The aim of this proposal is to understand the function of homeobox-containing genes in the differentiation and morphogenesis of the vertebrate endoderm. The endoderm gives rise to a major organ system with an ordered anteroposterior progression of regionalized parts: i.e. pharynx, esophagus, lung, stomach, liver, duodenum, pancreas, and intestine. Although there is good evidence for homeobox genes being involved in patterning the vertebrate mesoderm and neuroectoderm, virtually nothing is yet known regarding the genes controlling endodermal specification. We will test the hypothesis that new members of the homeobox gene family control critical early steps in the differentiation of the vertebrate endoderm. The basis for this study is the identification of a novel frog homeobox gene, XlHbox 8 (Wright et al. 1988). Immunolocalizations show that XlHbox 8 is expressed in a band of the early embryonic endoderm that gives rise to the pancreatic/duodenal region of the gut (Wright et a]. 1988). This distribution is in sharp contrast to that of all other homeobox genes so far studied, which are expressed in both neuroectoderm and mesoderm. We will characterize the XlHbox 8 gene and analyze its expression pattern in detail at the very earliest stages of endodermal development. Tissue recombination experiments will be carded out to analyze the mesoderm/endoderm interactions required for XlHbox 8 activation. In vitro cultures of explanted presumptive endoderm will be used to identify the endoderm-inducing factors produced by mesodermal cells. We will also directly test the function of XlHbox 8 in endodermal specification, using two strategies: a) loss-of-function experiments involving the microinjection of XlHbox 8-specific antibodies, and b) dominant gain-of-function experiments based on injecting synthetic MRNA encoding XlHbox 8. An endoderm-specific Xenopus CDNA library will be made, and screened for other homeobox genes that may control anteroposterior regionalization of endoderm. Products of new genes will be localized using antibodies against gene-specific fusion proteins. We will clone the mouse homolog of XlHbox 8, laying the foundation for genetic experiments based on transgenic animals and null mutations. Such approaches UGH help elucidate the biological function in embryogenesis of homeodomain-containing transcription factors expressed in specific regions of the endoderm, and how they become activated over these precise areas.

Agency
National Institute of Health (NIH)
Institute
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Type
Research Project (R01)
Project #
5R01HD028062-04
Application #
2200842
Study Section
Cellular Biology and Physiology Subcommittee 1 (CBY)
Project Start
1991-05-01
Project End
1996-04-30
Budget Start
1994-05-01
Budget End
1995-04-30
Support Year
4
Fiscal Year
1994
Total Cost
Indirect Cost
Name
Vanderbilt University Medical Center
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
004413456
City
Nashville
State
TN
Country
United States
Zip Code
37212
Gerrish, K; Gannon, M; Shih, D et al. (2000) Pancreatic beta cell-specific transcription of the pdx-1 gene. The role of conserved upstream control regions and their hepatic nuclear factor 3beta sites. J Biol Chem 275:3485-92
Frisch, A; Wright, C V (1998) XBMPRII, a novel Xenopus type II receptor mediating BMP signaling in embryonic tissues. Development 125:431-42
Wu, K L; Gannon, M; Peshavaria, M et al. (1997) Hepatocyte nuclear factor 3beta is involved in pancreatic beta-cell-specific transcription of the pdx-1 gene. Mol Cell Biol 17:6002-13
Peshavaria, M; Henderson, E; Sharma, A et al. (1997) Functional characterization of the transactivation properties of the PDX-1 homeodomain protein. Mol Cell Biol 17:3987-96
Sampath, K; Cheng, A M; Frisch, A et al. (1997) Functional differences among Xenopus nodal-related genes in left-right axis determination. Development 124:3293-302
Offield, M F; Jetton, T L; Labosky, P A et al. (1996) PDX-1 is required for pancreatic outgrowth and differentiation of the rostral duodenum. Development 122:983-95
Candia, A F; Wright, C V (1995) The expression pattern of Xenopus Mox-2 implies a role in initial mesodermal differentiation. Mech Dev 52:27-36
Jones, C M; Kuehn, M R; Hogan, B L et al. (1995) Nodal-related signals induce axial mesoderm and dorsalize mesoderm during gastrulation. Development 121:3651-62
Gamer, L W; Wright, C V (1995) Autonomous endodermal determination in Xenopus: regulation of expression of the pancreatic gene XlHbox 8. Dev Biol 171:240-51
Gamer, L W; Wright, C V (1993) Murine Cdx-4 bears striking similarities to the Drosophila caudal gene in its homeodomain sequence and early expression pattern. Mech Dev 43:71-81

Showing the most recent 10 out of 13 publications