Quantitative Trait Loci Involved in Sex Determination and Body Growth in the Gilthead Sea Bream (Sparus aurata L.) through Targeted Genome Scan

Among vertebrates, teleost fish exhibit a considerably wide range of sex determination patterns that may be influenced by extrinsic parameters. However even for model fish species like the zebrafish Danio rerio the precise mechanisms involved in primary sex determination have not been studied extensively. The zebrafish, a gonochoristic species, is lacking discernible sex chromosomes and the sex of juvenile fish is difficult to determine. Sequential protandrous hermaphrodite species provide distinct determination of the gender and allow studying the sex determination process by looking at the mechanism of sex reversal. This is the first attempt to understand the genetic basis of phenotypic variation for sex determination and body weight in a sequential protandrous hermaphrodite species, the gilthead sea bream (Sparus aurata). This work demonstrates a fast and efficient strategy for Quantitative Trait Loci (QTL) detection in the gilthead sea bream, a non-model but target hermaphrodite fish species. Therefore a comparative mapping approach was performed to query syntenies against two other Perciformes, the European sea bass (Dicentrarchus labrax), a gonochoristic species and the Asian sea bass (Lates calcarifer) a protandrous hermaphrodite. In this manner two significant QTLs, one QTL affecting both body weight and sex and one QTL affecting sex, were detected on the same linkage group. The co-segregation of the two QTLs provides a genomic base to the observed genetic correlation between these two traits in sea bream as well as in other teleosts. The identification of QTLs linked to sex reversal and growth, will contribute significantly to a better understanding of the complex nature of sex determination in S. aurata where most individuals reverse to the female sex at the age of two years through development and maturation of the ovarian portion of the gonad and regression of the testicular area. [Genomic sequences reported in this manuscript have been submitted to GenBank under accession numbers HQ021443–HQ021749.

The location of olfactory receptors within olfactory epithelium is independent of odorant volatility and solubility

<p>Abstract</p> <p>Background</p> <p>Our objective was to study the pattern of olfactory receptor expression within the dorsal and ventral regions of the mouse olfactory epithelium. We hypothesized that olfactory receptors were distributed based on the chemical properties of their ligands: e.g. receptors for polar, hydrophilic and weakly volatile odorants would be present in the dorsal region of olfactory epithelium; while receptors for non-polar, more volatile odorants would be distributed to the ventral region. To test our hypothesis, we used micro-transplantation of cilia-enriched plasma membranes derived from dorsal or ventral regions of the olfactory epithelium into Xenopus oocytes for electrophysiological characterization against a panel of 100 odorants.</p> <p>Findings</p> <p>Odorants detected by ORs from the dorsal and ventral regions showed overlap in volatility and water solubility. We did not find evidence for a correlation between the solubility and volatility of odorants and the functional expression of olfactory receptors in the dorsal or ventral region of the olfactory epithelia.</p> <p>Conclusions</p> <p>No simple clustering or relationship between chemical properties of odorants could be associated with the different regions of the olfactory epithelium. These results suggest that the location of ORs within the epithelium is not organized based on the physico-chemical properties of their ligands.</p