Localization of group IIc low molecular weight phospholipase A2 mRNA to meiotic cells in the mouse

We use in situ hybridization to demonstrate that the testicular expression of a novel, mouse, low molecular weight phospholipase A2 (PLA2 Group IIc) mRNA is specific to cells undergoing meiosis. A complete cDNA (1421 bp) encoding the mouse Pla2g2c gene was generated with reverse transcription-PCR (RT-PCR) and 5' and 3' RACE (rapid amplification of cDNA ends) RT-PCR, and its nucleotide sequence was determined. Northern blots of RNA from different tissues revealed a single 1.6 kb transcript only in testis. In situ hybridization indicated that this mouse gene is transcribed mainly in pachytene spermatocytes, secondary spermatocytes, and round spermatids. Expression of the gene is seen in all stages of the seminiferous epithelium, especially in stages VI-VII.

Identification and localization of secretin and secretin receptor mRNAs in rat testis

Secretin is a well-conserved member of the growth hormone-releasing hormone (GHRH) family of peptides expressed in brain, gut and gonads. To determine whether secretin may also play a physiological role in testis, we examined the level and cellular distribution of secretin and secretin receptor gene expression in rat testis. RNAs from total testis, Sertoli, germ and Leydig cells were amplified by comparative reverse transcription-polymerase chain reaction (RT-PCR). Southern blot analysis of the PCR products indicated secretin and secretin receptor mRNA expression primarily in germ cells. Sequence comparisons of cloned secretin and secretin receptor PCR products showed 100% identity with the previously reported sequences. To localize secretin and secretin receptor mRNAs at the cellular level within testis,in situ hybridization was performed. Specific hybridization to secretin mRNA was observed in low abundance in many germ cell types, but was heaviest over step 19 spermatids in stages VII and VIII tubules. Secretin receptor mRNA was detected in approximately the same cell types as was secretin mRNA, except that labeling was greatest in round spermatids (steps 6-8). Since the patterns of gene expression of secretin and its receptor overlap, these data suggest that there may be an intrinsic secretin system in testis.

Presence of a spermatogenic-specific promoter in the rat growth hormone-releasing hormone gene

A GH-releasing hormone (GHRH) messenger RNA (mRNA) has been identified in hypothalamus, placenta, and testicular germ cells. The GHRH mRNA produced by spermatogenic cells is approximately 1700 nucleotides in length, whereas GHRH transcripts in hypothalamus and placenta are 750 nucleotides. To correlate the structure of testicular GHRH mRNA with cell type-specific expression, we determined its sequence. A GHRH clone isolated from a rat testicular complementary DNA library was found to be identical in the coding sequence to hypothalamic GHRH. Rapid amplification of complementary DNA ends analysis of the 5'-end of germ cell GHRH mRNA and comparison with the genomic sequence revealed that GHRH transcription in testis initiates approximately 700 basepairs 5' to transcription initiation in placenta and 10.7 kilobasepairs 5' to that in hypothalamus. Reverse transcription-polymerase chain reaction analysis of germ cell RNA using primers from testicular exons 1 and 4 demonstrated that part of the placental exon 1 sequence is contained in some testicular GHRH transcripts, as an extra exon, between testicular exon 1 and the common exon 2. This was confirmed by a Northern blot of testicular mRNA using a testicular exon 1 probe. The 5'-flanking region of the testicular GHRH gene was analyzed and found to contain a TATA-like motif and sequences homologous to spermatogenic-specific cis-acting elements. Southern blot analysis of rat liver DNA suggested that just one GHRH gene is present in rat. These results indicate that both alternative transcription initiation and splicing of the GHRH gene exist in rat testicular germ cells.

Paracrine control of spermatogenesis

Spermatogenesis is a complex process that is both remarkable and enigmatic. While circulating hormones clearly play an important role in initiating and regulating the process, the Sertoli cell barrier prevents most substances from entering the seminiferous tubule compartment and directly influencing germ cell development. Therefore, the testis cannot rely solely upon the delivery of circulating hormones, nutrients, and growth factors, but must independently produce its own regulatory substances. A rapidly increasing number of testicular factors that appear to modulate spermatogenesis in a paracrine fashion are now being identified. These discoveries are beginning to contribute to our understanding of the intricate network of testicular cell-cell interactions that control male reproduction.

A new target for growth hormone releasing-hormone action in rat: the Sertoli cell

A GHRH-like mRNA and peptide (t-GHRH) have been detected in rat and human testis. In rat, t-GHRH mRNA is localized to developing spermatogenic cells. We predicted that the most likely target cell of t-GHRH action would be the Sertoli cell. To test this prediction, we evaluated GHRH action on Sertoli cell function. Rat GHRH at a concentration of 10 nM or 100 nM stimulated cAMP production 2-fold over control levels after a 30 min incubation. This stimulation was obliterated by preincubation with a 10-fold excess of the GHRH antagonist (N-Ac-Tyr1, D-Arg2)-GRF(1-29)-NH2. The effect of treatment with [His1,Nle27]GHRH(1-32)-NH2, a GHRH analog, on Sertoli cell mRNAs was also assessed. Treatment with the analog significantly increased levels of c-fos and steel factor (the product of the Steel gene, also termed SCF) mRNAs above controls, but had no effect on sulfated glycoprotein-2 mRNA. We conclude that GHRH acts via adenylate cyclase to modulate specific Sertoli cell products, possibly as part of a network of local interacting factors controlling Sertoli and germ cell function.

