Research interests

Genetic Analysis of Mouse Development and Disease

Our laboratory studies genes important for embryonic development in mice, and the connections between mutations in these genes and congenital human disease syndromes. Our analyses focus on a developmental signaling pathway termed the Notch pathway, and on genes of the Snail superfamily, which encode zinc finger transcriptional repressors.

Analysis of the Notch signaling pathway

The Notch signaling pathway is an evolutionarily conserved intercellular signaling mechanism. Genes of the Notch family encode large transmembrane receptors that interact with membrane-bound ligands encoded by the Jagged (Jag1 and Jag2) and Delta-like (Dll1, Dll3, and Dll4) gene families. The signal induced by ligand binding is transmitted intracellularly by a process involving proteolytic cleavage of the receptor and nuclear translocation of the intracellular domain of the Notch protein. Notch pathway genes are essential for normal embryonic development, and mutations in genes encoding components of the Notch signaling pathway are found in several types of cancer and in three inherited disease syndromes.

We have been conducting an extensive genetic analysis of the requirements for components of the Notch signaling pathway during mouse development. We have shown that the Notch ligand encoded by the Jag1 gene plays an essential role during inner ear development. Mice with conditional deletion of the Jag1 gene in the inner ear exhibit defects in formation of all six sensory patches in the inner ear. The Jag1 gene was required by the sensory precursors, the progenitor cells that give rise to both the supporting cells and the hair cells, the sensory cells responsible for hearing. By understanding how the sensory areas develop normally, it may be possible to develop molecular tools that will aid in sensory cell regeneration in the mammalian inner ear. We have also found that certain inner ear phenotypes exhibited by Notch pathway mutants are dependent on the genetic background of the mutant mice. For example, adult mice heterozygous for the Jag1 mutation exhibit semicircular canal defects on a C3H genetic background, but not on a C57BL/6 background. We are in the processing of mapping these genetic modifiers to specific regions of the genome.

 

Analysis of Snail family genes

We are studying the roles during mouse development of genes of the Snail family. These genes are homologs of the Drosophila gene Snail, which is required for mesoderm formation during Drosophila embryogenesis. Snail family genes encode DNA binding zinc finger proteins that act as transcriptional repressors. We have made and analyzed targeted null mutations of the Snail family genes snail homolog 1 (Snai1) and snail homolog 2 (Snai2). Embryos homozygous for a null mutation of the Snai1 gene die during gastrulation, while Snai2 mutant homozygotes survive until birth. Both Snai2-/- embryos and Snai1+/- Snai2-/- double mutant embryos exhibit cleft palate, one of the most common human birth defects. Approximately 50 percent of Snai2-/- embryos exhibit cleft palate, while in Snai1+/- Snai2-/- double mutants the incidence of cleft palate increases to 100 percent. Our research indicates that cleft palate in Snai1+/- Snai2-/- embryos is due to a failure of the elevated palatal shelves to fuse.

Snail family genes are key regulators of epithelial-mesenchymal transitions in vertebrates, including the transitions that generate the mesoderm and neural crest. We have demonstrated recently that, contrary to observations in frog and avian embryos, the Snail family genes Snai1 and Snai2 are not required for formation and delamination of the neural crest in mice. However, embryos with conditional inactivation of Snai1 function exhibit defects in left-right asymmetry determination. This work demonstrates that while some aspects of Snail family gene function, such as their role in left-right asymmetry determination, appear to be evolutionarily conserved, their role in neural crest cell formation and delamination is not. This work also demonstrates that species-specific differences in the regulation of neural crest formation and migration are more profound than previously appreciated. However, the neural crest cells that are formed in Snai1/Snai2 double mutant mice are not entirely normal. While tissue-specific deletion of the Snai1 gene in neural crest cells does not cause any obvious defects, neural crest-specific Snai1 deletion on a Snai2-/- genetic background results in multiple craniofacial defects, including a cleft palate phenotype distinct from that observed in Snai1+/- Snai2-/- embryos. In embryos with neural crest-specific Snai1 deletion on a Snai2-/- background, palatal clefting results from a failure of Meckel's cartilage to extend the mandible and thereby allow the palatal shelves to elevate. These defects are similar to those seen in humans with a disease termed the Pierre Robin Sequence.

