Carnegie Mellon University
January 29, 2021

Switches and Kernels Allow for Novelty in Early Development

By Jocelyn Duffy

Jocelyn Duffy
  • Associate Dean for Communications, MCS
  • 412-268-9982

Most animals are created in a similar way, starting with a fertilized egg that divides into many, many cells of differing types. Cells are told what to become — skin cells, nerve cells, etc. — by complex signaling pathways called gene regulatory networks (GRNs). During embryogenesis, this process is very precise, and any deviation could prove harmful, or even deadly, to the developing organism. 

But this doesn’t mean that change doesn’t happen – in fact it’s essential to the evolution of an organism. The shear diversity of living organisms on earth is evidence that changes to GRNs happen and happen often. 

“This presents a conundrum of how changes can be incorporated into development in ways that allow for developmental stability,” said Veronica Hinman, Dr. Frederick A. Schwertz Distinguished Professor of Life Sciences and head of the Department of Biological Sciences at Carnegie Mellon University.

To understand how changes, or novelty, is incorporated into early development without impacting viability, Hinman’s lab assembled the gene regulatory network of the sea urchin and compared it to the previously described GRN of the sea star. Their findings are published in Nature Communications

Sea urchins and sea star embryos begin life in an almost identical fashion. Early in development a novel gene, pmar1, signals the embryo to differentiate into a sea urchin. The researchers looked to discover how, in the course of evolution, the one species was able to survive the addition of pmar1 to its GRNs. The researchers found that the inclusion of pmar1 created a switch between two stable modes of a signaling pathway that regulates cell proliferation, fate and differentiation called Delta-Notch signaling. Furthermore, the found that each species maintained evolutionarily conserved network motifs, called kernels, that helped to “lock down” essential elements of development.

The researchers believe that these switches and kernels might be a common evolutionary mechanism that allows organisms to survive novelty in the early stages of development.

The team now seeks to understand how the GRNs for these embryos are used to reshape the animal during metamorphosis into its adult form. Many animals undergo a dramatic metamorphosis between two body plans, but it remains a mystery how one genome can encode two entirely different forms.

Additional study authors include senior scientist Gregory A. Cary, Brenna S. McCauley, Olga Zueva and Joseph Pattinato from Carnegie Mellon University’s Department of Biological Sciences and William Longabaugh from the Institute for Systems Biology.  Brenna, a former graduate student is now a postdoctoral scientist at Baylor College of Medicine and Jo Pattinato is now pursuing his Bachelor’s degree at the University of Pittsburgh.

The research was funded by the Binational Science Foundation (2015031), National Science Foundation (IOS 1557431, MCB 1715721) and the National Institutes of Health (P41HD071837).