Characterization and regulation of two testicular inhibin/activin beta B-subunit messenger ribonucleic acids that are transcribed from alternate initiation sites

Cloning and characterization of rat spermatid protein SSP411: a thioredoxin-like protein

In an attempt to identify new sperm-specific genes that are involved in sperm maturation, fertilization, and embryo development, such as the mammalian ortholog of the sperm-supplied protein gene, spe-11, in Caenorhabditis elegans, we cloned and characterized a new spermatid-specific protein gene, ssp411, from adult rat testes. The ssp411 cDNA shared >85% sequence identity with an unnamed human protein, FLJ21347, and an uncharacterized mouse testicular protein called transcript increased in spermiogenesis 78 (TISP78). A 2.8-kb ssp411 mRNA was expressed in a testis-specific and age-dependent manner; the mRNA was evident at 28 days and remained at high levels throughout adulthood. An SSP411 protein of molecular weight 88 000 was detected in testicular extracts by Western blot analysis. Ssp411 mRNA and SSP411 protein, as analyzed by in situ hybridization and immunohistochemistry, were both expressed in a stage-dependent fashion during the cycle of the seminiferous epithelium. The ssp411 mRNA was predominantly localized to round and elongated spermatids, with maximal expression at stages VII-XII. The SSP411 protein was mainly observed in elongated spermatids and reached its highest levels during stages V-VI. A conserved thioredoxin-like domain was detected in the N-terminal region of SSP411 and its orthologs. An analysis of the predicted 3-dimensional structural modeling and folding pattern further suggested that SSP411 is identifiable as a member of thioredoxin family. In summary, we have identified a new rat spermatid protein gene, ssp411, and its orthologs in human and mouse and demonstrated that SSP411 might belong to a testis-specific thioredoxin family. This suggests that SSP411 may play a role in sperm maturation, fertilization, and/or embryo development, as has been shown in thioredoxin family.

Gonadotropins, via cAMP, negatively regulate GATA-1 gene expression in testicular cells

We and others demonstrated that the mRNAs encoding GATA-binding proteins, GATA-1 and GATA-4, were detected in mouse and rat testis, and in isolated rat Sertoli cells and testicular tumor cell lines derived from Leydig and Sertoli cells. In this study, we investigated the possible effects of gonadotropins and cAMP on the expression of GATA-binding protein genes in testicular cells. Unexpectedly, FSH negatively regulated GATA-1 (but not GATA-4) mRNA in a dose-dependent manner in primary cultures of rat Sertoli cells isolated from 21-d-old animals. GATA-1 mRNA was also negatively regulated by cAMP in a dose- and time-dependent manner in MA-10, a mouse Leydig tumor cell line. When 0.3 mM cAMP was administered to MA-10 cell cultures for 4 h, more than 95% of the GATA-1 mRNA and protein was abolished. The reduction of GATA-1 mRNA by cAMP can be mimicked by treatment with forskolin, which elevates intracellular cAMP levels. The inhibitory effect of cAMP was specific to the GATA-1 gene, given that GATA-4 and alpha-tubulin mRNA levels were not changed by any of the cAMP treatments. Inhibin alpha-subunit mRNA, on the other hand, was evidently increased by cAMP treatment in both MA-10 and Sertoli cells. However, inhibin alpha-subunit mRNA levels were elevated at 60-90 min before the suppression of GATA-1 mRNA detected. The inhibitory effect of cAMP on GATA-1 mRNA and protein was shown to be specific to testicular cells. The GATA-1 mRNA expressed in MEL, a mouse erythroid leukemia cell line, was not affected by cAMP. The reduction of GATA-1 mRNA by cAMP can be prevented when a translational inhibitor, cycloheximide, is added. In summary, we demonstrated that gonadotropins via cAMP negatively regulate the mRNA and protein levels of GATA-1, but not GATA-4, in testicular cells. The inhibitory effect on GATA-1 gene expression was specific to testicular cells and was not observed in erythroid cells.

Molecular cloning and expression analysis of the complementary deoxyribonucleic acid for chicken inhibin/activin beta(B) subunit

