Research Interests of Dr. Richard H. Finnell

Research in Dr. Finnell's laboratory focuses on the interaction between specific genes and environmental toxicants as they influence normal embryonic development. The laboratory currently has four major research areas, all of which focus on determining susceptibility to environmentally induced birth defects. These four areas are summarized below.

Knockout and transgenic animal development to study the role of folic acid in the prevention of birth defects. We have used homologous recombination in embryonic stem cell technology in order to successfully knockout both of the murine folate binding protein genes (Folbp1 and Folbp2), as well as the reduced folate carrier gene (RFC1). The heterozygous Folbp1 animals have significantly lower serum folic acid levels and very high serum and brain homocysteine levels when the dams are maintained on a low folate diet. Embryos homozygous for the Folbp1 null allele fail to develop beyond gestational day 10, and these embryos all have neural tube defects (NTDs) and other serious congenital malformations. When the Folbp1 heterozygous dams are on placed on folate supplementation, we are able to rescue the phenotype and have observed grossly normal nullizygous gestational day 18 fetuses or, if provided lesser levels of supplementation, the nullizygous embryos have craniofacial and/or conotruncal heart defects. When the pups are delivered and the dams supplemented with folic acid during the weaning period, the nullizygotes survive into adulthood. While supplemental folic acid has been shown to reduce the risk for NTDs and other congenital malformations in humans, the mechanisms underlying this protective effect are unknown. Utilizing the knockout animals will help us to learn more about this phenomenon on both molecular and morphological levels. To this end, we are currently manipulating folic acid and homocysteine concentrations in the dams and the embryos by dietary means and then using cDNA microarray technology in order to identify which gene or genetic pathways are critical to the regulation of this response. We have also examined embryos that lack a functional folate transporter protein (RFC1). These knockout nullizygotes also lethal in utero, as the embryos have devastating congenital malformations. We are working on a rescue paradigm so that we have more fully developed embryos to study. When we make the compound heterozygotes, we will have embryos that have been compromised in their ability to bind folates, internalize them, and transport them intracellularly. We are also working on a high-throughput screening system in order to determine the relative importance of enhancer and regulatory regions of these genes as they impact susceptibility to selected birth defects.

Candidate genes for susceptibility to human neural tube defects (NTDs) and orofacial clefts. My laboratory serves as the mutation analysis laboratory for the States of California and Texas in support of their participation in the National Birth Defects Prevention Study. These are two of the eight CDC recognized Centers of Excellence. We use a variety of mutation analysis approaches to screen population based case-control samples for polymorphisms in several different candidate genes to identify significant gene-environment interactions. Many of these samples are stratified as to the vitamin status of the mother to enable us to focus in on various hypotheses concerning folates and birth defects. It has been shown in human epidemiological studies that certain populations fail to benefit from folate supplementation. Our hypothesis is that individuals with mutant folate receptors or transporter genes are less capable of binding both dietary and/or supplemental folic acid for transport to the placenta and harvest by the fetus during critical periods of neural tube closure, resulting in NTDs. We are currently testing this hypothesis examining the gene coding for the 5-methyltetrahydrofolate receptor (hFRa) as well as MTHFR, MTHFD, NAT1, NAT2, SHH, MTRR, PDGFR, BHMT, BHMT2, MS, and RFC1, using dideoxy-DNA fingerprinting and single strand conformational polymorphism analysis to screen the samples in a high-throughput manner as well as direct sequencing when indicated. We have also examined genes related to energy metabolism (UPC2), obesity (leptin and its receptor), and drug metabolism (mEH, GST). We are also interested in testing the hypothesis that homocysteine acts as an NMDA receptor antagonist which disrupts normal cardiac and neural tube development. We will examine the folate pathway genes in patients exposed in utero to a variety of pharmaceutical and environmental samples that can interfere with normal homocysteine remethylation. As an adjunction to these molecular epidemiology studies, the laboratory is actively cloning new human folate receptor and transporter genes that might serve as new targets for these epidemiological investigations.

Antiepileptic drug therapy and congenital malformations. The laboratory has a long-standing interest in the teratogenicity of anticonvulsant medications. Using animals models, we are trying to identify specific alterations in gene expression and function that can explain the craniofacial dysmorphia observed in human infants exposed in utero to phenytoin. We have observed this drug to act as a retinoic acid agonist, and increase the binding of the retinoic acid receptors. It is possible that the craniofacial defects could be related to altered expression of the retinoic acid receptors and RAREs (retinoic acid response elements) regulating downstream growth factors. Efforts are underway to characterize the functional significance of a truncated RARa transcript observed in target tissues following in utero exposure to teratogenic concentrations of phenytoin. In another series of experiments, we have we have finally established solid linkage with a gene that confers susceptibility to anti-epileptic drug induced NTDs. We are in the process of positionally cloning this gene and learning more about its characteristics. We are working with a critical region of less than one cM, and will soon receive a recombinant inbred mouse line derived from C57BL/6J and A/J mice from Dr. Joseph Nadeau, which should help use to further resolve the critical region. Once the mouse gene is positionally cloned, we will clone its human ortholog and then examine the clinical samples that have been collected which include sibships with both adverse and normal pregnancy outcomes in the face of maternal anticonvulsant drug therapy during pregnancy.

