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Activin is a dimeric glycoprotein hormone that was initially characterized by its ability to stimulate pituitary FSH secretion and was subsequently recognized as a growth factor with diverse biological functions in a large variety of tissues. In the testis, activin has been implicated in the auto/paracrine regulation of spermatogenesis through its cognate cell membrane receptors on Sertoli and germ cells. In this study we provide evidence for intranuclear activin/inhibin βAsubunit and show its distribution in the rat seminiferous epithelium. We have shown by transient expression in HeLa cells of β-galactosidase fusion proteins that the βAsubunit precursor contains a functional nuclear localization signal within the lysine-rich sequence corresponding to amino acids 231-244. In all stages of the rat seminiferous epithelial cycle, an intense immunohistochemical staining of nuclear βAwas demonstrated in intermediate or type B spermatogonia or primary spermatocytes in their initial stages of the first meiotic prophase, as well as in pachytene spermatocytes and elongating spermatids primarily in stages IX–XII. In some pachytene spermatocytes, the pattern of βAimmunoreactivity was consistent with the characteristic distribution of pachytene chromosomes. In the nuclei of round spermatids, βAimmunoreactivity was less intense, and in late spermatids it was localized in the residual cytoplasm, suggesting disposal of βAbefore spermatozoal maturation. Immunoblot analysis of a protein extract from isolated testicular nuclei revealed a nuclear βAspecies with a molecular mass of approximately 24 kDa, which is more than 1.5 times that of the mature activin βAsubunit present in activin dimers. These results suggest that activin/inhibin βAmay elicit its biological functions through two parallel signal transduction pathways, one involving the dimeric molecule and cell surface receptors and the other an alternately processed βAsequence acting directly within the nucleus. According to our immunohistochemical data, βAmay play a significant role in the regulation of nuclear functions during meiosis and spermiogenesis.

Antibodies against synthetic peptides selected from the amino acid sequences of human inhibin α- and β β β A-subunits were used to examine the distribution of inhibin subunit immunoreactivity in chicken embryos during the first week of development. Inhibin α.-subunit immunoreactivity was localized in skeletal and smooth muscle myoblasts as well as developing cardiac muscle cells. In somites, immunostaining was seen exclusively in myotomes. The appearance of α.-subunit immunore-activity was correlated with myogenic differentiation; immunoreactivity was not seen in non-differentiated mesenchymal cells or in terminally differentiated adult muscle cells. In cardiac muscle, some immunopositive myocytes were seen also in the adult. In the adult heart, the Purkinje fibers were strongly immunoreactive, suggesting a possible role of the immunoreactive protein in the impulse-conducting function of these specialized cells. Inhibin α.-subunit immunoreactivity was also seen in the visceral and parietal cells of the Bowman’s capsule in both mesonephric and metanephric kidneys. In addition to mesodermal derivatives, α.-subunit immunoreactivity was localized in neuroepithelial cells and axons in the developing central nervous system. Immunoblotting with anti-α.(1-32) revealed two protein bands with Mr values of 50 000 and 32 000 in cytosol samples of whole embryos under nonreducing conditions. In reduced samples an approximately 14 000 Mr protein species was detected. Inhibin β A-subunit immunoreactivity was detected only in chondrocytes, suggesting that the immunoreactive protein might represent a chicken homologue of the various cartilage and bone morphogenetic proteins expressed in mammals.

To determine if fertilization occurs unnoticed among Norplant users who are ovulatory.

The importance of monitoring luteinizing hormone (LH) secretion during gonadotropin stimulation remains controversial. In the present study, the authors evaluated the occurrence of spontaneous LH surges in 170 cycles stimulated by clomiphene citrate and human menopausal gonadotropin, and correlated the success rate of embryo cleavage to the time interval between the occurrence of the LH surge peak value and the time of human chorionic gonadotropin (hCG) administration. LH was quantitated from urine by an avidin-biotin enzyme immunoassay. The results indicated that a spontaneous LH surge occurred in 18% of the cycles. The number of oocytes recovered was not affected by the occurrence of a spontaneous LH surge. In 12% of all cases, the spontaneous LH surge occurred less than 12 hours before the administration of hCG, and in these cases embryo cleavage was not reduced. In 6% of all cases, the spontaneous LH surge occurred over 12 hours before hCG administration, and in these cases embryo cleavage was reduced significantly.

The expression of progesterone receptor (PR) and its induction by oestradiol during the embryogenesis of the chick bursa of Fabricius (BF) were studied by immunohistochemistry using three different polyclonal antibodies to the chicken oviduct PR. Mesenchymal cells of the cloacal area surrounding the bursa primordium in controls (without exogenous oestrogen) express the PR between 9 and 11 days of incubation. In the same cells, PR was induced experimentally by oestradiol at 9 days. Mesenchymal cells in the bursa did not express PR after oestradiol treatment before the age of 11 days. The PR was not inducible in the bursal epithelium or in haemopoietic cells. None of the bursal cells expressed the PR to a detectable level during embryonic life without exogenous treatment. Some haemopoietic cells showed strong artefactual staining in their nuclei. It is concluded that (1) the embryonic bursa of Fabricius is a sex-steroid-sensitive organ, (2) exogenous oestradiol is able to induce progesterone receptor in the mesenchymal cells, but (3) the PR is not expressed without exogenous oestrogen. This indicates that the PR becomes oestrogen inducible well before it is naturally expressed during sexual maturation and that the level of endogenous oestrogen during embryonic life is not high enough to affect the bursa significantly.