d4 family genes: Genomic organization and expression

A family of closely related genes, named the d4 family, has been previously identified in mammals. It comprises three genes encoding structurally related proteins. The hallmark of the family is D4 domain—a double-paired finger motif that consists of two tandemly arranged PHD finger domains. These genes are expressed in various tissues and at various developmental stages. Two of those, neuro-d4 and cer-d4, are strictly neurospecific and their expression is developmentally regulated. Another gene, ubi-d4/Requiem is ubiquitously expressed in all embryonic and adult tissues at the same levels. d4 family genes are evolutionary conserved. Human, mouse, rat, and chicken d4 genes have been cloned. The only d4-like gene was found in the genome of nematode C. elegans and hydra H. magnipapillata. The sole member of d4 family was identified also in the genome of D. melanogaster. However, d4 genes are not believed to be present in the genomes of prokaryotes and yeast. This review describes genomic organization and expression of d4 family genes in vertebrates.