Energy budget of Drosophila embryogenesis.

Eggs of oviparous animals must be prepared to develop rapidly and robustly until hatching. The balance between sugars, fats, and other macromolecules must therefore be carefully considered when loading the egg with nutrients. Clearly, packing too much or too little fuel would lead to suboptimal conditions for development. While many studies have measured the overall energy utilization of embryos, little is known of the identity of the molecular-level processes that contribute to the energy budget in the first place [1]. Here, we introduce Drosophila embryos as a platform to study the energy budget of embryogenesis. We demonstrate through three orthogonal measurements - respiration, calorimetry, and biochemical assays - that Drosophila melanogaster embryogenesis utilizes 10 mJ of energy generated by the oxidation of the maternal glycogen and triacylglycerol (TAG) stores (Figure 1). Normalized for mass, this is comparable to the resting metabolic rates of insects [2]. Interestingly, alongside data from earlier studies, our results imply that protein, RNA, and DNA polymerization require less than 10% of the total ATPs produced in the early embryo.

Temperature-independent energy expenditure in early development of the African clawed frog Xenopus laevis.

The thermal dissipation of activated eggs and embryos undergoing development from cleavage to the tailbud stage of the African clawed frog Xenopus laevis was measured as a function of incubation time at temperatures ranging from T = 288.2 K to 295.2 K, using a high-precision isothermal calorimeter. A23187-mediated activation of mature eggs induced stable periodic thermal oscillations lasting for 8-34 h. The frequency agreed well with the cell cycle frequency of initial cleavages at the identical temperature. In the developing embryo, energy metabolism switches from embryonic to adult features during gastrulation. The thermal dissipation after gastrulation fit well with a single modified Avrami equation, which has been used for modeling crystal-growth. Both the oscillation frequency of the activated egg and the growth rate of the embryo strongly depend on temperature with the same apparent activation energy of approximately 87 kJ mole(-1). This result suggests that early development proceeds as a single biological time, attributable to a single metabolic rate. A temperature-independent growth curve was derived by scaling the thermogram to the biological time, indicating that the amount of energy expenditure during each developmental stage is constant over the optimal temperature range.