 

Publications

• Escriva M, Peiro S, Herranz N, Villagrasa P, Dave N, Montserrat-Sent’s B, Murray SA, Franc’ C, Gridley T, Virtanen I, Garc’a de Herreros A . 2008. Repression of PTEN phosphatase by Snail1 transcriptional factor during gamma radiation-induced apoptosis. Mol Cell Biol 28(5):1528-40.
• Lozier J, McCright B, Gridley T . 2008. Notch signaling regulates bile duct morphogenesis in mice. PLoS ONE 3(3):e1851.
• Rodriguez S, Sickles HM, DeLeonardis C, Alcaraz A, Gridley T, Lin DM. 2008. Notch2 is required for maintaining sustentacular cell function in the adult mouse main olfactory epithelium. Dev Biol. 314(1):40-58.
• Gridley T, Woychik RP. 2007. Laser surgery for mouse geneticists. Nat Biotec 25:59-60.
• Amsen D, Antov A, Jankovic D, Sher FA, Radtke F, Souabni A, Busslinger M, McCright B, Gridley T, Flavell RA. 2007. Direct regulation of Gata3 expression determines the T helper differentiation potential of Notch. Immunity 27:89-99.
• Gridley T. 2007. Vessel guidance. Nature 445:722-723.
• Kiernan AE, Li R, Hawes NL, Churchill GA, Gridley T. 2007. Genetic background modifies inner ear and eye phenotypes of Jag1 heterozygous mice. Genetics 177:307-311.
• Gridley T. 2007. Notch signaling in vascular development and physiology. Development 134:2709-2718.
• Murray SA, Oram KF, Gridley T. 2007. Multiple functions of Snail family genes during palate development in mice. Deveopment 134:1789-1797.
• Murray SA, Gridley T. 2006. Snail family genes are required for left-right asymmetry determination, but not neural crest formation, in mice. Proc Natl Acad Sci USA 103:10300-10304.
• Kiernan AE, Xu J, Gridley T. 2006. The Notch Ligand JAG1 is required for sensory progenitor development in the mammalian inner ear. PLoS Genet 2:e4.
• McCright B, Lozier J, Gridley T. 2006. Generation of new Notch2 mutant alleles. Genesis 44:29-33.
• Casey LM, Lan Y, Cho ES, Maltby KM, Gridley T, Jiang R. 2006. Jag2-Notch1 signaling regulates oral epithelial differentiation and palate development. Dev Dyn 235:1830-1844.
• Gridley T. 2006. The long and short of it: Somite formation in mice. Dev Dyn 235:2330-2336.
• Oram KF, Gridley T. 2005. Mutations in Snail family genes enhance craniosynostosis of Twist1 haplo-insufficient mice: implications for Saethre-Chotzen Syndrome. Genetics 170:971-974.
• Kiernan AE, Cordes R, Kopan R, Gossler A, Gridley T. 2005. The Notch ligands DLL1 and JAG2 act synergistically to regulate hair cell development in the mammalian inner ear. Development 132:4353-4362.
• Mason HA, Rakowiecki SM, Raftopoulou M, Nery S, Huang Y, Gridley T, Fishell G. 2005. Notch signaling coordinates the patterning of striatal compartments. Development 132:4247-4258.
• Anthony TE, Mason HA, Gridley T, Fishell G, Heintz N. 2005. Brain lipid-binding protein is a direct target of Notch signaling in radial glial cells. Genes Dev 19:1028-1033.
• Domenga V, Fardoux P, Lacombe P, Monet M, Maciazek J, Krebs LT, Klonjkowski B, Berrou E, Mericskay M, Li Z, Tournier-Lasserve E, Gridley T, Joutel A. 2004. Notch3 is required for arterial identity and maturation of vascular smooth muscle cells. Genes Dev 18:2730-2735.
• Gridley T. 2004. Kick it up a Notch: Notch1 activation in T-ALL. Cancer Cell 6:431-432.
• Krebs LT, Shutter JR, Tanigaki K, Honjo T, Stark KL, Gridley T. 2004. Haploinsufficient lethality and formation of arteriovenous malformations in Notch pathway mutants. Genes Dev 18:2469-2473.
• Gridley T. 2003. Notch signaling and inherited disease syndromes. Hum Mol Genet 12 Spec No 1:R9-13.
• Krebs LT, Iwai N, Nonaka S, Welsh IC, Lan Y, Jiang R, Saijoh Y, O'Brien TP, Hamada H, Gridley T. 2003. Notch signaling regulates left-right asymmetry determination by inducing Nodal expression. Genes Dev 17:1207-1212.