Evolution of sex determining genes in fishes
Final Report Abstract
Main issues raised & general objectives. The genetic and cell biological mechanisms underlying the decision whether the undifferentiated gonad of the embryo develops either towards male or female are manifold and quite different. Sex determining (SD) mechanisms range from environmental to simple or complex genetic mechanisms and have evolved repeatedly and independently. In species with genetic monofactorial SD, master SD genes located on sex chromosomes initiate the gonadal differentiation process by switching on a developmental program that ultimately leads to testicular or ovarian differentiation. So far very few sex-determining genes have been identified in fish and in animals in general. Fish are uniquely suited to study the evolution of SD and the genes involved. Comprising about half of the about 60 000 species of vertebrates, fish show the greatest variety of SD mechanisms including species with either environmental or genetic SD (GSD). But the few currently known fish SD genes are apparently not conserved over related orders, families, genera or even species. This frequent evolutionary turnover of SD genes may be explained by a high turnover of fish sex chromosomes. This project had then two major objectives: (1) to screen for potential novel sex determining genes in many fish species; (2) to demonstrate the role of these genes as master sex determinants in a few selected species. A two-way genomic screen for sex to identify new sex determinants. To address these questions, we have developed two strategies based on RAD-tags and Pool-sequencing that make use of next generation sequencing technology to identify genetic markers that define sex specific segments of the male or female genome. The obtained markers were used to isolate candidate SD genes from these regions. By screening more than 50 species representing major branches of the fish tree of life (including teleosts and non-teleost species) markers have been used to identify sex chromosomal regions and coding sequences likely to be candidates for master SD gene. These candidate genes were evaluated by transcript profiling and a selection of genes were further investigated using functional gene inactivation and additive transgenesis. Main results. Our first results allowed us to characterize the SD system of many species in which we could clearly identify simple monofactorial genetic sex determinisms either with male or female heterogamety. Surprisingly for roughly half of the investigated species no sex-specific or sexpolymorphic sequence were identified suggesting either extremely low differentiation of sex chromosomes in these species, a polygenic sex-determination or interactions between a genetic sexdeterminism (GSD) and an environmental sex-determinism (ESD). In some species our results suggest the coexistence of both ESD and GSD. We identified genomic sequences corresponding to the sex locus region and in a few cases we found candidate master SD genes. In one species we successfully inactivated a candidate master SD gene providing the first functional evidence that this gene is indeed determining sex in this species. Our discoveries of new master SD genes strongly supports the hypothesis that some genes (or some signalization pathways) are more efficient than others to be selected as master SD genes at the top of the gene cascade or network. Future prospects. The finding of sex chromosome status and of new master SD genes, is of major importance in light of the so far still very low number of species, in which such genes have been characterized in vertebrates. From a comparative point of view, our results will have a strong impact on our understanding of the evolution of GSD in vertebrates in general and more specifically in fishes, in which the questions about the evolutionary significance of the high diversity of SD genes and the genomic mechanisms allowing these rapid turnovers are largely unanswered. Our project will also have important practical outcomes for molecular sexing needed for a better control of sex determination in aquaculture and for ecology and ecotoxicology research in species that are economically or environmentally very important.
Publications
- Dynamics of vertebrate sex chromosome evolution: from equal size to giants and dwarfs. Chromosoma, 125, 553-71, 2016
Schartl M, Schmid M, and Nanda I
(See online at https://doi.org/10.1007/s00412-015-0569-y) - Vertebrate sex-determining genes play musical chairs. C R Biol 339, 258-262
Pan Q, Anderson J, Bertho S, Herpin A, Wilson C, Postlethwait JH, Schartl M, Guiguen Y
(See online at https://doi.org/10.1016/j.crvi.2016.05.010) - Long-term experimental hybridisation results in the evolution of a new sex chromosome in swordtail fish. Nat Comm, 9,5136, 2018
Franchini P, Jones J, Xiong P, Kneitz S, Gompert Z, Warren W, Walter R, Meyer A, Schartl M
(See online at https://doi.org/10.1038/s41467-018-07648-2) - The unusual rainbow trout sex determination gene hijacked the canonical vertebrate gonadal differentiation pathway. PNAS 115, 12781–12786, 2018
Bertho S, Herpin A, Branthonne A, Jouanno E, Yano A, Nicol B, Muller T, Pannetier M, Pailhoux E, Miwa M, Yoshizaki G, Schartl M, Guiguen Y
(See online at https://doi.org/10.1073/pnas.1803826115) - Identification of the master sex determining gene in Northern pike (Esox lucius) reveals restricted sex chromosome differentiation. PLoS Genet. 2019 Aug 22;15(8):e1008013
Pan Q, Feron R, Yano A, Guyomard R, Jouanno E, Vigouroux E, Wen M, Busnel JM, Bobe J, Concordet JP, Parrinello H, Journot L, Klopp C, Lluch J, Roques C, Postlethwait J, Schartl M, Herpin A, Guiguen Y
(See online at https://doi.org/10.1371/journal.pgen.1008013) - Independent Origin of XY and ZW Sex Determination Mechanisms in Mosquitofish Sister Species. Genetics. 2019 Nov 8
Kottler VA, Feron R, Nanda I, Klopp C, Du K, Kneitz S, Helmprobst F, Lamatsch DK, Lopez-Roques C, Lluch J, Journot L, Parrinello H, Guiguen Y, Schartl M
(See online at https://doi.org/10.1534/genetics.119.302698) - Intersex, hermaphroditism, and gonadal plasticity in vertebrates: evolution of the Müllerian duct and Amh/Amhr2 signaling. Annu Rev Anim Biosci, 7, 149–172, 2019
Adolfi MC, Nakajima RT, Nóbrega RH, Schartl M
(See online at https://doi.org/10.1146/annurev-animal-020518-114955) - The genome of the arapaima (Arapaima gigas) provides insights into gigantism, fast growth and chromosomal sex determination system. Sci Rep, 9, 5293, 2019
Du K, Wuertz S, Adolfi M, Kneitz S, Stöck M, Oliveira M, Nóbrega R, Ormanns J, Kloas W, Feron R, Klopp C, Parrinello H, Journot L, He S, Postlethwait J, Guiguen Y, Schartl M
(See online at https://doi.org/10.1038/s41598-019-41457-x)
