Mitochondria, spermatogenesis, and male infertility – An update

•mtDNA is reduced to 70–80 copies per sperm during spermatogenesis.•Mitochondria are critical to germ cell division, apoptosis and differentiation.•Sperm mitochondria surround 9+2 microtubules to provide energy for motility.•Mutations in the mitochondrial DNA affect male fertility.•mtDNA deletions are often more deleterious than SNPs to spermatogenesis.•Ageing, obesity, and metabolic disorders may affect fertility via mitochondria. The incorporation of mitochondria in the eukaryotic cell is one of the most enigmatic events in the course of evolution. This important organelle was thought to be only the powerhouse of the cell, but was later learnt to perform many other indispensable functions in the cell. Two major contributions of mitochondria in spermatogenesis concern energy production and apoptosis. Apart from this, mitochondria also participate in a number of other processes affecting spermatogenesis and fertility. Mitochondria in sperm are arranged in the periphery of the tail microtubules to serve to energy demand for motility. Apart from this, the role of mitochondria in germ cell proliferation, mitotic regulation, and the elimination of germ cells by apoptosis are now well recognized. Eventually, mutations in the mitochondrial genome have been reported in male infertility, particularly in sluggish sperm (asthenozoospermia); however, heteroplasmy in the mtDNA and a complex interplay between the nucleus and mitochondria affect their penetrance. In this article, we have provided an update on the role of mitochondria in various events of spermatogenesis and male fertility and on the correlation of mitochondrial DNA mutations with male infertility.