Mechanisms of mitochondrial DNA escape to the nucleus in the yeast Saccharomyces cerevisiae.

The transfer of organelle nucleic acid to the nucleus has been observed in both plants and animals. Using a unique assay to monitor mitochondrial DNA escape to the nucleus in the yeast Saccharomyces cerevisiae, we previously showed that mutations in several nuclear genes, collectively called yme mutants, cause a high rate of mitochondrial DNA escape to the nucleus. Here we demonstrate that mtDNA escape occurs via an intracellular mechanism that is dependent on the composition of the growth medium and the genetic state of the mitochondrial genome, and is independent of an RNA intermediate. Isolation of several unique second-site suppressors of the high rate of mitochondrial DNA-escape phenotype of yme mutants suggests that there are multiple independent pathways by which this nucleic acid transfer occurs. We also demonstrate that the presence of centromeric plasmids in the nucleus can reduce the perceived rate of DNA escape from the mitochondria. We propose that mitochondrial DNA-escape events are manifested as unstable nuclear plasmids that can interact with centromeric plasmids resulting in a decrease in the number of observed events.

Mitochondrial morphological and functional defects in yeast caused by yme1 are suppressed by mutation of a 26S protease subunit homologue.

The absence of functional Yme1p, a putative ATP and zinc-dependent protease localized to mitochondria of yeast, results in abnormal mitochondrial function and morphology. Yeast lacking Yme1p lose DNA from mitochondria at an accelerated rate, fail to grow on nonfermentable carbon sources at 37 degrees C, and have severely deficient growth if mitochondrial DNA suffers large deletions or is completely lost. In place of the normal reticulated mitochondrial network, strains lacking Yme1p have punctate mitochondria with some grossly swollen compartments. The growth phenotypes and morphological alterations evident in these mutant yeast can be compensated by a mutation in YNT1, an essential gene in yeast. The sequence of the YNT1 gene product indicates that it is one of a number of related regulatory subunits of the 26S protease. This proteolytic activity is necessary for progression through the cell cycle and has been implicated in the regulation of transcription. Ynt1p is more distantly related to Yme1p.

AFG2, an essential gene in yeast, encodes a new member of the Sec18p, Pas1p, Cdc48p, TBP-1 family of putative ATPases.

A gene from Saccharomyces cerevisiae was sequenced that encodes a protein with homology to a family of putative ATPases. These homologous proteins include the yeast cell division cycle protein Cdc48p and its mammalian homologues VCP and p97; Sec18p and its mammalian homologue NSF, proteins necessary for fusion of transport vesicles to target membranes in the secretory pathway; Pas1p, a protein necessary for peroxisome biosynthesis in yeast; Yme1p, a yeast mitochondrial protein that influences the rate of DNA escape from mitochondria; and TBP-1, MSS1 and Sug1p, proteins that interact with transcription factors. This newly sequenced gene, named AFG2 for ATPase family gene, is located on chromosome XII 5' to the SLP1/VPS33 open reading frame and encodes an essential protein of 780 amino acids that is most homologous to Cdc48p.

Inactivation of YME1, a member of the ftsH-SEC18-PAS1-CDC48 family of putative ATPase-encoding genes, causes increased escape of DNA from mitochondria in Saccharomyces cerevisiae.

The yeast nuclear gene YME1 was one of six genes recently identified in a screen for mutations that elevate the rate at which DNA escapes from mitochondria and migrates to the nucleus. yme1 mutations, including a deletion, cause four known recessive phenotypes: an elevation in the rate at which copies of TRP1 and ARS1, integrated into the mitochondrial genome, escape to the nucleus; a heat-sensitive respiratory-growth defect; a cold-sensitive growth defect on rich glucose medium; and synthetic lethality in rho- (cytoplasmic petite) cells. The cloned YME1 gene complements all of these phenotypes. The gene product, Yme1p, is immunologically detectable as an 82-kDa protein present in mitochondria. Yme1p is a member of a family of homologous putative ATPases, including Sec18p, Pas1p, Cdc48p, TBP-1, and the FtsH protein. Yme1p is most similar to the Escherichia coli FtsH protein, an essential protein involved in septum formation during cell division. This observation suggests the hypothesis that Yme1p may play a role in mitochondrial fusion and/or division.

Recombinant human osteogenic protein-1 (hOP-1) induces new bone formation in vivo with a specific activity comparable with natural bovine osteogenic protein and stimulates osteoblast proliferation and differentiation in vitro.

