Sea stars can serve as a model to understand organ formation

“Most of our organs are tubular, because they need to transport fluids or gases or food or blood. And more complex organs like the heart start as a tube and then develop different structures. So, tubulogenesis is a very basic step to form all our organs,” explained  Margherita Perillo, who led this new study, in an official release.

However, not much is known about the general mechanisms that lead to the formation of hollow tubes during embryogenesis, as each animal use a different strategy to form these structures. That’s where these sea stars come in. 

Why were sea stars selected?

According to the study's authors, tube formation in sea stars could serve as a model for understanding the early stages of organ development. 

The mechanisms used to form tubes in a sea star are thought to be conserved by all vertebrates. Furthermore, this animal is said to be at the base of the Tree of life, before the chordates. Thus, it could provide an interesting insight into evolution. Reportedly, sea stars have been on Earth for millions of years.   

Furthermore, their embryos are transparent, making them an ideal candidate for studying the critical tubulogenesis mechanism without harming the animal. And, these sea stars can be found all year long. 

What do the sea stars teach us?

The initiation and early stages of tube formation were documented in this new study. The researchers examined gene function using techniques like CRISPR. Along with this, they also created long-duration time-lapse movies of the development stage of sea star larvae. Altogether, this aided in peering into sea star’s biology, and how tubes branch out from their gut. 

This finding may shed light on how a single cell proliferates to form complex 3D tubular structures in various organs. 

Perillo explains, “there is a big round of cell proliferation before all the cells start to make very complex migration patterns to elongate, change their shapes, and become a tube.”

While in the case of the sea star: “I found that, in order for tube formation, cells can proliferate and migrate at the same time. So, this means that this mechanism of making organs was already established at the base or root of the evolution of chordates,” she added.

Cell proliferation and migration occur concurrently in other animals, including mammals. The authors state that many biomedical studies can be modeled after sea stars, particularly to understand cancer. 

The new study has been published in the journal Nature Communications.

Study abstract:

A fundamental goal in the organogenesis field is to understand how cells organize into tubular shapes. Toward this aim, we have established the hydro-vascular organ in the sea star Patiria miniata as a model for tubulogenesis. In this animal, bilateral tubes grow out from the tip of the developing gut, and precisely extend to specific sites in the larva. This growth involves cell migration coupled with mitosis in distinct zones. Cell proliferation requires FGF signaling, whereas the three-dimensional orientation of the organ depends on Wnt signaling. Specification and maintenance of tube cell fate requires Delta/Notch signaling. Moreover, we identify target genes of the FGF pathway that contribute to tube morphology, revealing molecular mechanisms for tube outgrowth. Finally, we report that FGF activates the Six1/2 transcription factor, which serves as an evolutionarily ancient regulator of branching morphogenesis. This study uncovers distinct mechanisms of tubulogenesis in vivo and we propose that cellular dynamics in the sea star hydro-vascular organ represents a key comparison for understanding the evolution of vertebrate organs.