Quantifying temperature compensation of Bicoid gradients with a fast T-tunable microfluidic device

ABSTRACT As a reaction-diffusion system strongly affected by temperature, the early fly embryos surprisingly show highly reproducible and accurate developmental patterns during embryogenesis under temperature perturbations. To reveal the underlying temperature compensation mechanism, it is important to overcome the challenge in quantitative imaging on fly embryos under temperature perturbations. Inspired by a microfluidics generating temperature steps on fly embryos, here we design a microfluidic device capable of ensuring the normal development of multiple fly embryos as well as achieving real-time temperature control and fast temperature jumps for quantitative live imaging with a home-built two-photon microscope. We apply this system to quantify the temperature compensation of the morphogen Bicoid (Bcd) gradient in fly embryos. The length constant of the exponential Bcd gradient reaches the maximum at 25 °C within the measured temperatures of 18-29 °C and gradually adapts to the corresponding value at new temperatures upon a fast temperature switch. Such an adaption decreases to a less degree if temperature is switched in a later developmental stage. This age-dependent temperature compensation could not be explained with the traditional synthesis-diffusion-degradation (SDD) model assuming the static parameters but an extended SDD model incorporating the dynamic change of the parameters controlling the formation of Bcd gradients. SIGNIFICANCE Thermal robustness is important for biological systems experiencing temperature fluctuations. To reveal the temperature compensation mechanism, the fruit fly embryo is an ideal model system. It is intriguing how the early fly embryo achieves highly reproducible and accurate patterning despite it is a reaction-diffusion system strongly affected by temperature. However, it has been challenging to quantitatively measure the developmental patterns in fly embryos under temperature perturbations. To overcome this problem, we construct a fast temperature tunable microfluidic device for fly embryos. Combining quantitative imaging with this device and mathematical modeling, we successfully quantify the temperature response of the morphogen Bicoid (Bcd) gradient and reveal that the temperature compensation for the Bcd gradient is stronger in the later developmental stage.