Molinier, C. | bioRxiv Science

bioRxiv2018

Identification of general patterns of sex-biased expression in Daphnia, a genus with environmental sex determination

Daphnia reproduce by cyclic-parthenogenesis, where phases of asexual reproduction are intermitted by sexual production of diapause stages. This life cycle, together with environmental sex determination, allow the comparison of gene expression between genetically identical males and females. We investigated gene expression differences between males and females in four genotypes of Daphnia magna and compared the results with published data on sex-biased gene expression in two other Daphnia species, each representing one of the major phylogenetic clades within the genus. We found that 42% of all annotated genes showed sex-biased expression in D. magna. This proportion is similar both to estimates from other Daphnia species as well as from species with genetic sex determination, suggesting that sex-biased expression is not reduced under environmental sex determination. Among 7453 single copy, one-to-one orthologs in the three Daphnia species, 707 consistently showed sex-biased expression and 675 were biased in the same direction in all three species. Hence these genes represent a core-set of genes with consistent sex-differential expression in the genus. A functional analysis identified that several of them are involved in known sex determination pathways. Moreover, 75% were overexpressed in females rather than males, a pattern that appears to be a general feature of sex-biased gene expression in Daphnia.\n\nShort summaryIn some species with environmental sex determination, gene expression can be compared between genetically identical males and females. Here, we investigated sex-biased expression in one such species, D. magna, and compared it with data from two congeners. We found that all three species have a common set of 675 genes with consistent differential expression and with a strong bias towards overexpression in females rather than males. Moreover, the proportion of sex-biased genes in each of the three Daphnia species was similar to Drosophila species with genetic sex determination, suggesting that sex-biased expression is not necessarily reduced under environmental sex determination.

genomics↗

bioRxiv2017

Multiplexed temporally focused light shaping for high-resolutionmulti-cell targeting

Patterning light at the single-cell level over multiple neurons in the brain is crucial for optogenetic photostimulation that can recapitulate natural activity patterns and, thereby, determine the role of specific components of brain activity in behavior. To this end we have developed a method for projecting three-dimensional, 2-photon excitation patterns that are confined to many individual neurons. The new versatile optical scheme generates multiple extended excitation spots in a large volume with micrometric lateral and axial resolution. Two-dimensional temporally focused shapes are multiplexed several times over selected positions, thanks to the precise spatial phase modulation of the pulsed beam. This permits, under multiple configurations, the generation of tens of axially confined spots in an extended volume, spanning a range in depth of up to 500 m. We demonstrate the potential of the approach by performing multi-cell volumetric excitation of photoactivatable GCaMP in the central nervous system of Drosophila larvae, a challenging structure with densely arrayed and small diameter neurons, and by photoconverting the fluorescent protein Kaede in zebrafish larvae. Our technique paves the way for the optogenetic manipulation of a large number of neurons in intact circuits.

neuroscience↗