Exploring the protective role of jelly capsules in jelly-nest tree frog eggs based on proteomic and peptidomic studies

Typically, frog eggs are aquatic, being deposited and undergoing development within freshwater habitats. However, certain species within the Rhacophoridae have evolved reproductive modes that are non-aquatic. The jelly-nest tree frog (Feihyla palpebralis) has terrestrial eggs that are enclosed in gel, with embryos detaching from the aquatic milieu during the embryonic phase. The jelly enveloping these embryos performs a critical role in defense against biotic and abiotic threats in the terrestrial environment. To investigate the protective function of the jelly, we characterized its proteome and peptidome. In total, 83 proteins were identified and categorized into eight main groups: protease inhibitors, glycoproteins, cytoskeleton proteins, nucleotide-binding proteins, regulatory proteins, metabolic enzyme, glycoprotein hormones, and oxidative stress-related proteins. These proteins are believed to play a role in protecting the eggs by creating biochemical and physical barriers, maintaining moisture and structural integrity, and preventing oxidative damage. In addition, 1642 peptides were isolated from tree frog jelly envelopes. Among these, RPPGFSPFR showed predator deterrent properties, LPF and AVPYPQ performed anti-inflammatory and antioxidant activities, and IYSP functioned as a proteinase inhibitor. These findings help to clarify the protective mechanisms involved in the egg development process of the jelly-nest tree frog.