Mitochondrial protein import

Most polypeptides of mitochondria are imported from the cytosol. Precursor proteins contain targeting and sorting information, often in the form of amino-terminal presequences. Precursors first bind to receptors in the outer membrane. Two putative import receptors have been identified: a 19-kilodalton protein (MOM19) inNeurospora mitochondria, and a 70-kilodalton protein (MAS70) in yeast. Some precursors integrate directly into the outer membrane, but the majority are translocated through one or both membranes. This process requires an electrochemical potential across the inner membrane. Import appears to occur through a hydrophilic pore, although the inner and outer membranes may contain functionally separate translocation machineries. In yeast, a 42-kilodalton protein (ISP42) probably forms part of the outer membrane channel. After import, precursors interact with chaperonin ATPases in the matrix. Presequences then are removed by the matrix protease. Finally, some proteins are retranslocated across the inner membrane to the intermembrane space.     

Duplication of the PMP22 gene in 17p partial trisomy patients with Charcot-Marie-Tooth type-1A neuropathy

Autosomal dominant Charcot-Marie-Tooth type-1A neuropathy (CMT1A) is a demyelinating peripheral nerve disorder that is commonly associated with a submicroscopic tandem DNA duplication of a 1.5-Mb region of 17p11.2p12 that contains the peripheral myelin gene PMP22. Clinical features of CMT1A include progressive distal muscle atrophy and weakness, foot and hand deformities, gait abnormalities, absent reflexes, and the completely penetrant electrophysiologic phenotype of symmetric reductions in motor nerve conduction velocities (NCVs). Molecular and fluorescence in situ hybridization (FISH) analyses were performed to determine the duplication status of the PMP22 gene in four patients with rare cytogenetic duplications of 17p. Neuropathologic features of CMT1A were seen in two of these four patients, in addition to the complex phenotype associated with 17p partial trisomy. Our findings show that the CMT1A phenotype of reduced NCV is specifically associated with PMP22 gene duplication, thus providing further support for the PMP22 gene dosage mechanism for CMT1A. Received: 3 May 1995 / Revised: 1 August 1995     

Detection of Obesity QTLs on Mouse Chromosomes 1 and 7 by Selective DNA Pooling

The inheritance of obesity has been analyzed in an intercross between the lean 129/Sv mouse strain and the obesity-prone EL/Suz mouse strain. The weights of three major fat pads were determined on 4-month-old mice, and the sum of these weights, divided by body weight, was used as an adiposity index. The strategy of selective DNA pooling was used as a primary screen to identify putative quantitative trait loci (QTLs) affecting adiposity index. DNA pools representing the leanest 15% and fattest 15% of the F2 progeny were compared for differential allelic enrichment using widely dispersed microsatellite variants. To evaluate putative QTLs, individual genotyping and interval mapping were employed to estimate QTL effects and assess statistical significance. One QTL affecting adiposity index, which accounted for 12.3% of phenotypic variance in gender-merged data, was mapped to the central region of Chromosome (Chr) 7. The QTL allele inherited from EL conferred increased adiposity. A second QTL that accounts for 6.3% of phenotypic variance was identified on Chr 1 nearD1Mit211.At both QTLs, the data are consistent with dominant inheritance of the allele contributing to obesity. The possible relationships between these QTLs and previously described obesity QTLs, major obesity mutations, and candidate genes are discussed.     

Palisade mesophyll cell expansion during leaf development in Zinnia elegans (Asteraceae)

Temporal and spatial patterns of palisade mesophyll cell expansion in Zinnia elegans were characterized as a basis for developing a suspension culture model for mesophyll cell expansion. Our objectives were to 1) identify the leaf regions from which cells in various stages of expansion could be selectively isolated for culture, and 2) develop a basis for comparison of rate and extent of mesophyll cell expansion in culture with that in the leaf. Palisade mesophyll cells were isolated from expanding leaves by gentle physical maceration without the use of enzymes. Isolated cells from leaves in different stages of expansion were then measured by computer image analysis. Analysis of size frequency distributions showed that unexpanded cells can be isolated from the entire blade of small leaves or the basal regions of partially expanded leaves. Fully expanded cells can be obtained from the apical and middle regions of partially expanded leaves. Within the leaf, Zinnia mesophyll cells expanded from about 400 μm² to about 2.300 μm² at an estimated rate of 160 μm² d^-1. The percent increase in cell length exceeded the percent increase in cell width. Expansion of mesophyll cells continued for 6–8 d after epidermal expansion ceased. This difference in the timing of cell expansion in epidermal and mesophyll cells indicates that different regulatory factors may be operating in these adjacent tissues and underscores the importance of investigating the regulation of mesophyll cell expansion at the cellular level.     

