Germline cysts are formed by cells undergoing division without completing cytokinesis, thus producing a connected network of cells. This process is conserved across many animal species, but network topologies vary greatly and the mechanisms underpinning this variation are not well understood. Here, Matthew Smart, Stanislav Shvartsman and Hayden Nunley generate a mathematical model to explore how altering certain cell division parameters influences the organisation of the final germline cyst. In their model, each cell is represented by an oscillator, with each complete oscillation corresponding to one cell cycle and producing a new daughter cell. This daughter cell remains tethered to the mother cell, as observed in vivo, via an intercellular bridge. The cell cycle oscillations are initiated by pulses and are coupled by diffusion across the intercellular bridges. By varying pulse strength, coupling strength and division asymmetry, the authors are able to recapitulate the full range of germline cyst arrangements found in invertebrates. They also explore how variation within a species occurs. Overall, this work identifies key parameters that influence germline cyst formation and presents a mathematical model that could be applied to other situations in which incomplete division produces linked networks of cells, such as choanoflagellate colony formation.
