THE MOUSE TRANSCRIPTION FACTOR STAT4 IS EXPRESSED IN HAPLOID MALE GERM-CELLS AND IS PRESENT IN THE PERINUCLEAR THECA OF SPERMATOZOA

STAT (signal transducer and activator of transcription) proteins have been shown to be essential transcription factors which mediate biologi cal effects of cytokines. Although most of the STATs have been shown t o be widely expressed, Stat4 mRNA has been detected in only a few tiss ues, including the testis, In the present study, immunoblot analysis c onfirmed that the presence of Stat4 protein was similarly restricted, with the highest level observed in testis. In situ hybridization, immu noblot, and immunohistochemistry analyses revealed that in the testis, Stat4 was abundantly and exclusively expressed in male germ cells whi ch have completed meiosis, at the round and elongating spermatid stage s, Cytolocalization at various times of spermatid differentiation show ed that the level of Stat4 protein increased in parallel in both cytop lasm and nuclei, No specific nuclear translocation that would have bee n an indicator of Stat4 activation was observed at any stage of sperma togenic differentiation. Interestingly, the Stat4 transcription factor was localized to the condensing perinuclear theca of spermatids, a lo calization that was confirmed by selective biochemical extraction of t hecal proteins, Since the theca is known to depolymerize in the cytopl asm of the oocyte during the hours following fertilization, we hypothe sized that sperm Stat4 would represent an original paternal contributi on to the fertilized egg which may be involved in the onset of zygotic transcription.