A Kinetochore-Independent Mechanism Drives Anaphase Chromosome Separation During Acentrosomal Meiosis

摘要

The self-organized assembly of acentrosomal meiotic spindles has been extensively studied but little is known about how chromosomes segregate on these spindles. Here, we investigate two chromosome-microtubule interaction mechanisms—kinetochores and chromokinesins—during meiosis in fertilized C. elegans oocytes. We show that the conserved kinetochore protein KNL-1 directs assembly of meiotic kinetochores that orient chromosomes on the acentrosomal spindles. However, in contrast to mitosis, chromosome separation during meiotic anaphase was kinetochore-independent. The chromokinesin KLP-19 did not contribute to chromosome orientation or anaphase, but stabilized late anaphase spindles. Prior to anaphase separation, meiotic kinetochores and spindle poles disassembled along with microtubules on the poleward side of the chromosomes; during anaphase, microtubules were formed between the separating chromosomes. Functional analysis implicated a set of proteins that localize to a ring-shaped domain between the kinetochores in pre-anaphase spindle assembly and anaphase separation. Ring domain proteins are localized by the chromosomal passenger complex (CPC), whose local enrichment is patterned by recombination to control step-wise loss of meiotic cohesion^–. Thus, meiotic segregation in C. elegans is a two-stage process where kinetochores orient chromosomes but are dispensable for their separation. We suggest that separation is instead controlled by a meiosis-specific chromosomal domain to coordinate step-wise dissolution of cohesion with chromosome segregation.