Congenital heart disease (CHD) is a significant problem in our society. One percent of all newborns have congenital heart defects. Examination of spontaneously aborted fetuses has shown that 10% of all human fetuses have CHD. It is estimated that there are 1 million people in the United States over the age of 20 with CHD. The causes of CHD in humans are poorly understood. Regions on chromosome 21 and 22 have been associated with CHD but the genes that are responsible for causing the defects have still not been identified. A gene called Nkx-2.5 has been shown to be mutated in some infants with CHD. Another transcription factor, Tbx5, is mutated in Holt-Oram syndrome, in which patients have limb and heart defects. But these two genes cannot account for all forms of CHD in humans.
A method of screening for genes that can cause heart defects in an animal model such as the mouse would lead to identification of a series of candidate genes to examine for mutations in humans with CHD. One such method is to use retroviral gene trap constructs containing lacZ without a promoter (Baker et al. 1997) in embryonic stem (ES) cells to identify previously uncharacterized genes that are expressed in muscle cells and their precursors in the embryo. This is the main ongoing project in my lab. Currently, we are focusing on two genes, RNF4 and CtBP2. Both of these genes, when mutated by gene trap insertion, result in cardiovascular defects in homozygous null mice and cause embryonic lethality. Both function as nuclear proteins, transcriptional cofactors, although they have other functions in the cell. Our efforts are focused on characterizing the functions of these gene products during normal embryonic development. Other ES cell clones from the screen described in Baker et al. 1997 remain to be characterized.
A second approach my lab is using to investigate the molecular mechanisms that regulate cardiac and vascular cell differentiation in the mouse embryo is by analyzing ES cell differentiation in vitro and in vivo. Using gene trap cell lines that are labeled with ß-galactosidase and ES cells transfected with fluorescent proteins such as EGFP, we are examining the differentiation potential of these cells when injected into a mouse model of myocardial infarction. In vitro we are studying the ability of these cells to differentiate in a 3-D matrix to form structures that approximate embryonic organs.
Recent Publications
Baker, R.K., Haendel, M.A., Swanson, B.J., Shambaugh, J.C., Micales, B.K. and Lyons, G.E. (1997). In vitro preselection of gene-trapped embryonic stem cell clones for characterizing novel developmentally regulated genes in the mouse. Dev. Biol. 185:201-214.
Hunter, P.J., Swanson, B.J., Haendel, M.A., Lyons, G.E. and Cross, J.C. (1999) Mrj encodes a DnaJ-related chaperone that is essential for murine placental development. Development 126:1247-1258.
Jung, J, Kim, T.G. Lyons, G.E., Kim, H.R., Lee, Y. (2005) Jumonji regulates cardiomyocyte proliferation via interaction with retinoblastoma protein. J Biol. Chem, 280:30916-23.
Lee, Y., Baker, R.K., Song, A., Micales, B.K., Conway, S. and Lyons, G.E. (2000) Jumonji, a nuclear protein that is necessary for normal heart development. Circ. Res. 86:932-938.
Metcalfe, S.M., Muthukumarana, P., Thompson, H.L., Green, C., Adams, E., Haendel, M.A. and Lyons, G.E. (2005) Leukaemia inhibitory factor (LIF) is functionally linked to axotrophin and both LIF and axotrophin are linked to regulatory immune tolerance, FEBS Letts. 579: 609-614.
Singla, D.K., Hacker, T.A., Ma, L., Douglas, P.S., Sullivan, R., Lyons, G.E., Kamp, T.J. (2006) Transplantation of embryonic stem cells into the infarcted mouse heart: Formation of Multiple Cell Types, in press J Mol Cell Cardiol. 40:195-200.
