New circumstellar dust component in oxygen rich environments

Spectra of oxygen rich stars in the IRAS low-resolution spectra (LRS) catalog were found to display two distinct classes of curcumstellar excess emission. The first group has the normal silicate with emission peaking at 10 and 18 microns. The second group has an emission spectrum peaking at 13 and 20 microns. There are also spectra with a mixture of the above types. Generally the continuum temperature associated with the second group is much warmer than that associated with the normal silicate group. Laboratory spectra are compared with the new excess which associates the emission with a class of materials represented by hydrated aluminates and silicates. Possible interpretations include equilibrium condensation sequences and peculiar metal abundance ratios

Carbon stars with alpha-C:H emission

Many carbon stars in the IRS low resolution spectra (LRS) catalog were found which display emission spectra that compare favorable with the absorption spectrum of alpha-C:H. These stars have largely been classified as 4X in the LRS which has led to their interpretation by others in terms of displaying a mixture of the UIRF's 8.6 micron band and SiC at 11.5 microns. It was also found that many of these stars have a spectral upturn at 20+ microns which resembles the MgS band seen in carbon stars and planetary nebulae. It was concluded that this group of carbon stars will evolve into planetary nebulae like NGC 7027 and IC 418. In the presence of hard ultraviolet radiation the UIRF's will light up and be displayed as narrow emission bands on top of the broad alpha-C:H emission bands

Inventaire cytogénomique des petits mammifères du Maroc

International audienceUn inventaire cytogénomique des petits mammifères du littoral marocain a été effectué sur 43 spécimens correspondant à 10 espèces, utilisant les techniques de cytogénétique classique et d'hybridation in situ de séquences répétées télomériques et centromériques. Les caryotypes avec marquage chromosomique sont présentés pour la première fois, pour deux des espèces (Crocidura russula et Elephantulus rozeti). L'ensemble des données permet de confirmer le statut taxonomique des espèces. Aucune espèce cryptique n'a pu être identifiée chez Gerbillus campestris, Meriones shawii, Mus spretus, Apodemus sylvaticus et Lemniscomys barbarus alors que plusieurs cas sont connus chez les rongeurs. L'existence de séquences télomériques interstitielles chez M. shawii a pu être interprétée comme la trace d'évènements de fusions robertsoniennes survenues lors de l'évolution du genre Meriones. Enfin, la présence de chromosomes B chez G. campestris et M. shawii soulève la question de leur rôle dans l'évolution chomosomique de ces taxons. Abstract : A cytogenomic survey of Moroccan small mammals is proposed. It includes 43 individuals corresponding to 10 species. Cytogenetics and in situ hybridization with telomeric and centromeric probes were performed. Banded karyotypes of two species (Crocidura russula and Elephantulus rozeti) are shown for the first time. The taxonomic status of each specimen is confirmed. No sibling species can be identified in Gerbillus campestris, Meriones shawii, Mus spretus, Apodemus sylvaticus, Lemniscomys barbarus, while their presence is known for different rodents. Otherwise, telomeric sequences are observed in interstitial positions in Meriones shawii, which suggests that the Meriones genus evolved by Robertsonian fusions. Finally, the presence of B chromosomes in G. campestris and M. shawii raises the question of their role in the chromosomal evolution of these taxa

Diversity and distribution of alpha satellite DNA in the genome of an Old World monkey: Cercopithecus solatus

International audienceBackgroundAlpha satellite is the major repeated DNA element of primate centromeres. Evolution of these tandemly repeated sequences has led to the existence of numerous families of monomers exhibiting specific organizational patterns. The limited amount of information available in non-human primates is a restriction to the understanding of the evolutionary dynamics of alpha satellite DNA.ResultsWe carried out the targeted high-throughput sequencing of alpha satellite monomers and dimers from the Cercopithecus solatus genome, an Old World monkey from the Cercopithecini tribe. Computational approaches were used to infer the existence of sequence families and to study how these families are organized with respect to each other. While previous studies had suggested that alpha satellites in Old World monkeys were poorly diversified, our analysis provides evidence for the existence of at least four distinct families of sequences within the studied species and of higher order organizational patterns. Fluorescence in situ hybridization using oligonucleotide probes that are able to target each family in a specific way showed that the different families had distinct distributions on chromosomes and were not homogeneously distributed between chromosomes.ConclusionsOur new approach provides an unprecedented and comprehensive view of the diversity and organization of alpha satellites in a species outside the hominoid group. We consider these data with respect to previously known alpha satellite families and to potential mechanisms for satellite DNA evolution. Applying this approach to other species will open new perspectives regarding the integration of satellite DNA into comparative genomic and cytogenetic studies

The Targeted Sequencing of Alpha Satellite DNA in Cercopithecus pogonias Provides New Insight Into the Diversity and Dynamics of Centromeric Repeats in Old World Monkeys

International audienceAlpha satellite is the major repeated DNA element of primate centromeres. Specific evolutionary mechanisms have led to a great diversity of sequence families with peculiar genomic organization and distribution, which have till now been studied mostly in great apes. Using high throughput sequencing of alpha satellite monomers obtained by enzymatic digestion followed by computational and cytogenetic analysis, we compare here the diversity and genomic distribution of alpha satellite DNA in two related Old World monkey species, Cercopithecus pogonias and Cercopithecus solatus, which are known to have diverged about 7 Ma. Two main families of monomers, called C1 and C2, are found in both species. A detailed analysis of our data sets revealed the existence of numerous subfamilies within the centromeric C1 family. Although the most abundant subfamily is conserved between both species, our fluorescence in situ hybridization (FISH) experiments clearly show that some subfamilies are specific for each species and that their distribution is restricted to a subset of chromosomes, thereby pointing to the existence of recurrent amplification/homogenization events. The pericentromeric C2 family is very abundant on the short arm of all acrocentric chromosomes in both species, pointing to specific mechanisms that lead to this distribution. Results obtained using two different restriction enzymes are fully consistent with a predominant monomeric organization of alpha satellite DNA that coexists with higher order organization patterns in the C. pogonias genome. Our study suggests a high dynamics of alpha satellite DNA in Cercopithecini, with recurrent apparition of new sequence variants and interchromosomal sequence transfer

Additional file 2: Table S1. of Diversity and distribution of alpha satellite DNA in the genome of an Old World monkey: Cercopithecus solatus

Filtering steps from Cercopithecus solatus raw data to alpha satellite monomer and dimer datasets. Table S2. Alpha satellite family associations in Cercopithecus solatus dimer dataset. (DOCX 40 kb

Additional file 4: Text S2. of Diversity and distribution of alpha satellite DNA in the genome of an Old World monkey: Cercopithecus solatus

Alignment used to generate the phylogenetic tree from Fig. 7b. (TXT 48 kb

Additional file 3: Text S1. of Diversity and distribution of alpha satellite DNA in the genome of an Old World monkey: Cercopithecus solatus

Alignment used to generate the phylogenetic tree from Fig. 7a. (TXT 28 kb

Telomere regulation during ageing and tumorigenesis of the grey mouse lemur

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