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Updated: Aug 11, 2026
The Power of Simplicity: Sea Urchin Embryos as in Vivo Developmental Models for Studying Complex Cell-to-cell Signaling Network Interactions
Published on: February 16, 2017
Activation of pmar1 controls specification of micromeres in the sea urchin embryo
Paola Oliveri1, Eric H Davidson, David R McClay
1Division of Biology, 156-29, California Institute of Technology, Pasadena, CA 91125, USA.
Abstract:
pmar1 is a transcription factor in the paired class homeodomain family that was identified and found to be transcribed in micromeres beginning at the fourth cleavage of sea urchin development [Dev. Biol. 246 (2002), 209]. Based on in situ data, molecular perturbation studies, and QPCR data, the recently published gene regulatory network (GRN) model for endomesoderm specification [Science 295 (2002) 1669; Dev. Biol. 246 (2002), 162] places pmar1 early in the micromere specification pathway, and upstream of two important micromere induction signals. The goal of this study was to test these three predictions of the network model. A series of embryo chimeras were produced in which pmar1 activity was perturbed in one cell that was transplanted to control hosts. At the fourth cleavage, micromeres bearing altered pmar1 activity were combined with a normal micromereless host embryo. If beta-catenin signaling is blocked, the micromeres remain unspecified and are unable to signal to the host cells. When such beta-catenin-blocked micromeres also express Pmar1, all observed micromere functions are rescued. The rescue includes expression of the primary mesenchyme cell (PMC) differentiation program, expression and execution of the Delta signal to induce secondary mesoderm cell (SMC) specification in macromere progeny, and expression of the early endomesoderm induction signal necessary for full specification of the endoderm. Additionally, Pmar1 expressed mosaically from inserted DNA constructs causes induction of ectopic Endo 16 in adjacent cells, demonstrating further that Pmar1 controls expression of the early endomesoderm induction signal. Based on these experiments, Pmar1 is an important transcription factor necessary for initiating the micromere specification program and for the expression of two inductive signals produced by micromeres. Each of the tests we describe supports the placement and function of Pmar1 in the endomesoderm GRN model.
Insights
PMAR1 is a crucial transcription factor for sea urchin development. It initiates micromere specification and controls key inductive signals, ensuring proper endomesoderm formation and cell differentiation.
Area of Science:
- Developmental Biology
- Molecular Genetics
- Gene Regulatory Networks
Background:
- PMAR1, a paired class homeodomain transcription factor, is expressed in sea urchin micromeres starting at the fourth cleavage.
- A recently proposed gene regulatory network (GRN) model places PMAR1 upstream of key inductive signals in endomesoderm specification.
Purpose of the Study:
- To experimentally validate the predicted role and placement of PMAR1 within the endomesoderm GRN model.
- To investigate the necessity of PMAR1 for initiating micromere specification and inductive signaling.
Main Methods:
- Construction of sea urchin embryo chimeras with perturbed PMAR1 activity in transplanted micromeres.
- Utilizing beta-catenin signaling blockade to assess micromere function and PMAR1's rescue capabilities.
- Mosaic expression of PMAR1 via DNA constructs to evaluate its role in endomesoderm induction.
Main Results:
- PMAR1 activity perturbation in transplanted micromeres was tested in host embryos.
- PMAR1 expression rescued the function of beta-catenin-blocked micromeres, restoring primary mesenchyme cell (PMC) differentiation.
- PMAR1 rescued Delta signal expression for secondary mesoderm cell (SMC) specification and endoderm induction.
- Mosaic PMAR1 expression induced ectopic Endo 16, confirming its role in early endomesoderm induction.
Conclusions:
- PMAR1 is essential for initiating the sea urchin micromere specification program.
- PMAR1 controls the expression of critical inductive signals from micromeres, including those for SMC specification and endoderm formation.
- Experimental findings strongly support PMAR1's position and function within the established endomesoderm GRN model.