Environmental Toxicogenetics. The final area in which we work combines many aspects of the above-mentioned studies yet focuses the technology on addressing problems of true environmental significance. Funded through the Superfund Research Program, we are working with a variety of investigators at Texas A&M University to study the consequences of complex mixtures and petrochemical pollution on birth defects using both genetically modified mouse model systems and human molecular epidemiology studies. The mouse work involves test compounds (arsenic, TCDD, BAP) and embryos that should be genetically sensitive (Folbp1) or resistant (AhR-) to these exogenous agents. We will define the responses on both the morphological and molecular levels, using genetic microarray technology. In parallel, we are establishing the infrastructure to perform molecular epidemiology studies in the petrochemical producing country, Azerbaijan, which has very high anecdotal rates of congenital defects.

Representative Publications

Spiegelstein, O., Lu, X., Le, X.C., Troen, A., Selhub, J.,Melnyk, S., James, S.J. and Finnell, R.H. 2005. Effects of dietary folate intake and folate binding protein 2 (Folbp2) on urinary speciation of sodium arsenate in mice. Env. Toxicol. & Pharmacol. 19:1-7.

Birn, H., Spiegelstein, O., Christensen, E.I. and Finnell, R.H. 2005. Renal tubular reabsorption of folate mediated by folate binding protein 1. Am.J.Soc. Nephrol. 16:608-615.

Moretti, P., Sahoo, T., Hyland, K., Bottiglieri, T., Del Gaudio, D., Roa, B., Curry, S., Zhu, H., Finnell, R.H., Neul, J., Ramaekers, V.T., Blau, N., Bacino, C., Miller, G. and Scaglia, F. 2005. Cerebral folate deficiency with features of Angelman syndrome and response to folinic acid. Neurology. 64(6):1088-90.

Zhu, H., Curry, S., Wen, S., Shaw, G.M., Lammer, E.J., Wicker, N., Yang, W., Jafarov, T., and Finnell, R.H. 2005. Are the betaine-homocysteine methyltransferase (BHMT and BHMT2) genes risk factors for spina bifida and orofacial clefts? Am. J. Med. Genet. 135(3):274-277.

Ma, D., Finnell, R.H., Davidson, L.A., Callaway, E.S., Spiegelstein, O., Piedrahita, J.A., Salbaum, J.M., Kappen, C., Weeks, B., James, S.J., Bozinov, D., Lupton, J.R., and Chapkin, R.S. 2005. Folate transport gene inactivation in mice increases sensitivity to colon carcinogenesis. Cancer Res. 65:887-897.

Olshan, A.F., Shaw, G.M., Millikan, R.C., Laurent, C. and Finnell, R.H. 2005. Polymorphisms in DNA repair genes as risk factors for spina bifida and orofacial clefts. Am. J. Med. Genet. 135(3):268-273.

Pei, L., Zhu, H., Ren, A., Li, Z. Hao, L., Finnell, R.H. and Zhu, L. 2005. Reduced folate carrier gene is a risk factor for neural tube defects in a Chinese Population. Birth Defects Res A. 73:430-433.

Zhu, H., Lu, W., Laurent, C., Shaw, G.M., Lammer, E.J., and Finnell, R.H. 2005. Genes Encoding Catalytic Subunits of Protein Kinase A and Risk of Spina Bifida. Birth Defects Research A. 73:591-596.

Jafarov, T., Zhu, H., Finnell, R. and Kulieva, S. 2005. Epidemiologic study on HFE C282Y mutation in Azerbaijan. Eur. J. Haematol. 74:180-181.

Tang, L.S., Santillano, D.R., Miranda, R.C. and Finnell, R.H. 2005. Role of Folbp1 in the regional regulation of apoptosis and cell proliferation in the developing neural tube and craniofacies. Am J Med Genet C Semin Med Genet. 135(1):48-58.

Shaw, G.M., Carmichael, S.L., Yang, W., Harris, J.A., Finnell, R.H. and Lammer, E.J., 2005. Epidemiologic characteristics of anophthalmia and bilateral microphthalmia among 2.5 million births in California,
1989-1997. Am. J. Med. Genet. 137:36-40.

Shaw, G.M., Iovannisci, D.M, Yang, W., Finnell, R.H., Carmichael, S.L., Cheng, S., and Lammer, E.J. 2005. Risks of human conotruncal heart defects associated with 32 single nucleotide polymorphisms of selected cardiovascular disease-related genes. Am. J. Med. Genet. 138:21-26.

Blanton, S.H., Cortez, A., Stal, S., Mulliken, J.B., Finnell, R.H., and Hecht, J.T. 2005. Variation in IRF6 contributes to nonsyndromic cleft lip and palate. Am. J. Med. Genet. 137:259-262.

Lammer, E.J., Shaw, G.M., Iovannisci, D.M. and Finnell, R.H. 2005. Maternal smoking, genetic variation of glutathione s-transferases, and risk of orofacial clefts. Epidemiology 16:698-701.