Summary The ability to visualize endogenous proteins in living neurons provides a powerful means to interrogate neuronal structure and function. Here we generate recombinant antibody-like proteins, termed FingRs (Fibronectin intrabodies generated with mRNA display), that bind endogenous neuronal proteins PSD-95 and Gephyrin with high affinity and which, when fused to GFP, allow excitatory and inhibitory synapses to be visualized in living neurons. Design of the FingR incorporates a novel transcriptional regulation system that ties FingR expression to the level of the target and reduces background fluorescence. In dissociated neurons and brain slices FingRs generated against PSD-95 and Gephyrin did not affect the expression patterns of their endogenous target proteins or the number or strength of synapses. Together, our data indicate that PSD-95 and Gephyrin FingRs can report the localization and amount of endogenous synaptic proteins in living neurons and thus may be used to study changes in synaptic strength in vivo.

The role of GABAergic signaling in establishing a critical period for experience in visual cortex is well understood. However, the effects of early experience on GABAergic synapses themselves are less clear. Here, we show that monocular deprivation (MD) during the adolescent critical period produces marked enhancement of GABAergic signaling in layer 2/3 of mouse monocular visual cortex. This enhancement coincides with a weakening of glutamatergic inputs, resulting in a significant reduction in the ratio of excitation to inhibition. The potentiation of GABAergic transmission arises from both an increased number of inhibitory synapses and an enhancement of presynaptic GABA release from parvalbumin-and somatostatin-expressing interneurons. Our results suggest that augmented GABAergic inhibition contributes to the experience-dependent regulation of visual function.

Although neuronal activity can be modulated using a variety of techniques, there are currently few methods for controlling neuronal connectivity. We introduce a tool (GFE3) that mediates the fast, specific and reversible elimination of inhibitory synaptic inputs onto genetically determined neurons. GFE3 is a fusion between an E3 ligase, which mediates the ubiquitination and rapid degradation of proteins, and a recombinant, antibody-like protein (FingR) that binds to Gephyrin. Expression of GFE3 leads to a strong and specific reduction of Gephyrin in culture or in vivo and to a substantial decrease in phasic inhibition onto cells that express GFE3. By temporarily expressing GFE3 we showed that inhibitory synapses regrow following ablation. Thus, we have created a simple, reversible method for modulating inhibitory synaptic input onto genetically determined cells.

Black crystals of C 60 ‚µ-O{Fe III (OEP)} 2 ‚C 6 H 6 and 2C 60 ‚{Fe III (OEPO)} 2 ‚4C 6 H 6 suitable for single-crystal X-ray diffraction studies have been obtained by growth from benzene solutions of the appropriate binuclear metalloporphyrin and the fullerene. C 60 ‚µ-O{Fe III (OEP)} 2 ‚C 6 H 6 crystallizes with two molecules of µ-O{Fe III (OEP)} 2 , two fully ordered molecules of C 60 , and two molecules of benzene in the asymmetric unit. Each independent molecule of µ-O{Fe III (OEP)} 2 makes close contact with two fullerene molecules. In C 60 ‚µ-O{Fe III (OEP)} 2 ‚C 6 H 6 the Fe-O-Fe angles (150.18(11)°and 151.89(11)°) are markedly bent with a benzene molecule wedged into the opening between the two porphyrins, whereas in the triclinic and monoclinic polymorphs of µ-O{Fe III (OEP)} 2 the Fe-O-Fe angles are more nearly linear (172.16(17)°and 176.2(2)°, respectively). The structure of 2C 60 ‚{Fe III (OEPO)} 2 ‚4C 6 H 6 consists of a centrosymmetric {Fe III (OEPO)} 2 molecule in which the two macrocycles are connected to one another through axial coordination of the meso-oxygen atoms to iron ions in the neighboring porphyrin. Each molecule of {Fe III -(OEPO)} 2 engages a fullerene on its two exposed faces. The basic geometry of the central core of {Fe III (OEPO)} 2 is similar to that of the previously characterized {In III (OEPO)} 2 , but the distortion of the two macrocycles is greater in the former due to the shorter Fe-N and Fe-O bonds.

K- and H-Ras are the most commonly mutated genes in human tumors and are critical for conferring and maintaining the oncogenic phenotype in tumors with poor prognoses. Here, we design genetically encoded antibody-like ligands (intrabodies) that recognize active, GTP-bound K- and H-Ras. These ligands, which use the 10th domain of human fibronectin as their scaffold, are stable inside the cells and when fused with a fluorescent protein label, the constitutively active G12V mutant H-Ras. Primary selection of ligands against Ras with mRNA display resulted in an intrabody (termed RasIn1) that binds with a KD of 2.1 μM to H-Ras(G12V) (GTP), excellent state selectivity, and remarkable specificity for K- and H-Ras. RasIn1 recognizes residues in the Switch I region of Ras, similar to Raf-RBD, and competes with Raf-RBD for binding. An affinity maturation selection based on RasIn1 resulted in RasIn2, which binds with a KD of 120 nM and also retains excellent state selectivity. Both of these intrabodies colocalize with H-Ras, K-Ras, and G12V mutants inside the cells, providing new potential tools to monitor and modulate Ras-mediated signaling. Finally, RasIn1 and Rasin2 both display selectivity for the G12V mutants as compared with wild-type Ras providing a potential route for mutant selective recognition of Ras.