My colleagues and I have provided two lines of evidence suggesting that defects in Platelet-Derived Growth Factor-A (PDGF-A) function result in lethality or developmental deformities during early vertebrate embryogenesis. First, mRNA for PDGF-A and its receptor are maternally-encoded in Xenopus and mice, and are expressed throughout early development. Second, mice harboring a deletion of the receptor for PDGF-A fail to develop normally past 8.5 days and usually die in utero. I would like to extend these preliminary findings in the experimentally accessible Xenopus embryo. Because the temporal and spatial expression patterns of PDGF and receptor are conserved evolutionarily, these studies should have relevance to human physiology and development. The research has two broad objectives. The first is relatively straightforward and builds on my preliminary studies on the role of PDGF during early embryogenesis. The second is more complicated and relies on my observation that PDGF-A and its receptor are markers for anterior development. Using these markers, I propose to identify novel morphogens that specify antero-posterior pattern formation. The first objective is to determine the function of PDGF-A during development. Antiserum to PDGFA and its receptor will be used immunohistologically to identify those cells producing PDGF and receptor protein. This should extend my preliminary results localizing mRNA for PDGF-A and its receptor to ectoderm and mesoderm, respectively, in the gastrula. Recombinant Xenopus PDGF-A will be evaluated for effects on differentiation of mesodermal cells in culture. Finally, PDGF-deficient embryos will be produced and monitored for developmental abnormalities. To create PDGF-deficient animals, I have already constructed mutant PDGF genes that suppress wild-type activity in a trans-dominant fashion. Embryos will be made deficient in PDGF by the injection of synthetic mRNA encoding mutant PDGF. Abnormalities of these embryos may reveal the in vivo function(s) of the growth factor. Of particular interest will be abnormalities appearing at early gastrula to late neurula stages when PDGF and receptor mRNA levels are highest. The second objective is to use PDGF-A and its receptor as markers to identify factors that control antero-posterior patterns of differentiation. Preliminary results show that mRNA encoding PDGF and its receptor are expressed in an anterior to posterior gradient in the gastrula and neurula. Thus, PDGF-A appears to be expressed in anterior ectoderm, while its receptor is localized in the anterior mesoderm. Candidate agents thought to influence axial polarity will be studied in an attempt to induce (or suppress) the differentiation of cells expressing PDGF-A and its receptor. These factors will be evaluated in conjunction with tissues (such as the organizer) for their effect on expression of PDGF-A and its receptor. These experiments may lead to the identification of morphogens that control antero-posterior polarity in vertebrates.

Agency
National Institute of Health (NIH)
Institute
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Type
Research Project (R01)
Project #
5R01HD028460-03
Application #
3330093
Study Section
Cellular Biology and Physiology Subcommittee 1 (CBY)
Project Start
1991-08-01
Project End
1996-07-31
Budget Start
1993-08-01
Budget End
1994-07-31
Support Year
3
Fiscal Year
1993
Total Cost
Indirect Cost
Name
Harvard University
Department
Type
Schools of Medicine
DUNS #
082359691
City
Boston
State
MA
Country
United States
Zip Code
02115
Ataliotis, P; Mercola, M (1997) Distribution and functions of platelet-derived growth factors and their receptors during embryogenesis. Int Rev Cytol 172:95-127
Nascone, N; Mercola, M (1997) Organizer induction determines left-right asymmetry in Xenopus. Dev Biol 189:68-78
Payne, J; Shibasaki, F; Mercola, M (1997) Spina bifida occulta in homozygous Patch mouse embryos. Dev Dyn 209:105-16
Dunn, M K; Mercola, M (1996) Cloning and expression of Xenopus CCT gamma, a chaperonin subunit developmentally regulated in neural-derived and myogenic lineages. Dev Dyn 205:387-94
Symes, K; Mercola, M (1996) Embryonic mesoderm cells spread in response to platelet-derived growth factor and signaling by phosphatidylinositol 3-kinase. Proc Natl Acad Sci U S A 93:9641-4
Nascone, N; Mercola, M (1995) An inductive role for the endoderm in Xenopus cardiogenesis. Development 121:515-23
Dunn, M K; Mercola, M; Moore, D D (1995) Cyclopamine, a steroidal alkaloid, disrupts development of cranial neural crest cells in Xenopus. Dev Dyn 202:255-70
Ataliotis, P; Symes, K; Chou, M M et al. (1995) PDGF signalling is required for gastrulation of Xenopus laevis. Development 121:3099-110
Ho, L; Symes, K; Yordan, C et al. (1994) Localization of PDGF A and PDGFR alpha mRNA in Xenopus embryos suggests signalling from neural ectoderm and pharyngeal endoderm to neural crest cells. Mech Dev 48:165-74
Symes, K; Yordan, C; Mercola, M (1994) Morphological differences in Xenopus embryonic mesodermal cells are specified as an early response to distinct threshold concentrations of activin. Development 120:2339-46

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