Fertilization of Ascidians: Gamete Interaction, Self/Nonself Recognition and Sperm Penetration of Egg Coat

Takako Saito; Hitoshi Sawada

doi:10.3389/fcell.2021.827214

Fertilization of Ascidians: Gamete Interaction, Self/Nonself Recognition and Sperm Penetration of Egg Coat

Front Cell Dev Biol. 2022 Jan 21:9:827214. doi: 10.3389/fcell.2021.827214. eCollection 2021.

Authors

Takako Saito¹, Hitoshi Sawada^{2

3}

Affiliations

¹ Faculty of Agriculture Department of Applied Life Sciences, Shizuoka University, Shizuoka, Japan.
² Depatment of Food and Nutritional Environment, College of Human Life and Environment, Kinjo Gakuin University, Nagoya, Japan.
³ Graduate School of Science, Nagoya University, Nagoya, Japan.

Abstract

Fertilization is one of the most important events in living organisms to generate a new life with a mixed genetic background. To achieve successful fertilization, sperm and eggs must undergo complex processes in a sequential order. Fertilization of marine invertebrate Ciona intestinalis type A (Ciona robusta) has been studied for more than a hundred years. Ascidian sperm are attracted by chemoattractants from eggs and bind to the vitelline coat. Subsequently, sperm penetrate through the vitelline coat proteolytically and finally fuse with the egg plasma membrane. Here, we summarize the fertilization mechanisms of ascidians, particularly from sperm-egg interactions to sperm penetration of the egg coat. Since ascidians are hermaphrodites, inbreeding depression is a serious problem. To avoid self-fertilization, ascidians possess a self-incompatibility system. In this review, we also describe the molecular mechanisms of the self-incompatibility system in C. intestinalis type A governed by three allelic gene pairs of s-Themis and v-Themis.

Keywords: ascidian; egg; lysin; proteasome; self-incompatibility; self-sterility; sperm.

Publication types

Review