Steady-state cystatin mRNA levels in chicken tissues in response to estrogen

A full length cDNA clone coding for the cysteine proteinase inhibitor, chicken cystatin, was used to hybridize to RNA extracted from various tissues of the hen during several well defined stages of the 25 h ovulatory cycle. Measurements were made immediately after egg-laying (ovulation), 6 h prior to ovulation (estrogen surge), and 16 h prior to ovulation (minimum estrogen levels). Cystatin was expressed in all tissues examined, being most abundant in lung, followed by brain, heart, oviduct, pectoral muscle, and liver in decreasing order. There were no significant differences in the cystatin mRNA levels at the three different time points for any of the tissues examined, and no differences in the 0.95 kb size of the message. Pharmacological doses of estradiol administered to immature female chickens decreased the steady-state cystatin mRNA levels as analyzed by Northern blots. There were no differences in the pattern of expression in the different tissues between rooster and hens. Our data suggest that estrogen has no direct effect on the regulation of cystatin expression in chicken tissues.