In a recent study, published in Cell, researchers use the fruit fly as a system to dissect the links between metabolism and the development of eggs. As eggs, also known as oocytes, enter the final stages of development, they accumulate large amounts of proteins, lipids and sugars in order to fuel the embryo after fertilization. The authors were able to identify a functional and biochemical change in the developing oocytes that induces carbohydrate storage.

Mitochondria are the structures within cells that convert nutrients, such as sugar, into energy that fuels the cell, allowing it to function and grow. Authors found that during the final stages of oocyte development, insulin signaling is inactivated in oocytes, causing a fundamental change in the biochemical properties of the mitochondria and a reduction in mitochondrial activity. This change in mitochondrial function leads to a build-up of sugars in the oocyte. As a result, these sugars can then be used after fertilization to fuel the developing embryo.

This shift in mitochondrial function leads to extensive glycogen accumulation late in oogenesis and is required for the developmental competence of the oocyte. Decreased insulin signaling initiates ETC remodeling and mitochondrial respiratory quiescence through glycogen synthase kinase 3 (GSK3). 

Their findings are consistent with previous observations that show mammalian oocytes also display low levels of mitochondrial activity, suggesting similar changes in mitochondrial function and sugar storage may be an essential aspect of oocyte production in many species.

"We believe our findings are directly applicable to understanding human infertility," author said. "Polycystic ovary syndrome is the leading cause of female infertility and it is strongly associated with diabetes and insulin resistance, which suggests that defects in the metabolic aspects of oocyte maturation may be the underlying source of the disorder."

Furthermore, the team believes that mitochondrial defects during oocyte development may contribute to oocytes that fail during in vitro fertilization treatment (IVF), although further research is required.

http://www.cell.com/cell/abstract/S0092-8674(15)01684-0