Chicken epidermal growth factor (EGF): cDNA cloning, genomic organization, and characterization of its expression in the ovary

Abstract

Increasing evidences suggest that epidermal growth factor (EGF)plays important roles in the regulation of ovarian functions in mammals.However, in non-mammalian species, studies on EGF and its roles in theovary are rather limited, partially due to the limited sequence informationon EGF in lower vertebrates. In the present study, a full-length cDNAcoding for the precursor of EGF has been cloned from the chicken ovary.It encodes for a 1245 amino acid peptide and shares high sequencehomology (~50 %) with that of mouse, rat, and human. In comparisonwith mammalian EGF precursor, the extracellular domain of chickenEGF precursor contains a novel EGF-like motif at its N-terminal regionin addition to the mature EGF domain and 7 EGF-like motifs. Genomicstructure analysis reveals that chicken EGF gene consists of 25 exons,which spans over 52 kb in chromosome 4, and the novel EGF-like motifidentified is coded by an additional exon (exon 2). Although Northernblot analysis demonstrated that EGF is predominantly expressed in thebrain, muscle and pituitary, the mRNA of EGF was detected in all of thetissues examined when assayed by RT-PCR. Since EGF is capable ofstimulating chicken ovarian granulosa cell proliferation in vitro, therefore,we further examined the expression profiles of EGF and its receptor(EGFR) in the ovary. Interestingly, both EGF and EGFR were found tobe expressed not only in the developing ovarian follicles from adult chick-ens, but also in the growing ovaries from sexual immature chickens.These results suggest that chicken EGF plays an important role in con-trolling ovarian development, as has been demonstrated in mammals.