Tryptophan-requiring parental strains yield Salmonella typhimurium x Escherichia coli hybrid recombinants with functional tryptophan operons.

Crosses between an Escherichia coli Hfr trp strain and three Salmonella typhimurium F- trp strains produced some trp+ hybrids in which the tryptophan operon is composed of genes from both parental species.     

Contacts between pigmented retina epithelial cells in culture.

The behaviour of primary cultures of dissociated embryonic chick pigmented retina epithelial (PRE) cells has been investigated. Isolated PRE cells have a mean speed of locomotion of 7-16 mum/h. Collisions between the cells normally result in the development of stable contacts between the cells involved. This leads to a gradual reduction in the number of isolated cells and an increase in the number of cells incorporated into islands. Ultrastructural observations of islands of cells after 24 h in culture show that junctional complexes are present between the cells. These complexes consist of 2 components: (a) an apically situated region of focal tight junctions and/or gap junctions, and (b) a more ventrally located zonula adhaerens with associated cytoplasmic filaments forming a band running completely around the periphery of each cell. The intermembrane gap in the region of the zonula is 6-0-12-0 nm. The junctional complexes become more differentiated with time and after 48 h in culture consist of an extensive region of tight junctions and/or gap junctions and a more specialized zonula adhaerens. It is suggested that the development of junctional complexes may be responsible for the stable contacts that the cells display in culture.     

三苯基锡,二环己基碳二亚胺和寡霉素对叶绿体CF0与CF1功能联系的影响

作用于H~ —ATP酶复合体质子通道的能量传递抑制剂 TPT、DQCD和 OM能明显抑制叶绿体光合磷酸化反应和膜上 ATP酶活性,减小恒态ΛpH值,加速ΛpH和515 nm吸收衰减。这种在正常叶绿体加速H_(in)~ 经CF_0外流与在残缺膜中阻塞质子外流不一致。TPT等物质是干扰了CF_0与CF_1的构象连接,使 CF_0的质子传导失去CF_1的控制,H_(in)~ 无效漏失或质子逆向转移受影响,从而抑制与质子传导紧密相关的光合磷酸化反应和膜上ATP酶活性。     

The effects of chemokine, adhesion and extracellular matrix molecules on binding of mesenchymal stromal cells to poly(l-lactic acid)

Abstract Background aims. Mesenchymal stromal cells (MSC) are pluripotent adult stem cells capable of osteogenesis and chondrogenesis to form bone and cartilage. This characteristic gives them the potential for bone and cartilage regeneration. Synthetic polymers have been studied to examine whether they could be used as a scaffold for tissue engineering. In the current study a two-dimensional (2-D) poly(l-lactic acid) (PLLA) scaffold was treated with chemokine, adhesion and extracellular matrix molecules with the aim of using biologic molecules to improve the attachment of human MSC. Methods. MSC were isolated from human bone marrow and applied to a 2-D PLLA scaffold. Chemokines ligand (CXCL12 and CXCL13), adhesion molecules [P-selectin, vascular cell adhesion molecule (VCAM)-1 and heparin] and extracellular matrix molecules (fibronectin and type IV collagen) were coated on the scaffold and their effects on the number of MSC that adhered were recorded. Results. When used alone CXCL12 and CXCL13 enhanced MSC adhesion, as did VCAM-1, P-selectin, fibronectin and collagen, but not heparin. The effects of VCAM-1, P-selectin and heparin were enhanced by the addition of CXCL12. Incubation of MSC with antibodies to integrins α4 and α5β1 inhibited their adhesion to VCAM-1 and fibronectin-treated PLLA respectively, suggesting that these integrins were involved in the MSC interactions. Conclusions. The use of certain chemokines and adhesion and extracellular matrix molecules, alone or in combination, is beneficial for the attachment of MSC to PLLA, and may be helpful as natural molecules in scaffolds for regenerative medicine.     

Towards a Case Definition for Devil Facial Tumour Disease: What Is It?

In the mid 1990s an emerging disease characterised by the development of proliferative lesions around the face of Tasmanian devils (Sarcophilus harrisii) was observed. A multi-disciplinary approach was adopted to define the condition. Histopathological and transmission electron microscopic examination combined with immunohistochemistry help define Devil Facial Tumour Disease (DFTD) as a neoplastic condition of cells of neuroendocrine origin. Cytogenetic analysis of neoplastic tissue revealed it to be markedly different from normal devil tissue and having a consistent karyotype across all tumours examined. Combined with evidence for Major histocompatability (MHC) gene analysis there is significant evidence to confirm the tumour is a transmissible neoplasm.     

