Structure and expression of Strabismus 1 gene on human chromosome 1q21-q23

Xenopus Strabismus (Stbm) is a negative regulator of the WNT - β-catenin signaling pathway. Strabismus 1 (STB1/VangL2) and Strabismus 2 (STB2/Vangl1) are human homologues of Xenopus Stbm and Drosophila Stbm/ Van Gogh (Vang) STB1 and STB2 are four-transmembrane-type proteins with Dishevelled-binding motif. STB2 and CASQ2 genes are located on human chromosome 1p13.3-p11 with an interval less than 5 kb. Here, STB1 gene and CASQ1 gene were found to be located on human chromosome 1q21-q23 with an interval of about 210 kb including Nicastrin, COPA, PXF, H326 and PEA15 genes. Exon-intron structure was well conserved between STB1 and STB2 genes. STB1-CASQ1 gene cluster and STB2-CASQ2 gene cluster might be generated due to duplication of ancestral gene cluster, and several genes might be inserted into the STB1-CASQ1 intergenic region during or after gene-cluster duplication. STB1 mRNA was relatively highly expressed in prostate, trachea, thymus, lymph node, placenta, fetal kidney, fetal brain, and fetal lung. In adult brain, STB1 mRNA was more highly expressed in cerebellum, corpus callosum, amygdala, and medulla oblongata. STB1 mRNA was moderately expressed in K-562 (chronic myelogenous leukemia), G-361 (melanoma), and MKN7 (gastric cancer). On the other hand, STB1 mRNA was almost undetectable in several human cancer cell lines, and was down-regulated in 4 out of 14 cases of primary kidney tumors, and in 2 out of 3 cases of primary lung cancer. Loss-of-function mutation of STB1 gene might lead to carcinogenesis through activation of the WNT - β-catenin signaling pathway.