ARGININE VASOTOCIN GENE-EXPRESSION AND HORMONE SYNTHESIS DURING ONTOGENY OF THE CHICKEN-EMBRYO AND THE NEWBORN CHICK

Chicken embryos at different developmental stages (embryonal day (E) 6 to 21) and chicks at posthatch day 1 (Dl) were monitored for the deve lopment of their hypothalamo-neurohypophysial system as indicated by t he kinetics of arginine vasotocin (AVT) gene expression via mRNA conce ntration and brain AVT content. Our data concerning the onset of gene expression support previous results from our laboratory and others abo ut an early activation of the AVT gene transcriptional and translation al activity around E6. We could detect measurable amounts of AVT in ch icken embryo brains at E6 and an exponential increase during further d evelopment until Dl. Dot blots of hypothalamic RNA extracts indicated that AVT gene transcript concentrations rose between E12 and E17 and s lightly dropped thereafter. Northern hybridization showed that this dr op was caused by a decrease of full length message and an increase of smaller transcripts during late embryonal and Dl stages, probably an A VT mRNA specific degradation phenomenon. The dissociation between the increase of AVT concentration and AVT mRNA concentration visible at th e Dl stage might be due to accumulation and storage of AVT in the magn ocellular neurons, preferentially in their axon terminals in the neuro hypophysis. Blood samples taken from E14 onwards revealed a constant i ncrease in plasma osmolality and plasma AVT concentration. Our data su ggest that, in the chicken, AVT seems to be required early during embr yonal development, either for osmoregulatory or further unknown functi ons.