Structurization of Cortical Layer of Loach Yolk Cell after Wounding as a “Minimal” Model of Morphogenesis

Abstract

Structural rearrangements of the yolk cell surface were studied in loach embryos using SEM and TEM, which take place within 30 min after a point-like puncture at the late blastula stage. The effects of sucking off or addition of a part of yolk, lowered temperature, and absence of Ca2+ on structurization were studied. Around the area of puncture, the yolk granules were submerged, the number of vesicles increased, and numerous membrane folds were formed. The folds were aggregated to form two sharply distinct types of structures: a group of rounded evaginations around the site of puncture and a system of radial folds in the periphery. Small radial folds are aggregated in radial strands, several dozens folds in each. Sucking off a part of yolk accelerated the above processes, while addition of yolk, cooling, and absence of Ca2+ in the incubation medium slowed down or suppressed these processes. The observed structurization can be considered as self-organization at the level of the yolk cell cortical level, largely similar to that during normal morphogenesis at the level of multicellular sheets. Hence, the membrane dynamics in the yolk cell wall after its damage can be considered as one of simplified ("minimal") models of morphogenesis. A study of this model makes it possible to narrow down the circle of factors essential for self-organization of morphogenetic processes.