Hybrid Offspring of C57BL/6J Mice Exhibit Improved Properties for Neurobehavioral Research.

C57BL/6 is the most commonly used mouse strain in neurobehavioral research, serving as a background for multiple transgenic lines. However, C57BL/6 exhibit behavioral and sensorimotor disadvantages that worsen with age. We bred FVB/NJ females and C57BL/6J males to generate first-generation hybrid offspring (FVB/NJ x C57BL/6J)F1. The hybrid mice exhibit reduced anxiety-like behavior, improved learning, and enhanced long-term spatial memory. In contrast to both progenitors, hybrids maintain sensorimotor performance upon aging and exhibit improved long-term memory. The hybrids are larger than C57BL/6J, exhibiting enhanced running behavior on a linear track during freely-moving electrophysiological recordings. Hybrids exhibit typical rate and phase coding of space by CA1 pyramidal cells. Hybrids generated by crossing FVB/NJ females with transgenic males of a C57BL/6 background support optogenetic neuronal control in neocortex and hippocampus. The hybrid mice provide an improved model for neurobehavioral studies combining complex behavior, electrophysiology, and genetic tools readily available in C57BL/6 mice.

Bidirectional Optogenetic Control of Inhibitory Neurons in Freely-Moving Mice.

OBJECTIVE: Optogenetic manipulations of excitable cells enable activating or silencing specific types of neurons. By expressing two types of exogenous proteins, a single neuron can be depolarized using light of one wavelength and hyperpolarized with another. However, routing two distinct wavelengths into the same brain locality typically requires bulky optics that cannot be implanted on the head of a freely-moving animal. METHODS: We developed a lens-free approach for constructing dual-color head-mounted, fiber-based optical units: any two wavelengths can be combined. RESULTS: Here, each unit was comprised of one 450 nm and one 638 nm laser diode, yielding light power of 0.4 mW and 8 mW at the end of a 50 micrometer multimode fiber. To create a multi-color/multi-site optoelectronic device, a four-shank silicon probe mounted on a microdrive was equipped with two dual-color and two single-color units, for a total weight under 3 g. Devices were implanted in mice expressing the blue-light sensitive cation channel ChR2 and the red-light sensitive chloride pump Jaws in parvalbumin-immunoreactive (PV) inhibitory neurons. The combination of dual-color units with recording electrodes was free from electromagnetic interference, and device heating was under 7°C even after prolonged operation. CONCLUSION: Using these devices, the same cortical PV cell could be activated and silenced. This was achieved for multiple cells both in neocortex and hippocampus of freely-moving mice. SIGNIFICANCE: This technology can be used for controlling spatially intermingled neurons that have distinct genetic profiles, and for controlling spike timing of cortical neurons during cognitive tasks.

The effect of regulating molecules on the structure of the PPAR-RXR complex.

The PPAR-RXR complex is one of the most significant and prevalent regulatory systems, controlling lipid metabolism by gene expression. Both proteins are members of the nuclear hormone receptor family, consisting of a ligand-binding domain (LBD), a hinge and a DNA binding domain (DBD). The two proteins form a heterodimer in the nucleus. The ligand-free complex interacts with corepressor proteins and blocks the expression of the genes. With the activating ligands and coactivator segments of regulating proteins, the heterodimer becomes active and allows translation of the genes under its control. We implemented model-independent all-atom molecular dynamics simulations for clarifying the structure changes that the activating ligand and the regulatory peptides impose on the PPAR-RXR system, starting with an LBD up to the PPAR-RXR-DNA complex. The simulations were carried out first with an active state of the protein. Once the relaxed state was attained, it was transformed into the inactive-state, the resulting structure was simulated. As the complex alternates between the active-inactive conformations, most of the changes are noticed at the junction area between the two subunits, located on the surface of a long fused helical structure made of H10-H11 of the proteins. The significant differences between the states included enhanced rigidity of the inactive complex, enhancement of tight contacts. The main drive for the transformation is the relocation of the tip of H12 of the PPAR that drives the carboxylate of the C-terminal towards the junction between H10-H11 of the RXR, leading to rearrangement of the main contact zone of the proteins.

The Interaction of FABP with Kapα.

Gene-activating lipophilic compounds are carried into the nucleus when loaded on fatty-acid-binding proteins (FABP). Some of these proteins are recognized by the α-Karyopherin (Kapα) through its nuclear localization signal (NLS) consisting of three positive residues that are not in a continuous sequence. The Importin system can distinguish between FABP loaded with activating and non-activating compounds. In the present study, we introduced molecular dynamics as a tool for clarifying the mechanism by which FABP4, loaded with activating ligand (linoleate) is recognized by Kapα. In the first phase, we simulated the complex between KapαΔIBB (termed "Armadillo") that was crystallized with two NLS hepta-peptides. The trajectory revealed that the crystal-structure orientation of the peptides is rapidly lost and new interactions dominate. Though, the NLS sequence of FABP4 is cryptic, since the functional residues are not in direct sequence, implicating more than one possible conformation. Therefore, four possible docked conformations were generated, in which the NLS of FABP4 is interacting with either the major or the minor sites of Kapα, and the N → C vectors are parallel or anti-parallel. Out of these four basic starting positions, only the FABP4-minor site complex exhibited a large number of contact points. In this complex, the FABP interacts with the minor and the major sites, suppressing the self-inhibitory interaction of the Kapα, rendering it free to react with Kapß. Finally, we propose that the transportable conformation generated an extended hydrophobic domain which expanded out of the boundary of the FABP4, allowing the loaded linoleate to partially migrate out of the FABP into a joint complex in which the Kapα contributes part of a combined binding pocket.