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 t hyroid hormone (T-3)-dependent regulation of myosin heavy chain (myHC) genes in Xenopus tadpole dorsal muscle. One embryonic and one adult m yHC 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 exerte d transcriptional effects on mammalian embryonic and adult myHc promot ers injected into the same muscle. The kinetics and profiles of the tr anscriptional responses were superimposable on endogenous responses. T he results strengthen the use of in vivo approaches for determining th e roles of transcription factors and cis-regulatory sequences in integ rated contexts.