We reported previously that a 32-36-kDa osteogenic protein purified from bovine bone matrix is composed of dimers of two members of the transforming growth factor (TGF)-beta superfamily: the bovine equivalent of human osteogenic protein-1 (OP-1) and bone morphogenetic protein-2a, BMP-2a (BMP-2). In the present study, we produced the recombinant human OP-1 (hOP-1) in mammalian cells as a processed mature disulfide-linked homodimer with an apparent molecular weight of 36,000. Examination of hOP-1 in the rat subcutaneous bone induction model demonstrated that hOP-1 was capable of inducing new bone formation with a specific activity comparable with that exhibited by highly purified bovine osteogenic protein preparations. The half-maximal bone-inducing activity of hOP-1 in combination with a rat collagen matrix preparation was 50-100 ng/25 mg of matrix as determined by the calcium content of day 12 implants. Evaluation of hOP-1 effects on cell growth and collagen synthesis in rat osteoblast-enriched bone cell cultures showed that both cell proliferation and collagen synthesis were stimulated in a dose-dependent manner and increased 3-fold in response to 40 ng of hOP-1/ml. Examination of the expression of markers characteristic of the osteoblast phenotype showed that hOP-1 specifically stimulated the induction of alkaline phosphatase (4-fold increase at 40 ng of hOP-1/ml), parathyroid hormone-mediated intracellular cAMP production (4-fold increase at 40 ng of hOP-1/ml), and osteocalcin synthesis (5-fold increase at 25 ng of hOP-1/ml). In long-term (11-17 day) cultures of osteoblasts in the presence of beta-glycerophosphate and L(+)-ascorbate, hOP-1 markedly increased the rate of mineralization as measured by the number of mineral nodules per well (20-fold increase at 20 ng of hOP-1/ml). Direct comparison of TGF-beta 1 and hOP-1 in these bone cell cultures indicated that, although both hOP-1 and TGF-beta 1 promoted cell proliferation and collagen synthesis, only hOP-1 was effective in specifically stimulating markers of the osteoblast phenotype.

Diapering choices: a critical review of the issues.

Careful consideration is needed to determine which diapering system may be best suited to an institution's or individual's needs. A critical review of five issues--skin care, infection control, other health-related concerns, environmental and safety aspects, and time/cost issues--reveals that: (a) superabsorbent paper diapers reduce the incidence and severity of diaper dermatitis and control the spread of infection in caregiving surroundings; (b) cloth and paper diapers have different effects on the environment and neither type of diaper is clearly superior to the other; and (c) the cost of disposable diapers and reusable commercial-laundered diapers may be comparable, although home-laundered diapers are least expensive if the caregiver's labor is not considered.

Reversal of acute glomerular renal allograft rejection: a possible effect of OKT3.

A major cause of renal allograft loss is glomerulovascular rejection. This case report is about an episode of histologically proven acute glomerular rejection that was successfully reversed. Monoclonal antibody OKT3 may have been the effective agent.

Acute renal failure due to acute pyelonephritis.

We report a case of biopsy-proved acute pyelonephritis which caused acute renal failure. Despite appropriate antibiotic therapy, recovery of renal function was slow and incomplete. Renal papillary necrosis was an apparent complication, which the patient may have been predisposed to by alcoholism. Although rare, acute pyelonephritis is an important consideration in the differential diagnosis of acute renal failure because of the need for specific therapy.

Xanthogranulomatous pyelonephritis in a renal allograft: a case report.

We report a case of xanthogranulomatous pyelonephritis in a renal allograft. The kidney was not removed and there was an initial response to antibiotic therapy, with amelioration of toxicity and improvement in renal function. However, the kidney failed 10 months later in association with histological changes of chronic rejection.

Analgesic nephropathy: etiology, clinical syndrome, and clinicopathologic correlations in Australia.

Analgesic abuse is a major public health hazard in Australia, and analgesic nephropathy with consequent terminal renal failure is the underlying cause in 20% of the patients requiring dialysis and transplantation. Analgesics are invariably taken in the form of compounds and mixtures. In the aspirin-phenacetin-caffeine (APC) mixture, aspirin appears to be the major nephrotoxic agent and phenacetin appears to play a secondary and synergistic role. The renal disease associated with abuse of analgesics is characteristic and is part of a much wider clinical syndrome, the analgesic syndrome, which includes peptic ulcer disease (35%), anemia (60 to 90%), hypertension (15 to 70%), ischemic heart disease (35%), psychological and psychiatric manifestations, pigmentation, and possible gonadal- and pregnancy-related effects. The primary lesion in analgesic nephropathy is renal papillary necrosis (RPN), and this is a nephrotoxic effect common to all nonsteroid antiinflammatory agents. The most important factor in the management of patients with analgesic nephropathy is the cessation of analgesic abuse, and this leads to improvement and stabilization of renal function. A small proportion of patients will, however, deteriorate in relation to accelerated hypertension, persistent proteinuria, ischemic heart disease, and complications leading to nephrectomy. Patients with analgesic nephropathy are poor risk patients and have a poor prognosis, even after dialysis and transplantation.