Evolutionary strategies for the elucidation of cis and trans factors that regulate the developmental switching programs of the beta-like globin genes.

We describe three strategies for the identification of specific cis and trans factors that regulate globin gene expression, all three of which are based on the evolution of the globin genes and their expression patterns. The first approach, phylogenetic footprinting, relies on a search for sequence similarities and is designed to elucidate the factors that control those expression patterns which are shared by orthologous globin genes of all eutherian mammals (e.g., the expression of the epsilon globin genes in the embryonic yolk sac and its repression in fetal and adult hematopoietic tissues). The second approach, differential phylogenetic footprinting, relies on a search for sequence differences. This approach may be of value in identifying the mechanisms underlying the generation of novel expression patterns in specific lineages (e.g., the expression of gamma as a fetal gene in the simian primates in contrast with the embryonic expression of gamma in all other mammals). Finally, motif-based phylogenetic analysis takes into consideration the fact that many transcription factors are quite flexible in the recognition of their cognate sites. The approach allows the detection of functionally conserved binding sites despite their sequence variation.