Amini et al. describe how the Anillin protein ANI-2 promotes the opening of intercellular bridges that allow C. elegans germ cells to resist mechanical stress during oogenesis.
The germ cells of worm gonads form a syncytium in which each cell is connected to the others via small intercellular bridges that feed into a central cytoplasmic core called the rachis. Two Anillin proteins localize to the rachis and intercellular bridges. ANI-1 is an actomyosin scaffold protein that promotes cytokinesis. ANI-2, on the other hand, lacks the actin- and myosin-binding domains found in ANI-1, yet its depletion disrupts gonad organization and germline development.
Amini et al. found that germ cells became progressively more interconnected during the development of wild-type gonads, but the intercellular bridges were largely absent in worms lacking ANI-2. In contrast, depleting ANI-1 increased the number and width of intercellular bridges and rescued bridge stability in ani-2 mutant gonads, suggesting that the two Anillin proteins counteract each other to regulate the gonad’s syncytial architecture.
Late in larval development, germ cells lacking ANI-2 became multinucleate as the membranes separating individual nuclei collapsed. This multinucleation coincided with the onset of cytoplasmic streaming, in which maturing oocytes at one end of the gonad grow by sucking in cytoplasm from the rest of the organ. Blocking cytoplasmic streaming reduced the multinucleation of ani-2–deficient gonads, suggesting that intercellular bridges help germ cells resist the mechanical stresses associated with this process. Author Nicolas Chartier now wants to see if shorter Anillin isoforms have a similar function in higher organisms, including humans, whose germ cells are also connected via stable intercellular bridges.
Text by Ben Short