Thrombospondin-2 gene expression and protein localization during embryonicmouse palate development

The mammalian palate develops from projections of the paired maxillary proc esses termed palatal shelves. Shelf growth is an essential in normal palata l morphogenesis. Mesenchymal proliferation in the palatal shelves is modula ted by transforming growth factor-beta (TGF-beta), among other growth facto rs. Several pathways effect TGF-beta activation, including one which utiliz es thrombospondin (TSP). TSP-1 is a major activator of TGF-beta in vivo and has been localized in head mesenchyme, including palates. TSP-2 appears to inhibit TSP-1 activation of latent TGF-beta by competitively binding the l atent TGF-beta. Here the TSP-2 mRNA transcript and the immunolocalization o f TSP-2 protein with progressive palatogenesis were quantified. There was a significant (p < 0.05) decline of TSP-2 transcript with palatal maturation ; there was no evidence correlating the TSP-2 transcription with the amount of activated TGF-beta. At the vertical shelf stage of palatogenesis, TSP-2 protein was found throughout the extracellular matrix of shelf mesenchyme. By the horizontal shelf stage, TSP-2 protein was principally localized to the ossification centres of the developing maxilla, both in extracellular m atrix and bone; far less was seen in palatal shelves proper. These results suggest that TSP-2 is multifunctional during embryonic palate formation. (C ) 2000 Elsevier Science Ltd. All rights reserved.