Six3 Expression Is Augmented In The Facial Primordia Of Mice With Misexpression Of Six2 Associated With Frontonasal Dysplasia

We have previously described the Br mutant mouse displaying heritable frontonasal dysplasia. Linkage analysis mapped the mutation near the homeobox transcription factor six2, normally expressed in the facial mesenchyme during development. The purpose of this study is to determine expression patterns of six2, as well as possible upstream and downstream targets of six2, in the developing midface. The three sets of facial prominences (medial, lateral, and maxillary) of E11.5 embryos were dissected and RNA extracted for qPCR assays and microarray analysis. Medial nasal prominences (MNP) were also taken for cell culture. qPCR results indicated six2 expression is highest in the MNP and demonstrated haploinsufficient down-regulation in each of the three facial prominence sets in the Br mouse. Microarray results suggested the misregulation of several genes in the Br midface, including another member of the Six family of transcription factors: six3. qPCR and immunohistochemistry for six3 substantiated its upregulation in the microarray. Future work using RNA interference on six2 will be used to investigate possible pathways involving six2 and six3. Preliminary results using an in vitro knockdown of six2, performed on an MNP cell culture system utilizing siRNA, demonstrated a 65% knockdown of six2. These results may enable further in vitro work in order to elucidate a pathway in the developing midface involving six2. Grant Funding Source : NIH R01DK064752 (SL) & NCRR 5P20RR024206 (SJS)