[The Svedberg] – Manfred Schartl
October 17 @ 15:15 – 16:15 CEST
Developmental Biochemistry, University of Würzburg, Germany
Venue: C8:305, BMC, Uppsala
Host: Leif Andersson, Uppsala University
Title of the talk: Evolution of sex determination and sex chromosomes in fish
Bio: Prof. Manfred Schartl studied Biology and Chemistry at the University of Giessen, Germany, and graduated in Genetics. After postdoctoral research in Giessen and at the NIH in Bethesda he was team leader of a research group from 1985 to 1991 at the Gene Center of the Max Planck Institute for Biochemistry in Martinsried, Germany. Until 2019 he was full professor and chairman of Physiological Chemistry at the Biocenter of the University of Würzburg. Currently, he heads a research group as senior professor at the Biocenter and works as scholar in residence at the Xiphophorus Genetic Stock Center at Texas State University in San Marcos. He is member of the German Academy of Sciences, Leopoldina, and the European Academy of Sciences, Academia Europea. He holds an honorary doctorate from the University of Bergen, Norway.
He uses the small aquarium fish biomedical models Xiphophorus and Medaka to understand molecular processes of organ development and their malfunction in disease with a focus on pigment cells and melanoma and another one on sex determination and gonad development. Key to his research is taking an evolutionary perspective to answer these questions on the basis of comparative genomics and molecular biology experimental studies.
Abstract: Sex determination (SD) is unique biological process in showing an astonishing plasticity of mechanisms. Fish present the greatest variability of SD amongst vertebrates. In the case of genetic SD this is linked to a similarly high variability of sex chromosome differentiation. While in a handful of species with genetic SD the master SD genes have been identified, their molecular function in directing the development of the bipotential gonad primordium towards testis or ovary is unclear in many cases or incompletely known in the others. To obtain a deeper understanding of this diversity we need a better knowledge of the molecular basis of SD mechanisms and the structure and genetic organization of sex chromosomes across a broad diversity of fish. To identify sex chromosomes and primary SD genes, we use high throughput RAD-tag marker mapping, transcriptomics, Pool-Seq and whole genome sequencing to identify sex-specific chromosomal regions and candidate SD genes in sharks, sturgeons and teleosts. This led to the identification of sex-specific markers, allowing to delineate the extent of recombination suppression, which turned out to be highly variable between species. We identified several species with clear cut XX/XY or ZZ/ZW monofactorial systems but also species with more complex sex-determination systems including species with a mix of genetic SD and environmental SD and species with potential polygenic systems. In species with available genomic resources, sex-specific markers could be used to assign scaffolds to regions that are supposed to contain the primary SD gene. We identified candidate genes in several species and find that most of them belong to already known factors of the primary SD regulatory network including candidate genes that have not been found so far as being SD genes. We also find that many species harbor very poorly differentiated sex-chromosomes. The SD variety does not follow a phylogenetic pattern, and turnovers of the genetic SD system from male to female heterogamety and vice versa are frequent in some groups, making the evolutionary instability of SD a spectacular trait whose biological meaning is not yet understood.