Biochemical studies of mammalian oogenesis: possible existence of a ribosomal and poly(A)-containing RNA-protein supramolecular complex in mouse oocytes

Mouse follicles were labeled with [3H]uridine and then cultured in vitro for 3 days. When oocytes were disrupted, about 40% of the total radiolabeled RNA could be sedimented at 9,000g. Fractionation of this RNA on poly(U)-Sepharose revealed that about 30% and 60% of the total amount of radiolabeled poly(A)- and poly(A)+ RNA, respectively, were in the pellet fraction. Treatments that disrupt protein structure reduced the amount of 9,000g sedimentable RNA and affected to the same extent the distribution of Poly(A)- and poly(A)+ RNA in the pellet and supernatant fractions. CsCl centrifugation of formaldehyde-fixed pellets revealed that virtually all of the radiolabeled RNA had a density significantly lower than that of ribosomes. The sedimentable RNA appeared not to be polysomal, membrane bound or associated wih a cytoskeleton. Agarose gel electrophoresis after poly(U)-Sepharose fractionation of either the pellet or supernatant revealed the presence of 28S, 18S, 5S + 4S, and heterodisperse poly(A)+ RNA. The size of distribution of poly(A)+ RNA in the pellet and supernatant fractions was fairly similar. Pulse-chase experiments revealed that the stability of poly(A)- RNA in the pellet and supernatant fractions was the same within the experimental error and a similar situation was found for poly(A)+ RNA. RNA in pellet translated in vitro coded for discrete size classes of protein. Since the relative band intensities were similar for both total and pellet RNA translated in vitro there seemed to be no major partitioning of specific size classes of mRNA into the pellet fraction. These results are discussed in terms of a possible composition of the lattice structures that accumulate during mouse oocyte growth and have been postulated to be a storage form for ribosome (Burkholder et al., '71).     

Biology of the relict fungus-farming ant Apterostigma megacephala Lattke,including descriptions of the male,gyne, and larva

Insectes Sociaux - Fungus-farming “attine” ant agriculture consists of five distinct agricultural systems characterized by a remarkable symbiont fidelity in which five phylogenetic...     

5.8S-28S rRNA interaction and HMM-based ITS2 annotation

The internal transcribed spacer 2 (ITS2) of the nuclear ribosomal repeat unit is one of the most commonly applied phylogenetic markers. It is a fast evolving locus, which makes it appropriate for studies at low taxonomic levels, whereas its secondary structure is well conserved, and tree reconstructions are possible at higher taxonomic levels. However, annotation of start and end positions of the ITS2 differs markedly between studies. This is a severe shortcoming, as prediction of a correct secondary structure by standard ab initio folding programs requires accurate identification of the marker in question. Furthermore, the correct structure is essential for multiple sequence alignments based on individual structural features. The present study describes a new tool for the delimitation and identification of the ITS2. It is based on hidden Markov models (HMMs) and verifies annotations by comparison to a conserved structural motif in the 5.8S/28S rRNA regions. Our method was able to identify and delimit the ITS2 in more than 30 000 entries lacking start and end annotations in GenBank. Furthermore, 45 000 ITS2 sequences with a questionable annotation were re-annotated. Approximately 30 000 entries from the ITS2-DB, that uses a homology-based method for structure prediction, were re-annotated. We show that the method is able to correctly annotate an ITS2 as small as 58 nt from Giardia lamblia and an ITS2 as large as 1160 nt from humans. Thus, our method should be a valuable guide during the first and crucial step in any ITS2-based phylogenetic analysis: the delineation of the correct sequence. Sequences can be submitted to the following website for HMM-based ITS2 delineation: http://its2.bioapps.biozentrum.uni-wuerzburg.de.     

Positive Selection in Tick Saliva Proteins of the Salp15 Family

When taking their blood meal on the mammalian host, ticks transfer a multitude of different proteins from their saliva into the host. Some of these proteins are hijacked by pathogens for their own purposes. Borrelia burgdorferi, the Lyme disease agent, is critically dependent on the presence of the tick protein Salp15 when infecting the host. Similarly, Anaplasma phagocytophilum, which causes anaplasmosis, needs Salp16, a homologue of Salp15, to get transferred from the host into the tick. Here we analyzed whether adaptive evolution has shaped the Salp15 protein family. Using site-specific estimates of K_A/K_S ratios, we identified different positions within the Salp15 protein family which have undergone a phase of positive selection. Additionally, we analyzed the B. burgdorferi protein interacting with Salp15, OspC. Again, sites showing signs of positive selection were identified, although they are more likely a result of the antigenic features of OspC than of the influence of Salp15. The identification of probably functionally relevant sites in the Salp15 family might direct the detailed experimental analysis of their interaction with human and bacterial proteins. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Three sweet receptor genes are clustered in human Chromosome 1

A search of the human genome database led us to identify three human candidate taste receptors, hT1R1, hT1R2, and hT1R3, which contain seven transmembrane domains. All three genes map to a small region of Chromosome (Chr) 1. This region is syntenous to the distal end of Chr 4 in mouse, which contains the Sac (saccharin preference) locus that is involved in detecting sweet tastants. A genetic marker, DVL1, which is linked to the Sac locus, is within 1700 bp of human T1R3. Recently, the murine T1Rs and its human ortholog have been independently identified in combination as sweet and umami receptors near the Sac locus. All three hT1Rs genes are expressed selectively in human taste receptor cells in the fungiform papillae, consistent with their role in taste perception.