Day 84: ‘Inner Fish,’ huh? Tell that to my Pentecostal neighbor

Nope, this doesn't have much to do with the content below. I just thought it was funny.

 

Living in the Deep South for the past year and a half has been culturally enlightening. It has also, at times, been shocking.

I’m not likely to forget one of the first muggy summer evenings I sat around a picnic table with a couple of my neighbors. I’m not even sure how the subject of evolution came up, but both ladies — cigarette-smoking Christians — looked at me with their eyes wide when I said I believed in evolution. 

“Well, I don’t know about you,” said the one. “But I didn’t come from a fish.”

The divide was so wide, and my bafflement so complete, that I readily moved onto another subject, and we’ve stuck with other subjects ever since.

The neighbor who did not come from a fish and I have become close; I like her. And so I probably won’t show her the study that came out this week, which invokes the term “Inner Fish” in a new explanation for the extent of tissue conservation between even evolutionarily distant species.

(a) "Eyes of the world" by Paul Freed. When isolated from other aspects of head morphology, the remarkable conservation of eye morphology among animals is striking. Reproduced with permission. (b) Photos of eyes of various vertebrates shown above their gene-expression profiles. Data taken from Chan et al.

Esther Chan is lead author on the new study, which appeared Thursday in the open access Journal of Biology.  

Differences in the DNA between organisms — the actual code — is a common way to decipher evolutionary relatedness between species. It’s fairly intuitive that we would have more genes in common with a chimp, for example, than a bobcat.

But besides differences in the gene sequence, there’s another way to introduce variability between organisms: differences between the ways those genes are expressed. The timing, location and amount of expression of various genes can yield widely different results, even if the genes are the same. 

Previous studies have proposed that phenotypic (outwardly visible) differences among primates are mainly due to adaptive changes in gene regulation, rather than to changes in the actual genes. 

And so Chan and the research team wanted to know: In genetically distant organisms, how similar are the processes that lead to the gene expression?

They studied 3074 genes in widely different vertebrates (animals with backbones): chickens, frogs, pufferfish, mice and people. They found similar expression patterns across the species,  suggesting a basic ancestral pattern of expression in each tissue, the so-called ‘inner fish’.

The strongest similarities were seen in brain tissue.

“Genes involved in the more conserved processes on the whole tend to be preferentially expressed in tissues with a limited number of cell types (brain, eye, liver, heart and muscle) that carry out specialized functions particular to those tissues,” the authors wrote.

They think genes in tissues that interact more with the environment — such as the intestines, stomach and spleen — may be more likely to take on new roles and diverge, as they adapt.

They found that although the specialized DNA sequences that regulate the expression of the genes seem to have changed beyond recognition over the hundreds of millions of years since the organisms diverged, the actual patterns of gene expression held true.

The authors think some conserved patterns of expression may extend to non-vertebrates as well. Even nematodes, for example, show similarities to vertebrates in the way their nerve cells work.

Sources: A Eurekalert press release about the findings, the journal article and a mini-review, also in the Journal of Biology.