Neuronal control of hatching in fish: An emerging perspective.

Hatching is a critical developmental transition during which an organism emerges from the protection of the egg into a different external environment. To date, most studies have focused on the environmental factors that affect hatching and the molecular and cellular mechanisms underlying hatching enzyme secretion and chorion digestion, whereas the neuronal and sensory mechanisms that initiate and coordinate hatching remain poorly understood across the animal kingdom. Following our finding of a hatching hormone in fish, we present here a perspective on the neuroendocrine regulation of hatching, highlighting neuropeptides, neurotransmitters, and sensory mechanisms that may regulate this process, with particular emphasis on fishes. This mini-review is meant to create further interest in the neuronal basis of hatching and encourage future studies to uncover the neural circuits and mechanisms that integrate environmental cues to regulate this dramatic developmental transition.