Phylogeny of mitochondrial DNA clones in tassel-eared squirrels Sciurus aberti

The tassel-eared squirrel, Sciurus aberti , includes six subspecies which occupy restrictive and apparently identical habitats in Ponderosa pine forests in the south-western United States and Mexico; the strict habitat requirement of this species is based on dietary requirements which are only fulfilled in these forests. To examine evolutionary relationships among certain subspecies of S. aberti , we obtained estimates of nucleotide diversity within subspecies as well as nucleotide divergence between subspecies using mitochondrial DNA (mtDNA) analysis. Restriction site polymorphisms were identified in samples of the four US subspecies: S. a. aberti (Abert), S. a. kaibabensis (Kaibab), S. a. ferreus (Ferreus), and S. a. chuscensis (Chuska) Fourteen mtDNA clones were resolved that were, with one exception, uniquely subspecific. Dendrograms constructed by neighbour-joining and maximum parsimony methods revealed two major assemblages: (1) an Abert/Kaibab group; and (2) a Ferreus/Chuska group. The Abert vs. Ferreus clones exhibited the greatest net nucleotide divergence, with a lineage separation estimate approximating 572 000 years ago assuming a nucleotide substitution rate of 7.15 × 10^-9/year/site. Five out of ten Chuska squirrels shared a clone with one Abert sample; the relative sizes of these two populations and their respective ranges as well as their close proximity support the proposal for relatively recent intermixing of Abert and Chuska populations resulting in what appears to be Abert → Chuska migration. Nucleotide diversity within subspecies ranked as Kaibab < Ferreus < Abert < Chuska; the relatively high diversity for the Chuska sample is based on the apparent introgression of Abert mtDNA. The relative diversity exhibited by Kaibab, Ferreus and Aberti samples corresponds to the range size of the respective subspecies.     

Human T Cell Leukemia Virus Type 1 (HTLV-1) Antibodies in Healthy Populations and Renal Transplanted Patients in the North-East of Brazil

The seroprevalence of human T cell leukemia virus type 1 (HTLV-1) infection was investigated in Brazilians (570): native inhabitants (298) and descendants from Japanese (272) living in Recife and its neighborhoods—North-east of Brazil. Furthermore, polytransfused renal transplanted patients (54) were also examined for the serological status to this virus. The seropositivity to HTLV-1, screened by enzyme-linked immunosorbent assay (ELISA), was low: 1.34% for the local population and 0.73% for the descendants from Japanese. However, the seropositivity for the renal transplanted patients was found to be 11.1%. This higher value suggests that this retrovirus infection seems to be of importance in this clinical condition.     

A tRNA Val(GAC) gene of chloroplast origin in sunflower mitochondria is not transcribed

A tRNA^Val (GAC) gene is located in opposite orientation 552 nucleotides (nt) down-stream of the cytochrome oxidase subunit III (coxIII) gene in sunflower mitochondria. The comparison with the homologous chloroplast DNA revealed that the tRNA^Val gene is part of a 417 nucleotides DNA insertion of chloroplast origin in the mitochondrial genome. No tRNA^Val is encoded in monocot mitochondrial DNA (mtDNA), whereas two tRNA^Val species are coded for by potato mtDNA. The mitochondrial genomes of different plant species thus seem to encode unique sets of tRNAs and must thus be competent in importing the missing differing sets of tRNAs.     

The Role of Cellular and Extracellular Matrix Adhesion Proteins in Organ Transplantation

The specific adhesion of cells to other cells or to particular tissue microenvirorvments is a basic function of cell migration and recognition, and underlines many biologic processes including embryogenesis, repair and immunity. Leukocytes express an array of surface receptors broadly known as “accessory adhesion molecules.” which mediate most cell -cell interactions, direct lymphocyte traffic between anatomical compartments, and facilitate cellular adhesion to the inflammation or alloantigenic sites (Springer 1990). In addition, adhesion molecules are involved in the process of antigen recognition, and may costimulate cell activation and transformation. These proteins are thought to affect the very early antigen independent events between host leukocytes and vascular endothelium. Because of these activities, the subject of adhesion molecules is gaining interest in the field of organ transplantation, in both conceptualization and development of novel therapeutic strategies (de Sousa et al. 1991, Kupiec-Weglinski et al. 1993a, Heemann et al. 1993).     

Regulation of immediate-early gene expression in rat retinal ganglion cells after axotomy and during regeneration through a peripheral nerve graft

To determine mechanisms of structural plasticity in adult CNS neurons, we investigated the expression of immediate early genes (IEGs) in the rat retina. Gene products of different IEG families (JUN and FOS proteins) and cAMP-responsive element binding protein (CREBP) were examined by immunohistochemistry under three different paradigms. Normal rats which were not axotomized were compared with axotomized animals, where retinal ganglion cells (RGCs) were axotomized by intraorbital optic nerve cut and retrogradely labeled with fluorogold (FG). Under these circumstances, RGCs show only transient sprouting, followed by continuous retrograde RGC degeneration. In the third group, after the optic nerve lesion, adult rats additionally received a sciatic nerve graft to the transected optic nerve stump. This allows some RGCs to regenerate an axon into the grafted nerve. In both groups, the time course of RGC survival and JUN, CREB, and FOS protein expression was monitored. In normal animals, JUN-Immunoreactivity (JUN-Ir) was not detectable in the retinal ganglion cell layer. JUN-Ir was induced in about 70% of all FG-positive RGCs 5 days after axotomy. The expression of JUN-Ir started to decline 8 days after axotomy. Only a few JUN-Ir-positive RGCs were found after 2 weeks. In transplanted animals, however, the numbers of JUN-Ir-positive RGCs were significantly higher 2 and 3 weeks after transplantation compared to animals that exclusively received axotomy. Furthermore, in grafted rats about 70% of the regenerating RGCs expressed JUN-Ir 2 weeks after grafting as compared to only 38% JUN-positive RGCs among the surviving but not regenerating RGCs. In normal animals CREBP-Ir was constitutively expressed in nearly all cells of the retinal ganglion cell layer. The decline in number of CREBP-Ir-positive cells paralleled the axotmy-induced RGC death. FOS-Ir-positive cells were not found in the ganglion cell layer at any time. These results demonstrate a selective and transient JUN expression of RGCs after axotomy which is sustained during axonal regeneration. This suggests that sciatic nerve grafts are able to regulate the expression of JUN proteins in axotomized RGCs of adult rats. 1994 John Wiley & Sons, Inc.     

