An ancient evolutionary mechanism for the regulation of hemoglobin expression in vertebrate erythroid cells

In all jawed vertebrates (Gnathostomata) studied to date, one of the hemoglobin gene clusters is linked to the widely expressed Nprl3 gene. Where examined, introns of Nprl3 contain remote erythroid-specific enhancers which activate the linked hemoglobin genes. In sea lamprey (Petromyzon marinus), a jawless vertebrate (Agnatha), one of the hemoglobin clusters is also linked to an nprl3 orthologue suggesting that this regulatory mechanism may have been established in a common ancestor to Agnatha and Gnathostomata. Here, we show that the nprl3-linked hemoglobin locus of the river lamprey Lampetra fluviatilis corresponds to the Gnathostomata Nprl3-linked hemoglobin locus. Functional analysis demonstrates that an erythroid-specific enhancer located in intron 7 of lamprey nprl3 corresponds to the erythroid-specific hemoglobin enhancer (MCS-R1) present in the same intron of mammalian Nprl3. Thus, an nprl3-linked hemoglobin locus, regulated by a remote enhancer driving expression in erythroid cells, was established prior to the divergence of Agnatha and Gnathostomata.