Prdm16 and Mecom mutants exhibit cleft secondary palate as a result of perturbations that affect different stages of palatogenesis

The paralogous Prdm16 and Mecom transcription factor genes play widespread and important roles during mouse embryogenesis and postnatal development. Each gene is required for the maintenance of various stem cell populations (i.e. hematopoietic and neuronal stem cells). Our studies have focused on increasing understanding of Prdm16 function in developing orofacial structures, specifically mandible, tongue and palate. Prdm16 loss‐of‐function mutations result in cleft secondary palate (CP) due to failed palate shelf elevation secondary to micrognathia. This mechanism of clefting models that observed in human Pierre Robin Sequence CP. We are examining the requirement for Prdm16 during palate formation through neural crest‐, mandible‐ and palate‐specific ablation or rescue of Prdm16 using an invertible conditional gene trap null allele of Prdm16 . These experiments largely support a palate‐extrinsic mechanism of clefting in Prdm16 mutants, since null and mandible‐specific Prdm16 mutant embryos exhibit micrognathia and CP and palate‐specific loss results in CP with reduced penetrance. To characterize the underlying cellular defects, we are assessing cell proliferation and apoptosis in the palate shelves and Meckel's cartilage. We also continue to screen craniofacial markers by in situ hybridization and have carried out RNA‐seq expression profiling in the developing mandible of wt and Prdm16 mutant embryos to identify and validate differential gene expression as a consequence of Prdm16 loss. We also hypothesized that Mecom is also required during orofacial development. Mecom or Mds1‐Evi1 complex locus includes the genes Mds1 and Evi1 and the product of intergenic splicing, Mds1‐Evi1 . This study characterizes two targeted Mecom alleles, Evi1 ko1 ( ko1 ) and Evi1 ko3 ( ko3 ), which knockout Evi1 alone or both Evi1 and Mds1‐Evi1 , respectively. To maintain a consistent strain background as our Prdm16 mutants, we initiated a series of successive outcrosses matings between Mecom heterozygotes and FVB/NJ mice. We observed incompletely penetrant CP in ko1 homozygotes examined at birth after the 4 th generation, although this penetrance did not increase beyond 25% by the 10 th generation (F10). In contrast, ko3 homozygous mutants exhibit CP with very high, but incomplete penetrance by F10. Histologic assessment of coronal head sections showed that mutant palate shelves had elevated but failed to fuse at the midline, in contrast to Prdm16 mutants that exhibit failed palate shelf elevation. To explore a potential genetic interaction between Prdm16 and Mecom , we examined Prdm16; Mecom ( ko3 ) double heterozygous newborn pups and identified CP with high penetrance. Interestingly, these pups show both pre‐ and post‐elevation CP. These studies demonstrate a requirement for both Prdm16 and Mecom during normal palate formation, albeit via alternate mechanisms, and also evidence for the influence of Prdm16‐Mecom genetic interactions. Support or Funding Information NIH/NIDCR R15 DE023982 and Intramural funding from the Midwestern University Office of Research and Sponsored Programs and College of Health Sciences Biomedical Sciences Program. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .