EXPRESSION OF 140-KDA NEURAL CELL-ADHESION MOLECULE IN DEVELOPING TESTES IN-VIVO AND IN LONG-TERM SERTOLI CELL-GONOCYTE COCULTURES

The basis far 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 approach es for the following reasons: 1) to ask whether neural cell adhesion m olecule (NCAM) underlies cell-cell interactions in vivo, as we previou sly showed for cells in vitro, 2) to characterize the isoform or isofo rms of NCAM expressed during testicular development, and 3) to study N CAM expression in long-term Sertoli cell-gonocyte cocultures and to co mpare and contrast this pattern of expression with that in vivo. Our f indings indicate that NCAM is found ubiquitously at cell-cell interfac es within the seminiferous cord from birth through day 10 and thereaft er 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 bo th a direct modifier of cell function and an indirect influence on cel l responses mediated by other external factors. In addition, we found that germ cells, potentially gonocytes or Type A spermatogonia, persis t in longterm cocultures maintained for 15 days after isolation from 5 -day-old rat pups and that NCAM continues to be expressed at high leve ls in these cultures. This observation is in marked contrast to our ob servation that NCAM gradually decreases and eventually disappears in v ivo by postnatal day 15. Thus, our findings indicate that 140-kDa NCAM is prominent in neonatal testes but is down-regulated by as yet unide ntified mechanisms thereafter. Our findings also indicate that down-re gulation of NCAM fails to occur in hormone-and serum-free Sertoli cell -germ cell cocultures.