Knockdown of hspg2 is associated with mandibular jaw joint fusion and neural crest cell dysfunction in zebrafish

Background: Heparan sulfate proteoglycan 2 (HSPG2) encodes for perlecan, a large proteoglycan that plays an important role in cartilage formation, cell adhesion, and basement membrane stability. Mutations in HSPG2 have been associated with Schwartz-Jampel syndrome and Dyssegmental Dysplasia Silverman-Handmaker Type, two disorders characterized by skeletal abnormalities. These data indicate a function for HSPG2 in cartilage development/maintenance. However, the mechanisms in which HSPG2 regulates cartilage development are not completely understood. Here, we explored the relationship between this gene and craniofacial development through morpholino-mediated knockdown of hspg2 in zebrafish. Results: Knockdown of hspg2 resulted in a fusion of the mandibular jaw joint at 5 days post fertilization (dpf). We surmised that defects in mandible development were a consequence of neural crest cell (NCC) dysfunction, as these multipotent progenitors produce the cartilage of the head. Early NCC development was normal in morphant animals as measured by distal-less homeobox 2a (dlx2a) and SRY-box transcription factor 10 (sox10) expression at 1 dpf. However, subsequent analysis at later stages of development (4 dpf) revealed a decrease in the number of Sox10 + and Collagen, type II, alpha 1a (Col2a1a)+ cells within the mandibular jaw joint region of morphants relative to random control injected embryos. Concurrently, morphants showed a decreased expression of NK3 homeobox 2 (nkx3.2), a jaw joint molecular marker at 4 dpf. Conclusions: Collectively, these data suggest a complex role for hspg2 in jaw joint formation and late stage NCC differentiation.