A chromosome-level genome assembly enables the identification of the follicule stimulating hormone receptor as the master sex determining gene in the flatfish Solea senegalensis

Sex determination (SD) shows huge variation among fish and a high evolutionary rate, as illustrated by the Pleuronectiformes (flatfishes). This order is characterized by its adaptation to demersal life, compact genomes and diversity of SD mechanisms. Here, we assembled the Solea senegalensis genome, a flatfish of great commercial value, into 82 contigs (614 Mb) combining long- and short-read sequencing, which were next scaffolded using a highly dense genetic map (28,838 markers, 21 linkage groups), representing 98.9% of the assembly. Further, we established the correspondence between the assembly and the 21 chromosomes by using BAC-FISH. Whole genome resequencing of six males and six females enabled the identification of 41 SNP variants in the follicle stimulating hormone receptor (fshr) consistent with an XX / XY SD system. The observed sex association was validated in a broader independent sample, providing a novel molecular sexing tool. Fshr displayed differential gene expression between male and female gonads from 86 days post-fertilization, when the gonad is still an undifferentiated primordium, concomitant with the activation of amh and cyp19a1a, testis and ovary marker genes, respectively, in males and females. The Y-linked fshr allele, which included 24 non-synonymous variants and showed a highly divergent 3D protein structure, was overexpressed in males compared to the X-linked allele at all stages of gonadal differentiation. We hypothesize a mechanism hampering the action of the follicle stimulating hormone driving the undifferentiated gonad toward testis.info:eu-repo/semantics/acceptedVersio

Methods for Seafood Authenticity Testing in Europe

56 pages, 5 figuresSeafood authenticity is a key parameter for seafood quality, particularly in Europe where regulations provide a strict framework for seafood labeling. A wide variety of methods are commonly used in control laboratories (private or public) to identify seafood species, but emergent approaches for the development of new and fast DNA- and protein-based methods for species differentiation are also considered. To address the challenges in controlling further labeling requirements in the latest European legislation on seafood product traceability and labeling (Regulation (EU) 1379/2013), a review of the development of methods to identify fishing areas and to distinguish between wild and farmed fish, as well as an overview of the advanced methods that could be used for differentiation of fresh and frozen-thawed fish, is given. These methods will become increasingly important in the near future as the risk-based control of food authenticity is prescribed by the new EU control regulation (Regulation (EU) 2017/625)N