Extracellular matrix (ECM) molecules are known to play a pivotal role in the morphogenesis of the secondary palate. The maintenance and degradation of the ECM is mediated in part by the matrix metalloproteinases (MMPs) and their endogenous inhibitors TIMPs. MMPs and TIMPs have previously been shown to be developmentally regulated within the palatal shelf during secondary palate morphogenesis. This study was conducted to examine the temporospatial distribution of these enzymes and their inhibitors within the palatal shelves using immunofluorescent localization to determine if specific changes occur in their distribution concomitant with events in palatal shelf formation and reorientation. Frontal sections through the posterior palatal shelves at gestational day (gd) 12, 13 and 14 were immunofluorescently stained for MMPs 2, 3, 9, and 13 and TIMPs 1, 2, and 3 using standard protocols and commercially available antibodies. The results demonstrated that MMPs and TIMPs were already present within the palatal shelf mesenchyme 30 h prior to reorientation and closure and that their expression within the shelf mesenchyme increased as the shelves remodeled, then decreased with closure and fusion. Increased distribution of MMPs and TIMPs within specific regions of the palatal mesenchyme and palatal epithelial basement membrane preceded decreases previously observed within these areas for their substrates, fibronectin, collagen III and collagen I. In addition, MMP-3 and TIMP-3 were immunolocalized to regions of the palatal epithelium that undergo reorganization concomitant with reorientation. The results of this study indicate that MMPs and TIMPs are developmentally regulated during palatal shelf morphogenesis and that their distribution correlates with the distribution of the ECM components of the palatal shelf they regulate. These results provide support for the idea that temporospatially controlled interactions between MMPs and their substrates may be pivotal in modulating events in palatal morphogenesis.

Although it has been long accepted that innervation by a taste nerve is essential for maintenance of taste buds, it is not clear what role, if any, innervation plays in the morphogenesis of taste papillae and taste bud development. The following study was undertaken to determine what effects lack of sensory innervation have on the development of taste papillae and the formation of taste buds in the mouse. Timed-pregnant female mice (n = 3) at gestational day 12 (gd12) were anesthetized and a 1 microl solution (1 microg/microl) of beta-bungarotoxin (beta-BTX), a neurotoxin that disrupts sensory and motor neuron development, was injected into the amniotic cavity of two embryos per dam. Two shams were injected with PBS. Fetuses were harvested at gd18, 1 day before birth, and four beta-BTX-injected embryos, two shams and two controls were fixed in buffered paraformaldehyde. Serial sections were examined for the presence and morphology of taste papillae and taste buds. No nerve profiles were observed in beta-BTX-injected tongues. Although circumvallate papillae were present on beta-BTX tongues, only five fungiform papillae could be identified. Taste buds were present on a large percentage of fungiform papillae profiles (24%) and on circumvallate papillae in sham and control fetuses; in contrast, no taste buds were associated with taste papillae in beta-BTX fetuses. These results implicate a significant role for innervation in taste papillae and taste bud morphogenesis.