Meeting Abstract
The arboreal embryos of red-eyed treefrogs, Agalychnis callidryas, can hatch in response to threats to eggs, escaping to the pond below. They hatch in seconds by releasing a hatching enzyme (HE) to digest a small hole in their membrane, then squeezing out. These embryos have two distinct types of hatching gland cells (HGCs) and one HE. From prior scanning electron microscopy, early HGCs appear at 3 d on the snout and dorsal head surface, begin regressing at 4 d and are scarce by 5 d, regardless of hatching. Late HGCs appear at 4 d, become densely concentrated on the snout, and regress only after embryos hatch. Using confocal microscopy and a new, custom antibody to mark A. callidryas hatching enzyme (AcHE), we present a more complete description of hatching enzyme expression in A. callidryas, and comparisons to other anurans. Abundant AcHe expression is present long before embryos are able to hatch and it increases rapidly over development. HE visualization reveals an astonishing amount of HE accumulation, greater than is known in other species, and HE expression outside the previous reported surface localization of Ac HGCs, such as in the dorsal tail region. Hatching assays indicate that embryos release HE locally from patches of HGC, leaving large amounts unutilized. Unused HE remains in HGCs localized at the skin surface, suggesting retention is related to HGC function rather than localization. Work in progress addresses when and how HGCs become functional. A large, spatially distributed HE reserve may facilitate high-speed hatching and enable embryos to make multiple holes if displaced during the hatching process, or to escape from challenging conditions such as drying egg capsules.
