Mechanism of Na+/H+ antiporting

Na+/H+ antiporters are central to cellular salt and pH homeostasis. The structure of Escherichia coli NhaA was recently determined, but its mechanisms of transport and pH regulation remain elusive. We performed molecular dynamics simulations of NhaA that, with existing experimental data, enabled us to propose an atomically detailed model of antiporter function. Three conserved aspartates are key to our proposed mechanism: Asp164 (D164) is the Na+-binding site, D163 controls the alternating accessibility of this binding site to the cytoplasm or periplasm, and D133 is crucial for pH regulation. Consistent with experimental stoichiometry, two protons are required to transport a single Na+ ion: D163 protonates to reveal the Na+-binding site to the periplasm, and subsequent protonation of D164 releases Na+. Additional mutagenesis experiments further validated the model.     

Flow Characteristics of Human Erythrocytes through Polycarbonate Sieves

We used polycarbonate sieves with uniform cylindrical pores (2.4 to 6.8 microns in diameter) to filter suspensions of human erythrocytes (mean major diameter is 7.2 microns) in Eagle-albumin solution. With 6.8-micron sieves the pressure-flow curves are convexed to the pressure-axis at low pressures and become linear with high pressures. With 4.5-micron sieves, however, the pressure-flow relationship is linear throughout the range of study. In both types of sieves, flow rate is reduced progressively with increasing concentration of red blood cells (RBC) over a range of 0.5 to 95 percent. The resistance to flow of RBC suspensions is higher in 4.5-micron than in 6.8-micron pores. With filter pore diameters of 3.0 microns or more, the RBC concentration in the filtrate was 100 percent of that in the solution being filtered, but only 70 percent with 2.4-micron pores. The observed critical pore diameter for 100 percent cell transmission agrees with theoretical calculation based on the assumption that the RBC membrane is deformable but nonextensible. The importance of cell deformation in the passage of RBC's through small pores is shown by the inability of RBC hardened in acetaldehyde to pass pores with 6.8-micron diameter.     

Strong association of de novo copy number mutations with autism

We tested the hypothesis that de novo copy number variation (CNV) is associated with autism spectrum disorders (ASDs). We performed comparative genomic hybridization (CGH) on the genomic DNA of patients and unaffected subjects to detect copy number variants not present in their respective parents. Candidate genomic regions were validated by higher-resolution CGH, paternity testing, cytogenetics, fluorescence in situ hybridization, and microsatellite genotyping. Confirmed de novo CNVs were significantly associated with autism (P = 0.0005). Such CNVs were identified in 12 out of 118 (10%) of patients with sporadic autism, in 2 out of 77 (3%) of patients with an affected first-degree relative, and in 2 out of 196 (1%) of controls. Most de novo CNVs were smaller than microscopic resolution. Affected genomic regions were highly heterogeneous and included mutations of single genes. These findings establish de novo germline mutation as a more significant risk factor for ASD than previously recognized.     

Triploblastic animals more than 1 billion years ago: trace fossil evidence from india

Some intriguing bedding plane features that were observed in the Mesoproterozoic Chorhat Sandstone are biological and can be interpreted as the burrows of wormlike undermat miners (that is, infaunal animals that excavated tunnels underneath microbial mats). These burrows suggest that triploblastic animals existed more than a billion years ago. They also suggest that the diversification of animal designs proceeded very slowly before the appearance of organisms with hard skeletons, which was probably the key event in the Cambrian evolutionary explosion, and before the ecological changes that accompanied that event.     

Clinical skills and knowledge used by veterinary graduates during their first year in small animal practice

Objective To determine the clinical skills and areas of knowledge used by veterinarians in small animal practice during their first year after graduation and the degree of assistance and supervision they received while developing these skills. Design A postal survey was sent in December 1999 to 59 veterinarians who completed their training at Murdoch University in December 1998. Procedure The first part of the survey asked for information on veterinary work patterns since leaving university. The second part consisted of a list of diagnostic and therapeutic skills of varying complexity and the graduates were asked to indicate whether they had used these skills in practice and whether they had been assisted or supervised while doing them. The respondents were also asked if they had had the opportunity to practise these skills as undergraduates at university or during extramural experience. In the third part the areas of knowledge used in practice were assessed by analysis of a series of consecutive cases. Results Forty replies were received but since three graduates had done no small animal work the analysis of the skills section is based on 37 responses. Thirty graduates supplied information on 994 canine cases and 308 feline cases. The distribution of the mean work time was dogs and cats 69%, horses 13%, farm animals 11%, birds 3% and others 4%. Skills used by over 90% of graduates included general anaesthesia, examination of the tympanic membrane, taking and interpreting an abdominal radiograph, catheterising a male cat, fine needle aspiration of a mass, neutering dogs and cats, tooth scaling and extraction and treating an aural haematoma. The survey also identified the opportunities for undergraduates to practise some of these skills during extramural experience and the extent of assistance given to new graduates during their first year in practice. The areas of knowledge used in over 10% of the cases included vaccination, anaesthesia/sedation, skin/coat problems, general advice on pet health, neutering and musculoskeletal diseases. Conclusion Veterinarians, in their first year after graduation, use a wide range of complex diagnostic and therapeutic skills. Although many of these skills are acquired during the undergraduate training, a significant contribution is made by extramural practical work undertaken during the clinical years of the undergraduate course and in the first year following graduation. Practising veterinarians play an important role in providing opportunities and supervision for clinical training.