  Understanding the coordination of cell division timing is one of the
outstanding questions in the field of developmental biology. One active control
parameter of the cell cycle duration is temperature, as it can accelerate or
decelerate the rate of biochemical reactions. However, controlled experiments
at the cellular-scale are challenging due to the limited availability of
biocompatible temperature sensors as well as the lack of practical methods to
systematically control local temperatures and cellular dynamics. Here, we
demonstrate a method to probe and control the cell division timing in
Caenorhabditis elegans embryos using a combination of local laser heating and
nanoscale thermometry. Local infrared laser illumination produces a temperature
gradient across the embryo, which is precisely measured by in-vivo nanoscale
thermometry using quantum defects in nanodiamonds. These techniques enable
selective, controlled acceleration of the cell divisions, even enabling an
inversion of division order at the two cell stage. Our data suggest that the
cell cycle timing asynchrony of the early embryonic development in C. elegans
is determined independently by individual cells rather than via cell-to-cell
communication. Our method can be used to control the development of
multicellular organisms and to provide insights into the regulation of cell
division timings as a consequence of local perturbations.
