| dc.description.abstract |
The evolutionary origin of the neural crest, an embryonic stem cell population unique
to vertebrates, has eluded biologists since its discovery. The neural crest is characterized
by its epithelial to mesenchymal transition (EMT), migration, and differentiation
into stereotyped tissues of the embryo. These processes require an intricate gene
regulatory network (GRN) that controls the signaling required for successful neural
crest formation and differentiation into target tissue types. It is hypothesized that
the neural crest, like other complex tissues, arose from co-option of existing developmental
GRNs, but this has not been tested. Here, I will use an invertebrate deuterostome,
the sea urchin L. variegatus, to look for ancestrally conserved circuits of the neural
crest GRN. I hypothesize that genes operating in the neural crest GRN will be found
in cells of the L. variegatus embryo that undergo similar processes to vertebrate
neural crest cells (EMT, migration, etc.), namely primary mesenchyme cells (PMCs),
secondary mesenchyme cells (SMCs), pigment cells, and neurons. I have cloned orthologs
of vertebrate neural crest genes in the developing embryo of L. variegatus including
foxd, phb1, musk, elk3, egr/krox20, and csnrp. Using RNA in situ hybridization, I
have found that these genes are expressed in the predicted cell types in sea urchin
embryos. Double in situs were then performed for musk / pks and foxd / phb1 to demonstrate
co-expression of the gene pairs. Both pairs of genes were co-expressed, indicating
that they may be part of the same GRNs. If these connections are shared with the neural
crest GRN, it will provide evidence that these small GRNs are ancestral to deuterostomes
and were co-opted into a single tissue in the vertebrate lineage, which gave rise
to the neural crest.
|
|
