Control of limb initiation and antero-posterior patterning by Meis transcription factors
Meis1 and Meis2 are highly similar homeodomain transcription factors that regulate organogenesis through cooperation with Hox proteins. Elimination of Meis genes after limb induction has shown their role in limb proximo-distal patterning; however, limb development in the complete absence of Meis function has not been studied. Meis1 and Meis2 are co-expressed during limb development, first in the lateral plate mesoderm before limb induction and then becoming restricted to a proximal domain of the growing limb bud. Here, we report that complete double conditional Meis1/2 inactivation in the lateral plate mesoderm leads to limb agenesis. Meis factors converge with Tbx factors in this function, extensively co-binding with Tbx to genomic sites and co-regulating enhancers of Fgf10, a critical factor in limb initiation. Limbs with three deleted Meis alleles develop a complete PD set of limb skeletal elements, but show proximal-specific skeletal hypoplasia and agenesis of posterior skeletal elements. This failure in posterior skeletal element specification reveals an early role of Meis factors in establishing the limb AP prepattern required for Shh activation at later stages. Our results uncover novel roles for Meis transcription factors in early limb development and identify their involvement in new molecular interaction networks that regulate organogenesis.