Studies on sex-organ development. Changes in the oestrogenic response of the chick Müllerian duct as measured by chromatin template and ribonucleic acid initiation capacity.

Assays of transcription in vitro, with Escherichia coli RNA polymerase or wheat-germ RNA polymerase II, were used to characterize chromatin templates isolated from the left Müllerian duct of the chick embryo during normal development, and during development in the presence of diethylstilboestrol. Control Müllerian-duct template capacity with E. coli RNA polymerase decreased from 6.42% on day 10 to 4.34% by day 15 of development. Similar results were found with wheat-germ RNA polymerase II. In the presence of rifampicin and heparin, the prokaryotic enzyme transcribed a number-average RNA chain of 670 nucleotide residues, at an average rate of 110 nucleotide residues/min, from Müllerian-duct chromatin of all developmental stages. From day 10 to day 15 there was a 44% decrease in the number of initiation sites for E. coli RNA polymerase on Müllerian-duct chromatin. A 47% decline was observed when these chromatins were transcribed with excess RNA polymerase II in the presence of rifamycin Af/013. Signs of increasing responsiveness to oestrogen developed between days 10 and 16. Embryos exposed to maximally responsive doses of diethylstilboestrol for 2 days showed increases in Müllerian-duct chromatin template capacity, RNA-chain initiation sites, wet weight, protein and RNA. The changes seen in the oviduct of the 1-week-old chick injected for 2 days with diethylstilboestrol were defined as 100% responses. By comparison, the Müllerian duct, after exposure to diethylstilboestrol from day 10 to day 12, from day 13 to day 15 or from day 16 to day 18, showed a 15%, 39% and 72% template response respectively, and a 42%, 56% and 85% initiation-site change respectively. A similar developmental trend was observed in all parameters. It is concluded that oestrogenic responsiveness in the developing Müllerian duct increases from day 10 to nearly maximal values by day 16 of development, and that this transition is paralleled by a progressive restriction of genomic activity.