Germ cell localization of a testicular growth hormone-releasing hormone-like factor

GH-releasing hormone (GHRH)-like mRNA and immunoreactivity (t-GHRH-li) are present in the testes of rats and humans. To learn more about the physiology of t-GHRH-li mRNA, we performed a series of experiments that disrupted various testicular functions. We employed ethylene dimethanesulfonate, a Leydig cell toxin, to assess the effects of Leydig cell ablation on t-GHRH-li mRNA and protein levels in prepubertal and postpubertal male rats. The ethylene dimethanesulfonate treatment resulted in decreases in serum testosterone, but had no effect on t-GHRH-li mRNA or peptide levels. To assess the effect of GHRH on Leydig cell steroidogenesis, Leydig cells were isolated by Percoll gradient centrifugation and cultured in the presence or absence of hCG, GHRH, or hCG plus GHRH. GHRH had no effect on steroidogenesis by Leydig cells, either alone or in combination with hCG. To localize t-GHRH-li mRNA within rat testis, in situ hybridization analysis was performed on testicular sections from normal rats, using a [35S]GHRH riboprobe. Grains were detected in spermatogenic cells with the antisense probe, whereas none was detected with the sense strand (control) probe. To verify these results, Northern blot analysis of RNA from separated testicular cells was performed. t-GHRH-li mRNA was detected in spermatocytes and round spermatids and to a lesser extent in Sertoli cells, but not in elongating spermatids, Leydig cells, or peritubular myoid cells. t-GHRH-li mRNA was also not found in epididymis. Since our experiments localized t-GHRH-li mRNA to spermatogenic cells, methoxyacetic acid (MAA), a pachytene spermatocyte toxin, was administered to postpubertal rats to determine whether t-GHRH-li is expressed primarily in pachytene spermatocytes. MAA treatment caused a decrease in testicular weight, which gradually returned to control levels by 42 days. Serum FSH levels in the treated animals fluctuated over the course of the experiment, while those in control animals remained steady. However, there was no difference in testicular GHRH-li mRNA levels between control and treated animals at any treatment time. Insulin-like growth factor-I and -II mRNA levels were also unaltered by the MAA treatment. We conclude from these results that t-GHRH-li is synthesized in early spermatogenic cells, but not in mature sperm, and that testicular GHRH-li does not play a major role in steroidogenesis by the Leydig cell.

Parvovirus B19 replication in human umbilical cord blood cells

The human parvovirus B19 is now known to be one of the causative agents of nonimmune hydrops fetalis and spontaneous abortions in pregnant women. The presence of the viral proteins and antibodies in fetuses of B19-infected women suggests that the virus can cross the placental barrier. In order to gain an insight into the mechanism of intrauterine fetal infection and the virus-induced hydrops fetalis, we examined whether human umbilical cord blood cells were permissive for B19 replication. Cord blood cells were infected with B19 in vitro, and Southern blot analyses of low M(r) DNA isolated from these cells revealed the presence of the characteristic replicative intermediates of B19 DNA. In addition, B19 genome expression in cord blood cells was detected by Northern blot analysis. Quantitative DNA dot blot analysis of culture supernatants documented complete assembly and release of B19 progeny virions in these cells. The progeny virions were biologically active in secondary infections of normal human bone marrow cells. The human umbilical cord blood cells may be a useful alternative to bone marrow and fetal liver culture systems for further studies on B19 since the need for bone marrow donors is obviated and, unlike fetal tissues, there are no ethical questions associated with the experimental use of cord blood because it is normally discarded. These studies also suggest that the umbilical cord blood may be a site for active replication of parvovirus B19 in vivo and may thus provide a means for transmission of the virus during intrauterine fetal infections.

Growth hormone-releasing hormone-like messenger ribonucleic acid and immunoreactive peptide are present in human testis and placenta

Although the sequence of human GH-releasing hormone (GHRH) has been determined, all of the information concerning gene expression has been based on pathological sources of ectopic GHRH, since the only established physiological source of GHRH in humans is the hypothalamus. We recently reported the presence of extrahypothalamic GHRH-like mRNA and immunoreactive material in rat testis and placenta. To determine if human testis and placenta also contain immunoreactive GHRH-like peptides, tissue extracts were analyzed using enzyme-linked immunosorbent assay methodology. Both tissues had detectable quantities of immunoreactive peptide recognized by a monoclonal antibody to synthetic human GHRH-(1-44) (testis, 2.4 ng/g tissue, 0.68 ng/mg protein; placenta, 2.6 ng/g tissue, 0.36 ng/mg protein). The origin of these peptides was confirmed by extracting total RNA from human testis and placenta, with analysis on Northern blots probed with riboprobes for rat hypothalamic GHRH cDNA and human pancreatic tumor GHRH cDNA. Human testis and placenta total RNA both contain an approximately 790-nucleotide RNA species similar in size to that reported in ectopic GHRH-producing human tumors. In addition, two larger hybridization signals were seen at 3000 and 4900 nucleotides. These data suggest that testis and placenta are extrahypothalamic sites of expression of the human GHRH gene. Normal expression of the GHRH gene in extrahypothalamic sites may include transcription of larger mRNA species than those observed in ectopic pathological sources of GHRH expression.

