Neural crest, the great vertebrate innovation! Or not?
Neural crest-like cells were discovered in ascidians, although previously it was thought chordates other than vertebrates had neural crest. That is all the Neural crest markers are expressed in these cells and they give rise to pigment cells, one of the fates that neural crest also has in verterbrates.
Neural crest-like cells were discovered in ascidians, although previously it was thought chordates other than vertebrates had neural crest. That is all the Neural crest markers are expressed in these cells and they give rise to pigment cells, one of the fates that neural crest also has in verterbrates.
http://www.nature.com/nature/journal/v431/n7009/full/nature02975.htmlWe conclude that migratory neural crest-like cells are present in the ascidian Ecteinascidia. Although these cells could have evolved independently within the urochordate line or even within Ecteinascidia, HNK-1 and Zic expression suggests that they are likely to share a common origin with vertebrate neural crest cells. In support of a common evolutionary heritage of ascidian migratory cells and vertebrate neural crest cells, one of us (W.R.J.; manuscript in preparation) has recently discovered similar HNK-1 positive cells in four other ascidian species from evolutionarily diverse families. We therefore propose the following scenario for neural crest evolution in the chordates.
First, the neural tube/CNS attained the capacity to generate migratory pigment cells, possibly as a means to protect a sessile ascidian-like chordate ancestor from the harmful effects of sunlight in shallow marine habitats. These migratory pigment-generating cells may have been lost secondarily in amphioxus, which live buried in marine sediment and lack body pigmentation. Alternatively, it is conceivable that urochordates are the true sister group of vertebrates and that the migratory cells evolved in their common ancestor after the divergence of amphioxus from the chordate lineage. Later in chordate evolution, probably at or near the base of the vertebrate radiation, the primitive migratory cells gained additional functions and/or were joined by other cell types to generate the multiple derivatives characteristic of the neural crest.