AN ANDROGEN RECEPTOR MESSENGER-RNA ISOFORM ASSOCIATED WITH HORMONE-INDUCED CELL-PROLIFERATION

The larynx of male Xenopus laevis undergoes an androgen-driven develop mental transformation that enables the adult to produce his complex ma te attraction song. During the early postmetamorphic period, androgen directs proliferation and differentiation of laryngeal muscle and cart ilage. To explore the cellular and molecular basis of androgen control , we have cloned an androgen receptor cDNA from juvenile larynx. Here we identify two androgen receptor mRNA isoforms, alpha and beta, diffe ring within the A/B, or hypervariable, domain. Northern blot analyses reveal that the beta isoform is transiently expressed during early juv enile stages, whereas the alpha transcript is expressed throughout pos tmetamorphic life. Using in situ hybridization and [H-3]thymidine auto radiography, we examined the expression of androgen receptor mRNA isof orms during androgen-evoked cell proliferation and differentiation. Th e alpha and beta transcripts are coexpressed in proliferating tissues of the juvenile larynx; in postmitotic differentiated tissues, only th e a transcript is expressed. Because androgen receptor beta mRNA is sp ecifically expressed during hormone-evoked cell proliferation, we prop ose that this developmentally regulated mRNA isoform is required for t he masculine program of cell addition within the developing vocal orga n.