Project description:The Notch signaling pathway functions in a number of processes during embryologic development, especially the maintenance or aquisition of cell fate. We purturb the Notch signalling pathway in embryonic Xenopus laevis in order to 1) better characterize the downstream targets of Notch signalling, and 2) determine the extent to which early embryos can recover from transient purturbations to critical signalling pathways, if at all.
Project description:The Notch signaling pathway functions in a number of processes during embryologic development, especially the maintenance or aquisition of cell fate. We purturb the Notch signalling pathway in embryonic Xenopus laevis in order to 1) better characterize the downstream targets of Notch signalling, and 2) determine the extent to which early embryos can recover from transient purturbations to critical signalling pathways, if at all. Xenopus laevis embryos were unilaterally injected at the two cell stage with either GFP, GFP and ICD (Notch intracellular domain, an up-regulator of the Notch pathway), or GFP and DBM (domain-binding mutant, a downregulator of the Notch pathway). At stages 18, 28, and 38, for each injection, pooled total RNA from 10 embryos was extracted. Extraction was performed for three biological replicates for each time/injection condition. cDNA from total RNA was hybridized on Affymetrix Xenopus laevis Genome 2.0 arrays.
Project description:Analysis of epithelial explants injected with the intracellular domain of Notch (ICD) to block the formation of multi-ciliate and proton secreting cells or with dominant negative human Mastermind (HMM) or a DNA binding mutant of Mastermind (DBM) to induce the formation of ectopic multi-ciliate and proton secreting cells. Results show which genes are up or down-regulated when DBM/HMM are compared to ICD. Epithelial cells projecting hundreds of motile cilia are prominent in the respiratory system, brain ependyma and female reproductive tract where they generate a vigorous fluid flow along luminal surfaces. Despite their importance for organ function, how multiciliate cells arise developmentally in diverse epithelia is poorly understood. Notch signaling has been shown in a variety of tissues, including the Xenopus epithelium, to regulate the formation of multiciliate cell precursors. In order to identify early downstream targets of Notch signaling which contribute to multiciliate cell fate we blocked or activated Notch signaling in explants of Xenopus epithelium and looked at changes in gene expression to identify candidates that regulate multiciliate cell fate. Here we identify a novel coiled-coil protein, called multicilin (MCI), whose expression is Notch-regulated and restricted to epithelia where multiciliate cells forms in Xenopus embryos. Inhibiting MCI activity blocks the formation of multiciliate cell precursors while ectopic MCI activity is sufficient to induce multiciliate cell differentiation within epithelial progenitors. 2-cell stage Xenopus embryos were injected with synthetic mRNA encoding ICD, DBM or HMM. At stage 9/10 the presumptive ectoderm was cut off the embryo and cultured on a fibronectin coated coverslip. At stage 12 RNA was harvested from explants and used as the starting material for arrays.
Project description:Geminin cooperates with Polycomb to restrain multi-lineage commitment in the early embryo: Transient maintenance of a pluripotent embryonic cell population followed by the onset of multi-lineage commitment is a fundamental aspect of development. However, molecular regulation of this transition is not well characterized in vivo. Here we demonstrate that the nuclear protein Geminin is required to restrain commitment and spatially restrict mesoderm, endoderm, and non-neural ectoderm to their proper locations in the Xenopus embryo. We used microarray analyses to demonstrate that Geminin overexpression represses many genes associated with cell commitment and differentiation, while elevating expression levels of genes that maintain pluripotent early and immature neurectodermal cell states. We characterized Geminin’s relationship to cell signaling and found that Geminin broadly represses Activin-, FGF-, and BMP-mediated cell commitment. Conversely, Geminin knockdown enhances commitment responses to growth factor signaling and causes ectopic mesodermal, endodermal, and epidermal fate commitment in the embryo. We also characterized Geminin’s functional relationship with transcription factors that had similar activities and found that Geminin represses commitment independent of Oct4 ortholog (Oct25/60) activities, but depends upon intact Polycomb repressor function. Consistent with this, chromatin immunoprecipitation assays directed at mesodermal genes demonstrate that Geminin promotes Polycomb binding and Polycomb-mediated repressive histone modifications, while inhibiting modifications associated with gene activation. This work defines Geminin as an essential regulator of the embryonic transition from pluripotency through early multi-lineage commitment, and demonstrates that functional cooperativity between Geminin and Polycomb contributes to this process.