During meiosis, the cell division process central to sexual reproduction, all chromosomes must figure out where to destroy the protein cohesin -- the molecular glue holding chromosomes together -- and where to protect it.
In human chromosomes, cohesin is always protected in the same region, but in the nematode worm C elegans, chromosomes have to figure it out from scratch every time they divide. They somehow measure both sides from the crossover -- the point at which chromosomes from each parent exchange genetic material -- to each chromosomal end, picking the shorter side as the place to dissolve the glue.
Now a team of researchers at Kyoto University has found a key to how these worm chromosomes measure their lengths. They did so by studying extra-long chromosomes with two or more crossovers.
"Taking advantage of fusion chromosomes with multiple crossovers was a critical step in unlocking the mystery of length measurement," explains corresponding author Peter Carlton.
The team found that regions bounded by two crossovers have twice the "short arm"-generating power as those bounded by one crossover and a chromosome end.
"Rather than the chromosome using tiny rulers, this phenomenon is best explained by a signal spreading from each crossover and piling up on each side," adds first author Carlos Rodriguez.
Shorter segments will naturally have more of this molecular signal piled up inside them, which can then be used to measure length. The team asserts that this work has brought the field a step closer to understanding both how information can spread along chromosomes and how cells can measure their own components.
