A noncanonical meiotic cohesin complex associates with specific MCM complexes to promote cohesion establishment and homolog bias

A meiosis-specific cohesin complex is essential for the segregation of homologous chromosomes and sister chromatids during meiosis, yet its composition and mechanism in Drosophila remain elusive. Here, we demonstrate that SOLO directly interacts with SUNN, SSEP, and SMC1 and that these interactions are conserved between Drosophila melanogaster and Zeugodacus cucurbitae , a Tephritidae species within Diptera. SOLO associates with SMC1 via specific conserved residues within its highly conserved carboxyl-terminal domain. Furthermore, SOLO directly interacts with the MCM4 and MCM6 subunits of the MCM complex and with MMS22L to establish cohesion; consequently, postreplicative expression of SOLO results in a complete function loss. SOLO also interacts with the MEI-217 and MEI-218 subunits of the meiosis-specific minichromosome maintenance complex to promote homolog bias during meiosis. We propose that in Diptera, an evolutionarily diverged meiotic cohesin complex, composed of SOLO, SUNN, SSEP, SMC1, and SMC3, interacts with various complexes to fulfill its diverse meiotic functions.