Identification of downstream transcriptional targets of Dlx5 during early mouse inner ear (otocyst/otic vesicle) development

ABSTRACT: Several transcription factors are known to be expressed in discrete regions of the otic vesicle and Dlx5 is one of those that is expressed highly in the presumptive dorsal vestibular region. Mice lacking Dlx5 have vestibular defects. Specifically, they fail to form the endolymphatic duct (a defect visible as early as E10) as well as the anterior and posterior semi-circular canals. The lateral canal does form but is smaller, whereas the saccule, the utricle and the cochlea appear relatively normal. The goal of this study was to use microarrays to identify differentially expressed genes between wild-type and Dlx5-null otic vesicles microdissected from E10 and 10.5 and identify downstream targets of Dlx5 by searching the immediate 3kb promoter regions of the differentially expressed genes for homeodomain binding sites followed by chromatin immunoprecipitation in an otic vesicle-derived cell line over-expressing Dlx5. Normal vestibular morphogenesis is compromised in mice lacking Dlx5, a member of the Distal-less family of homeobox transcription factors. We identified its direct downstream targets in the developing mouse inner ear by gene expression profiling wild-type and Dlx5 null otic vesicles from embryonic stages E10 and E10.5. Four hundred genes were differentially expressed in mutants when compared to wild-type in at least one of the two stages. To further constrain the list of likely direct targets of Dlx5, we examined the genomic DNA sequences in the 3kb promoter regions immediately proximal to the transcriptional start sites of these genes. We searched for (i) one or more previously described binding site for Dlx5, (ii) one or more novel 12bp-long motifs with a canonical homeodomain response element (HDRE) shared by promoters of two or more genes, and (iii) 100% conservation of the 12bp-long HDRE-containing motifs in promoter regions of human orthologs. Forty genes passed one or more of these filters, 12 of which are known to be expressed in the developing otic vesicle in domains that at least partially overlap with that of Dlx5 in one or both stages that we examined. Chromatin immunoprecipitation using a Dlx5 antibody confirmed direct binding of Dlx5 to promoter regions of seven of these genes (Atbf1, Bmper, Large, Lrrtm1, and Msx1, all of which were down-regulated in mutants, and Ebf1 and Lhx1, both of which were up-regulated in mutants) in an otic vesicle-derived cell line over-expressing Dlx5. Gene expression profiling of this cell line showed that Bmper and Lrrtm1 transcripts were up-regulated, further supporting their identification as direct targets of Dlx5 activity. Otic vesicles from wild-type and Dlx5-null embryos were microdissected from mouse developmental stages E10 and E10.5 and expression profiled in duplicate for each stage and genotype. Dlx5-transfected and empty vector-transfected 2B1 cell line samples were also profiled in duplicate (independent cell cultures).

ORGANISM(S): Mus musculus

SUBMITTER: Samin Sajan 

PROVIDER: E-GEOD-22381 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress