Clonal Dynamics in the Male Germline from Development to Next Generation

Germ cells support the continuation and evolution of species. In mammals, the germline trajectory originates from a limited number of primordial germ cells (PGCs), persists through the lifespan of the organism, and continues across generations. Yet, the dynamics and contributions of individual PGC lineages remain enigmatic. Here, we employ Polylox ¹ DNA barcoding to unveil the clonal dynamics of mouse male germline from development to the next generation and find that disparate probabilities for trans-generational inheritance from individual PGCs are established in early embryogenesis and persist throughout adulthood. Indeed, >30% of PCG clones are lost before colonisation in the testis, suggesting early quality control, with surviving PGC clones expanding unevenly. Thereafter, clone sizes remain stable lifelong, and inheritance to offspring is proportional to clone size, arguing against strong variability in sperm fitness. Mathematical analysis of the barcoding data indicates that early clonal dynamics follow probabilistic rules, whereas the subsequent compartmentalisation of clones into seminiferous tubules in the testis preserves the clonal repertoire and may guard against large-scale selection of mutant clones. This study defines the quantitative dynamics of male germline development and transmission and thus reveals constraints for how de novo mutations that arise in germ cells can be transmitted to offspring.