Low Frequency Vibrations Disrupt Left-Right Patterning in the Xenopus Embryo

The development of consistent left-right (LR) asymmetry across phyla is a fascinating question in biology. While many pharmacological and molecular approaches have been used to explore molecular mechanisms, it has proven difficult to exert precise temporal control over functional perturbations. Here, we took advantage of acoustical vibration to disrupt LR patterning in Xenopus embryos during tightly-circumscribed periods of development. Exposure to several low frequencies induced specific randomization of three internal organs (heterotaxia). Investigating one frequency (7 Hz), we found two discrete periods of sensitivity to vibration; during the first period, vibration affected the same LR pathway as nocodazole, while during the second period, vibration affected the integrity of the epithelial barrier; both are required for normal LR patterning. Our results indicate that low frequency vibrations disrupt two steps in the early LR pathway: the orientation of the LR axis with the other two axes, and the amplification/restriction of downstream LR signals to asymmetric organs

Horizontal gene transfer promoted evolution of the ability to propagate under anaerobic conditions in yeasts

The ability to propagate under anaerobic conditions is an essential and unique trait of brewer's or baker's yeast ( Saccharomyces cervisiae). To understand the evolution of facultative anaerobiosis we studied the dependence of de novo pyrimidine biosynthesis, more precisely the fourth enzymic activity catalysed by dihydroorotate dehydrogenase (DHODase), on the enzymes of the respiratory chain in several yeast species. While the majority of yeasts possess a mitochondrial DHODase, Saccharomyces cerevisiae has a cytoplasmatic enzyme, whose activity is independent of the presence of oxygen. From the phylogenetic point of view, this enzyme is closely related to a bacterial DHODase from Lactococcus lactis. Here we show that S. kluyveri, which separated from the S. cerevisiae lineage more than 100 million years ago, represents an evolutionary intermediate, having both cytoplasmic and mitochondrial DHODases. We show that these two S. kluyveri enzymes, and their coding genes, differ in their dependence on the presence of oxygen. Only the cytoplasmic DHODase promotes growth in the absence of oxygen. Apparently a Saccharomyces yeast progenitor which had a eukaryotic-like mitochondrial DHODase acquired a bacterial gene for DHODase, which subsequently allowed cell growth gradually to become independent of oxygen

Epistasis regulates the developmental stability of the mouse craniofacial shape.

12 pagesInternational audienceFluctuating asymmetry is a classic concept linked to organismal development. It has traditionally been used as a measure ofdevelopmental instability, which is the inability of an organism to buffer environmental fluctuations during development.Developmental stability has a genetic component that influences the final phenotype of the organism and can lead tocongenital disorders. According to alternative hypotheses, this genetic component might be either the result of additivegenetic effects or a by-product of developmental gene networks. Here we present a genome-wide association study of thegenetic architecture of fluctuating asymmetry of the skull shape in mice. Geometric morphometric methods were applied toquantify fluctuating asymmetry: we estimated fluctuating asymmetry as Mahalanobis distances to the mean asymmetry,correcting first for genetic directional asymmetry. We applied the marginal epistasis test to study epistasis among genomicregions. Results showed no evidence of additive effects but several interacting regions significantly associated withfluctuating asymmetry. Among the candidate genes overlapping these interacting regions we found an over-representation ofgenes involved in craniofacial development. A gene network is likely to be associated with skull developmental stability, andgenes originally described as buffering genes (e.g., Hspa2) might occupy central positions within these networks, whereregulatory elements may also play an important role. Our results constitute an important step in the exploration of themolecular roots of developmental stability and the first empirical evidence about its genetic architecture