Analysis of the effects of Streptomyces hyaluronidase on formation of the neural tube

Chick embryos at stages 8 to 9 were treated in ovo with Streptomyces hyaluronidase (SH) to determine whether neurulation occurs normally in embryos depleted of hyaluronic acid, a major component of the extracellular matrix. Open neural tube defects occurred in 60–94 % (depending on the particular enzyme batch) of the embryos treated with SH and examined after an additional 24 h of incubation. Defects were confined mainly to the spinal cord. The neural folds underwent elevation in defective regions but failed to converge and fuse across the dorsal midline. The extracellular matrix of embryos treated with SH was depleted consistently, as determined with sections stained with Alcian blue. Control experiments were done to ensure that neural tube defects were not caused by non-specific protease contamination of SH, or by digestion products of hyaluronic acid. We propose several plausible and testable mechanisms through which the extracellular matrix might influence the complex developmental process of neurulation.