Human evolution: our amazingly complex cells (Introduction)

by David Turell , Sunday, June 30, 2024, 16:42 (144 days ago) @ David Turell

Cataloging cells by DNA expression finds we have thousands of differently acting cells:

https://www.quantamagazine.org/new-cell-atlases-reveal-untold-variety-in-the-brain-and-...

"Powerful sequencing and imaging technologies invented in the last decade are revealing with unprecedented detail the composition of human organs and tissues, from the pancreas and liver to the placenta, as well as those of other animals like the mouse and fruit fly. With these new tools, researchers can fingerprint individual cells based on which genes they are expressing. That information has revealed subtle and unsuspected distinctions among cells and has begun to illuminate how the diversity of cell types can be essential to the healthy functioning of organs.

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"Today in Nature, a coalition of laboratories published nine studies that collectively form a detailed atlas of the mouse brain — the most comprehensive mammalian brain atlas to date. It describes more than 5,300 types of cells found throughout the organ. How these cells are distributed and are related to one another suggests many intriguing ideas about the evolution of the mammalian brain.

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"Because of that work, it’s clear that the human brain contains at least 3,300 distinct types of neurons, each expressing a different set of genes, which hints that the cells could serve a range of slightly different functions. Much of this diversity, it turns out, is in the less studied and more evolutionarily ancient regions of the brain.

"This human brain cell atlas is merely an early edition. As scientists continue the task of tallying and classifying every single cell in the brain, they will likely identify thousands of additional cell types.

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"The differences in our cells don’t come from differences in the genes themselves: Every cell in your body contains a copy of your distinctive DNA and the 20,000 genes for making proteins it encodes. “The genome is a parts list,” Quake said. “There’s no way to predict which cell types come out of a given genome.” (my bold)

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"Using a powerful set of single-cell genomics tools, scientists can read these expression patterns to fingerprint a cell. These tools have matured over the past few years so that scientists can now quickly and efficiently look at tens of thousands or even millions of cells in a single experiment.

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"With each new cell atlas, researchers have had to reckon with how much complexity they were missing before. Reviewing the data sometimes made Angelo feel as if he were looking at endlessly looping videos of fractals, he said. “You keep zooming in” and the pattern goes on indefinitely; the more you uncover, the more you realize there’s more to uncover. “A lot of this is kind of daunting.”

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"The analysis revealed “an extreme amount of diversity,” Doege said. They identified more than 350 distinct neuron populations and 19 non-neuron cell populations from 10 different regions within the hypothalamus. (my bold)

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"Across the entire brain, the research teams discovered more than 3,300 different types of neurons — and that account is surely incomplete. The most comprehensive atlas of the mouse brain to date, published today, identified 5,300 cell types, including both neurons and glia. The project is missing cell census data from some areas, such as the medulla. Still, researchers think that the full count of cell types for the human brain, when it is compiled, will likely be similar.

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"The findings inside the brain cell atlas alone are dizzying. But then consider that other cell atlases are uncovering similar trends. In organ after organ, researchers seem to be finding a greater diversity of cell types than they expected. These discoveries suggest that the healthy functioning of tissues often depends on having the right mix of cells doing slightly different jobs. Each individual cell atlas therefore provides almost incalculable new possibilities for understanding a region of the body, and all the things that can go wrong with it.

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"Future cell atlases will probably also probe cell identity more deeply. Most cell maps are looking only at messenger RNA, which is “not even the only kind of RNA in the cell,” Quake said. Moreover, an expressed gene doesn’t necessarily mean that a specific protein is present in a cell. A future goal is to gather data on which proteins and other molecular products are present in single cells, Rhea said."

Comment: the microscopic level is passé. RNA studies will show us how many differently functioning cells exist. We are finally looking at the basis of life's functions as expressed in the cellular genome. Not by chance.