Anillin forms linear structures and facilitates furrow ingression after septin and formin depletion

Abstract

During cytokinesis a contractile ring consisting of unbranched filamentous actin (F-actin) and myosin II filaments assembles and constricts at the cell equator. Unbranched F-actin is de novo generated by formin and without formin cleavage furrow ingression fails. In C. elegans depletion of septin restores cleavage furrow ingression in formin (CYK-1) mutants. How the cleavage furrow ingresses without a detectable unbranched F-actin ring is not known. We report, that in this setting anillin (ANI-1) is essential for furrow ingression and forms a meshwork of linear structures, which circumferentially align around the cell equator. Although equatorial ANI-1 recruitment is facilitated by septins, the formation of linear ANI-1 structures is septin independent. Analysis of ANI-1 deletion mutants reveals that its disordered linker region is required for linear structure formation and furrow ingression. We also found that myosin II (NMY-2) decorates linear ANI-1 structures and promotes their circumferential alignment. NMY-2 also interacts with various lipids and forms membrane localized clusters in absence of F-actin and anillin binding. This suggests that NMY-2 represents an independent link between the F-actin / ANI-1 network and the plasma membrane. Collectively, our data reveals a compensatory mechanism, mediated by ANI-1 linear structures and membrane-bound NMY-2, that promotes furrow formation and ingression when formins are depleted and therefore unbranched F-actin polymerization is compromised.

Heteroallelic combination of anillin mutants reveals cytoskeletal uncoupling during cytokinesis.

“…Rather, different Anillin molecules capable of interacting with either Sticky or with Rho1/septins can functionally complement one another. It has been suggested that the unstructured N-terminus of C. elegans ANI-1 might oligomerize (Lebedev et al, 2023). However, unless oligomerization requires the first five amino acids and is not required for function, our observations of Drosophila Anillin do not support this prediction, since the two co-expressed Anillin species localized independently under all conditions, including in LatA.…”