Making Sense of Mitochondria

While all living organisms inherit mitochondria from their mothers, the father’s mitochondria are destroyed at the time of fertilization. Special cellular vesicles that originate in female fruit flies’ egg actively seek out and destroy the father’s mitochondria, according to research conducted by Dr. Eli Arama and a team in the Weizmann Institute’s Molecular Genetics Department. In the study, recently published in Development Cell, the Weizmann team discovered that as soon as the sperm enters the egg, the cellular vesicles, which are already present in the fruit fly egg, immediately attract to the sperm like a magnet. They then proceed to disintegrate the sperm’s outer membrane and separate the mitochondria from the tail section. Then the tail section is cut into smaller pieces that are then consumed by conventional selective autophagy. According to Prof. Arama, “We were not witnessing classic autophagy machinery. These structures were too large and morphologically distinct to be typical autophagosomes.” He added that the team’s findings suggest that the egg’s special cellular vesicles represent a new type of system that combines three separate biological processes whose pathways may have diverged from their classic functions. These new discoveries, which the scientists believe hold true for other organisms with flagellated sperm, including humans, may lead to an understanding of why only a quarter of in vitro fertilization (IVF) pregnancies carry to term. Possibly, this invasive procedure somehow renders the egg unable to destroy the paternal mitochondria. Arama his team hope that further research will help to elaborate on a variety of issues pertaining to paternal mitochondria, with an ultimate goal of understanding mitochondrial turnover and male fertility. The Weizmann research team was led by Ph.D. students Liron Gal and Yoav Politi in Arama’s group, together with former senior intern Yossi Kalifa and former Ph.D. student Liat Ravid, and also included Prof. Zvulun Elazar of the Biological Chemistry Department.