September 27, 2007
Over 20 years ago, scientists Glenn Northcutt and Carl Gans published two seminal papers that advanced what’s called the “New Head” hypothesis. The scientists proposed that in the distant past some invertebrate species passed through a series of transitional developmental stages that eventually produced the vertebrate head. Among the hypothesis’s four supportive claims is neural crest cells are utterly unique to vertebrates, and they played a fundamental role in the evolution of the vertebrate head, from fish to human. Left unanswered - and the subject of a great deal of research ever since - is how neural crest cells evolved from our invertebrate ancestors?
In the September issue of the journal Developmental Cell, a team of NIDCR grantees take a closer look at this question using the lamprey, a jawless, primitive vertebrate that straddles the evolutionary line just above invertebrates. Although endowed with a bona fide neural crest, the lamprey has some differences from higher vertebrates in both the pathways of its neural crest migration and types of derivative cells. This suggests an obvious evolutionary window to explore whether the molecular mechanisms of neural crest specification are similar or different between jawed and jawless vertebrates. In the study, the scientists isolated in the lamprey various components of a proposed gene regulatory network within its neural crest cells. Importantly, the scientists also were able to temporarily shut down various gene-activating transcription factors that are expressed early on as the neural crest forms. This work marks the first collective analysis of the function of a set of transcription factors within a purported vertebrate gene regulatory network. Comparing their data with those in the scientific literature from higher vertebrates, the scientists propose that “the upstream core of the network was fixed at the base of the vertebrate lineage more than 500 million years ago. However, some specifier and downstream effector genes, which function later in the regulatory network, appear to be more divergent and less evolutionarily constrained in their deployment.”