The identification of Hoxc8 target genes.

Hox genes encode transcription factors that control spatial patterning during embryogenesis. To date, downstream targets of Hox genes have proven difficult to identify. Here, we describe studies designed to identify target genes under the control of the murine transcription factor Hoxc8. We used a mouse 16,463 gene oligonucleotide microarray to identify mRNAs whose expression was altered by the overexpression of Hoxc8 in C57BL/6J mouse embryo fibroblasts (MEF) in cell culture (in vitro). We identified a total of 34 genes whose expression was changed by 2-fold or greater: 16 genes were up-regulated, and 18 genes were down-regulated. The majority of genes encoded proteins involved in critical biological processes, such as cell adhesion, migration, metabolism, apoptosis, and tumorigenesis. Two genes showed high levels of regulation: (i) secreted phosphoprotein 1 (Spp1), also known as osteopontin (OPN), was down-regulated 4.8-fold, and (ii) frizzled homolog 2 (Drosophila) (Fzd2) was up-regulated 4.4-fold. Chromatin immunoprecipitation (ChIP) analysis confirmed the direct interaction between the OPN promoter and Hoxc8 protein in vivo, supporting the view that OPN is a direct transcriptional target of Hoxc8.