Inhibins and activins are dimeric peptide hormones that play an integral role in the intraovarian regulation of folliculogenesis. The domestic hen, with its well-defined follicular hierarchy, provides a unique model in which to study the role of these hormones in follicular development. In the present study, the complete coding sequence and deduced amino acid sequence for the chicken inhibin/activin beta(B) subunit has been determined from cDNA clones isolated from a chicken ovarian granulosa cell library. This beta(B)-subunit cDNA predicts a precursor protein of 392 amino acids containing the mature C-terminal 115 amino acid beta(B) subunit. When compared to the beta(B) subunit isolated from a variety of species, the chicken cDNA clone showed high nucleotide identity in the full-length coding region (>70%) and in the mature coding region (>80%). In addition, the deduced amino acid sequence of chicken beta(B) subunit showed greater than 95% identity compared to other species in the mature peptide region. Expression of the beta(B)-subunit mRNA was detected by reverse transcription-polymerase chain reaction in both gonadal and extragonadal tissues. Northern blot analysis detected expression in the gonadal tissues only, specifically in the granulosa tissue from the F3-F5 follicles, small yellow follicles (SYF), large white follicles, and immature and mature rooster testes. A major transcript of approximately 4.1 kilobases (kb) and three minor transcripts of approximately 8.4 kb, 6.5 kb, and 1.7 kb were detected in the SYF granulosa samples. To examine the expression pattern of the beta(B) subunit around the stage of follicle selection, the SYF granulosa was subdivided into two groups: 6-8 mm and 9-12 mm. Quantification of RNA expression (n = 3) showed that expression of the beta(B) subunit was maximal in the 6-8 mm SYF. Activin B, as well as other intraovarian signals, may regulate early follicle selection and/or development in the chicken.

Definition of regulatory sequence elements in the promoter region and the first intron of the myotonic dystrophy protein kinase gene

Myotonic dystrophy is the most common inherited adult neuromuscular disorder with a global frequency of 1/8000. The genetic defect is an expanding CTG trinucleotide repeat in the 3'-untranslated region of the myotonic dystrophy protein kinase gene. We present the in vitro characterization of cis regulatory elements controlling transcription of the myotonic dystrophy protein kinase gene in myoblasts and fibroblasts. The region 5' to the initiating ATG contains no consensus TATA or CCAAT box. We have mapped two transcriptional start sites by primer extension. Deletion constructs from this region fused to the bacterial chloramphenicol acetyltransferase reporter gene revealed only subtle muscle specific cis elements. The strongest promoter activity mapped to a 189-base pair fragment. This sequence contains a conserved GC box to which the transcription factor Sp1 binds. Reporter gene constructs containing a 2-kilobase pair first intron fragment of the myotonic dystrophy protein kinase gene enhances reporter activity up to 6-fold in the human rhabdomyosarcoma myoblast cell line TE32 but not in NIH 3T3 fibroblasts. Co-transfection of a MyoD expression vector with reporter constructs containing the first intron into 10 T1/2 fibroblasts resulted in a 10-20-fold enhancement of expression. Deletion analysis of four E-box elements within the first intron reveal that these elements contribute to enhancer activity similarly in TE32 myoblasts and 10 T1/2 fibroblasts. These data suggest that E-boxes within the myotonic dystrophy protein kinase first intron mediate interactions with upstream promoter elements to up-regulate transcription of this gene in myoblasts.

Testicular GATA-1 factor up-regulates the promoter activity of rat inhibin alpha-subunit gene in MA-10 Leydig tumor cells

We have previously demonstrated that the basal transcription of rat inhibin alpha-subunit gene in a mouse testicular Leydig tumor cell line, MA-10, depends upon a 67-bp DNA fragment at the position of -163 to -97. Within this promoter region two GATA motifs were observed. In this study, we investigated the possible role of GATA-binding proteins in the regulation of inhibin alpha-subunit gene transcription in testicular cells. Northern blot and RT-PCR analyses showed that mRNAs encoding GATA-binding proteins, GATA-1 and GATA-4, were detected in mouse and rat testis and in MA-10 and rat Sertoli cells. Testis-specific GATA-1 mRNA, which is transcribed from a promoter 8 kb upstream to the erythroid exon I of mouse GATA-1 gene, was also identified in MA-10 cells. Mutations of GATA sequences in alpha-subunit promoter markedly decreased the transcriptional activity of alpha-subunit gene when measured by their ability of transient expression of a bacterial reporter gene, chloramphenicol acetyltransferase (CAT), in MA-10 cells. Cotransfection of alphaCAT chimeric construct with cDNA expression plasmid coding for mouse GATA-1 or GATA-4 protein revealed that GATA-1 but not GATA-4 can transactivate alpha-subunit promoter in a dose-dependent manner. The transactivation by GATA-1 was inhibited if GATA sequences in alpha-subunit promoter were mutated. Furthermore, electrophoretic mobility shift assay demonstrated that GATA-binding proteins present in nuclear extracts of MA-10 cells and rat testis interacted with the GATA motifs in alpha-subunit promoter, and the GATA-1 in these nuclear extracts formed a supershifted immunocomplex with antibody raised against mouse GATA-1 protein. We therefore concluded that the basal transcription of inhibin alpha-subunit gene in testicular MA-10 cells is up-regulated by testicular GATA-1 but not GATA-4 through its interaction with the GATA motifs in alpha-subunit promoter. In summary, we have provided the first evidence of the functional role of a GATA-binding protein in the regulation of testicular gene expression.