Biological complexity: cell division is complicated (Introduction)

by David Turell , Sunday, September 15, 2019, 23:38 (1677 days ago) @ David Turell

Newly discovered cell division by microtubules purse-string mechanism:

https://www.sciencedaily.com/releases/2019/09/190913191442.htm

"Cell biologist Thomas Maresca and senior research fellow Vikash Verma at the University of Massachusetts Amherst say they have, for the first time, directly observed and recorded in animal cells a pathway called branching microtubule nucleation, a mechanism in cell division that had been imaged in cellular extracts and plant cells but not directly observed in animal cells.

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"In particular, they want to understand how structures called microtubules help to define where the cell splits in half during the division process.

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"In normal cell division, chromosomes line up near the center of the cell, where a structure called the spindle aligns copies of each chromosome by interacting with a bridge-like structure called the kinetochore. When all the chromosomes have been aligned, microtubules pull the chromosome copies apart like a zipper. The cell then physically divides at a location positioned between the segregated chromosomes to produce two daughter cells, each with a complete copy of the genome.

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"...the division plane requires microtubules, Maresca says. "They grow out to touch the edges inside the cell membrane. Vikash found that the growing tips of the tubes, the 'plus-ends' that touch the membrane, say to the cell, 'This is where to divide.' Regulatory proteins get recruited to the site contacted by the plus-ends kicking into gear and a whole new pathway assembles a ring that will constrict like a purse string to split one large cell into two smaller ones."

"Timing plays a role, as well, the researchers found. "It seems that all the microtubule tips have the special ability to trigger the purse-string pathway," Maresca says, "but over time, something changes and only the tips in the middle of the cell retain that ability." Referring to work published in eLife in February, he adds, "We found what we think is a very important spatial cue for how the cell positions its division plane."

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"Once they could visualize the entire process of branching nucleation in a cell, he adds, "We knew we could next 'tag' proteins that regulate the process with different colors to further quantify fundamental parameters of the phenomenon. All of a sudden we realized that this is the first time one could see this happening in living animals cells."

"Branching nucleation is fundamental and conserved, one of the essential parts of mitosis, but it's been difficult to directly visualize in other model systems, Maresca points out. "The course of this project was a reminder that some of the most exciting work we do as scientists is unplanned and, especially for microscopists, begins with seeing something in the cell unfold right before your eyes.'"

Comment: Highly complex protein molecular movements of this type require exact design so that each new daughter cell is the same as the original cell. This cannot be accomplished by chance, and requires guidance by a designing mind.