Mouse Wnt9b transforming activity, tissue-specific expression, and evolution

The members of the Wnt family of secreted factors have oncogenic potential and important roles as developmental regulators. We report an analysis of mouse Wnt9b (also called Wnt15 and Wnt14b), including its cDNA sequence, chromosomal mapping, epithelial cell transforming activity, adult and embryonic tissue expression patterns, and evolution. We also deduced the full-length amino acid sequence of its close relative, Wnt9a (also called Wnt14), from unannotated genomic DNA sequences in GenBank. Full-length comparisons among Wnt amino acid sequences provide evidence that Wnt9b and Wnt9a are close paralogs of each other and are orthologs of Wnt9 genes from shark and hagfish. Mapping Wnt9b to The Jackson Laboratory BSS interspecific backcross panel places it at 63.0 cM on chromosome 11. Sequence comparisons of two pairs of linked Wnt genes (the Wnt9a-Wnt3a pair and the Wnt9b-Wnt3 pair) suggest that they arose from the relatively recent duplication of a single ancestral Wnt gene pair, confirming the close paralogous relationship of Wnt9a and Wnt9b. Wnt9b expression is primarily restricted to the kidney in the adult mouse, with lower levels detected in the preputial gland, liver, and mammary gland. Testing of staged whole mouse embryos from 9.5 to 17.5 days of gestation showed expression at all stages with a peak at day 10.5. In situ hybridization analysis showed expression in most but not all tissues of the 16.5-day embryo. No significant elevation of Wnt9b expression was detected in 29 mouse mammary tumor virus-induced tumors. Overexpression of Wnt9b in C57MG mammary epithelial cells caused small transformed foci in cell monolayers and a moderate morphological transformation in pooled colonies compared with Wnt1.