NOEL, Megan; RAMSEY, Mary; CREWS, David; BREUNER, Creagh; University of Texas, Austin; University of Texas, Austin; University of Texas, Austin; University of Texas, Austin: Cloning and Characterization of Corticosteroid Binding Globulin (CBG) in an Avian Species, Passer domesticus

Traditionally, stress research has focused solely on circulating hormone levels to gain estimates of the organismal stress response. However, there are binding globulins present in the plasma that can bind hormone, and limit access to target tissues. Corticosteroid Binding Globulins (CBG) can have significant effects altering the availability of stress hormone to target tissues. Thus, it is important to incorporate measures of these binding proteins into the analysis of stress physiology. CBG has been cloned in several mammalian species, and possibly one fish species (though this has been contested); but there are no known sequences from other vertebrates. We have cloned CBG from House sparrows (Passer domesticus). Using a nested primer strategy with degenerate primers derived from mammalian CBG sequences, we have cloned a 316 bp putative CBG fragment from house sparrow liver total RNA. CBG belongs to a large and conserved family of serine protease inhibitors, or serpins, so our primers were designed to span the conserved cysteine residue of the glucocorticoid-binding pocket. Sequencing results show 61% homology to human CBG at the amino acid level. With the sequence in hand, we can begin characterizing CBG mRNA expression in the liver as well as extra-hepatic tissues.