Mad1’s ability to interact with Mad2 is essential to regulate and monitor meiotic synapsis in C. elegans

Abstract

Meiotic homolog synapsis is essential to ensure accurate segregation of chromosomes during meiosis. In C. elegans, proper regulation of synapsis and a checkpoint that monitors synapsis relies on the spindle checkpoint components, Mad1 and Mad2, and Pairing Centers (PCs), cis-acting loci that interact with the nuclear envelope to mobilize chromosomes within the nucleus. Here, we test what specific functions of Mad1 and Mad2 are required to regulate and monitor synapsis. We find that a mutation that prevents Mad1’s localization to the nuclear periphery abolishes the synapsis checkpoint but has no effect on Mad2’s localization to the nuclear periphery or synapsis. By contrast, a mutation that prevents Mad1’s interaction with Mad2 abolishes the synapsis checkpoint, delays synapsis and fails to localize Mad2 to the nuclear periphery. These data indicate that Mad1’s primary role in regulating synapsis is through control of Mad2 and that Mad2 can bind other factors at the nuclear periphery. We also tested whether Mad2’s ability to adopt a specific conformation associated with its activity during spindle checkpoint function is required for its role in meiosis. A mutation that prevents Mad2 from adopting its active conformer fails to localize to the nuclear periphery, abolishes the synapsis checkpoint and exhibits substantial defects in meiotic synapsis. Thus, Mad2, and its regulation by Mad1, is an important regulator of meiotic synapsis in C. elegans.

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“…MAD1L1 was initially discovered during a screening analysis and was identified as an important mitotic checkpoint protein that played a role in attachment of chromosomes to the mitotic spindle by delaying separation of the replicated sister chromatids. MAD1L1 forms a heterotetrameric complex with MAD2 at unattached kinetochores, and has an evolutionarily conserved role in the mitotic checkpoint processes [ 36 , 37 ]. Once the kinetochores of all sister chromatids are accurately attached to spindle microtubules, the heterotetrameric complex of MAD1L1 and MAD2 is not recruited.…”