Genome complexity: sorting sperm and egg chromosomes (Introduction)

by David Turell , Wednesday, July 01, 2020, 19:36 (1396 days ago) @ David Turell

There is a special process:

https://phys.org/news/2017-08-marriage-microscopy-techniques-reveals-d.html

"Researchers at the Stowers Institute for Medical Research have solved the three-dimensional structure of a complex that is essential for the correct sorting of chromosomes into eggs and sperm during reproductive cell division or meiosis.

"When this structure, called the synaptonemal complex, doesn't assemble properly in the cell, it can lead to chromosomal abnormalities, miscarriages, and birth defects.

"Since the synaptonemal complex was first discovered in 1956, researchers have been trying to identify its many moving parts and how they fit together.

***

"'The structure was so much more complicated and beautiful than we ever imagined," says R. Scott Hawley, Ph.D., an investigator at the Stowers Institute and senior author of the study. "We thought it just looked like a railroad track, but we discovered that it is actually more like two railroad tracks, one stacked on top of the other. That changes the way we think about this structure and what it does."

"In meiosis, the cell copies all its chromosomes, pairs them up, and then divides them into eggs or sperm. This carefully choreographed process is helped along by the synaptonemal complex, an assembly of proteins that forms between the paired homologous chromosomes and keeps them properly aligned and in position. Errors during meiosis are a leading cause of miscarriages in humans.

***

"What they found was startling: the structure was divided into two identical layers, which had been indistinguishable at lower resolution. Basically, the synaptonemal complex connects two homologous chromosomes, each with two sister chromatids stacked on one another. The researchers showed that this complex uses a two-tiered approach to connect the two upper chromatids and the two lower chromatids separately. They created a computer model of the structure showing coils of DNA connected by two sets of railroad tracks, which are made up of the four known proteins that are part of the synaptonemal complex. Although in this study the researchers looked at only four proteins, many more unknown proteins likely reside in the structure as well, so there are still more details to fill in.

"'This was a really incredible insight, a technical leap using this new methodology of expansion microscopy and merging it with structured illumination to create a way to look at a structure that hasn't been resolved before," says Hawley. "There is a lot more we can learn. The deeper we dive into structure, the more complexity we see, the more amazing the structure becomes. Structure provides so much insight into function.'"

Comment: Look at the picture. It has to be designed.

https://scx2.b-cdn.net/gfx/news/hires/2017/marriageofmi.png