Subtractive hybridization reveals tissue-specific expression of ahnak during embryonic development

The gene product ahnak has been identified from extra-embryonic mesoderm cD NA enriched using a subtractive hybridization approach modified for using s mall amounts of starting material. Clones for cyclin D2 and H19 have also b een isolated as being preferentially enriched in the extra-embryonic mesode rm compared with the embryo proper of embryonic day (E) 7.5 neural plate st age mouse embryos. The differential expression of these genes was confirmed at gastrulation stage using in situ hybridization. More detailed analysis of the human genomic ahnak sequence suggests that its highly repetitive str ucture was formed by unequal cross-over and gene conversion. During organog enesis, ahnak is expressed in a variety of tissues, including migratory mes enchyme. By E12.5, the major site of expression of ahnak is craniofacial me senchyme. Immunohistochemical analysis has shown that ahnak protein is expr essed mainly at the cell membrane of migratory mesenchymal cells, primarily in the nucleus of bone growth plate cells and mostly in the cytoplasm of d ifferentiating nasal epithelia. The potential functions of ahnak are discus sed in light of these results.