Meeting Abstract
Adults of the California grunion spawn on beaches during spring high tides, and embryos develop within the sand until triggered to hatch by wave action during a subsequent spring high tide. Hatching involves digestion of the chorion from within, and must occur very rapidly in grunion. We have previously identified putative hatching gland cells in embryos while within the chorion and after manual removal from the chorion, but not after embryos are stimulated to hatch. These cells form a distinctive pattern along the length of the embryo, starting anterior-dorsally near the head and continuing down the length of the body at the lateral midline. In this study, we have identified the cells that contain the choriolytic enzyme required for hatching. Grunion gametes were stripped from adults collected while spawning, and eggs were fertilized and maintained in laboratory incubators set at 20°C for up to 30 days post-fertilization (dpf). Embryos and hatched larvae were examined by light microscopy, transmission electron microscopy, and immunohistochemistry using antibodies specific for the high choriolytic enzyme (HCE) of medaka. Cells located dorsally in the embryo, posterior to the developing brain, stained for HCE at 3 dpf. At 4-5 dpf, cells along the body midline also stained for HCE. The membrane of individual hatching gland cells contacts the embryo surface and therefore the cells can release the choriolytic enzymes into the peri-vitelline space to act directly on the inner chorion. These numerous cells are unicellular hatching glands similar to those that have been described in several other fish species.
