Cellular/Molecular
Comparing Genetically Encoded Probes of Neural Activity
Dierk F. Reiff, Alexandra Ihring, Giovanna Guerrero, Ehud Y. Isacoff, Maximilian Joesch, Junichi Nakai, and Alexander Borst
(see pages 4766-4778)
Anyone who has used a new reagent knows that performance does not always measure up to expectations. This week, Reiff et al. do us a favor by comparing the in vivo activity of several classes of genetically encoded calcium indicators (GECIs) as well as the pH-sensitive indicator synapto-pHluorin (SpH). These biosynthesized dyes can be targeted to discrete subpopulations of neurons, and even subcellular compartments, for use as detectors of neural activity. GECIs incorporate calmodulin or troponin domains and thus change their fluorescence after binding calcium. SpH detects the pH change associated with presynaptic vesicle fusion. The authors engineered transgenic flies; then they monitored synaptic activity at synaptic boutons at the larval neuromuscular junction. The GECIs differed considerably in their characteristics, including three that did not produce detectable fluorescence changes under the conditions used by the authors. The authors' observations should help in the choice of reagents and in additional refinements of indicator design.
Development/Plasticity/Repair
Oligodendrocyte Progenitor Transplants and Spinal Cord Injury
Hans S. Keirstead, Gabriel Nistor, Giovanna Bernal, Minodora Totoiu, Frank Cloutier, Kelly Sharp, and Oswald Steward
(see pages 4694-4705)
Human embryonic stem cells (hESCs) hold tremendous therapeutic promise, provided they can be harnessed to fulfill specific cellular or tissue functions. This week, Keirstead et al. show that after spinal cord injury in the rat, hESC-derived oligodendrocyte progenitor cells (OPCs) can be useful indeed. After spinal cord injury, neuronal loss is compounded by the loss of oligodendrocytes both near and distant from the injury site. Using a 42 d protocol, the authors differentiated the H7 hESC line into OPCs. They then transplanted the OPCs into the site of a contusion injury that caused moderate hindlimb motor impairment. Cells transplanted at 7 d or 10 months after injury survived, differentiated into oligodendrocytes, and traveled a few millimeters from the site. However, only those transplanted 1 week after injury went on to remyelinate axons and improve locomotion. Prominent astrogliosis may have contributed to the failure of OPCs to enhance remyelination when transplanted at 10 months after injury.
Behavioral/Systems/Cognitive
Why Two Clock Genes May Be Better Than One
Satoru Masubuchi, Noritoshi Kataoka, Paolo Sassone-Corsi, and Hitoshi Okamura
(see pages 4719-4724)
The mammalian homologs of the Drosophila period gene, mPer1 and mPer2, show oscillating expression in the supra-chiasmatic nucleus, the central time-keeper. Consistent with an important role in master clock function, mice lacking mPer2 lose behavioral rhythms in constant darkness, but the role of mPer1 is not as clear. This week, Masubuchi et al. probe the ability of mPer1 to reset the clock in response to environmental conditions. They kept wild-type, mPer1+/-, and mPer1-/- mice on a 12 h light/dark cycle and then prolonged their light exposure by 4-16 h. The mPer1-deficient mice responded to light extension with larger behavioral phase-delay shifts. Although mRNA levels of mPer2 remained steady, light exposure altered mPER2 protein expression in mPer1 knock-out mice, suggesting that mPer1 alters mPER2 protein synthesis or degradation. Interestingly, mPer1-/- mice did not entrain to long photoperiods of dim light, suggesting that mPer1 may be necessary for adaptation in natural light conditions.
Neurobiology of Disease
SNPs, T-Channel Gating, and Absence Epilepsy
Iuliia Vitko, Yucai Chen, Juan M. Arias, Yen Shen, Xi-Ru Wu, and Edward Perez-Reyes
(see pages 4844-4855)
The brief staring spells characteristic of childhood absence epilepsy (CAE) are accompanied by rhythmic spike discharges in the brain. Because T-type voltage-gated calcium channels contribute to rhythmic neuronal firing and are prominent in thalamic neurons, they are candidate genes in this polygenic disorder. This week, Vitko et al. report a third CAE patient with a single nucleotide polymorphism (SNP) contained in the T-type calcium channel gene CACNA1H. The polymorphism, G773D, is one of a dozen nonsynonymous SNPs found only in CAE patients. Interestingly, this particular SNP occurs in combination with a common SNP, perhaps indicative of a cooperative effect. To test the impact on channel function, the authors introduced each polymorphism into human Cav3.2a cDNA and expressed the mutant channels in human embryonic kidney 293 cells. Several of the SNPs altered channel activation and inactivation in a way that would promote oscillations and sustained neuronal firing. The SNPs thus may be susceptibility genes for CAE.