Involvement of tryptophan 209 in the allosteric interactions of Escherichia coli aspartate transcarbamylase using single amino acid substitution mutants

Five mutant versions of aspartate transcarbamylase have been isolated, all with single amino acid substitutions in the catalytic chain of the enzyme. A previously isolated pyrB nonsense mutant was suppressed with supB, supC, supD and supG to create enzymes with glutamine, tyrosine, serine or lysine, respectively, inserted at the position of the nonsense codon. Each of these enzymes was purified to homogeneity and kinetically characterized. The approximate location of the substitution was determined by using tryptic fingerprints of the wild-type enzyme and the enzyme obtained with a tyrosine residue inserted at the position of the nonsense codon. By first cloning the pyrBI operon, from the original pyrB nonsense strain, followed by sequencing of the appropriate portion of the gene, the exact location of the mutation was determined to be at position 209 of the catalytic chain. Site-directed mutagenesis was used to generate versions of aspartate transcarbamylase with tyrosine and glutamic acid at this position. The Tyr209 enzyme is identical with that obtained by suppression of the original nonsense mutation with supC. The two enzymes produced by site-directed mutagenesis were purified using a newly created overproducing strain. Kinetic analysis revealed that each mutant has an altered affinity for aspartate, as judged by variations in the substrate concentration at one-half maximal activity. In addition, the mutants exhibit altered Hill coefficients and maximal activities. In the wild-type enzyme, position 209 is a tryptophan residue that is involved in the stabilization of a bend in the molecule near the subunit interface region. The alteration in homotropic cooperativity seems to be due to changes induced in this bend in the molecule, which stabilizes alternate conformational states of the enzyme.     

Hydrochory,seed banks,and regeneration dynamics along the landscape boundaries of a forested wetland

Following the environmental sieve concept, the setting in which the recruitment of Taxodium distichum occurs in, becomes increasingly restrictive from the seed to seedling stage in an impounded forested wetland. Although a wide elevational band of dispersing seed moves across the boundary of a swamp-field in the water sheet, the zone of germination is relegated to that portion of the forested wetland that draws down during the growing season. Seedling recruitment is further restricted to the uppermost zone of the winter water sheet. These patterns are likely applicable to other species of dominant swamp species, e.g., Cephalanthus occidentalis crossed the boundary of a forested wetland and abandonded field in winter flooding (November–December and November–March, respectively) in Buttonland Swamp. The elevation of the boundary was 101.3 m NGVD. While the seeds of at least 40 swamp species were dispersed across the boundary, few viable seeds were dispersed after the winter season. Kriged maps showed seeds of T. distichum and C. occidentalis dispersed in patches in the water depending on the position of the water sheet. Most species of both water- and gravity-dispersed species had a localized pattern of seed distribution (either spherical or exponential) and this indicated that seeds may not be dispersed for great distances in the swamp. Water-dispersed T. distichum and C. occidentalis had larger dispersal ranges (A ₀=225 and 195 m, respectively) than Bidens frondosa and B. discoidea (A ₀=14 and 16 m, respectively). Seed dispersal varied with season depending on the availability of seeds. In Buttonland Swamp, viable seeds typically were dispersed for T. distichum in November–June, and for C. occidentalis in November-July. Low water occurred in August 1993 and high in February 1994 (99.8 and 101.6 m NGVD, respectively). The seed banks along the landscape boundary varied in species composition according to elevation (r ² = 0.996). While the similarity of species richness between water-dispersed seeds and the seed bank at elevations that flooded (during June 1993 through May 1995) was high (10–17%), it was low between water-dispersed seeds and the seed bank at elevations that did not flood (5%). T. distichum seeds had a short germination window in that seeds germinated within a year following their production in zones that were flooded in the winter followed by drawdown during the next growing season. After 1 year, less than 5% of the T. distichum seeds remained viable on the surface of the soil. Germination of T. distichum was confined to specific elevations (above 99.3 but below 101.6 m NGVD) during this study with 4.1% of the seedlings surviving for more than 2 years at a mean of 101.4 m NGVD. All seedlings below this elevation died. To maximize natural regeneration along the boundaries of swamps in abandoned farm fields targeted for restoration, this study suggests a flood pulse regime consisting of high water in the winter to maximize dispersal of live seeds followed by low water in the summer to facilitate seed germination and seedling recruitment. Hydrologic restoration could assist in the natural recovery of damaged wetlands if a seed source exists nearby.     

Age at onset in two common neurodegenerative diseases is genetically controlled

To identify genes influencing age at onset (AAO) in two common neurodegenerative diseases, a genomic screen was performed for AAO in families with Alzheimer disease (AD; n=449) and Parkinson disease (PD; n=174). Heritabilities between 40%–60% were found in both the AD and PD data sets. For PD, significant evidence for linkage to AAO was found on chromosome 1p (LOD = 3.41). For AD, the AAO effect of APOE (LOD = 3.28) was confirmed. In addition, evidence for AAO linkage on chromosomes 6 and 10 was identified independently in both the AD and PD data sets. Subsequent unified analyses of these regions identified a single peak on chromosome 10q between D10S1239 and D10S1237, with a maximum LOD score of 2.62. These data suggest that a common gene affects AAO in these two common complex neurodegenerative diseases.