Expression of 140-kDa neural cell adhesion molecule in developing testes in vivo and in long-term Sertoli cell-gonocyte cocultures

The basis for cell—cell adhesion in the seminiferous epithelium of the developing testis is doubtless critical in supporting events that are essential for the onset and maintenance of normal spermatogenesis. In this study, we applied immunoblotting and immunolocalization approaches for the following reasons: 1) to ask whether neural cell adhesion molecule (NCAM) underlies cell—cell interactions in vivo, as we previously showed for cells in vitro, 2) to characterize the isoform or isoforms of NCAM expressed during testicular development, and 3) to study NCAM expression in long‐term Sertoli cell—gonocyte cocultures and to compare and contrast this pattern of expression with that in vivo. Our findings indicate that NCAM is found ubiquitously at cell—cell interfaces within the semi‐niferous cord from birth through day 10 and thereafter is restricted to interstitial cells. Moreover, only polysialic acid—negative 140‐kDa NCAM is expressed in the testis or in coculture, an isoform whose properties are compatible with the concept of NCAM as both a direct modifier of cell function and an indirect influence on cell responses mediated by other external factors. In addition, we found that germ cells, potentially gonocytes or Type A spermatogonia, persist in long‐term cocultures maintained for 15 days after isolation from 5‐day‐old rat pups and that NCAM continues to be expressed at high levels in these cultures. This observation is in marked contrast to our observation that NCAM gradually decreases and eventually disappears in vivo by postnatal day 15. Thus, our findings indicate that 140‐kDa NCAM is prominent in neonatal testes but is down‐regulated by as yet unidentified mechanisms thereafter. Our findings also indicate that down‐regulation of NCAM fails to occur in hormone‐ and serum‐free Sertoli cell—germ cell cocultures.