Ofer Rog @theroglab.bsky.social from @utah.edu will talk about "Regulating sister interactions during meiosis" on May 21st

Learn more about Dr. Rog's work :
theroglab.org

--> Register here: meiosis.cornell.edu/mayosis2025/...

Much more inside. As usual, hit us up if you have any feedback!

Finally, we used our kinetic information to derive the total number of DSBs. We found an average of 40 DSBs per nucleus in wild-type meiosis suggesting a ratio of 7:1 of DSBs to crossovers, and more DSBs in mutant scenarios.

Second, strand invasion kinetics were similar for repair events templated by the homolog versus the sister. This was surprising, since a leading hypothesis is that DSBs that don't find the homologs stall and are only repaired at the end of meiosis using the sister chromatid.

We made 3 crucial findings. First, we found that most repair events finish the strand-invasion step in 1-2 hours. This is true for both endogenous (SPO-11-induced) and irradiation-induced DSBs.

The inspiration was beautiful work by Sarit and Nicola, who used auxin-mediated degradation of SPO-11 to extinguish new meiotic DSBs. We used a cytological marker - RAD-51 - which marks strand-invasion and quantified the kinetics of their disappearance.
pubmed.ncbi.nlm.nih.gov/36170820/

We’d love to get feedback and suggestions. Kudos to Kewei, an amazing grad student who developed CheC-PLS over the last 5 years; to Chloe and Lexy (now with her own lab, new-car-smell and all, at UMinnesota); and to Lisa and a super-talented undergrad, Kaan.

So Skp1 has been moonlighting for >100 million years. Which adds a new twist to the SC paradox: how does a highly conserved protein (Skp1) maintains intimate interaction with quickly diverging proteins in a way that does not leave a clear evolutionary mark in their sequence?

In both nematode, Skp1 is not only necessary for assembly of the SC onto chromosomes - without dimerization-competent Skp1, SC proteins are absent.

Lisa turned to the distantly related nematode P. pacificus, and found that the answer is a resounding ‘yes’. Ppa-SKR-1 localize to the middle of the SC, and a conserved dimerization interface in Skp1 is specifically required for SC assembly in Pristi, as it is in elegans.

Recently, Yumi Kim's lab made an intriguing discovery: Skp1, a conserved subunit of the SCF ubiquitin ligase complex (SKR-1 in C. elegans), moonlights as a structural component of the SC. Lisa decided to test whether this function is conserved. 10.1126/sciadv.adl4876

On the other hand, the protein sequence is incredibly divergent between and within clades, so much so that the genes had to be independently cloned in different model organisms. (More on that in Lisa’s previous paper.) elifesciences.org/articles/30823

#3: Skp1 in the SC. SC proteins have intriguing evolutionary history: they build a highly conserved structure AND (almost) all subunits are co-dependent for assembly.

That has crucial implications: ZHP-3 can sample the entire 6um chromosome in tens of minutes, whereas SYP-3 cannot. By extension, ZHP-3 is capable of efficiently transducing a crossover signal, whereas SYP-3 would be unlikely to.

The second important finding came from comparing the diffusion of an SC component (SYP-3) vs a regulator of crossovers (ZHP-3). ZHP-3 diffuses 4-9 times faster than SYP-3 (depending on meiotic stage).

(Black-boxing some amazing tech here; check out the preprint for details.) This finding confirmed a crucial aspect of the coarsening hypothesis.

However, a crucial piece of this model has not been tested: do molecules diffuse within the SC? Lexy directly tested that. By sparsely labeling SC components and crossover regulators, she was able to observe single molecules in live gonads.

This idea, and beautiful data from worms and plants (from Raphael Mercier, Chris Morgan and others) suggested coarsening regulates genetic exchanges (crossovers).