Temperature dependence of multiple high voltage activated Ca2+ channels in chick sensory neurones

The temperature dependence of high voltage activated Ca²⁺ channels has been investigated in cultured dorsal root ganglion neurones from chick embryos, using the cell-attached patch-clamp technique. The dihydropyridine sensitive L-type Ca²⁺ channel had a conductance of 23 pS, with 110 mM Ba²⁺ as charge carrier and in the presence of 3 M Bay K 8644. When the temperature was raised from 15 to 30 °C, the unitary channel current amplitude increased, with Q₁₀ value equal to 1.4. The rising phase of the averaged single-channel current became faster, with Q₁₀ value 2.7, whereas the decay phase showed a lower temperature sensitivity. Channel open probability decreased according to an exponential distribution of open and closed times. A second type of Ca²⁺ channel was identified, which was DHP-insensitive and had a lower conductance with a mean value equal to 13 pS. For the current amplitude, the Q₁₀ value was 1.3. Both activation and inactivation kinetics were strongly accelerated by an increase in temperature. The corresponding time constants gave Q₁₀ values equal to 5.9 for activation, and 2.0 for inactivation. Peak channel open probability was highly sensitive to a change in temperature, with a Q₁₀ value of 1.6. Finally, in -conotoxin GVIA pre-treated neurones, a non-inactivating DHP-insensitive Ca²⁺ channel with the lowest unitary conductance (10 pS) and a much lower temperature dependence was recorded. Single-channel current was increased by heating, with Q₁₀ value 1.3, whereas the channel kinetics were almost unaffected by temperature. Our data are consistent with the assumption that the different temperature dependence of the Ca²⁺ channel behaviours may be explained by separate gating processes of three types of Ca²⁺ channels.     

A refined restriction map of YAC clones spanning the entire human dystrophin gene

The enormous size of the human dystrophin gene (2300 kb) has so far hindered the analysis of its organization and the characterization at the genomic level of the deletion and duplication mutations causing Duchenne or Becker muscular dystrophy. A detailed physical map of the gene locus would considerably simplify these studies. We constructed a refined, long-range restriction map of the entire human dystrophin gene, using 12 overlapping YAC clones as DNA sources. The sites for six rare cutting enzymes (SfiI, NruI, EagI, BssHII, SacII, and NotI) were mapped by partial digest analysis of YACs over a region of 2600 kb, within a level of resolution of about 10 kb. Such a map provides the first detailed representation of the physical structure of the dystrophin gene. It will be useful for mapping unlocalized exons and, eventually, for the characterization of deletions and duplications leading to disease.     

Length–weight and length–length relationships for 23 fish species of Porto Primavera reservoir,Upper Paraná River,Brazil

The study presents length–weight relationships (LWR) and length–length relationships (LLR) for 23 fish species captured in the Porto Primavera Reservoir, Upper Paraná River. Seventeen of the LWRs and 20 of the LLRs are reported for the first time. New maximum standard lengths are presented for 17 species as well as weights for three species and new total weight records for 19 species.     

Analysis of 22 deletion breakpoints in dystrophin intron 49

Over 60% of Duchenne and Becker muscular dystrophies are caused by deletions spanning tens or hundreds of kilobases in the dystrophin gene. The molecular mechanisms underlying the loss of DNA at this genomic locus are not yet understood. By studying the distribution of deletion breakpoints at the genomic level, we have previously shown that intron 49 exhibits a higher relative density of breakpoints than most dystrophin introns. To determine whether the mechanisms leading to deletions in this intron preferentially involve specific sequence elements, we sublocalized 22 deletion endpoints along its length by a polymerase-chain-reaction-based approach and, in particular, analyzed the nucleotide sequences of five deletion junctions. Deletion breakpoints were homogeneously distributed throughout the intron length, and no extensive homology was observed between the sequences adjacent to each breakpoint. However, a short sequence able to curve the DNA molecule was found at or near three breakpoint junctions.     

ZAP-70 kinase regulates HIV cell-to-cell spread and virological synapse formation

HIV efficiently spreads in lymphocytes, likely through virological synapses (VSs). These cell-cell junctions share some characteristics with immunological synapses, but cellular proteins required for their constitution remain poorly characterized. We have examined here the role of ZAP-70, a key kinase regulating T-cell activation and immunological synapse formation, in HIV replication. In lymphocytes deficient for ZAP-70, or expressing a kinase-dead mutant of the protein, HIV replication was strikingly delayed. We have characterized further this replication defect. ZAP-70 was dispensable for the early steps of viral cycle, from entry to expression of viral proteins. However, in the absence of ZAP-70, intracellular Gag localization was impaired. ZAP-70 was required in infected donor cells for efficient cell-to-cell HIV transmission to recipients and for formation of VSs. These results bring novel insights into the links that exist between T-cell activation and HIV spread, and suggest that HIV usurps components of the immunological synapse machinery to ensure its own spread through cell-to-cell contacts.