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Tigra Scientifica: Embryonic link to the common vertebrate form

Courtesy of monicore via Pexels

While taking a comparative vertebrate course here at Clemson, you will begin to notice that all vertebrates generally have the same form. 

The ubiquity of the vertebrate body has perplexed scientists for years. Since the evolution of the bilaterally symmetric body plan, little has changed as far as the chordate form. A chordate is an animal belonging to the phylum Chordata. 

A recent study published in Nature has found that the genes that govern the mid-embryonic developmental stages are more intensely recruited or expressed than any other genes during development. The paper suggests it is the favoring of these genes that has led to the consistency in vertebrate body plans throughout chordate evolution. 

Bilateral symmetry is a body plan that is oriented so that there is one line of symmetry that separates the left and right sides of the body. This body plan evolved sometime during late invertebrate evolution and was carried over in early vertebrate relatives. 

It is this body plan that has allowed for the evolution of cephalization (having a region called a head) as well as the complex locomotive system in vertebrates which typically consist of four “limbs.” 

In this study, Haiyang Hu and colleagues compared early and late embryonic developmental transcriptomes (the messenger RNA molecules expressed from the genes of an organism) to determine which genes were more intensely recruited, and found that it was the mid-developmental genes. 

They also found that the degree to which these genes were recruited correlated with the vertebrates “essentiality for normal development.” That is, without this recruitment of these genes, the embryo won’t fully develop. 

The researchers hypothesize that it is these genes and the essential nature of the mid-developmental stages that has led to the ubiquity of the bilateral symmetry among all vertebrates. 

This necessity of the gene expression has led to the common form we see from fish, to dogs, to humans and all vertebrates in-between. 

Comparative vertebrate biology classes may not have a fun work load but they give important insight into the commonalities we share with our evolutionary relatives, and studies like these present interesting hypotheses to explain these commonalties. 

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