Mechanism of Self-Sterility in a Hermaphroditic Chordate

Abstract

Hermaphroditic organisms avoid inbreeding by a system of self-incompatibility (SI). A primitive chordate (ascidian) Ciona intestinalis is an example of such an organism, but the molecular mechanism underlying its SI system is not known. Here, we show that the SI system is governed by two gene loci that act cooperatively. Each locus contains a tightly linked pair of polycystin 1-related receptor (s-Themis) and fibrinogen-like ligand (v-Themis) genes, the latter of which is located in the first intron of s-Themis but transcribed in the opposite direction. These genes may encode male- and female-side self-recognition molecules. The SI system of C. intestinalis has a similar framework to that of flowering plants but utilizing different molecules.

The molecular basis of allorecognition in ascidians

“…The minimum number of loci that can explain these six clusters under the assumption of ''haploid-sperm hypothesis'' is two polymorphic SI loci. Harada et al (1) than found two genetic markers that segregated in similar manner, one on chromosome 2q and the other on 7q. Fine mapping narrowed the search regions and, among the transcription units situated in these regions of the chromosomes, they suggested two polycystin-1-like (PDK1) genes that code for transmembrane receptors, as the putative SI genes.…”

“…the primary sperm receptors, is located in the vitelline coat (VC) -the matrix surrounding the egg. (1,(11)(12)(13) Self sterility probably results from the failure of the sperm to bind to the VC of the autologous eggs. (14) However, self-sterility is not absolute and some are self-fertile.…”

“…(14) However, self-sterility is not absolute and some are self-fertile. (1,11,14) Attempts to determine the rules governing self-incompatibility in C. intestinalis were initiated in the 1930s by T.H. Morgan (15,16) who conducted various selfing and sibling crosses experiments.…”

“…The molecular basis governing both types of allorecognition, self incompatibility and non-self negative response, has been studied recently in several species of ascidian urochordate. (1,2,3,8,9) The subphylum Urochordata represents invertebrate chordates, considered as the ancestor of vertebrates, and thus may present an insight to the evolution of the vertebrate immune response.…”

Phospho-Signaling at Oocyte Maturation and Fertilization: Set Up for Embryogenesis and Beyond Part I. Protein Kinases

“…More recent studies have demonstrated that a similar system of the allogenic authentication (that utilizes gamete coat/membrane-associated proteins) is also present in animal hermaphrodite organisms (e.g. ascidian) (Harada et al 2008). Whether such animal system involves protein kinase signaling is unknown.…”