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.