Summary
Crossovers (COs) between homologous chromosomes ensure their faithful segregation during meiosis. We identify C. elegans COSA-1 as a key component required to convert double-strand breaks (DSBs) into COs. COSA-1 localizes to foci during late meiotic prophase that correspond to the single CO site on each homolog pair. These foci represent sites of eventual concentration of other conserved CO proteins that initially exhibit broader distribution. Chromosomes gain and lose competence to load CO proteins at DSBs during meiotic progression, with competence to load COSA-1 requiring a prior licensing event. Our data further suggest a self-reinforcing mechanism maintaining CO designation. Modeling of a non-linear dose-response relationship between IR-induced DSBs and COSA-1 foci reveals efficient conversion of DSBs into COs when DSBs are limiting, and a robust capacity to limit the number of cytologically-differentiated CO sites when DSBs are in excess. COSA-1 foci serve as a biodosimeter for DSB levels and a unique live-cell readout of CO interference.
In optogenetics, researchers use light and genetically encoded photoreceptors to control biological processes with unmatched precision. However, outside of neuroscience, the impact of optogenetics has been limited by a lack of user-friendly, flexible, accessible hardware. Here, we engineer the Light Plate Apparatus (LPA), a device that can deliver two independent 310 to 1550 nm light signals to each well of a 24-well plate with intensity control over three orders of magnitude and millisecond resolution. Signals are programmed using an intuitive web tool named Iris. All components can be purchased for under $400 and the device can be assembled and calibrated by a non-expert in one day. We use the LPA to precisely control gene expression from blue, green, and red light responsive optogenetic tools in bacteria, yeast, and mammalian cells and simplify the entrainment of cyanobacterial circadian rhythm. The LPA dramatically reduces the entry barrier to optogenetics and photobiology experiments.
CNTD1 coordinates the maturation and designation of meiotic crossover sites from an excess pool of double-strand break intermediates by regulating dynamic changes in key protein complexes associated with these sites.
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