Researchers have discovered a key component which helps sperm and eggs develop exactly 23 chromosomes each. In addition to shedding light on the processes of fertility, this could lead to new discoveries in spontaneous miscarriage, cancer and developmental disorders.
Humans have 46 chromosomes, 23 from the sperm and 23 from the egg. When there is a deviation, usually a miscarriage occurs.
During meiosis, the process that creates sperm and eggs, matching chromosomes pair up and connect or crossover. These connections are necessary for the precise chromosome sorting and the formation of sperm and eggs with exactly the right number of chromosomes to reproduce. Crossovers also play a fundamental role in evolution allowing segments of DNA to exchange providing variety in the next generation.
Each pair of chromosomes must have one crossover, but not more than two. Neil Hunter, a professor of microbiology at UC Davis and senior author has found the “missing tool” that explains how crossovers are regulated. “There must be enzymes that ensure at least one crossover but not too many,” said Hunter.
In their experiments using yeast, they discovered the missing tool for crossing-over: three yeast enzymes, Mih1., Mih3 and Sgs1. They work together to cut DNA and make the crossovers.
In humans, these enzymes are well known for their role in suppressing tumors. When mutated they are associated with colon cancer and Bloom’s syndrome.
“Sgs1 was the biggest surprise,” Hunter explained. “We previously knew it as an enzyme that unwinds DNA to prevent crossovers. Its role in making crossovers had been hidden by other enzymes that can step in when it is absent.”
He concluded, “This unique activity is essential for meiosis and its discovery is a huge step forward.”
Source: MedicalNewsToday, Cell
