Hedgehog-Wnt Crosstalk Orchestrates Submandibular Gland Morphogenesis in Mice

The development of the mouse submandibular gland (SMG) is a classic model for branching morphogenesis, orchestrated by key signaling pathways such as Hedgehog (Hh) and Wnt. While Sonic Hedgehog (Shh) is known to be essential for early SMG development, its downstream mechanisms and potential crosstalk with other pathways remain unclear. This study investigates the functional interaction between Hh and Wnt signaling during SMG morphogenesis. Using both in vivo (pharmacological inhibition in pregnant mice) and ex vivo (organ culture) models, we inhibited Hh signaling with vismodegib from embryonic day 13.5 (E13.5). Hh inhibition led to severe morphological defects, including reduced epithelial branching and disorganized ductal structures. As expected, the expression of Hh target genes Ptch1 and Gli1 was downregulated. Notably, Hh suppression resulted in a concomitant upregulation of Wnt pathway activity, evidenced by increased nuclear β-catenin and elevated expression of the target genes Axin2 and Lef1. This suggested that Hh signaling normally acts to repress Wnt activity during SMG development. Critically, the co-administration of the Wnt inhibitor XAV939 with vismodegib in ex vivo cultures partially rescued the branching defects caused by Hh inhibition. We conclude that Hh signaling promotes murine SMG morphogenesis, at least in part, by tonically inhibiting the Wnt pathway. This study unveils a novel inhibitory crosstalk between Hh and Wnt signaling that is essential for normal salivary gland development.