A Wnt7a-Hoxa13 pathway for Müllerian duct fusion at the body midline for uterine morphogenesis

During embryonic development, the Müllerian ducts and adjacent mesenchyme differentiate into the tissues of the oviducts, uterus, cervix, and upper vagina. Variations in the fusion process can alter typical uterine morphology, correlating with an increased incidence of infertility, high-risk pregnancy, and miscarriage. We show that Wnt7a is required for Müllerian duct fusion at the body midline to generate the bipartite uterus of the mouse. Wnt7a null female mice form Müllerian ducts, but the ducts do not fuse at the midline resulting in a duplex reproductive tract (two separate uterine horns, two cervices, and two vaginas). Spatial transcriptome analysis of Wnt7a null and control fusion regions identified a downregulation of Hoxa13 in Wnt7a-null mesenchyme compared to wild type. Reduction in Hoxa13/HOXA13 is associated with didelphic uterine formation. These studies identify a Wnt7a-Hoxa13 genetic pathway that regulates uterine morphology. Overall design: Spatial transcriptomics is an approach that quantifies gene transcripts at specific locations in tissues. We used the NanoString GeoMx® Digital Spatial Profiling transcriptomic platform to analyze wild-type and Wnt7a null embryos at E13.5 (prior to Müllerian duct fusion) and E14.5 (at apposition of the two Müllerian ducts at the body midline with initial basement membrane breakdown) at the region of Müllerian duct fusion at the body midline. Three biological replicates for each genotype and time point were analyzed for a total of 12 biological replicates. Laminin immunofluorescence was used to identify Regions of Interest (ROI). ROI1 was the Müllerian duct epithelial cells (MDE), and ROI2 was the Müllerian duct mesenchymal cells (MDM) adjacent to the Müllerian ducts for a total of 24 ROIs.