Proposal abstract: 

The neural crest is a vertebrate innovation, sometimes referred to as the fourth germ layer.  The neural crest gives rise to migrating cells that differentiate into cartilage, melanocytes, the peripheral nervous system, and the outflow tract of the heart.

Defects in the neural crest are involved in over 400 human syndromes and result in craniofacial, heart, pigmentation, peripheral and central nervous system defects.  Our focus has been on the environmentally regulated and developmentally important transcription factor NFκB and its regulatory targets in the early embryo.

NFκB activation has been implicated in the teratogenic effects of environmental factors such as ethanol. Early embryonic defects impacting the neural crest underlie the neurological, craniofacial, and dental malformations associated with Fetal Alcohol Syndrome (FAS) and the less severe, but still significant alcohol-related neurodevelopmental disorder (ARND) and alcohol-related birth defects (ARBD). The goal of this proposal is to better understand the molecular nature of these defects, particularly those involving the regulatory targets of NFκB.

Using the clawed frog Xenopus as a model system, we found that NFκB regulates the levels of twist, snail1, and snail2(slug) RNA levels. twist encodes a bHLH transcription factor, while snail1 and snail2 encode the related zinc-finger transcription factors Snail1 and Snail2; these three transcription factors are also implicated tumor metastasis and resistance to genotoxic agents.

In the early Xenopus embryo, Twist, Snail1, and Snail2 regulate one another’s expression and are required for the formation of mesoderm and the subsequent formation, survival, and differentiation of the neural crest. Surprisingly, they can rescue each other’s loss of function phenotypes. There is evidence that a similar network of interactions may be active in the early mouse embryo, arguing for the relevance of this system to human embryonic/neural crest defects.

Our project seeks tol i) define the unique and complementary mesodermal roles of twist, snail1, and snail2 on neural crest induction, survival, and differentiation and ii) identify the temporal and spatial requirement for mesodermal signals in neural crest specification.

Supporting publications:

Carl, T.F., C. Dufton, J. Hanken & M.W. Klymkowsky. 1999. Inhibition of neural crest migration in Xenopus using anti-sense Slug RNA. Developmental Biology. 213:101-115. 

Zhang, C., Timothy F. Carl, E. Trudeau, Thomas Simmet & M.W. Klymkowsky.  2006. An NF-kB and Slug regulatory loop active in early vertebrate mesoderm. PLoS ONE, 1:e106 (1-14).

Zhang, C, & M.W. Klymkowsky, 2007. The Sox Axis, Nodal Signaling, & Germ Layer Specification. Differentiation 75: 536-545. (in memory of Larry Etkin)

Klymkowsky, M.W. & P. Savagner.  2009. Epithelial-mesenchymal transition (EMT): a cancer researcher's conceptual friend and foe. American Journal of Pathology. in press.

Zhang, C. & M.W. Klymkowsky. 2009. Unexpected functional redundancy between Twist and Slug (Snail2) and their feedback regulation of NF-kB via Nodal and Cerberus. Developmental Biology, in press.