Genome complexity: yeast evolution by expression (Introduction)

by David Turell , Tuesday, March 12, 2024, 17:11 (255 days ago) @ David Turell

Old genes used in a different way:

https://mail.google.com/mail/u/0/#inbox/FMfcgzGxSHgkzbptQmvlbsKKRccQvqzp

"...when researchers propagated only the biggest yeast cells for thousands of generations, these single-celled fungi went from making snowflake-esque clusters “weaker than gelatin” to clumps “as strong as wood” and 20,000 times the size of initial flakes (see above). Partly to thank for this impressive transformation is the chaperone protein Hsp90, which helps fold other proteins into their proper shapes, they report.

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"Georgia Institute of Technology evolutionary biologist William Ratcliff and colleagues originally set out to recreate the evolutionary origins of multicellular organisms in the lab. To do this, they cultured brewer’s yeast in tubes for some 3000 generations...
selecting only the largest ones. Within two months, their single-celled starters had become ‘snowflakes’: conjoined clusters of elongated cells. And these flakes got bigger and bigger until their branches began to tangle with one another, creating dense clumps that withstood mechanical testing as well as some varieties of wood.

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"They found that the tougher yeasts—which evolved in five separate runs of the experiment—had dialed down the gene for Hsp90, making about 40% less of it. That had knock-on effects: Because Hsp90 stabilizes a protein called Csc28, 40% less Hsp90 resulted in 25% less Cdc28. And Cdc28 happens to be involved in telling the cell when to progress through certain stages of the cell cycle.

"All of this ultimately means that the yeast cells take longer to complete the process of budding into new cells—and during that delay, they grow, leading to the elongated shape. Intriguingly, neither the gene for Hsp90 nor the one for Cdc28 were mutated. Instead, the altered activity of a transcription factor was responsible for the morphological change. “We tend to focus on genetic change and were quite surprised to find such large changes in the behavior of chaperone proteins,” Ratcliff says . “This underscores how creative and unpredictable evolution can be when finding solutions to new problems, like building a tough body.” (my bold)

From the original paper:

https://www.science.org/doi/10.1126/sciadv.adn2706?utm_source=sfmc&utm_medium=email...

"Abstract
The evolution of multicellularity paved the way for the origin of complex life on Earth, but little is known about the mechanistic basis of early multicellular evolution. Here, we examine the molecular basis of multicellular adaptation in the multicellularity long-term evolution experiment (MuLTEE). We demonstrate that cellular elongation, a key adaptation underpinning increased biophysical toughness and organismal size, is convergently driven by down-regulation of the chaperone Hsp90. Mechanistically, Hsp90-mediated morphogenesis operates by destabilizing the cyclin-dependent kinase Cdc28, resulting in delayed mitosis and prolonged polarized growth. Reinstatement of Hsp90 or Cdc28 expression resulted in shortened cells that formed smaller groups with reduced multicellular fitness. Together, our results show how ancient protein folding systems can be tuned to drive rapid evolution at a new level of biological individuality by revealing novel developmental phenotypes." (my bold)

Comment: the complexity of the various levels of genetic controls is shown in this study. A simple change in controls of folding in chaperone proteins caused major phenotypical changes. No new mutations needed. We do not know how often this type of transcription alteration is used in creating new modified forms. What it does infer is how human are formed with only a catalog of 20,000+ genes by the possible interplay of varying gene expressions, by modification of transcription factors.