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. http://www.nature.com/nature/journal/v431/n7009/full/nature02975.html
Spurious, I like your posts, but they're sucking my life away. It takes me hours to just skim the surface of the fascinating topics you share!
The interesting thing about the Neural crest cells is that they are a 'new' cell type! A epithelial cell that can migrate through the body and undergo epithelal-mesenchymal transformation. That goes quite a lot further than 'inventing' a new structure, or allowing new functions for genes by duplicating genes and then modifying them. A whole new type of cells that give rise to a whole new set of structures. But how did they arise in evolution? They can't just come out of nothing. So this kind of research is addressing this basic question. How did neural crest come about. The authors in the paper I mentioned in the previous post suggest that an ancestor of vertebrates and urochordates (ascidians) did evolve neural crest cells before the lines split up. And it could be suggested that the first function of these new cells was to become pigment cells. --------- wikipedia http://en.wikipedia.org/wiki/Neural_crest Please Register or Log in to view the hidden image!
basically there are three main tissue types, derived from 3 germlayers formed during embrygenesis. Ectoderm, endoderm and mesoderm. Here is a general Wiki link: http://en.wikipedia.org/wiki/Germ_layer The ectoderm gives rise to the surface tissues (epithelium) on the outside of the body, such as the skin (well, only the surface, deeper down the skin consists of mesodermal tissue). The endoderm gives rise to endothelia tissues (the surface tissue inside the body, such as the lining of your gut). The mesoderm gives rise to all the tissues inbetween (mesenchyme). And there is the neural crest of course in vertebrates. It's often referred to as the 4th germ layer, but it is formed much later during development and starts of as an ectodermal tissue. It's formed from cells of the developing neural tube. The cells then migrate through the body through different migratory pathways. And end up in weird places. One such place is for instance underneath the oral epithelium inside the developing mouth. The original ectodermal tissue of the neural crest is transformed into mesoderm to form the dental mesenchyme. A transformation from ectoderm to mesoderm. The characteristics of being an epithelial cell are lost and the cell acquires mesenchymal properties.
This could provide a non-controversial substitute for embryonic stem cells. Embryonic stem cells are unique, because they can differentiate into any cell type of the body. Their use, however, raises ethical concerns because embryos are being destroyed in the process. In contrast, neural crest stem cells from adults have several advantages: similar to embryonic stem cells, they have the innate ability to differentiate into many diverse cell types; they are easily accessible in the skin of adults; and the patient's own neural crest stem cells could be used for cell therapy. The latter avoids both rejection of the implant and graft-versus-host disease. Studies in the mouse showed that neural crest stem cells from adult hair follicles are able to differentiate into neurons, nerve supporting cells, cartilage/bone cells, smooth muscle cells, and pigment cells. Preliminary data indicate that equivalent stem cells reside in human hair follicles. The goal of our research is to apply neural crest stem cells from adult hair follicles in cell replacement therapy in selected instances. This may include, spinal cord injury, Parkinson's disease, multiple sclerosis, Hirschsprung's disease, peripheral neuropathies, certain defects of the heart, and bone degeneration. Though promising, this research is still in the animal testing stage. Additional research is required before it could benefit patients.
The neural crest are stem cells. More accurately: neural crest stem cells. The neural crest is a population of stem cells that migrate and differentiate extensively during development. Neuralation evolved out of the dorsal hollow nerve cord that all Urochordata have. You know this. Amphioxus is the standard used as the evolutionary model for the origin of the neural crest in phylogeny. Homologous structure to the neural crest is also seen in deuterostome invertebrates such as in lamprey, agnathan. The regulation of undifferentiated neural crest cells in embryonics is the same as stem cell research - the evolution of the differentiated functions - and this is a hot area of research. "Measurements of organismal complexity in relation to the genome and evolution....it seems useful to consider certain simplifying assumptions about organismal complexity. The most extreme simplification is to consider only the most drastic changes in organismal complexity as relevant landmarks for comparisons. Among multicellular eukaryotes such changes might include the origin of new embryological tissue layers, i.e., the emergence of the diploblastic, triploblastic and neural crest tissue layers and the structures derived from them." See: Stellwag, Edmund J. (2004) "Are Genome Evolution, Organism Complexity and Species Diversity Linked?" Integrative and Comparative Biology 2004 44(5):358-365. http://icb.oxfordjournals.org/cgi/content/full/44/5/358
"Following ablation of neural crest cells, replacement neural crest cells migrate into gaps, most frequently from anterior/posterior locations. Cells from surrounding epidermal and neural ectoderm may have limited regulative ability, while compensation by cells from the ventral neural tube has been demonstrated to an even lesser extent. Regulation by such non-crest cells would require their transformation into neural crest cells. The potential for regulation of neural crest by placodal cells supports a closer relationship between neural crest and placodal ectoderm than previously recognized." http://www.ijdb.ehu.es/abstract.march99/43321.html
