Practice question

Mice deficient in Wnt7a show dorsal-to-ventral transformation demonstrating dorsalizing role convincingly. Loss of dorsal Wnt7a eliminates Lmx1b expression in dorsal mesoderm, causing dorsal paw surfaces to form ventral-type footpads, ventral-like skin, absence of nails, double-ventral pattern with duplicate pads. Additionally Wnt7a is required to maintain SHH expression posteriorly; mutants exhibit shortened posterior digits and reduced posterior patterning. Phenotype reveals dual requirement for dorsal fate and posterior development. Engrailed1 expands dorsally in absence of Wnt7a, reinforcing ventralization and demonstrating reciprocal repression system governing dorsoventral axis establishment and maintenance.