Regulation of human bone marrow lactoferrin and myeloperoxidase gene expression by tumor necrosis factor-alpha

Lactoferrin (LF) and myeloperoxidase (MPO) are glycoproteins synthesized in early myeloid cells (promyelocytes, myelocytes) and stored in granules of polymorphonuclear neutrophilic granulocytes. Both proteins are involved in the host inflammatory response, and LF has been found to have myelosuppressive activity in vivo and in vitro. Little is known, however, about the regulation of their production. We investigated the stability of LF and MPO mRNA and the effects of purified recombinant human TNF-alpha on LF and MPO levels in normal human bone marrow. Low density human bone marrow cells were cultured in the presence or absence of actinomycin D (10 micrograms/ml) or TNF-alpha (200 U/ml). LF and MPO RNA levels were analyzed by Northern blots using, respectively, a 650-bp insert from the plasmid pHL41, and a 2.3-kb insert from the plasmid pMPO2 as probes. It was found that: 1) LF mRNA is a fairly stable molecule, with a half-life of between 8 and 9 h, whereas MPO is less stable, with a half-life of between 4 and 5 h; 2) TNF-alpha decreases both LF and MPO mRNA levels, an effect seen by 24 h with MPO mRNA and 48 h with LF mRNA; 3) nuclear run-on assays revealed that TNF decreases transcription of the LF gene by 70% and the MPO gene by 50%; and 4) the suppressive effect of TNF-alpha on LF and MPO mRNA levels is not due to cell killing or selective differentiation and is reversible.

Regulation of human bone marrow lactoferrin and myeloperoxidase gene expression by tumor necrosis factor-alpha

Lactoferrin (LF) and myeloperoxidase (MPO) are glycoproteins synthesized in early myeloid cells (promyelocytes, myelocytes) and stored in granules of polymorphonuclear neutrophilic granulocytes. Both proteins are involved in the host inflammatory response, and LF has been found to have myelosuppressive activity in vivo and in vitro. Little is known, however, about the regulation of their production. We investigated the stability of LF and MPO mRNA and the effects of purified recombinant human TNF-alpha on LF and MPO levels in normal human bone marrow. Low density human bone marrow cells were cultured in the presence or absence of actinomycin D (10 micrograms/ml) or TNF-alpha (200 U/ml). LF and MPO RNA levels were analyzed by Northern blots using, respectively, a 650-bp insert from the plasmid pHL41, and a 2.3-kb insert from the plasmid pMPO2 as probes. It was found that: 1) LF mRNA is a fairly stable molecule, with a half-life of between 8 and 9 h, whereas MPO is less stable, with a half-life of between 4 and 5 h; 2) TNF-alpha decreases both LF and MPO mRNA levels, an effect seen by 24 h with MPO mRNA and 48 h with LF mRNA; 3) nuclear run-on assays revealed that TNF decreases transcription of the LF gene by 70% and the MPO gene by 50%; and 4) the suppressive effect of TNF-alpha on LF and MPO mRNA levels is not due to cell killing or selective differentiation and is reversible.

Construction of a recombinant human parvovirus B19: adeno-associated virus 2 (AAV) DNA inverted terminal repeats are functional in an AAV-B19 hybrid virus

To facilitate genetic analysis of the human pathogenic parvovirus B19, we constructed a hybrid B19 viral genome in which the defective B19 inverted terminal repeats were replaced with the full-length inverted terminal repeats from a nonpathogenic human parvovirus, the adeno-associated virus 2 (AAV). The hybrid AAV-B19 genome was rescued from a recombinant plasmid and then the DNA was replicated upon transfection into adenovirus 2-infected human KB cells in the presence of AAV genes coding for proteins required for AAV DNA replication (AAV-Rep proteins). In addition, in the presence of AAV genes coding for the viral capsid proteins (AAV-Cap proteins), the rescued/replicated hybrid AAV-B19 genomes were packed into mature AAV progeny virions, which were subsequently released into culture supernatants. The recombinant AAV-B19 progeny virions were infectious for normal human bone marrow cells and strongly suppressed erythropoiesis in vitro. The availability of an infectious recombinant B19 virus should facilitate the mutational analysis of the viral genome, which, in turn, may yield information on individual viral gene functions in B19-induced pathogenesis. The hybrid AAV-B19 genome may also prove to be a useful vector for gene transfer in human bone marrow cells.