This research project will defme the role of TGFB signaling in mechanisms of all-trans-retmoic acid (atRA) teratogenesis in the embryonic inner e&, using mutant mice and a mouse model of atRA teratogenesis to probe developmental mechanisms of inner ear malformation. The hypothesis which will be tested is that embryonic exposure to teratogenic levels of all-trans-retinoic acid at a critical period of otic development disrupts normal TGFB signaling in the developing inner ear.
Four specific aims will be tested in a stepwise manner to address this hypothesis: 1) Determine if inductive interactions between otic epitheium and penotic mesenchyme are compromised by loss of the TGFB signal; 2) Determine if exposure of the developing mouse inner ear to teratogenic levels of atRA modifies the pattern of expression of TGFB receptors; 3) Determine if levels of expression of Smad2 and Smad3, i.e. intracellular mediators of TGFf3 signaling, are altered by exposure of the developing mouse inner ear to teratogenic levels of atRA; and 4) Determine if normal development of the mouse inner ear is disrupted by loss or partial loss of Smad2 and Smad3. Experiment 1 (Specific Aim 1) will determine the inductive capability of inner ear tissues from mice deficient in TGFB. Experiment 2 (Specific Aim 2) will define the expression patterns of TGFD receptors and receptors that use Smad signaling (eg. activin receptors) in in utero atRA-exposed inner ears in comparison to control specimens. Experiment 3 (Specific Aim 3) will determine if expression levels of Smad2 and Smad3 are disrupted by in utero exposure to atRA and by targeted disruption of TGFB and activin genes. Experiment 4A (Specific Aim 4) will determine if phenotypic anomalies to the mouse inner ear are incurred by targeted mutation of Smad2 and Smad3, while Experiment 4B will determine if functional consequences to otic epitheium and periotic mesenchyme are evoked by deficiency in Smad genes. These experiments will employ the techniques of tissue and organ culture, immunohistochemistry, Western blotting, polymerase chain reaction (PCR), paint filling of the membranous labyrinth, and confocal microscopy. Achievement of the aims of this proposal, in addition to advancing our understanding of atRA teratogenesis in the embryonic mouse inner ear, will be a major step forward in understanding normal and abnormal inner ear development in humans, with implications for the molecular pathogenesis of deficiencies of TGFB and its signaling mechanisms in patients with congenital disorders of the inner ear.
