Sox4 participates in the modulation of Schwann cell myelination.

In order to identify new regulators of Schwann cell myelination potentially playing a role in peripheral nervous system (PNS) pathologies, we analysed gene expression profiling data from three mouse models of demyelinating neuropathies and from the developing PNS. This analysis revealed that Sox4, which encodes a member of the Sry-related high-mobility group box protein family, was consistently upregulated in all three analysed models of neuropathy. Moreover, Sox4 showed a peak in its expression during development that corresponded with the onset of myelination. To gain further insights into the role of Sox4 in PNS development, we generated a transgenic mouse that specifically overexpresses Sox4 in Schwann cells. Sox4 overexpression led to a temporary delay in PNS myelination without affecting axonal sorting. Importantly, we observed that, whereas Sox4 mRNA could be efficiently overexpressed, Sox4 protein expression in Schwann cells was strictly regulated. Finally, our data showed that enforced expression of Sox4 in the mouse model for Charcot-Marie-Tooth 4C aggravated its neuropathic phenotype. Together, these observations reveal that Sox4 contributes to the regulation of Schwann cell myelination, and also indicates its involvement in the pathophysiology of peripheral neuropathies.

Sex-Chromosome Homomorphy in Palearctic Tree Frogs Results from Both Turnovers and X-Y Recombination.

Contrasting with birds and mammals, poikilothermic vertebrates often have homomorphic sex chromosomes, possibly resulting from high rates of sex-chromosome turnovers and/or occasional X-Y recombination. Strong support for the latter mechanism was provided by four species of European tree frogs, which inherited from a common ancestor (∼5 Ma) the same pair of homomorphic sex chromosomes (linkage group 1, LG1), harboring the candidate sex-determining gene Dmrt1. Here, we test sex linkage of LG1 across six additional species of the Eurasian Hyla radiation with divergence times ranging from 6 to 40 Ma. LG1 turns out to be sex linked in six of nine resolved cases. Mapping the patterns of sex linkage to the Hyla phylogeny reveals several transitions in sex-determination systems within the last 10 My, including one switch in heterogamety. Phylogenetic trees of DNA sequences along LG1 are consistent with occasional X-Y recombination in all species where LG1 is sex linked. These patterns argue against one of the main potential causes for turnovers, namely the accumulation of deleterious mutations on nonrecombining chromosomes. Sibship analyses show that LG1 recombination is strongly reduced in males from most species investigated, including some in which it is autosomal. Intrinsically low male recombination might facilitate the evolution of male heterogamety, and the presence of important genes from the sex-determination cascade might predispose LG1 to become a sex chromosome.

No Accumulation of Transposable Elements in Asexual Arthropods.

Transposable elements (TEs) and other repetitive DNA can accumulate in the absence of recombination, a process contributing to the degeneration of Y-chromosomes and other nonrecombining genome portions. A similar accumulation of repetitive DNA is expected for asexually reproducing species, given their entire genome is effectively nonrecombining. We tested this expectation by comparing the whole-genome TE loads of five asexual arthropod lineages and their sexual relatives, including asexual and sexual lineages of crustaceans (Daphnia water fleas), insects (Leptopilina wasps), and mites (Oribatida). Surprisingly, there was no evidence for increased TE load in genomes of asexual as compared to sexual lineages, neither for all classes of repetitive elements combined nor for specific TE families. Our study therefore suggests that nonrecombining genomes do not accumulate TEs like nonrecombining genomic regions of sexual lineages. Even if a slight but undetected increase of TEs were caused by asexual reproduction, it appears to be negligible compared to variance between species caused by processes unrelated to reproductive mode. It remains to be determined if molecular mechanisms underlying genome regulation in asexuals hamper TE activity. Alternatively, the differences in TE dynamics between nonrecombining genomes in asexual lineages versus nonrecombining genome portions in sexual species might stem from selection for benign TEs in asexual lineages because of the lack of genetic conflict between TEs and their hosts and/or because asexual lineages may only arise from sexual ancestors with particularly low TE loads.

Phylogenomics Controlling for Base Compositional Bias Reveals a Single Origin of Eusociality in Corbiculate Bees.

As increasingly large molecular data sets are collected for phylogenomics, the conflicting phylogenetic signal among gene trees poses challenges to resolve some difficult nodes of the Tree of Life. Among these nodes, the phylogenetic position of the honey bees (Apini) within the corbiculate bee group remains controversial, despite its considerable importance for understanding the emergence and maintenance of eusociality. Here, we show that this controversy stems in part from pervasive phylogenetic conflicts among GC-rich gene trees. GC-rich genes typically have a high nucleotidic heterogeneity among species, which can induce topological conflicts among gene trees. When retaining only the most GC-homogeneous genes or using a nonhomogeneous model of sequence evolution, our analyses reveal a monophyletic group of the three lineages with a eusocial lifestyle (honey bees, bumble bees, and stingless bees). These phylogenetic relationships strongly suggest a single origin of eusociality in the corbiculate bees, with no reversal to solitary living in this group. To accurately reconstruct other important evolutionary steps across the Tree of Life, we suggest removing GC-rich and GC-heterogeneous genes from large phylogenomic data sets. Interpreted as a consequence of genome-wide variations in recombination rates, this GC effect can affect all taxa featuring GC-biased gene conversion, which is common in eukaryotes.

Genomic evidence for adaptive inversion clines in Drosophila melanogaster.

