Cloning and uterus/oviduct-specific expression of a novel estrogen-regulated gene (ERG1)

The steroid hormone estrogen profoundly influences growth and differentiation programs in the reproductive tract of cycling and pregnant mamals. It is thought that estrogen exerts its cellular effects by regulating the expression of specific target genes. We utilized a messenger RNA differential display method to identify the genes whose expression is modulated by estrogen in the preimplantation rat uterus. Here we report the cloning of a novel gene (ERG1) that is tightly regulated by estrogen in two key reproductive tissues, the uterus and oviduct. Spatio-temporal analyses reveal that ERG1 mRNA is expressed in a highly stage-specific manner in the uterus and oviduct, and its expression is restricted to the surface epithelium of both of these tissues. Nucleotide sequence analysis of the full-length ERG1 cDNA indicates that it has an open reading frame of 1821 nuceotides encoding a putative protein of 607 amino acids with a single transmembrane domain and a short cytoplasmic tail. The extracellular part of the protein contains several distinct structural motifs. These include a zona pellucida binding domain, which is present in a number of proteins such as the zona pellucida sperm binding proteins, and uromodulin, In addition, there is a repeat of a motif called CUB domain, which exists in a number of genes involved in development and differentiation such as bone morphogenetic protein 1 (BMP1). Although the precise function of ERG1 eludes us presently, its unique pattern of expression in the uterus and oviduct and its regulation by estrogen, a principal reproductive hormone, lead us to speculate that this novel gene plays an important role in events during the reproductive cycle and early pregnancy.