testicular development and in other tissues of the male reproductive system. We also analyzed the effects of cellular interactions on POMC gene expression in the testis. Blot-hybridization analysis revealed that POMC transcripts of approximately equal to 800 nucleotides were present in enriched populations of meiotic prophase spermatocytes and in caput epididymis but were absent in cauda epididymis and vas deferens. POMC transcripts were present in fetal testis (day 17 of gestation to newborn), could not be detected in prepuberal testis (days 7-8 postpartum), but reappeared in the adult testis. No difference in the size or abundance of POMC transcripts was seen in testes from mouse mutant strains in which spermatogenesis is arrested in early spermiogenesis. In contrast, POMC transcripts were virtually undetectable in testes that are devoid of germ cells. These results emphasize the importance of interactions between germ cells and interstitial cells and the regulation of the POMC gene in the mammalian testis.

Genetic and cytogenetic localisation of the homeo box containing genes on mouse chromosome 6 and human chromosome 7

Probes from the m6 homeo box cluster were mapped to mouse chromosome 6 by somatic cell genetics, in situ hybridisation, and by a Mus spretus--Mus musculus backcross mapping system. In addition, the testis-specific homeo box containing cDNA, clone, HBT-1, has been mapped using the same back-cross system and the B X D recombinant inbred strain set. Close genetic and physical linkage between the m6 cluster and HBT-1 was demonstrated, positioning these sequences to the same local cluster of homeo box containing genes. The map location of this cluster between IgK and Tcrb coincides with the morphological mutation hypodactyly (Hd). Synteny has been observed between a region of mouse chromosome 6 and the long arm of human chromosome 7 encompassing the markers Cpa, Tcrb and Try-1. Here we localise human sequences hybridising to the mouse m6 probes to the short arm of chromosome 7, breaking the region of synteny.

Isolation of a mouse cDNA coding for a developmentally regulated, testis-specific transcript containing homeo box homology

A clone, pHBT-1, containing sequences homologous to Drosophila homeo boxes has been isolated from a mouse testis cDNA library. The sequence is 80% homologous at the DNA level and 88% homologous at the amino acid level to the homeo box sequence of the Antennapedia gene of Drosophila. Sequences flanking the 3' end of the homeo box are highly diverged from other murine homeo box-containing genes characterized to date. RNA blot hybridization analysis of mouse testis poly(A)+ RNA revealed transcripts of approximately 1.4 kb in length. Within the limits of sensitivity of detection of Northern blot analysis, no transcripts were seen in any of the adult somatic tissues examined. Other tissues that contain stem cells, namely those of the hemopoietic system, also lacked detectable amounts of HBT-1 transcripts. HBT-1 transcripts were limited to male germ cell-containing tissues, since RNAs from juvenile and adult ovaries did not contain detectable amounts of the 1.4-kb transcripts. Expression of the HBT-1 gene was not detected in embryonic testes, nor in tests of neonatal animals which contain germ cells up to the Type B stage of spermatogonial development. A role for the expression of the HBT-1 gene in the meiotic stages of male germ cell differentiation is postulated.

Localization of mRNAs in mouse testes by in situ hybridization: distribution of alpha-tubulin and developmental stage specificity of pro-opiomelanocortin transcripts

Gene expression of mouse testicular germ cells and surrounding somatic cells during spermatogenesis was examined by RNA:cDNA hybridization in situ and concomitant Northern and dot blot analysis. Particular attention was paid to obtaining fixation and hybridization procedures for use with mouse testes to accomplish sensitive and precise localization with the in situ technique. alpha-Tubulin mRNAs were localized in virtually all testis cell types. In elongating spermatids, a unique labeling pattern was visualized; possibly corresponding to the position of the asymmetrically displaced cytoplasm. Pro-opiomelanocortin (POMC) transcripts in the adult mouse testis detected by Northern blot analysis were shown to be of a smaller size (approximately 600-800 nt) than the pituitary POMC transcripts, similar to what has been reported recently for POMC expression in the rat testis and mouse Leydig cell lines. Localization of POMC mRNAs by in situ hybridization was primarily to Leydig cells, although some labeling of spermatogonia and spermatocytes within the seminiferous epithelium was detected. A cellular or developmental specificity of the pattern of POMC localization was observed: obvious labeling of Leydig cells was limited to interstitial regions which were surrounded completely or in part by tubules in stages IX to XII of the cycle of the seminiferous epithelium.

