Biological complexity: cell division reidentification (Introduction)

by David Turell , Sunday, September 17, 2017, 18:52 (2624 days ago) @ David Turell

How do cells know how to return to their functional capacity after division? After all they contain all the DNA of all functions, but must active some and suppress others. The mechanism is identified:

https://www.sciencedaily.com/releases/2017/09/170914152248.htm

"Prior to cell division, chromosomes are seemingly a jumbled mess. During cell division, parent cell chromosomes and their duplicates sort themselves out by condensing, becoming thousands of times more compact than at any other time. Researchers have long assumed that genes become "silent" during cell division, not being transcribed into proteins or regulatory molecules. This has left open the question of how genes get properly re-activated after cell division. Now, researchers in the Perelman School of Medicine at the University Pennsylvania have found that gene expression actually continues during cell replication.

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"First author Katherine C. Palozola, a doctoral candidate in the Zaret lab, is the first to find a way to look at gene activity in a living cell during division. Using a human liver cell line, she labeled the nucleic acid uridine (one of the four gene messenger building blocks) and followed it to see which genes were still active during replication.

"'We were surprised that gene expression was still on -- albeit at a low level -- during replication," Palozola said.

"Although chromosomes are extremely compact during cell division, with sequences for regulatory molecules buried and previously presumed to be unavailable to be transcribed, Palozola found that most genes and their nearby regions that promote gene function are still actively expressed. She discovered how cells wake up after cell division and recall "who they are." What ultimately drives cell differentiation are sequences of enhancer molecules located away from the gene they act on.

"The laboratory of Gerd Blobel at the Children's Hospital of Philadelphia had previously shown that these far-away modifiers "nap" during division, since it only lasts about 30 minutes -- relatively quickly in biological terms -- and come back online after a cell division cycle is complete.

""The most amazing thing about this study is that in the end, we had to throw what we thought we knew about this basic aspect of gene regulation out the window," Zaret said. "The findings indicate that we need to think about how promoters, rather than enhancers, are regulated during cell division. This refocusing will tell us how a cell's identity, as defined by the genes it expresses, is retained through cell division.'

Comment: Cell division is highly complex. Cell division occurred with first life. Therefore the mechanism had to exist from the beginning. It could not develop bit by bit, but was designed all at once. No other conclusion is logical.