The long term goal of this proposal is to define the roles of Bone Morphogenetic Proteins (BMPs), members of the TGF- superfamily of secreted signaling molecules, during mammalian eye development. BMPs have been implicated in many aspects of embryonic inductive tissue interactions. In particular, we have recently shown that one family member, Bmp4, plays an essential role during lens induction in the mouse embryo. In recent studies, chromosomal deletions in humans at 14q22- q23, where the BMP4 gene is mapped, have been linked with dominant anopthalmia and pituitary hypoplasia. Moreover, it has been shown that another family member, Bmp7, is required for normal eye development in the mouse. However, the molecular mechanisms by which BMPs regulate specific processes in vertebrate eye development are poorly understood. Here, we propose genetic and experimental embryological approaches to address this question, focusing on the roles of Bmp4 and a type-I Bmp receptor, Alk3. We will test the following three hypotheses; (1) that Bmp4 function is required, not only during lens induction, but also during subsequent steps in eye formation, (2) that Bmp4 and another signaling factor, Fgf15, directly mediate the lens inductive signal of the optic vesicle, (3) and that Bmp signaling is required independently in both the lens ectoderm and the retinal neuroectoderm during early eye development. Our strategy utilizes an embryonic eye explant culture technique we have established. We will treat both mutant and wildtype embryonic eye tissues with exogenous Bmp4 and/or Fgf15 proteins to explore their functions in eye formation. Furthermore, we will generate mouse embryos that lack Alk3 receptor function specifically in the developing eye using the Cre-loxP system for conditional gene disruption. The original homozygous AIk3 mutation causes pre-gastrulation embryonic lethality, and therefore the eye specific gene disruption is crucial for studying function of this gene during embryonic eye development. The embryos generated by this technique will provide mutant eye tissues which will be used for recombination organ cultures to study tissue-type specific functions of BMP signaling. These studies will contribute significantly to our understanding of the fundamental roles of secreted signaling molecules in mammalian eye development. Moreover, the results will shed light on the possibility that abnormal regulation of intercellular signaling contributes to congenital eye defects and associated postnatal eye dysfunctions in humans.
