The study of animal developmental mechanisms provides valuable insights into how life forms have evolved and diversified over millions of years. Researchers can trace the evolutionary changes that have occurred within different lineages by examining the embryonic development of various species. These studies shed light on how some of Earth’s earliest animals evolved into the diverse array of species we see today.
Simple animals’ body plans, lacking bones, brains, and even a complete gut, appear to have little in common with humans and their vertebrate relatives. Nonetheless, new research from Stowers Institute for Medical Research Investigator Matt Gibson, Ph.D., shows that appearances can be deceiving, and that a common genetic toolkit can be used in different ways to drive embryological development, resulting in very different adult body plans.
It is well established that sea anemones, corals, and jellyfish relatives shared a common ancestor with humans over 600 million years ago in the Earth’s ancient oceans. A new study from the Gibson Lab, published on June 13, 2023 in Current Biology, sheds light on the genetic basis for body plan development in the starlet sea anemone, Nematostella vectensis. This new information paints a vivid picture of how some of the world’s earliest animals evolved from egg to embryo to adult.
“Studying the developmental genetics of Nematostella is sort of like taking a time machine into the very distant past,” said Gibson. “Our work allows us to ask what life looked like long ago – hundreds of millions of years before the dinosaurs. How did ancient animals develop from egg to adult, and to what extent have the genetic mechanisms that guide embryonic development endured across millennia?”
Our work allows us to ask what life looked like long ago – hundreds of millions of years before the dinosaurs. How did ancient animals develop from egg to adult, and to what extent have the genetic mechanisms that guide embryonic development endured across millennia?
Matt Gibson
Most modern animals, from insects to vertebrates, develop by forming a series of head-to-tail segments with distinct identities depending on their position. A further polarity axis within a given segment informs cells whether they are at the front or back of the segment. This is referred to collectively as segment polarisation.
Shuonan He, Ph.D., a former Gibson Lab postdoctoral researcher, discovered genes involved in the development of the sea anemone, Nematostella vectensis, that guide segment formation and others that direct segment polarity programmes that are strikingly similar to organisms higher up the evolutionary tree of life, including humans.
“The significance is that the genetic instructions underlying the construction of extremely different animal body plans, for example, a sea anemone and a human, are incredibly similar,” said Gibson. “The genetic logic is largely the same.”
This new study builds on a Gibson Lab study published in Science in 2018 that found sea anemones have internal bilateral symmetry early in development with eight radial segments. The study found that Hox genes, which are master development genes important for human development, act to delineate segment boundaries and may have played an ancient role in segment construction.
The team’s most recent discovery investigates how segments form and what accounts for differences in their identities. Hundreds of new segment-specific genes were discovered using spatial transcriptomics, or differences in gene expression between segments. These include two critical genes that encode transcription factors that govern segment polarisation and are required for the proper placement of sea anemone-muscles.
The astonishing diversity of organisms on Earth can be compared to the assembly of Legos. “Whether you construct a dinosaur, a sea anemone, or a human, many of the core genetic building blocks are largely the same despite drastically different animal forms,” said Gibson.
This is the first time scientists have discovered a molecular basis for segment polarisation in a pre-bilaterian animal. While bilateral species such as fruit flies and humans have been extensively studied, the idea that cnidarian animals possess segmentation was unexpected. The team now has evidence that these segments are also polarised.
“This provides more evidence that studying a wide range of animals can have direct implications for understanding general principles, including those that apply to human biology,” Gibson said. “We can extrapolate back in time to understand how animals likely developed hundreds of millions of years ago by understanding the logic of sea anemone development and comparing it to what we see in vertebrates.”
