title: N-terminal region of progesterone receptor B isoform in human spermatozoa.
abstract: Progesterone is known to act on human spermatozoa by an unidentified membrane receptor. Previous studies have demonstrated the existence of transcripts of conventional progesterone receptor (PR) in sperm RNA; antibodies directed against the C-terminal region of the conventional PR recognize a protein in sperm extracts. The present study aimed at characterizing the sperm PR using probes unique to the N-terminal region of the PR-B isoform. PR-B transcripts that were homologous to the conventional PR were detected in sperm RNA and localized in the midpiece region. Using specific antibody against the N-terminal region of PR-B, strong immunoreactivity was observed on the acrosomal region of digitonin-treated spermatozoa; Western blot analysis revealed a single band of approximately 55 kDa. Immunogold labelling studies using the same antibody localized the protein at the inner acrosomal membrane of testicular spermatids. This antibody blocked the binding of fluorescent-tagged progesterone to digitonin-treated spermatozoa and inhibited the progesterone-mediated kinase activation. The results of the present study gives an insight to speculate that the sperm membrane PR may have homology at the N-terminal region of the conventional PR-B isoform, or the membrane PR protein may share structural motifs that allows progesterone binding and interactions with the antibodies against the conventional PR.
authors.affiliation: Primate Biology Division, National Institute for Research in Reproductive Health, Indian Council of Medical Research, Jehangir Merwanji Street, Parel, Mumbai 400-012, Maharashtra, India.
authors.forename: Chirag
authors.initials: C
authors.lastname: Shah
authors.forename: Deepak
authors.initials: D
authors.lastname: Modi
authors.forename: Geetanjali
authors.initials: G
authors.lastname: Sachdeva
authors.forename: Sushama
authors.initials: S
authors.lastname: Gadkar
authors.forename: Serena
authors.initials: S
authors.lastname: D'Souza
authors.forename: Chander
authors.initials: C
authors.lastname: Puri
mesh_terms: D000595:Amino Acid Sequence; D006801:Humans; D008297:Male; D011374:Progesterone / Q000378:metabolism / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism; D011980:Receptors, Progesterone / Q000737:chemistry* / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013094:Spermatozoa / Q000737:chemistry* / Q000378:metabolism
chemical_list: D011980:Receptors, Progesterone; C097314:progesterone receptor B; D011374:Progesterone; D011494:Protein Kinases