Mitochondria as indispensable yet replaceable components of germ plasm: insights into PGCs specification in sturgeons

While it is widely recognised that mitochondria are components of germ plasm, their specific role in the formation and specification of PGCs remains poorly understood. Furthermore, it has not been established whether mitochondria in germ plasm possess unique characteristics essential for their function. In this study, we demonstrate that mitochondria are indispensable for PGC development in non-teleost fishes and that their role is not dependent on their origin from germ plasm. Using sturgeon embryos, we showed that UV radiation applied to the vegetal pole effectively eliminates germ plasm, including mitochondria, and prevents PGC formation. Remarkably, we restored germ plasm function and PGC development by injecting mitochondria derived from donor eggs, even when these mitochondria were not originally part of the germ plasm. Transplanted mitochondria were successfully identified in larval PGCs using a fluorescent PKH26 tracer, and in interspecies transplantation experiments, their presence was confirmed using species-specific mtDNA and mtRNA primers in larvae and individual PGCs. Our findings reveal that mitochondria are critical but not germ plasm-specific determinants of PGC formation. This study provides novel insights into the developmental pathways of germ cells and establishes a previously unrecognised flexibility in mitochondrial functionality within the germ line. These findings also offer a potential method for conserving matrilineal genetics in critically endangered species such as sturgeons while simultaneously opening new avenues for studying germ lines with high interspecies mitochondrial heteroplasmy and contributing to broader evolutionary and conservation biology.