Maternal TGF-β ligand Panda breaks the radial symmetry of the sea urchin embryo by antagonizing the Nodal type II receptor ACVRII.

In the highly regulative embryo of the sea urchin Paracentrotus lividus, establishment of the dorsal-ventral (D/V) axis critically depends on the zygotic expression of the TGF-β nodal in the ventral ectoderm. nodal expression is first induced ubiquitously in the 32-cell embryo and becomes progressively restricted to the presumptive ventral ectoderm by the early blastula stage. This early spatial restriction of nodal expression is independent of Lefty, and instead relies on the activity of Panda, a maternally expressed TGF-β ligand related to Lefty and Inhibins, which is required maternally for D/V axis specification.

Developmental toxicity of pre-production plastic pellets affects a large swathe of invertebrate taxa.

Microplastics pose risks to marine organisms through ingestion, entanglement, and as carriers of toxic additives and environmental pollutants. Plastic pre-production pellet leachates have been shown to affect the development of sea urchins and, to some extent, mussels. The extent of those developmental effects on other animal phyla remains unknown.

RAS-independent ERK activation by constitutively active KSR3 in non-chordate metazoa.

During early development of the sea urchin embryo, activation of ERK signalling in mesodermal precursors is not triggered by extracellular RTK ligands but by a cell-autonomous, RAS-independent mechanism that was not understood. We discovered that in these cells, ERK signalling is activated through the transcriptional activation of a gene encoding a protein related to Kinase Suppressor of Ras, that we named KSR3. KSR3 belongs to a family of catalytically inactive allosteric activators of RAF.

Deciphering and modelling the TGF-β signalling interplays specifying the dorsal-ventral axis of the sea urchin embryo.

During sea urchin development, secretion of Nodal and BMP2/4 ligands and their antagonists Lefty and Chordin from a ventral organiser region specifies the ventral and dorsal territories. This process relies on a complex interplay between the Nodal and BMP pathways through numerous regulatory circuits. To decipher the interplay between these pathways, we used a combination of treatments with recombinant Nodal and BMP2/4 proteins and a computational modelling approach.

Maternal factors regulating symmetry breaking and dorsal-ventral axis formation in the sea urchin embryo.

Specification of the main axes of polarity of the embryo is an essential process during embryonic development. In many species, this process is achieved by the localization of maternal factors into discrete regions of the egg. However, in other animals, like in amniotes and in echinoderms, the considerable plasticity of the early blastomeres seems to preclude the existence of maternal determinants and the mechanisms by which the radial symmetry of the egg is broken remain largely enigmatic.

Expression of exogenous mRNAs to study gene function in echinoderm embryos.

With the completion of the genome sequencing projects, a new challenge for developmental biologists is to assign a function to the thousands of genes identified. Expression of exogenous mRNAs is a powerful, versatile and rapid technique that can be used to study gene function during development of the sea urchin. This chapter describes how this technique can be used to analyze gene function in echinoderm embryos, how it can be combined with cell transplantation to perform mosaic analysis and how it can be applied to identify downstream targets genes of transcription factors and signaling pathways.

p38 MAPK as an essential regulator of dorsal-ventral axis specification and skeletogenesis during sea urchin development: a re-evaluation.

Dorsal-ventral axis formation in the sea urchin embryo relies on the asymmetrical expression of the TGFβ Nodal. The p38-MAPK pathway has been proposed to be essential for dorsal-ventral axis formation by acting upstream of expression. Here, we report that, in contrast to previous studies that used pharmacological inhibitors of p38, manipulating the activity of p38 by genetic means has no obvious impact on morphogenesis.

The Maternal Maverick/GDF15-like TGF-β Ligand Panda Directs Dorsal-Ventral Axis Formation by Restricting Nodal Expression in the Sea Urchin Embryo.

Specification of the dorsal-ventral axis in the highly regulative sea urchin embryo critically relies on the zygotic expression of nodal, but whether maternal factors provide the initial spatial cue to orient this axis is not known. Although redox gradients have been proposed to entrain the dorsal-ventral axis by acting upstream of nodal, manipulating the activity of redox gradients only has modest consequences, suggesting that other factors are responsible for orienting nodal expression and defining the dorsal-ventral axis. Here we uncover the function of Panda, a maternally provided transforming growth factor beta (TGF-β) ligand that requires the activin receptor-like kinases (Alk) Alk3/6 and Alk1/2 receptors to break the radial symmetry of the embryo and orient the dorsal-ventral axis by restricting nodal expression.

Planarian regeneration: achievements and future directions after 20 years of research.

Planarians can undergo dramatic changes in body size and regenerate their entire body plan from small pieces after cutting. This remarkable morphological plasticity has made them an excellent model in which to analyze phenomena such as morphogenesis, restoration of pattern and polarity, control of tissue proportions and tissue homeostasis. They have a unique population of pluripotent stem cells in the adult that can give rise to all differentiated cell types, including the germ cells.