Rycroft part of a team to study early development in cricket embryos

5 snapshots showing nucleus as they divide over time.
Five snapshots showing nuclei (white) as they divide and spread through the embryo of the cricket Gryllus bimaculatus during the initial 24 hours of development. Credit: Taro Nakamura and Seth Donoughe.

Professor Christopher Rycroft worked with the Extavour Laboratory to study the early stages of development in cricket embryos. In humans, an embryo starts from a single cell that undergoes repeated divisions. But in crickets and many other insect species, the cell nuclei initially move and divide within a shared cytoplasm, with cell boundaries only forming later. Using light-sheet microscopy, the team tracked the complicated motion of the nuclei over the first 24 hours of development. During this period, the nuclei spread out through the embryo to form the blastoderm, which is an important precursor for the formation of body parts of the cricket.

The microscopy data showed that the nuclei are remarkably efficient in filling the embryo volume, and do so far faster than would be expected via just random motion. Rycroft and the team developed a geometrical model that explains this process. Each nucleus has a cloud of microtubules growing out radially from it. Those clouds grow outward until they reach clouds from other nuclei. The cloud shapes are closely related to Voronoi cells, a technique in computational geometry that is used in many different scientific fields.

The team hypothesized that microtubules exert pulling forces on the nuclei. If a nucleus borders empty space, then its microtubule cloud extends further in that direction. Nuclei are therefore preferentially pulled toward empty space. The team developed a computational model to test this hypothesis. Across a range of different conditions, the model was able to predict the rapid expansion of nuclei inside the embryo volume.