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Time-lapse Microscopy of Early Embryogenesis in Caenorhabditis elegans
Published on: August 25, 2011
Time-dependent responses to glp-1-mediated inductions in early C. elegans embryos
1Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403-1229, USA.
Insights
In Caenorhabditis elegans embryos, GLP-1 (a Notch homolog) acts as a receptor for P2 and MS signals. Cell age, not signal identity, dictates AB descendant fate, suggesting time-dependent internal changes.
Area of Science:
- Developmental Biology
- Cell Signaling
- Genetics
Background:
- In Caenorhabditis elegans, early embryonic blastomeres ABa and ABp initially possess equivalent developmental potential.
- Inductive signaling from P2 and MS blastomeres at specific embryonic stages establishes distinct developmental fates for ABa and ABp descendants.
Purpose of the Study:
- To investigate the molecular mechanisms underlying differential cell fate determination in C. elegans early embryos.
- To identify the genes and signaling pathways involved in P2 and MS mediated inductions of AB descendants.
Main Methods:
- In vitro culture of isolated C. elegans embryonic blastomeres.
- Analysis of gene activity, including glp-1, apx-1, and SKN-1, during inductive signaling events.
- Experimental manipulation to assess the role of cell age versus signal identity in determining developmental responses.
Main Results:
- The glp-1 gene, encoding a Notch homolog, is essential for AB descendants responding to both P2 and MS signals, suggesting GLP-1 acts as a common receptor.
- P2 signaling requires the apx-1 gene (a Delta homolog), while MS signaling requires the SKN-1 transcription factor.
- The age of the responding AB descendants, rather than the identity of the signaling cell or ligand, is the primary determinant of their differential responses.
Conclusions:
- GLP-1 functions as a shared receptor for distinct inductive signals (P2 and MS) in C. elegans development.
- Time-dependent changes in intracellular factors within AB descendants mediate their varied responses to common receptor-mediated signaling pathways.
- This study elucidates a novel mechanism where developmental timing, rather than signal specificity, governs cell fate decisions in early embryogenesis.
Abstract:
In an embryo of the nematode Caenorhabditis elegans, two blastomeres at the 4-cell stage, ABa and ABp, are born with equivalent developmental potential. Subsequently, interactions with the P2 blastomere at the 4-cell stage and the MS blastomere at the 12-cell stage generate differences in developmental fate among descendants of ABa and ABp. We have reproduced these inductions in vitro using embryonic blastomeres isolated in cell-culture medium. We show that during these inductions only the responding AB descendants require the activity of the glp-1 gene, which is similar in sequence to Drosophila Notch, supporting models in which GLP-1 protein acts as a receptor for both the P2 and MS signals. We also show that P2 signaling requires the activity of the apx-1 gene, similar in sequence to Drosophila Delta, and that MS signaling requires the putative transcription factor SKN-1. We present evidence that the primary factor determining the different responses to these two signals is the age of the AB descendants, not the identity of the signaling cell or ligand. Therefore, we suggest that time-dependent changes in factors within AB descendants are responsible for their different responses to inductive signals that use a common receptor.
