CLONING OF AN AVIAN ANTITHROMBIN - DEVELOPMENTAL AND HORMONAL-REGULATION OF EXPRESSION

We present the complete amino acid sequence of a non-mammalian antithr ombin together with a structural comparison to its mammalian homologs. In the majority of cases, but not all, the analyses indicate high deg rees of primary structural identity within regions of predicted or dem onstrated functional importance. We have also taken advantage of the a vian model to define the ontogeny of antithrombin mRNA expression. Nor thern analyses indicate chicken antithrombin mRNA levels to be detecta ble in the liver early during development and increase to reach adult levels just prior to hatching. Although no sex-dependent differences i n antithrombin mRNA levels were detected, the administration of estrog en to male roosters was observed to cause a 3-fold decrease in antithr ombin mRNA levels, suggesting that the hormone may alter circulating a ntithrombin levels via a pre-translational mechanism.