Developmental expression of the angiotensinogen gene in rat embryos

Angiotensin II is a potent octapeptide vasoconstrictor and regulator of cardiovascular and electrolyte homeostasis. Angiotensinogen, the protein precursor of angiotensin II, is synthesized by the liver and many other organs of the adult rat. To determine whether angiotensin may be present in early fetal development we analyzed rat embryonic tissues (chorionic membranes, head, and body) for the expression of the angiotensinogen gene during days 11-21 of embryogenesis. Angiotensinogen mRNA was detected at low levels in embryo bodies and yolk sac placenta from day 11 of gestation. An initial rise in the level was noted on day 13, reaching a plateau from day 17 of gestation to birth. Angiotensinogen mRNA levels of the embryonic head were about 10-fold less than those of the body on days 17-19 and increased to levels similar to those of the body on days 20-21. Angiotensinogen mRNA levels of the yolk sac placenta were about 20-fold higher than those in the embryonic body, but no angiotensinogen mRNA was detected in the chorioallantoic placenta. Angiotensinogen mRNA from both embryos and yolk sac placenta was larger by about 200 bases than the mRNA obtained from adult rat liver; this was shown to be a consequence of both the utilization of more distal polyadenylation sites and a longer poly(A) tract. These observations suggest the possibility of a biological function for angiotensinogen in the early development of the rat, and that polyadenylation site selection may alter the functional expression of the angiotensinogen gene in a developmentally specific manner.