Researchers have made groundbreaking discoveries about the role of β-catenin signaling during the embryonic development of the sea anemone Nematostella vectensis, challenging traditional views of evolutionary biology.
For many years, it has been believed among scientists studying animal development, particularly the embryological processes of cnidarians compared to bilaterians, such as humans, frogs, and sea urchins, β-catenin played a consistent role as a signaling molecule both as activator and repressor during early stages of life formation. The oral-aboral axis of Nematostella vectensis is known to be patterned by β-catenin signaling. This study now demonstrates, for the first time, its conflicting role, with β-catenin signaling repressing endomesoderm specification. This research indicates potential evolutionary adaptations surrounding the processes of development.
Utilizing advanced genetic techniques, researchers tagged the endogenous β-catenin with superfolder GFP (sfGFP) using CRISPR/Cas9 genome editing methods, allowing for precise observation of the molecule's behavior and function. Live imaging techniques revealed nuclear sfGFP-β-catenin, indicating the presence of this important compound at various developmental stages of the embryo, particularly before and around the time of gastrulation.
The investigation highlighted key findings such as the detection of distinctly localized nuclear β-catenin signal, which revealed peaks at specific points along the oral-aboral (O-A) axis of the developing embryo. This showed conclusive evidence of the gradient effect of β-catenin within the area immediately surrounding the invaginating mesoderm, marking it as distinctly associated with gastrulation patterns.
“Strikingly, we show... Nematostella endomesoderm specification is repressed by β-catenin and takes place in the maternal nuclear β-catenin-negative part of the embryo,” stated the authors of the article. This finding indicates the establishment of endomesoderm specifications operates distinctly within the animal kingdom, especially when comparing cnidarians with the bilaterians.
One experiment involved live imaging tracking the dynamics of the fluorescently tagged β-catenin throughout various cell stages. The imaging revealed the endomesoderm invaginated contrarily from where the nuclear sfGFP-β-catenin was detectable, providing surprising insights about how cnidarians develop distinctly compared to bilaterians.
Additonally, the researchers conducted experiments breeding homozygous sfGFP-β-catenin females with wild-type males, confirming the maternal origins of the detected nuclear signals at different developmental stages. This established the groundwork for examining the traditional view of endomesoderm specification.
When Nematostella embryos were treated with the GSK3β inhibitor alsterpaullone, they displayed defects consistent with altered β-catenin signaling—an unexpected result compared to past studies of sea urchin embryos. These observations suggest β-catenin might possess opposing effects on embryonic development between these two biological evolutionary branches. Such different associations indicate greater complexity in cnidarian development than previously accepted.
The findings resonate with the overall evolutionary narrative concerning body plan diversification, providing insights about early multicellular organism evolution. “Our finding... confirms... the intended roles for β-catenin have been mischaracterized,” the researchers noted, highlighting the necessity for reevaluations surrounding concepts of germ layers and gastrulation.
This research opens several pathways for future investigations, linking the inherited placental features alongside the divergent developmental pathways between species. Future studies may build upon these findings, possibly examining embryonic developmental processes across differnet animal classifications to unravel other functional variances due to evolutionary adaptations.
The authors summarize their contributions, asserting the importance of recognizing how endomesoderm specification by β-catenin likely evolved throughout the Bilateria lineage, tethering gastrulation events to pivotal moments of early embryonic polarity formation. This exploration of the bushy tree of life may require significant adaptations to long-standing biological theories about embryonic development, potentially reshaping existing doctrines surrounding aquatic animals.