Genome complexity: sperm set up DNA in 3-D (Introduction)

by David Turell , Monday, February 18, 2019, 17:31 (2104 days ago) @ David Turell

DNA is carefully packed in sperm cells to help control the fertilized egg cell:

https://phys.org/news/2019-02-scientists-reveal-d-dna-perpetuate.html

"Using new technology to reveal the 3-D organization of DNA in maturing male reproductive cells, scientists revealed a crucial period in development that helps explain how fathers pass on genetic information to future generations.

"The period was captured during a stage of male sperm development called meiosis. This is when reproductive cells, called germ cells, are maturing into sperm that can fertilize a female egg, laying the foundation to make all the cells of a child.

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"reproductive biologists at Cincinnati Children's Hospital Medical Center say nature prepares the 3-D organization of DNA before packing it into sperm.

"By the time the germ cells actually become fertile sperm, the genetic material is tightly arranged. The male germ cell's hereditary material has precise 3-D organization in the cell's genetic control center, the nucleus. Researchers report that this 3-D organization is necessary for a male to help produce the next generation of life.

"'We propose that male sperm is not just a carrier of DNA. Our data suggest that the three-dimensional organization in the cell nucleus helps establish a molecular foundation that can reproduce a complete zygote capable of becoming the next generation," said Satoshi Namekawa Ph.D., a principal investigator on the study and member of the Division of Reproductive Sciences.

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"Using the maturing germ cells of male mice for their study, the researchers honed in on meiosis, the stage when male germ cells shed half of their chromosomes while shuffling around genetic material.

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"Using a technology called Hi-C, researchers were able to show the 3-D organization and interactions of chromosomes, as well as the genes in the nucleus of meiotic male germ cells. The authors propose that preparing 3-D organization in meiosis is vital for genes that allow germ cells to regain their ability to produce all the cells of the body after fertilizing a female egg.

"'In meiosis, gene expression is extremely high and diverse," said Kris Alavattam, the study's first author and member of the Namekawa laboratory. "Many of these genes are essential for germ cells to develop, and many are expressed nowhere else but germ cells and at no other time." (my bold)

"During this time, the hereditary material in germ cells is organized in spatially related compartments called genomic compartments. In meiotic male germ cells, the researchers noticed genomic compartments are weaker than those in other cells of the body. This weakness helps facilitate what they call a global reprogramming of 3-D chromatin organization. This organization of chromatin—the packaging of DNA with DNA-binding proteins—promotes essential gene expression and germ cell development. After meiosis, genomic compartments of chromatin become stronger and stronger, packing DNA in a highly organized manner as cells ready for procreation."

Comment: Note my bold. There are specialized genes just for control of growing the embryo. In the new stage of sexual reproduction during evolution, all of these moving parts must have appeared all at once by design. It cannot have appeared stepwise by chance.