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Abstract
Genetic diversity in offspring is induced by meiotic recombination, which is initiated between homologs at >200 sites originating from meiotic double-strand breaks (DSBs). Of this initial pool, only 1–2 DSBs per homolog pair will be designated to form meiotic crossovers (COs), where reciprocal genetic exchange occurs between parental chromosomes. Cyclin-dependent kinase 2 (CDK2) is known to localize to so-called “late recombination nodules” (LRNs) marking incipient CO sites. However, the role of CDK2 kinase activity in the process of CO formation remains uncertain. Here, we describe the phenotype of 2 Cdk2 point mutants with elevated or decreased activity, respectively. Elevated CDK2 activity was associated with increased numbers of LRN-associated proteins, including CDK2 itself and the MutL homolog 1 (MLH1) component of the MutLγ complex, but did not lead to increased numbers of COs. In contrast, reduced CDK2 activity leads to the complete absence of CO formation during meiotic prophase I. Our data suggest an important role for CDK2 in regulating MLH1 focus numbers and that the activity of this kinase is a key regulatory factor in the formation of meiotic COs.
Highlights
In most eukaryotic organisms, crossover (CO) is required for the proper disjunction of homologous chromosomes at the first meiotic division
We found that interstitial Cyclin-dependent kinase 2 (CDK2) foci do not form in the Cdk2T160A mutant. This suggests that the process of late recombination nodule (LRN) formation requires activation of CDK2/complexes via T-loop phosphorylation, we cannot infer from these results whether this was a direct effect, arising from the absent activity of CDK2 at these sites, or indirect, arising from the additional meiotic defects we have described for this model
Our results indicate that increased CDK2 activity is correlated with elevated numbers of LRN-associated CDK2 and MutL homolog 1 (MLH1) foci in a manner that is associated with decreased MLH1 interfocus distancing
Summary
Crossover (CO) is required for the proper disjunction of homologous chromosomes at the first meiotic division. It promotes the genetic heterogeneity of gametes through the reciprocal exchange of genetic material [1]. During meiosis I prophase, interhomolog recombination is initiated via the deliberate or “programmed” induction of double-strand breaks (DSBs) by the endonuclease SPO11 Research Foundation Singapore grant NRF2016CRP001-103 to PK, the Swedish Foundation for Strategic Research Dnr IRC15-0067, and Swedish Research Council, Strategic Research Area EXODIAB, Dnr 2009–1039. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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