New tech reveals secrets of animal evolution

A model for germ-layer evolution
A model for germ-layer evolution.

Technology developed in Israel has helped decipher the secrets of animal evolution – and it may have a side benefit in helping to understand cancer.

Most animal embryos contain three layers of cells that transform into every part of the body — from brains to bones to guts. Since the 19th century, biologists have been puzzling over which of these layers came first in animal evolution.

Using a method called CEL-Seq that can spy on the activity of every gene within a cell at once, Technion-Israel Institute of Technology Associate Professor Itai Yanai and his colleagues have provided compelling evidence that the layer called the endoderm evolved first, followed by the ectoderm layer and finally the mesoderm layer.

Yanai has other big plans for CEL-Seq. “We applied this unbelievably powerful tool to figuring out the evolution of the germ layers, a 19th century problem, but it will also be useful in things like cutting-edge cancer research as well,” he said.

Yanai and his colleagues used CEL-Seq to show that genes turned on in the endoderm of a worm embryo are the first to turn on in development, followed by genes turning on in the ectoderm and then mesoderm. They also detected that endoderm genes are older than genes mostly found in the ectoderm and mesoderm.

In their paper published in Nature, the researchers argue that the endoderm layer dates back to ancient single-celled organisms that banded together to form the first multicellular animals. Endoderm cells kept up their ancestral feeding function in the new animals, which freed up the other cells to evolve into new layers in the animal.

Understanding how evolution has altered cells in the past can also “reveal to us what is easily changeable and what is not changeable in a cell,” Yanai added. “If a cell goes into a disease state, for instance, we might know more about what we could do to reverse this state and what might be more difficult to reprogram in the cell.”

CEL-Seq was invented at Technion in 2012 by the Yanai lab. Yanai said that one way to envision the method’s power is to consider a single human cell and the 20,000 genes it contains as a room with 20,000 light switches.

“Each room can have a different mood, because we can turn on or turn off those switches in many different ways. This is why cells with the same genes can have many, many different types of behavior,” he explained. “With this method, we can take a given cell and know the position of every switch — whether it’s on or off — and from this infer what functions are going on.”

Currently a Fellow at the Radcliffe Institute of Advanced Study at Harvard University, Yanai is using the method to study the development of tumors in zebrafish. “For the last ten years I’ve been working on development and evolution, all seen through the eyes of gene expression,” he said, “and I’ve realized that cancer is actually a natural extension of this work since here you also have cells developing and evolving.”

Yanai’s team hasn’t finished unleashing CEL-Seq on other big questions in biology, either. One of their ongoing studies uses the method to look at all the genes in ten vastly different animal species and compare how they are regulated throughout the development of the embryo. “We want to see what makes an animal an animal, what is universal across all of them,” Yanai said.

One thought on “New tech reveals secrets of animal evolution

  • March 10, 2015 at 8:40 am

    This work is indeed interesting, but wordings used in articles such as this (and sometimes even by the researchers) can all too easily help propagate the myth that structural and behavioral changes are driven by the gene (or group of genes) rather than by selection pressure, a function of the overall evolutionary network.

    That the evolutionary processes of biology are not nearly as simple as that naively portrayed by Dawkins in “The Selfish Gene” has long been apparent and is now widely recognized. The importance of gene transfer in bacterial species, for instance, finally achieved scientific recognition as a result of the dogged efforts of Lynn Marguilis, who was also a proponent of the Gaia hypothesis, which actually preempts Kaufmans more recent realization of the enormously high degree of interactivity and synergy between the myriad components of the biosphere.

    Dawkins’ books found popular favor in the wave of “gene fever” that developed from the elucidation of the structure of DNA by Rosalind Franklin et al. His anthropomorphic allusions and dogmatic support of the gene-centric hype promulgated in the media has engendered gross misunderstandings among the public and even led to skewed mind-sets among some biologists.

    The average layman today seems to be convinced of such bizarre notions that there are genes for being a smoker, homosexual, watching a particular TV show and practically any other kind of behavior or attribute!

    Some with a little more biological knowledge similarly hold the opinion that DNA is somehow “the brains of the cell”. That DNA controls cellular activities.

    It is important to bear in mind that the genome is merely a rather small library of protein recipes. It is entirely passive. It is actively manipulated, maintained and accessed by RNA and other cellular machinery.

    In my writings I use the analogy of a piano rather than a switch-bank to represent DNA. The piano itself is entirely passive, as is DNA. But a pianist can produce innumerable musical variations by using this passive array of strings.
    In biology, the pianist corresponds to the machinery of the cell together with the inputs from its environment.

    Biological evolution is, after all, a network function.

    The network model of inheritance and morphogenesis is explored more fully in my latest book “The Intricacy Generator: Pushing Chemistry and Geometry Uphill“, a 336 page illustrated paperback now available from Amazon, etc


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