Identification of tissue-specific microRNAs from mouse

MicroRNAs (miRNAs) are a new class of noncoding RNAs, which are encoded as short inverted repeats in the genomes of invertebrates and vertebrates. It is believed that miRNAs are modulators of target mRNA translation and stability, although most target mRNAs remain to be identified. Here we describe the identification of 34 novel miRNAs by tissue-specific cloning of approximately 21-nucleotide RNAs from mouse. Almost all identified miRNAs are conserved in the human genome and are also frequently found in nonmammalian vertebrate genomes, such as pufferfish. In heart, liver, or brain, it is found that a single, tissue-specifically expressed miRNA dominates the population of expressed miRNAs and suggests a role for these miRNAs in tissue specification or cell lineage decisions. Finally, a miRNA was identified that appears to be the fruitfly and mammalian ortholog of C. elegans lin-4 stRNA.     

The cardiac mechanical stretch sensor machinery involves a Z disc complex that is defective in a subset of human dilated cardiomyopathy

Muscle cells respond to mechanical stretch stimuli by triggering downstream signals for myocyte growth and survival. The molecular components of the muscle stretch sensor are unknown, and their role in muscle disease is unclear. Here, we present biophysical/biochemical studies in muscle LIM protein (MLP) deficient cardiac muscle that support a selective role for this Z disc protein in mechanical stretch sensing. MLP interacts with and colocalizes with telethonin (T-cap), a titin interacting protein. Further, a human MLP mutation (W4R) associated with dilated cardiomyopathy (DCM) results in a marked defect in T-cap interaction/localization. We propose that a Z disc MLP/T-cap complex is a key component of the in vivo cardiomyocyte stretch sensor machinery, and that defects in the complex can lead to human DCM and associated heart failure.     

Phytotoxicity and ultrastructural effects of gymnopusin from the orchid Maxillaria densa on duckweed (Lemna pausicostata) frond and root tissues

The effect of life cycle on the distributions of C(25) and C(30) highly branched isoprenoid (HBI) alkene lipids has been investigated for the marine diatom Rhizosolenia setigera. The concentrations of the C(30) compounds are largely independent of the cell volume, though the ratios of the individual isomers possessing five and six double bonds show a dependence on the position of the cell during its life cycle, especially during auxosporulation. In contrast to the C(30) pseudo-homologues, the C(25) isomers are not always detected in cultures of R. setigera. The biosynthesis of the C(25) HBIs would appear to result from the onset of auxosporulation, with further changes to their distributions taking place after this phase, including the formation of more unsaturated isomers. The results of this investigation may be used in part to explain the large variations in these lipids reported previously.     

Distinct mechanisms of internalization of Neisseria gonorrhoeae by members of the CEACAM receptor family involving Rac1- and Cdc42-dependent and -independent pathways

Opa adhesins of pathogenic Neisseria species target four members of the human carcinoembryonic antigen-related cellular adhesion molecule (CEACAM) family. CEACAM receptors mediate opsonization-independent phagocytosis of Neisseria gonorrhoeae by human granulocytes and each receptor individually can mediate gonococcal invasion of epithelial cells. We show here that gonococcal internalization occurs by distinct mechanisms depending on the CEACAM receptor expressed. For the invasion of epithelial cell lines via CEACAM1 and CEACAM6, a pathogen-directed reorganization of the actin cytoskeleton is not required. In marked contrast, ligation of CEACAM3 triggers a dramatic but localized reorganization of the host cell surface leading to highly efficient engulfment of bacteria in a process regulated by the small GTPases Rac1 and Cdc42, but not Rho. Two tyrosine residues of a cytoplasmic immune receptor tyrosine-based activating motif of CEACAM3 are essential for the induction of phagocytic actin structures and subsequent gonococcal internalization. The granulocyte-specific CEACAM3 receptor has properties of a single chain phagocytic receptor and may thus contribute to innate immunity by the elimination of Neisseria and other CEACAM-binding pathogens that colonize human mucosal surfaces.     

Isomerization and oxidation of vitamin a in cone-dominant retinas: a novel pathway for visual-pigment regeneration in daylight

The first step toward light perception is 11-cis to all-trans photoisomerization of the retinaldehyde chromophore in a rod or cone opsin-pigment molecule. Light sensitivity of the opsin pigment is restored through a multistep pathway called the visual cycle, which effects all-trans to 11-cis re-isomerization of the retinoid chromophore. The maximum throughput of the known visual cycle, however, is too slow to explain sustained photosensitivity in bright light. Here, we demonstrate three novel enzymatic activities in cone-dominant ground-squirrel and chicken retinas: an all-trans-retinol isomerase, an 11-cis-retinyl-ester synthase, and an 11-cis-retinol dehydrogenase. Together these activities comprise a novel pathway that regenerates opsin photopigments at a rate 20-fold faster than the known visual cycle. We suggest that this pathway is responsible for sustained daylight vision in vertebrates.     

The Xmrk oncogene can escape nonfunctionalization in a highly unstable subtelomeric region of the genome of the fish Xiphophorus

The Xmrk oncogene involved in melanoma formation in the fish Xiphophorus was formed relatively recently by duplication of the epidermal growth factor co-orthologue egfrb. In the platyfish X. maculatus, Xmrk is located close to the major sex-determining locus in a subtelomeric region of the X and Y sex chromosomes that frequently undergoes duplications and other rearrangements. This region accumulates repetitive sequences: more than 80% of the 33-kb region 3' of Xmrk is constituted by retrotransposable elements. The high degree of nucleotide identity between X- and Y-linked sequences and the rarity of gonosome-specific rearrangements indicated that the instability observed was not a manifestation of gonosome-specific degeneration. Seven other duplicated genes were found, all corresponding, in contrast to Xmrk, to pseudogenes (nonfunctionalization). Functional persistence of Xmrk in a highly unstable region in divergent Xiphophorus species suggests a beneficial function under certain conditions for this dispensable and potentially injurious gene.