Embryo, Nonmammalian; Germ Layers; Notochord; Organizers, Embryonic; Neural Plate
Our laboratory is interested in understanding congenital birth defects. Many children are born with various birth defects including defects of the heart, brain, lungs, and face. These birth defects often require surgery and can be difficult to treat for the child. We hope to discover the genes that lead to these birth defects with the hope of improving our understanding of how human development (embryology) occurs.
Extensive Research Description
My laboratory is interested in the problem of embryonic patterning. A fertilized egg must activate a complex genetic program in order to form functional adult structures. Failure to do so correctly leads to congenital malformations in children, a significant cause of inherited childhood diseases. We are particularly interested in cellular signals and transcriptional regulation that lead to particular fate changes that specify new tissue types during development. We are also interested in morphogenesis that provides shape to the developing embryo. We have three approaches to discover these patterning events: 1) genetic screens in Xenopus tropicalis 2) quantitative analysis of Xenopus epidermis to create a coordinated field of cells 3) human genetic studies of children with congenital malformations. We focus on Xenopus as a model system because of the power of the frog system for gain of function and experimental embryology (“cut-and-paste” developmental biology). In addition, we have pioneered X. tropicalis as an amphibian genetic system because of its diploid genome and genomic tools.
- Analysis of X. tropicalis mutants A number of mutants have been identified in previous genetic screens and additional screens are ongoing. Mutants that have been identified are now being cloned using next-gen sequencing and exon capture arrays. Once cloned, we are using all the power of the Xenopus system to analyze gene function.
- Analysis of human mutations using Xenopus In collaboration with Lifton and Brueckner labs, we have identified a number of genes that are mutated in patients that have congenital heart disease, a failure to properly pattern the heart. We have validated a number of these genes by showing that they also cause abnormal development of frog hearts and are now analyzing the mechanisms of their development. Many of these genes are novel and identifying their mechanisms of cardiac morphogenesis will lead to new understanding of congenital malformations and the underlying developmental biology.
- Quantitative analysis of a field of ciliated cells that create fluid flow Specific cells on the epidermis of the Xenopus embryos are ciliated. These ciliated cells beat in a coordinated fashion to create flow across the entire length of the embryo. How these cells generate flow and sense flow to coordinate their beating remains uncertain. We are using advanced imaging techniques and quantitative biology to better understand how cilia driven flow is established and maintained. In addition, we have identified cilia mutants that have abnormal flow and so combining mutants, morpholino knockdowns, ablations, and transplants, we hope to better understand how local cells can coordinate cellular pattern over a large field of cells.
- Fakhro KA, Choi M, Ware SM, Belmont JW, Towbin JA, Lifton RP, Khokha MK, Brueckner M. Rare copy number variations in congenital heart disease patients identify unique genes in left-right patterning. PNAS. 2011 Jan 31.
- Hellsten U, Harland RM, Gilchrist MJ, Hendrix D, Jurka J, Kapitonov V, Ovcharenko I, Putnam NH, Shu S, Taher L, Blitz IL, Blumberg B, Dichmann DS, Dubchak I, Amaya E, Detter JC, Fletcher R, Gerhard DS, Goodstein D, Graves T, Grigoriev IV, Grimwood J, Kawa
- Grammer, T.C., Khokha, M.K., Lane, M.A., Lam, K., and Harland, R.M. (2005). Identification of mutants in inbred Xenopus tropicalis. Mech. Dev. 122(3):263-72.
- Khokha, M.K., Yeh, J., Grammer, T.C., and Harland, R.M. (2005). Depletion of three BMP antagonists from Spemann’s Organizer leads to a catastrophic loss of dorsal structures. Dev. Cell 8(3):401-411.
- Khokha MK, Hsu D, Brunet LJ, Dionne MS, Harland RM (Jul 2003) Gremlin is the BMP antagonist required for maintenance of Shh and Fgf signals during limb patterning., Nature Genetics, 34(3)303-7