Evaluation of Electrical Performance and Properties of Electroretinography Electrodes.

Purpose: The aim of this study was to evaluate and compare the electrical performance and properties of commercially available electroretinography (ERG) electrodes. Methods: A passive ionic model was used to measure impedance, noise, and potential drift in 10 types of ocular surface and skin ERG electrodes. Results: The impedance for silver-based ocular electrodes are generally lower (range, 65.35-343.3 Ω) with smaller phase angles (range, -6.41° to -33.91°) than gold-based electrodes (impedance ranged from 285.95 Ω to 2.913 kΩ, and phase angle ranged from -59.65° to -70.01°). Silver-based ocular electrodes have less noise (median line noise of 6.48 x 104nV2/Hz) than gold-based electrodes (median line noise of 2.26 x 105nV2/Hz). Although silver-based electrodes usually achieve a drift rate less than 5 µV/s within 15 minutes, gold-base ocular electrode cannot achieve a stable potential. The exception is the RETeval strip type of silver electrode, which had an unusual drift at 20 minutes. The noise spectral density showed no change over time indicating that noise was not dependent on the stabilization of the electrode. Conclusions: From the range of electrodes tested, lower impedance, lower capacitance, and lower noise was observed in silver-based electrodes. Stabilization of an electrode is effective against drift of the electrode potential difference but not the noise. Translational Relevance: Application of electrodes with optimized materials improve the quality of clinical electrophysiology signals and efficiency of the recording.

Imaging centrosomes in fly testes.

Centrosomes are conserved microtubule-based organelles whose structure and function change dramatically throughout the cell cycle and cell differentiation. Centrosomes are essential to determine the cell division axis during mitosis and to nucleate cilia during interphase. The identity of the proteins that mediate these dynamic changes remains only partially known, and the function of many of the proteins that have been implicated in these processes is still rudimentary. Recent work has shown that Drosophila spermatogenesis provides a powerful system to identify new proteins critical for centrosome function and formation as well as to gain insight into the particular function of known players in centrosome-related processes. Drosophila is an established genetic model organism where mutants in centrosomal genes can be readily obtained and easily analyzed. Furthermore, recent advances in the sensitivity and resolution of light microscopy and the development of robust genetically tagged centrosomal markers have transformed the ability to use Drosophila testes as a simple and accessible model system to study centrosomes. This paper describes the use of genetically-tagged centrosomal markers to perform genetic screens for new centrosomal mutants and to gain insight into the specific function of newly identified genes.

Tubulin nucleotide status controls Sas-4-dependent pericentriolar material recruitment.

Regulated centrosome biogenesis is required for accurate cell division and for maintaining genome integrity. Centrosomes consist of a centriole pair surrounded by a protein network known as pericentriolar material (PCM). PCM assembly is a tightly regulated, critical step that determines the size and capability of centrosomes. Here, we report a role for tubulin in regulating PCM recruitment through the conserved centrosomal protein Sas-4. Tubulin directly binds to Sas-4; together they are components of cytoplasmic complexes of centrosomal proteins. A Sas-4 mutant, which cannot bind tubulin, enhances centrosomal protein complex formation and has abnormally large centrosomes with excessive activity. These results suggest that tubulin negatively regulates PCM recruitment. Whereas tubulin-GTP prevents Sas-4 from forming protein complexes, tubulin-GDP promotes it. Thus, the regulation of PCM recruitment by tubulin depends on its GTP/GDP-bound state. These results identify a role for tubulin in regulating PCM recruitment independent of its well-known role as a building block of microtubules. On the basis of its guanine-bound state, tubulin can act as a molecular switch in PCM recruitment.

The structural basis for methylmalonic aciduria. The crystal structure of archaeal ATP:cobalamin adenosyltransferase.

ATP:cobalamin adenosyltransferase MMAB was recently identified as the gene responsible for a disorder of cobalamin metabolism in humans (cblB complementation group). The crystal structure of the MMAB sequence homologue from Thermoplasma acidophilum (TA1434; GenBank identification number gi|16082403) was determined to a resolution of 1.5 A. TA1434 was confirmed to be an ATP:cobalamin adenosyltransferase, which depended absolutely on divalent metal ions (Mg2+ > Mn2+ > Co2+) and only used ATP or dATP as adenosyl donors. The apparent Km of TA1434 was 110 microM (kcat = 0.23 s(-1)) for ATP, 140 microM (kcat = 0.11 s(-1)) for dATP, and 3 microM (kcat = 0.18 s(-1)) for cobalamin. TA1434 is a trimer in solution and in the crystal structure, with each subunit composed of a five-helix bundle. The location of disease-related point mutations and other residues conserved among the homologues of TA1434 suggest that the active site lies at the junctions between the subunits. Mutations in TA1434 that correspond to the disease-related mutations resulted in proteins that were inactive for ATP:cobalamin adenosyltransferase activity in vitro, confirming that these mutations define the molecular basis of the human disease.