An estrogen-dependent secretory protein, which shares identity with chitinases, is expressed in a temporally and regionally specific manner in the sheep oviduct at the time of fertilization and embryo development.

Abstract

An estrogen (E2)-dependent 90,000-92,000 M(r) protein is synthesized and released by the sheep oviduct in a temporally and regionally specific manner during the first few days of pregnancy, where it associates with the embryo. The present study was undertaken to further define the nature of this protein and its regulation at a time when fertilization and early embryonic cleavage occur in the oviduct. The complete complementary DNA (cDNA) sequence for the 90,000-92,000 M(r) protein was determined, and steady state messenger RNA (mRNA) levels were measured during early pregnancy (estrus and days 1, 2, 3, 4, 6, and 16). The composite cDNA possessed an open reading frame of 1633 bases with a single potential N-glycosylation site. The inferred amino acid (aa) sequence predicted a prepolypeptide of 539 aa (69,151 M(r)) and a mature polypeptide of 518 aa (66,477 M(r)). Nucleotide and deduced aa sequence shared identity with translated E2-dependent cow, human, and partially sequenced baboon oviduct protein cDNAs; a human articular cartilage protein, gp 39; and chitinases. Northern blot hybridization revealed a single RNA species (2.2 kilobases) in the fimbria and ampulla, which was not detected in the isthmus or other reproductive and nonreproductive tract tissue RNAs. Steady state levels of mRNA encoding the 90,000-92,000 M(r) were highest in the fimbria and ampulla at estrus and on day 1 of pregnancy, when gamete transport and fertilization occur in the E2-dominated fallopian tube. Oviduct protein mRNA levels declined significantly (P < 0.05) on day 2 and underwent a further significant reduction on day 3 of pregnancy coincident with transport of the embryo from the oviduct to the uterus, a reproductive stage associated with rising progesterone levels. By day 16 of pregnancy, the mRNA encoding the E2-dependent oviduct protein was virtually undetectable. The temporally and regionally specific regulation of gene expression for the 90,000-92,000 M(r) E2-dependent protein correlates with protein synthesis data and emphasizes the precise regulation of its synthesis at a time when fertilization and embryonic cleavage are taking place in the oviduct. Identity with a growing class of steroid-regulated oviduct secretory proteins and chitinase enzymes suggests a possible structural and/or functional relationship, which may be important in mediating these latter reproductive events.