Related Experiment Videos
Evidence for both tyrosine kinase and G-protein-coupled pathways leading to starfish egg activation
F M Shilling1, D J Carroll, A J Muslin
1Department of Physiology, University of Connecticut Health Center, Farmington 06032.
Abstract:
To investigate possible pathways leading to egg activation at fertilization, the ability of exogenously introduced tyrosine kinase and G-protein-coupled receptors to mimic events of fertilization was examined. Oocytes of the starfish Asterina miniata were injected with RNA for a chimeric receptor consisting of the extracellular domain of the beta form of the mouse platelet-derived growth factor (PDGF) receptor and the transmembrane/intracellular domain of the human fibroblast growth factor (FGF) receptor, or with RNA for the rat serotonin 1c receptor. These oocytes were cultured for 1 to 3 days and then matured with 1-methyladenine. In response to PDGF or serotonin, the injected eggs underwent responses like those at fertilization: cortical granule exocytosis, a rise in intracellular free calcium, and DNA synthesis. Some of these artificially activated eggs cleaved, and some of the PDGF-activated eggs were observed to form larvae. A PDGF/FGF receptor with a point mutation which eliminated its ability to interact with phospholipase C-gamma did not cause fertilization-like responses. Thus components of a signaling pathway involving phospholipase C-gamma, characteristic of tyrosine kinase receptors, as well as components of a pathway involving a G-protein and phospholipase C-beta, characteristic of G-protein-coupled receptors, appear to be present in starfish eggs. Either or both could function in egg activation at fertilization.
Insights
Starfish eggs can be artificially activated using specific receptors, mimicking fertilization events like calcium release and DNA synthesis. This suggests conserved signaling pathways involved in egg activation across species.
Area of Science:
- Reproductive Biology
- Cell Signaling
- Developmental Biology
Background:
- Egg activation is a critical event in fertilization, initiating embryonic development.
- The precise molecular pathways triggering egg activation are not fully understood.
- Tyrosine kinase and G-protein-coupled receptors are known signaling molecules in various cellular processes.
Purpose of the Study:
- To investigate if exogenous tyrosine kinase and G-protein-coupled receptors can trigger egg activation in starfish.
- To identify potential signaling pathways involved in starfish egg activation.
Main Methods:
- Starfish oocytes were injected with RNA encoding chimeric PDGF/FGF receptors or serotonin receptors.
- Injected oocytes were matured and stimulated with platelet-derived growth factor (PDGF) or serotonin.
- Fertilization-like responses, including cortical granule exocytosis, calcium influx, and DNA synthesis, were monitored.
- A mutated PDGF/FGF receptor lacking phospholipase C-gamma interaction was used to assess pathway specificity.
Main Results:
- PDGF and serotonin successfully induced fertilization-like responses in injected starfish oocytes.
- These responses included cortical granule exocytosis, intracellular calcium increase, and DNA synthesis.
- Some artificially activated eggs underwent cleavage and even developed into larvae.
- A mutated receptor unable to interact with phospholipase C-gamma failed to elicit these responses.
Conclusions:
- Starfish eggs possess components of signaling pathways utilized by both tyrosine kinase and G-protein-coupled receptors.
- These pathways, involving phospholipase C-gamma and G-protein/phospholipase C-beta, are likely involved in natural egg activation.
- The findings suggest conserved mechanisms for egg activation in marine invertebrates.