Mouse centromere mapping using oligonucleotide probes that detect variants of the minor satellite

Cytologically, the centromere is found at the very end of most Mus musculus chromosomes, co-localizing with an array of minor satellite sequences. It is separated from the euchromatin of the long arm by a large domain of heterochromatin, composed in part of arrays of major satellite sequences. We used oligonucleotide probes that specifically detect regions of sequence variation found in certain cloned minor satellite sequences. They detect a limited subset of the minor satellite arrays in the mouse genome, based on both pulsed-field gel electrophoresis and in situ hybridization data, and provide direct molecular genetic markers for individual centromeres in some inbred mouse strains. Array size polymorphisms detected by these probes map to positions consisten with the centromeres of chromosomes 1 and 14 in the BXD recombinant inbred (RI) strains. The genetic distances between these minor satellite arrays and loci on the long arms of chromosomes 1 and 14 are consistent with repression of meiotic recombination in the heterochromatic domains separating them. The existence of chromosome-specific minor satellite sequences implies that the rate of sequence exchange between non-homologous chromosomes relative to the rate between homologous chromosomes is much lower than has previously been postulated. We suggest that the high degree of sequence homogeneity of mouse satellite sequences may instead reflect recent common ancestry.     

Detection of molecular variation in the insect pathogenic fungus Metarhizium using RAPD-PCR

Abstract DNA polymorphism among isolates of the insect pathogenic fungus Metarhizium anisopliae and M. flavoviride was investigated by RAPD-PCR. DNA fragments of between 0.3 and 2.7 kb were obtained using eight 10-mer PCR primers of arbitrary nucleotide sequence, and each isolate differed in the size and number of RAPD products, indicating considerable polymorphism. Isolate-specific RAPD fingerprints were used to calculate relative genetic similarity; this differentiated isolates into two major groups, separating nine of the ten isolates of M. anisopliae from the two of M. flavoviride . However, an Australian M. anisopliae isolated from an Orthopteran host exhibited a higher degree of genetic similarity to the M. flavoviride group. M. anisopliae isolates were further segregated into three subgroups which were loosely related to their geographical origins. although considerable polymorphism was observed within these groups. There was no apparent association between genotype and original insect host.     

Widespread formation of intracellular calcium carbonates by the bloom-forming cyanobacterium Microcystis

The formation of intracellular amorphous calcium carbonates (iACC) has been recently observed in a few cultured strains of Microcystis, a potentially toxic bloom-forming cyanobacterium found worldwide in freshwater ecosystems. If iACC-forming Microcystis are abundant within blooms, they may represent a significant amount of particulate Ca. Here, we investigate the significance of iACC biomineralization by Microcystis. First, the presence of iACC-forming Microcystis cells has been detected in several eutrophic lakes, indicating that this phenomenon occurs under environmental conditions. Second, some genotypic (presence/absence of ccyA, a marker gene of iACC biomineralization) and phenotypic (presence/absence of iACC) diversity have been detected within a collection of strains isolated from one single lake. This illustrates that this trait is frequent but also variable within Microcystis even at a single locality. Finally, one-third of publicly available genomes of Microcystis were shown to contain the ccyA gene, revealing a wide geographic and phylogenetic distribution within the genus. Overall, the present work shows that the formation of iACC by Microcystis is common under environmental conditions. While its biological function remains undetermined, this process should be further considered regarding the biology of Microcystis and implications on the Ca geochemical cycle in freshwater environments.     

Mapping and monitoring tick (Acari,Ixodida) distribution,seasonality, and host associations in the United Kingdom between 2017 and 2020

Tick-borne disease risk is intrinsically linked to the distribution of tick vector species. To assess risk and anticipate disease emergence, an understanding of tick distribution, host associations, and seasonality is needed. This can be achieved, to some extent, using passive surveillance supported by engagement with the public, animal health, and public health experts. The Tick Surveillance Scheme (TSS) collects data and maps tick distribution across the United Kingdom (UK). Between 2017 and 2020, 3720 tick records were received and 39 tick species were detected. Most records were acquired in the UK, with a subset associated with recent overseas travel. The dominant UK acquired species was Ixodes ricinus (Ixodida: Ixodidae, Linnaeus), the main vector of Lyme borreliosis. Records peaked during May and June, highlighting a key risk period for tick bites. Other key UK species were detected, including Dermacentor reticulatus (Ixodida: Ixodidae, Fabricius) and Haemaphysalis punctata (Ixodida: Ixodidae, Canestrini & Fanzago) as well as several rarer species that may present novel tick-borne disease risk to humans and other animals. Updated tick distribution maps highlight areas in the UK where tick exposure has occurred. There is evidence of increasing human tick exposure over time, including during the COVID-19 pandemic, but seasonal patterns remain unchanged.