Diffusion within the synaptonemal complex can account for signal transduction along meiotic chromosomes

Meiotic chromosomes efficiently transduce information along their length to regulate the distribution of genetic exchanges within and between chromosomes. However, the mode of signal transduction remains unknown. Recently, a conserved chromosomal interface, the synaptonemal complex, was shown to be a biomolecular condensate, offering an attractive mechanism for signal transduction: diffusion of signaling molecules within the synaptonemal complex to allow transmission of information along each pair of chromosomes. Here, we test the feasibility of this mechanism in live C. elegans gonads. Single-molecule tracking shows that a component of the synaptonemal complex (SYP-3) and a conserved regulator of exchanges (ZHP-3) both diffuse within the synaptonemal complex. However, ZHP-3 diffuses 4- and 9-fold faster than SYP-3 before and after crossovers formation, respectively. We use these measurements to parameterize a physical model for signal transduction. We find that ZHP-3, but not SYP-3, explores the lengths of chromosomes on the time scale of crossover maturation, consistent with a role in the spatial regulation of exchanges. Given the conservation of ZHP-3 paralogs across eukaryotes, we propose that diffusion within the synaptonemal complex may be a conserved mechanism of meiotic regulation. More broadly, our work explores how diffusion contained within condensates regulates crucial cellular functions.