Identification of four CCCH zinc finger proteins in Xenopus, including a novel vertebrate protein with four zinc fingers and severely restricted expression

Tristetraprolin (TTP, the prototype of a class of CCCH zinc finger proteins , is a phosphoprotein that is rapidly and transiently induced by growth fac tors and serum in fibroblasts. Recent evidence suggests that a physiologica l function of TTP is to inhibit tumor necrosis factor alpha secretion from macrophages by binding to and destabilizing its mRNA (Carballo, E., Lai, W. S., Blackshear, P.J., 1998. Science, 281, 1001-1005). To investigate possib le functions of CCCH proteins in early development of Xenopus, we isolated four Xenopus cDNAs encoding members of this class. Based on 49% overall ami no acid identity and 84% amino acid identity within the double zinc finger domain, one of the Xenopus proteins (XC3H-1) appears to be the homologue of TTP. By similar analyses, XC3H-2 and XC3H-3 are homologues of ERF-1 (cMG1, TIS11B) and ERF-2 (TIS11D). A fourth protein, XC3H-4, is a previously unid entified member of the CCCH class of vertebrate zinc finger proteins; it co ntains four Cx(8)Cx(5)Cx(3)H repeats, two of which are YKTEL Cx(8)Cx(5)Cx(3 )H repeats that are closely related to sequences found in the other CCCH pr oteins, Whereas XC3H-1, XC3H-2, and XC3H-3 were widely expressed in adult t issues, XC3H-4 mRNA was not detected in any of the adult tissues studied ex cept for the ovary. Its expression appeared to be limited to the ovary, ooc yte, egg and the early embryonic stages leading up to the mid-blastula tran sition. Its mRNA was highly expressed in oocytes of all ages, and was enric hed in the animal pole cytosol of mature oocytes. Maternal expression was a lso seen with the other three messages, suggesting the possibility that the se proteins are involved in regulating mRNA stability in oocyte maturation and/or early embryogenesis. (C) 1999 Elsevier Science B.V. All rights reser ved.