Haploid expression of a unique c-abl transcript in the mouse male germ line

RNA from immature mouse testes was shown to lack a low-molecular-weight c-abl transcript previously noted to be the predominant species in adult testes. The developmental pattern of appearance of this c-abl variant was determined by analyzing RNA obtained from purified populations of testicular cells in different stages of spermatogenesis. The appearance of the c-abl testicular variant was coincident with the entry of the germ cells into their haploid state and suggested that the regulated expression of this proto-oncogene may be important in the normal differentiation of the male germ line.

Formation of the rabbit zona pellucida and its relationship to ovarian follicular development

The zona pellucida is the unique extracellular glycoprotein matrix which is assembled during growth of the mammalian oocyte. The present studies were carried out to examine the formation of this structure in relation to the differentiation of ovarian cell types during follicular development. Specific antibodies were developed against total rabbit ZP proteins as well as against ZP proteins electrophoretically purified by high-resolution two-dimensional polyacrylamide electrophoresis gels (2D-PAGE). Antibodies were characterized by (a) immunoelectrophoresis, (b) a Staphylococcus aureus protein A binding assay, and (c) immunoblotting following 2D-PAGE separation of ZP proteins. Immunoperoxidase localization with these antibodies was used to determine the stage of ovarian follicular development at which ZP antigens first appear as well as to evaluate the cellular and extracellular distribution of these proteins throughout folliculogenesis. The ZP proteins were first observed in the cytoplasm and at the periphery of the oocytes surrounded by a thin squamous follicular cell layer. No staining was observed in the cytoplasm of follicle cells during early folliculogenesis. As the ZP matrix was assembled extracellularly, the intensity of staining of the outer and inner regions could be distinguished. This differentiation of the matrix coincided with the differentiation of the follicular cells into a multilayer cell complex. At this stage, specific ZP proteins are localized within the cytoplasm of the inner layers of these follicular cells. The staining is then diminished in cells of preantral follicles. These studies demonstrate that the formation of the ZP is an excellent model system to study the early stages of follicular development and cell differentiation.

Methylation of satellite sequences in mouse spermatogenic and somatic DNAs

The distribution of 5-methyl cytosine (5-MeC) residues in a highly repetitive sequence, mouse major satellite, was examined in germinal versus somatic DNAs by digestion with the methylation sensitive isoschizomers Msp I and Hpa II and Southern blot analysis, using a cloned satellite probe. DNA from liver, brain, and a mouse fibroblast cell line, C3H 10T1/2, yielded a multimeric hybridization pattern after digestion with Msp I (and control Eco RI) but were resistant to digestion with Hpa II, reflecting a high level of methylation of the satellite sequences. In contrast, DNA from mature sperm was undermethylated at these same sequences as indicated by the ability of Hpa II to generate a multimeric pattern. DNAs from purified populations of testis cells in different stages of spermatogenesis were examined to determine when during germ cell differentiation the undermethylation was established. As early as in primitive type A, type A, and type B spermatogonia, an undermethylation of satellite sequences was observed. This suggest that this highly specific undermethylation of germ cell satellite DNA occurs very early in the germ cell lineage, prior to entry into meiosis.

Transcription and accurate polyadenylation in vitro of RNA from the major late adenovirus 2 transcription unit

Nucleoprotein complexes with in vitro transcription activity were isolated from HeLa cells late in lytic infection with Adenovirus type 2 (Ad2). Both polymerase II and polymerase III were active in these extracts, and greater than 85% of the labeled RNA was Ad2-specific. Electrophoretic analyses and Southern blot analyses demonstrated that RNA complementary to the entire 30 kb late transcription unit including RNA near the presumed termination site was synthesized. The addition of DRB (5,6,dichloro-1-beta-D-ribofuranosyl-benzimidazole) in vivo prior to the isolation of the complexes resulted in accumulation of polymerase II at the promoter proximal sites, but nascent chains started in vivo in DRB were successfully elongated in vitro. Approximately 10% of the RNA labeled in vitro contained poly(A), and the length of poly(A) was very similar to that of nuclear RNA isolated from Ad2-infected cells. The in vitro sites of poly(A) addition were specific--labeled poly(A)-terminated RNA molecules ended at a point on the genome coincident with previously mapped poly(A) sites of mRNAs produced in vivo. In addition, the polyadenylation enzyme (or enzymes) cosediment with the nucleoprotein complexes during sucrose gradient centrifugation since gradient purified complexes synthesize poly(A) containing RNA in vitro in the absence of any added nuclear extract.