Clines in chromosomal inversion polymorphisms-presumably driven by climatic gradients-are common but there is surprisingly little evidence for selection acting on them. Here we address this long-standing issue in Drosophila melanogaster by using diagnostic single nucleotide polymorphism (SNP) markers to estimate inversion frequencies from 28 whole-genome Pool-seq samples collected from 10 populations along the North American east coast. Inversions In(3L)P, In(3R)Mo, and In(3R)Payne showed clear latitudinal clines, and for In(2L)t, In(2R)NS, and In(3R)Payne the steepness of the clinal slopes changed between summer and fall. Consistent with an effect of seasonality on inversion frequencies, we detected small but stable seasonal fluctuations of In(2R)NS and In(3R)Payne in a temperate Pennsylvanian population over 4 years. In support of spatially varying selection, we observed that the cline in In(3R)Payne has remained stable for >40 years and that the frequencies of In(2L)t and In(3R)Payne are strongly correlated with climatic factors that vary latitudinally, independent of population structure. To test whether these patterns are adaptive, we compared the amount of genetic differentiation of inversions versus neutral SNPs and found that the clines in In(2L)t and In(3R)Payne are maintained nonneutrally and independent of admixture. We also identified numerous clinal inversion-associated SNPs, many of which exhibit parallel differentiation along the Australian cline and reside in genes known to affect fitness-related traits. Together, our results provide strong evidence that inversion clines are maintained by spatially-and perhaps also temporally-varying selection. We interpret our data in light of current hypotheses about how inversions are established and maintained.

Gadolinska samlingen

Samlingen har varit kemiprofessorn Johan Gadolins (1760-1852) privatbibliotek. I samlingen ingår böcker som tillhört Johan Gadolins far, Jacob Gadolin (1719-1802), som var professor i fysik och teologi och sedemera biskop i Åbo stift. I samlingen ingår också böcker som tillhört Johan Gadolins morfar, Johan Browallius (1707-1755), som likaså var professor i fysik och teologi och sedemera biskop i Åbo stift. Samlingen är katalogiserad i Alma och har signum HB Gad.

Das Landgut Monrepos in Finnland. 1804

Ludwig von Nicolay (1737-1820) oli Strassburgissa syntynyt oppinut, Venäjän hovin kotiopettaja, sittemmin salaneuvos ja Venäjän tiedeakatemian presidentti, tieteen ja taiteen suosija. Von Nicolay hankki itselleen Viipurin lähellä sijaitsevan Monrepos'n kartanon vuonna 1788. Yhdessä erään ystävänsä kanssa hän kokosi kartanoonsa merkittävän, 1700-luvun valistuskulttuuria kuvastavan kirjaston, jonka von Nicolayn jälkeläiset lahjoittivat ensimmäisen maailmansodan aikana Helsingin yliopistolle. Kartanon puistosta von Nicolay kehitti maineikkaan, englantilaistyylisen maisemapuiston. Hän kirjoitti puistosta runoteoksen Das Landgut Monrepos 1804 (St Petersburg 1806), jonka hänen poikansa Paul julkaisi uudelleen vuonna 1840. Tähän teokseen liitettiin ranskalaisen taiteilijan Jean Louis Jacottet'n puistoa esittäviä litografioita, jotka pohjautuivat tanskalaisen Christian Ferdinand Christensenin akvarelleihin.

Symphony no. 39 : in E-flat, K. 543

Soitinnus: ork.

Symphony no. 41 : in C, K. 551 ("Jupiter")

Soitinnus: ork.

Symphony no. 40 : in g minor, K. 550

Soitinnus: ork.

Das Landgut Monrepos in Finnland. 1804.

Ludwig von Nicolay (1737-1820) oli Strassburgissa syntynyt oppinut, Venäjän hovin kotiopettaja, sittemmin salaneuvos ja Venäjän tiedeakatemian presidentti, tieteen ja taiteen suosija. Von Nicolay hankki itselleen Viipurin lähellä sijaitsevan Monrepos'n kartanon vuonna 1788. Yhdessä erään ystävänsä kanssa hän kokosi kartanoonsa merkittävän, 1700-luvun valistuskulttuuria kuvastavan kirjaston, jonka von Nicolayn jälkeläiset lahjoittivat ensimmäisen maailmansodan aikana Helsingin yliopistolle. Kartanon puistosta von Nicolay kehitti maineikkaan, englantilaistyylisen maisemapuiston. Hän kirjoitti puistosta runoteoksen Das Landgut Monrepos 1804 (St Petersburg 1806), jonka hänen poikansa Paul julkaisi uudelleen vuonna 1840. Tähän teokseen liitettiin ranskalaisen taiteilijan Jean Louis Jacottet'n puistoa esittäviä litografioita, jotka pohjautuivat tanskalaisen Christian Ferdinand Christensenin akvarelleihin.

La Connoissance des temps, ou calendrier et éphémérides du lever & coucher du soleil, de la lune, & des autres planètes...

1788.

Psicología de la adolescencia

Estamos ante una edición actualizada de un clásico, cuya primera edición en castellano data de 1985, y que habia sido reimpreso en 1987 y 1994. Aunque la actualización nos llega en castellano con unos pocos años de retraso, le damos la bienvenida porque está trabajada a fondo. Sólo con revisar la bibliografia, por cierto, amplisima, se aprecia inmediatamente que un alto porcentaje de las referencias es de los años 90

De asparago

Invocatio: I.N.D.