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CRISPR-Cas9-based Mutagenesis in the Entomopathogenic Nematode Steinernema hermaphroditum and the Maintenance of Mutant Lines
Published on: December 30, 2025
Mutations in two independent pathways are sufficient to create hermaphroditic nematodes
Chris Baldi1, Soochin Cho, Ronald E Ellis
1Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey, Stratford, NJ 08084, USA.
Science (New York, N.Y.)
|December 8, 2009
Summary
The evolution of hermaphroditism in nematodes likely involved two key genetic changes. These include a mutation enabling XX individuals to produce sperm and another allowing this sperm to activate independently.
Area of Science:
- Evolutionary genetics
- Developmental biology
- Nematode reproductive strategies
Background:
- The nematode Caenorhabditis elegans exhibits self-fertile hermaphroditism, offering insights into the evolution of novel traits from ancestral gonochoristic (male/female) species.
- The related species Caenorhabditis remanei possesses distinct male and female sexes, serving as a model to investigate the genetic underpinnings of sex determination and reproduction.
- Understanding the genetic basis of hermaphroditism in Caenorhabditis can elucidate the evolutionary pathways leading to the emergence of this reproductive mode.
Purpose of the Study:
- To investigate the genetic requirements for the evolution of self-fertile hermaphroditism in the Caenorhabditis genus.
- To determine the specific genetic mutations that could facilitate the transition from a male/female system to a self-fertile hermaphroditic system.
- To model the potential two-step evolutionary process leading to hermaphroditism in Caenorhabditis.
Main Methods:
- Utilized RNA interference (RNAi) to reduce the activity of specific genes involved in sex determination and sperm activation.
- Manipulated gene expression in the XX (hermaphrodite) animals of Caenorhabditis remanei.
- Assessed the ability of sperm produced by manipulated XX animals to activate and fertilize oocytes.
Main Results:
- Reducing tra-2 gene activity in XX C. remanei animals induced spermatogenesis, but the sperm required male seminal fluid for activation.
- Simultaneously reducing tra-2 and swm-1 gene expression in XX C. remanei animals resulted in self-fertile hermaphrodites with active sperm.
- The gene swm-1, which regulates sperm activation in C. elegans, was found to be crucial for enabling self-fertility in manipulated XX animals.
Conclusions:
- The evolution of hermaphroditism in Caenorhabditis likely occurred in two distinct genetic steps.
- The first step involved a mutation in the sex-determination pathway leading to XX spermatogenesis.
- The second step involved a mutation in a gene like swm-1, enabling self-activation of sperm and thus self-fertility.
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