Ontogeny and regulation of variant thyroid hormone receptor isoforms in developing rat testis

High affinity-low capacity nuclear triiodothyronine (T-3) receptors (TRs), identified as a product of c-erbA alpha proto-oncogene, are expressed in pr epubertal rat Sertoli cell. At this age, exogenous T-3 treatment as well as hypothyroidism affects Sertoli cell functions. We examined the ontogenetic expression pattern of TRs in the rat testis. Northern analysis confirms th at TRs are expressed at high level from fetal development until prepubertal period. RNase protection analysis demonstrates that TRalpha 2, the variant isoform of TRalpha 1, is constitutively expressed at all ages, while TRalp ha 3 is absent in the adult gonad. While TRalpha 1 and TRalpha 2 expression declines during development, Rev-erbA(alpha) (Rev), the antisense mRNA enc oded by the same c-erbA(alpha) genomic locus, increases beginning 5 days af ter birth and maximizing in adulthood. TRalpha 1, TRalpha 2, and Rev mRNA(s ) do not appear to be directly regulated by thyroid hormone in testis; howe ver, short-term neonatal hypothyroidism leads to the expression of TRalpha 1 and its variant in adult testis, which is absent in control coeval animal s. Thus, during development of rat testis, the levels of messages of genes encoded in the c-erbA(alpha) genomic locus have different ontogenetic contr ol. The ontogenetic profile of TRalpha 1 and its variant isoforms within th e seminiferous epithelium suggests that these receptors are involved in the differentiation of the male gonad. (J. Endocrinol. Invest. 22: 843-848, 19 99) (C) 1999, Editrice Kurtis.