Cytokinesis

Adapted from M. Fuller

Cytokinesis, the splitting of one cell into two, is achieved by the purse string-like constriction of an actomyosin-based contractile ring and its associated plasma membrane. At the end of cytokinesis, the contractile ring disassembles and the two daughter cells separate. A remarkable variation of this universal process occurs during gametogenesis in many organisms: instead of separating, the daughter cells develop as a syncytium, with clonally related cells connected by intercellular bridges called ring canals.

Drosophila male germ line ring canals contain the actin binding-proteins anillin and the septins, together with one or more tyrosine phosphorylated protein(s). Phosphotyrosine epitopes accumulate first as puncta (shown as green dots, right) and then as a ring coincident with filamentous actin in the constricted contractile ring (shown in red; Hime, Brill and Fuller, J. Cell Sci. 1996).

Following constriction, actin and myosin II are disassembled from the contractile ring; however, the daughter cells remain connected by a stable cytoplasmic bridge or ring canal. This structure is marked by the presence of several cleavage furrow components - the actin-binding proteins anillin and the septins - as well as one or more tyrosine-phosphorylated proteins.

Left: Fluorescence micrographs of dividing cells stained for (left) CD2 (green; plasma membrane marker) and anillin (red; contractile ring and ring canal protein) and (right) Drosophila adducin-like protein (green; fusome marker) and anillin (red).

Drosophila male germ cells undergoing meiotic cytokinesis are large and their cytology is well characterized, making them ideal for the study of this fundamental cellular process. In addition, genetic studies have identified more than thirty genes required for this process.

Left: Male sterile mutants defective in meiotic cytokinesis are easy to identify by the presence of multinucleate spermatids. Normal round haploid spermatids contain a single pale nucleus accompanied by a dark mitochondrial derivative of similar size. A failure in cytokinesis during meiosis results in spermatids containing two or four haploid nuclei accompanied by an enlarged mitochondrial derivative. Company of Biologists Ltd. 2000

Adapted from A. Tates, 1971