Project description:The amino acid homocysteine increases in the serum when there is insufficient folic acid or vitamin B12, or with certain mutations in enzymes important in methionine metabolism. Elevated homocysteine is related to increased risk for cardiovascular and other diseases in adults and elevated maternal homocysteine increases the risk for certain congenital defects, especially those that result from abnormal development of the neural crest and neural tube. Experiments with the avian embryo model have shown that elevated homocysteine perturbs neural crest / neural tube migration in vitro and in vivo. While there have been numerous studies of homocysteine-induced changes in gene expression in adult cells, there is no previous report of a homocysteine-responsive transcriptome in the embryonic neural crest. We treated neural crest cells in vitro with exogenous homocysteine in a protocol that induces significant changes in neural crest cell migration. We used microarray analysis and expression profiling to identify 65 transcripts of genes of known function that were altered by homocysteine. The largest set of effected genes (19) included those with a role in cell migration and adhesion. Other major groups were genes involved in metabolism (13); DNA / RNA interaction (11); cell proliferation / apoptosis (10); and transporter / receptor (6). Although the genes identified in this experiment were consistent with prior observations of the effect of homocysteine upon neural crest cell function, none had been identified previously as response to homocysteine in adult cells. Keywords: homocysteine ● microarray ● expression profiling ● embryo ● neural crest
Project description:The stress of nucleotide pool reduction regulates transcription in neural crest and melanoma cells. To better understand the molecular response caused by nucleotide stress, we designed a chemical suppressor screen for leflunomide, an inhibitor of dihydroorate dehydrogenase. We found that alterations in the progesterone receptor (Pgr) activity suppressed the neural crest effects of leflunomide. To clarify the mechanism of action, we found that the RNA helicase protein, Ddx21, binds to Pgr, and loss of function of Ddx21 conferred resistance to nucleotide stress in zebrafish embryos. At the molecular level, nucleotide stress reduces DDX21 chromatin occupancy and thus, target gene expression. Together our results show that DDX21 is a transcriptional sensor and mediator of the nucleotide stress response.
Project description:Neural crest cells are multipotent cells that delaminate from the neuroepithelium, migrating throughout the embryo. Aberrant migration causes developmental defects. Animal models are improving our understanding of neural crest anomalies, but in vivo migration behaviours are poorly understood. Here, we demonstrate that murine neural crest cells display actin-based lamellipodia and filopodia in vivo. Using neural crest-specific knockouts or inhibitors, we show that the serine-threonine kinase Glycogen Synthase Kinase-3 (GSK3), and the cytoskeletal regulator Lamellipodin (Lpd), are required for lamellipodia formation whilst preventing focal adhesion maturation. Lpd is a novel substrate of GSK3 and phosphorylation of Lpd favours interactions with the Scar/WAVE complex (lamellipodia formation) at the expense of VASP and Mena interactions (adhesion maturation and filopodia formation). This improved understanding of cytoskeletal regulation in mammalian neural crest migration has general implications for neural crest anomalies and cancer.