Paternal source of germ plasm determinants in the viviparous teleost, Gambusia holbrooki; dads do matter.

The identity of germ cells, the progenitors of life, is thought to be acquired by two modes; either by maternal signals (preformed) or induced de novo from pluripotent cells (epigenesis) in the developing embryos. However, paternal roles seem enshrouded or completely overlooked in this fundamental biological process. Hence, we investigated the presence of germplasm transcripts in the sperm of Gambusia holbrooki, a live-bearing fish, demonstrating their presence and suggesting paternal contributions. Interestingly, not all germplasm markers were present (nanos1 and tdrd6) in the sperm, but some were conspicuous (dazl, dnd-α, piwi II, and vasa), indicating that the latter is required for establishing germ cell identity in the progeny, with a possible parent-specific role. Furthermore, there were also spatial differences in the distribution of these determinants, suggesting additional roles in sperm physiology and/or fertility. Our results support the hypothesis that dads also play a vital role in establishing the germ cell identity, especially in G. holbrooki, which shares elements of both preformation and induction modes of germline determination. This, coupled with its life history traits, makes G. holbrooki an excellent system for dissecting evolutionary relationships between the two germline determination modes, their underpinning mechanisms and ultimately the perpetuity of life.
Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. They also declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported. The funder had no role in the design of the study, in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
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