Use of heterologous DNA-based gene transfer to follow physiological, T-3-dependent regulation of myosin heavy chain genes in Xenopus tadpoles.

In vivo gene transfer and RNase protection assay were used to follow thyroid hormone (T-3)-dependent regulation of myosin heavy chain (myHC) genes in Xenopus tadpole dorsal muscle. One embryonic and one adult myHC form were measured by each approach. RNase protection assay showed that T-3 decreased expression of endogenous embryonic mRNA (E3), but increased adult (A7) transcripts. Gene transfer showed that T-3 exerted transcriptional effects on mammalian embryonic and adult myHc promoters injected into the same muscle. The kinetics and profiles of the transcriptional responses were superimposable on endogenous responses. The results strengthen the use of in vivo approaches for determining the roles of transcription factors and cis-regulatory sequences in integrated contexts.