If a species wants to survive, genetic information has to be passed successfully from one generation to the next. For fathers and sons, DNA must be carefully packaged in sperm. Now scientists have learned more about the three-dimensional arrangement of DNA in the mature cells of the male reproductive system, revealing more about a critical stage of development. The findings have been reported in Nature Structural & Molecular Biology.
Reproductive biologists at the Cincinnati Children's Hospital Medical Center studied germ cells - cells of the reproductive system, during meiosis, when sperm mature so they can fertilize a female egg. The genetic material has to be tightly organized before the sperm will be fertile, and it has to be arranged in a precise way. The researchers determined that this process is imperative to create the next generation.
"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," explained Satoshi Namekawa Ph.D., a principal investigator of the study and member of the Division of Reproductive Sciences.
This work suggests that the arrangement of genetic material may impact pregnancies in various ways.
During meiosis, male germ cells get rid of half of their chromosomes. In mammals, males and females pass on half of their genetic material to their offspring, so each human parent contributes 23 chromosomes, and their child has 46.
In this work, the researchers assessed the structure of chromosomes and how they interacted. They also looked at genes during meiosis. They found that three-dimensional organization is critical for the genes that enable germ cells to fertilize a female egg and then go on to produce all the cells a body needs to grow.
"In meiosis, gene expression is extremely high and diverse," said the first author of the work Kris Alavattam. "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."
The genetic material in germ cells has to be arranged in compartments during meiosis. The researchers found that male meiotic cells have weaker genomic compartments than other cells, which encourages reprogramming in chromatin organization. Chromatin is packaged DNA and proteins, and its structure has a major impact on gene expression. After meiosis, chromatin genomic compartments get stronger.
The researchers now want to know more about whether disruptions in chromatin organization have a detrimental effect on fertility.
Learn more about germ cells from the video.