DEVELOPMENTAL EXPRESSION OF GTP-BINDING PROTEINS IN RAT TESTES

The expression of guanine nucleotide-binding proteins (G proteins) dur ing the development of rat testes was investigated. Immunohistochemica l studies on frozen sections and isolated testicular cells demonstrate d that the expression of the GTP-binding proteins was developmentally regulated and specific for different cell types. The alpha subunit of the cholera toxin-sensitive stimulatory G protein (Gs alpha) was first detected in testes from 7-day-old rats; its value reached a maximum a t 23 days and then decreased to very low or undetectable amounts in te stes-of 45-day-old and adult rats (60-90 days of age). The Gs alpha su bunit appears to be expressed by Sertoli, peritubular myoid and inters titial cells. The common beta subunit (G beta) was present at air ages during development and was more prominent around the periphery of the tubules in younger animals but then became more evident in the cytopl asm of germ cells with increasing age. The pertussis toxin-sensitive i nhibitory G proteins, Gi1/2 and Gi3, showed a similar pattern of expre ssion. Sertoli cells and peritubular cells expressed Gi1/2 and Gi3 at very low levels at all ages, whereas pachytene spermatocytes and round spermatids expressed the inhibitory binding proteins only at later ag es of development (45-day-old and adult testis). Northern blot analysi s showed that with increasing age the Gs alpha mRNA in the testis decr eased and this was confirmed by in situ hybridization. These latter st udies showed localization of the transcripts to somatic cells but not to germ cells. Thus, the cellular expression of G proteins is temporal ly linked to testicular development and this suggests that there is an age-dependent regulation of the effects of hormones and intratesticul ar factors acting via G protein-linked receptor and effector systems.