• cleft lip;
  • craniofacial development;
  • microRNA;
  • mouse;
  • p63

Clefts of the lip and palate are thought to be caused by genetic and environmental insults but the role of epigenetic mechanisms underlying this common birth defect are unknown. We analyzed the expression of over 600 microRNAs in the murine medial nasal and maxillary processes isolated on GD10.0–GD11.5 to identify those expressed during development of the upper lip and analyzed spatial expression of a subset. A total of 142 microRNAs were differentially expressed across gestation days 10.0–11.5 in the medial nasal processes, and 66 in the maxillary processes of the first branchial arch with 45 common to both. Of the microRNAs exhibiting the largest percent increase in both facial processes were five members of the Let-7 family. Among those with the greatest decrease in expression from GD10.0 to GD11.5 were members of the microRNA-302/367 family that have been implicated in cellular reprogramming. The distribution of expression of microRNA-199a-3p and Let-7i was determined by in situ hybridization and revealed widespread expression in both medial nasal and maxillary facial process, while that for microRNA-203 was much more limited. MicroRNAs are dynamically expressed in the tissues that form the upper lip and several were identified that target mRNAs known to be important for its development, including those that regulate the two main isoforms of p63 (microRNA-203 and microRNA-302/367 family). Integration of these data with corresponding proteomic datasets will lead to a greater appreciation of epigenetic regulation of lip development and provide a better understanding of potential causes of cleft lip.