Conservation of steroidogenic acute regulatory (StAR) protein structure and expression in vertebrates

Complementary DNAs for the open reading frames of the chicken, Xenopus and zebrafish StAR homologs were cloned along with a partial cDNA of the zebraf ish homolog to MLN64, a StAR-related protein. A comparison of the amino aci d sequences of piscine. amphibian, avian and mammalian StARs, indicates str ong conservation of the protein across divergent vertebrate groups. On Nort hern blots probed with species specific StAR cDNAs, expression of StAR tran scripts was observed in the ovary and adrenal of chicken, and the ovary, te stis, kidney and head of zebrafish. The expression of StAR mRNA in various compartments of the hen ovary was consistent with the results of past studi es on steroidogenesis; expression was first observed in follicles selected into the preovulatory hierarchy and was greatest in the largest preovulator y Follicle. The expression of StAR mRNA was also consistent with aromatase expression in zebrafish ovaries. The conserved deduced protein sequence and expression pattern of StAR transcripts in chicken and zebrafish tissues, s trongly suggest that StAR is also involved in the regulation of steroidogen esis in nonmammalian vertebrates. (C) 2000 Elsevier Science Ireland Ltd. Al l rights reserved.