Decreasing glycolysis increases sensitivity to mitochondrial inhibition in primary cultures of renal proximal tubule cells

Summary We have previously shown that shaking the culture plates (SHAKE) of rabbit renal proximal tubule cells (RPTC) to maintain adequate aeration increased aerobic metabolism and decreased the induction of glycolysis compared to RPTC cultured under standard conditions (STILL). However, glycolysis in SHAKE RPTC remained elevated compared to glycolysis in proximal tubules in vivo. In the present study the contribution of culture medium sugar composition and concentration to glycolytic metabolism was assessed in RPTC. SHAKE and STILL RPTC cultured in 5 mM glucose contained lactate levels equivalent to the respective SHAKE and STILL RPTC cultured in standard culture medium which contains 17.5 mM glucose. Similarly, the activity of lactate dehydrogenase was unchanged by lowering the medium glucose concentration. Substituting 5 mM galactose for 5 mM glucose in the culture medium significantly reduced the lactate content of both SHAKE and STILL RPTC but had no effect on lactate dehydrogenase activity. Cell growth was equivalent under all culture conditions. Sensitivity to mitochondrial inhibition was determined for each culture condition by measuring cell death after exposure to the respiratory inhibitor antimycin A. The results showed a hierarchy of sensitivity to antimycin A (5 mM galactose SHAKE >5 mM glucose SHAKE >17.5 mM glucose SHAKE = 17.5 mM glucose STILL), which was generally inversely correlated with the level of glycolysis as measured by lactate content (17.5 mM glucose STILL >17.5 mM glucose SHAKE = 5 mM glucose SHAKE >5 mM galactose SHAKE).     

The genetic structure and microdistribution of shoals of Phoxinus phoxinus, the European minnow

Efficient foraging and a reduction in predation risk have been proposed as reasons for shoal formation. Some behaviours in cyprinid shoals are at first sight altruistic (e.g. predator inspection behaviour, reactions to alarm substance), such that kin selection may have been involved in their evolution. If shoaling behaviour does evolve through kin selection, then genetic differentiation is expected to be greater between shoals than within shoals. Such a hypothesis was tested here by examining shoal integrity and the relatedness of individuals within and between shoals in the European minnow, Phoxinus phoxinus , using nuclear and mitochondrial DNA markers. The breeding structure of 13 minnow shoals collected from Dorset and North Wales, U.K., was examined using allozymes. Genetic affinity within and between shoals was tested using mitochondrial DNA and multi-locus DNA fingerprinting. Shoals consisted of a random assortment of allozyme genotypes, shoal members did not share the same maternal mtDNA lineages and DNA fingerprint profiles were as varied within shoals as between them. The data indicate that it is unlikely that kin selection occurs in P. phoxinus and there is no apparent relationship between shoaling behaviour and genotype distribution in this species.     

A molecular perspective on the phylogeny of placental mammals based on mitochondrial 12S rDNA sequences,with special reference to the problem of the Paenungulata

Part of the 12S rDNA gene was amplified and sequenced for 11 placental mammals, 3 marsupials, and 2 monotremes. Multiple alignments for these sequences and nine additional placental sequences taken from GenBank were obtained using CLUSTAL. Phylogenetic analyses were performed using standard parsimony, transversion parsimony, and Lake's method of invariants. All of our analyses uniteLoxodontia withDugong. Procavia, in turn, is a sister group to these taxa, thus supporting the monophyly of the Paenungulata. Perissodactyls are a sister group to paenungulates when transitions and transversions are both included but not when transitions are omitted. Likewise, cetaceans are a sister group to artiodactyls on minimum length trees under standard parsimony but not under transversion parsimony. Rodent monophyly and bat monophyly also receive mixed support, as does a putative alliance between primates and lagomorphs. Interestingly, the percentage divergence between the echidna and the platypus is less than for the rat and mouse.     

Metabolic defects shared by Alzheimer's disease and diabetes: A focus on mitochondria

Type 2 diabetes (T2D) and Alzheimer's disease (AD) are two global epidemics that share several metabolic defects, such as insulin resistance, impaired glucose metabolism, and mitochondrial defects. Importantly, strong evidence demonstrates that T2D significantly increases the risk of cognitive decline and dementia, particularly AD. Here, we provide an overview of the metabolic defects that characterize and link both pathologies putting the focus on mitochondria. The biomarker potential of mitochondrial components and the therapeutic potential of some drugs that target and modulate mitochondria are also briefly discussed.