An initiation site for meiotic crossing-over and gene conversion in the mouse

During meiosis, the reductional segregation of homologous chromosomes at the first meiotic division requires reciprocal exchange (crossing over) between homologs. The number of crossovers is tightly regulated (one to two per homolog in mice), and their distribution in the genome is not random-recombination 'hot' and 'cold' regions can be identified. We developed a molecular assay to study these events directly in mouse germ cells. This analysis was developed with reference to the proteosome subunit beta type 9 (Psmb9, previously called Lmp2) hot-spot region identified through genetic analysis. Here we show that this hot spot is an initiation site of meiotic recombination on the basis of two observations: (i) crossover density is maximal in an interval of 210 bp and decreases on both sides of this region; (ii) a high frequency of gene conversion is found in the region of highest crossover density. We then used this strategy to carry out the first temporal analysis of meiotic recombination in mouse spermatogenesis and demonstrate that crossover events occur during the pachytene stage of meiotic prophase.     

Seriation in the Presence of Errors: NP-Hardness of <Emphasis Type=Italic>l</Emphasis><Subscript><Emphasis Type=Italic>∞</Emphasis></Subscript> -Fitting Robinson Structures to Dissimilarity Matrices

In this paper, we establish that the following fitting problem is NP-hard: given a finite set X and a dissimilarity measure d on X (d is a symmetric function from X ² to the nonnegative real numbers and vanishing on the diagonal), we wish to find a Robinsonian dissimilarity d _R on X minimizing the l _∞ -error ||d − d _R || _∞ = max_x,y ∈X{|d(x, y) − d _R (x, y)|} between d and d _R . Recall that a dissimilarity d _R on X is called monotone (or Robinsonian) if there exists a total order ≺ on X such that x ≺ z ≺ y implies that d(x, y) ≥ max{d(x, z), d(z, y)}. The Robinsonian dissimilarities appear in seriation and clustering problems, in sparse matrix ordering and DNA sequencing.     

Wnt and lithium: a common destiny in the therapy of nervous system pathologies?

Wnt signaling is required for neurogenesis, the fate of neural progenitors, the formation of neuronal circuits during development, neuron positioning and polarization, axon and dendrite development and finally for synaptogenesis. This signaling pathway is also implicated in the generation and differentiation of glial cells. In this review, we describe the mechanisms of action of Wnt signaling pathways and their implication in the development and correct functioning of the nervous system. We also illustrate how a dysregulated Wnt pathway could lead to psychiatric, neurodegenerative and demyelinating pathologies. Lithium, used for the treatment of bipolar disease, inhibits GSK3β, a central enzyme of the Wnt/β-catenin pathway. Thus, lithium could, to some extent, mimic Wnt pathway. We highlight the possible dialogue between lithium therapy and modulation of Wnt pathway in the treatment of the diseases of the nervous system.     

Factors influencing fish assemblages of a high-elevation desert stream system in Wyoming

Seven fish species were found in the Bitter Creek drainage of southwest Wyoming, but only speckled dace ( Rhinichthys osculus ), flannelmouth sucker ( Catostomus latipinnis ), and mountain sucker ( Catostomus platyrhynchus ) were indigenous. No relationships were found between fish standing stocks and habitat features, but species richness was related to elevation and stream width. No fish were found above an elevation of 2192 m. Only the most downstream study read had more than three species present. Two indigenous species, speckled dace and mountain sucker, and a nonnative species, fathead minnow ( Pimephales promelas ), were predominant fishes in the drainage. These three species withstand intermittent stream flows that are common in the drainage.     

A mutation creating a potential illegitimate microRNA target site in the myostatin gene affects muscularity in sheep

Texel sheep are renowned for their exceptional meatiness. To identify the genes underlying this economically important feature, we performed a whole-genome scan in a Romanov x Texel F2 population. We mapped a quantitative trait locus with a major effect on muscle mass to chromosome 2 and subsequently fine-mapped it to a chromosome interval encompassing the myostatin (GDF8) gene. We herein demonstrate that the GDF8 allele of Texel sheep is characterized by a G to A transition in the 3' UTR that creates a target site for mir1 and mir206, microRNAs (miRNAs) that are highly expressed in skeletal muscle. This causes translational inhibition of the myostatin gene and hence contributes to the muscular hypertrophy of Texel sheep. Analysis of SNP databases for humans and mice demonstrates that mutations creating or destroying putative miRNA target sites are abundant and might be important effectors of phenotypic variation.