Functional Imaging of Dentate Granule Cells in the Adult Mouse Hippocampus.

UNLABELLED: The hippocampal dentate gyrus is critically involved in learning and memory. However, methods for imaging the activity of its principal neurons, the dentate gyrus granule cells, are missing. Here we demonstrate chronic two-photon imaging of granule cell population activity in awake mice using a cortical window implant that leaves the hippocampal formation intact and does not lead to obvious alteration of animal behavior. Using virus delivery, we targeted expression of genetically encoded calcium indicators specifically to dentate gyrus granule cells. Calcium imaging of granule cell activity 600-800 µm below the hippocampal surface was facilitated by using 1040 nm excitation of the red indicator R-CaMP1.07, but was also achieved using the green indicator GCaMP6s. We found that the rate of calcium transients was increased during wakefulness relative to an extremely low rate during anesthesia; however, activity still remained sparse with, on average, approximately one event per 2-5 min per cell across the granule cell population. Comparing periods of running on a ladder wheel and periods of resting, we furthermore identified state-dependent differences in the active granule cell population, with some cells displaying highest activity level during running and others during resting. Typically, cells did not maintain a clear state preference in their activity pattern across days. Our approach opens new avenues to elucidate granule cell function, plasticity mechanisms, and network computation in the adult dentate gyrus. SIGNIFICANCE STATEMENT: We describe a technique that allows for chronic, functional imaging of dentate gyrus granule cells in awake, behaving mice in an intact hippocampal circuitry using genetically encoded calcium indicators. This novel approach enables the analyses of individual granule cell activity over time and provides a powerful tool to elucidate the mechanisms underlying structural and functional plasticity of the adult dentate gyrus.

Phylogeny and expression of canonical transient receptor potential (TRPC) genes in developing zebrafish.

BACKGROUND: Canonical transient receptor potential (TRPC) channels are nonselective, calcium-permeable cation channels that are expressed in a great variety of organisms, tissues, and cell types. TRPC channels are known to be involved in the transduction of polymodal sensory input. Additionally, they are implicated in a variety of developmental processes. Distinct gating mechanisms have been elucidated so far, but their exact functional role in vertebrate organisms still needs to be resolved. RESULTS: We now used the teleost Danio rerio to perform a comprehensive expression analysis of the trpc gene subfamily. Based on the sequence homology to the seven described mammalian TRPC channels, we identified 12 trpc genes in the zebrafish genome. All but trpc1 and trpc3 are represented by two paralogs. We further describe the specific expression patterns of trpc transcripts in whole-mounts during the first 5 days of development. CONCLUSIONS: Consistent with their proposed role in sensory transduction zebrafish trpcs are predominantly expressed in neural structures such as the olfactory, visual, mechanosensitive, and motor systems. Intriguingly, zebrafish paralogs show mainly nonoverlapping expression patterns, suggesting that duplicated genes have either split their functions or have adapted new ones.

CD9 and folate receptor overexpression are not sufficient for VSV-G-independent lentiviral transduction.

Extracellular vesicles have become a research focus for their potential as therapeutic vehicles that carry cargo substances. Extracellular vesicles may origin from the endosomal compartment and share several characteristics with the envelope of lentiviruses. A previous study reported that constitutive expression of the tetraspanin CD9, an extracellular vesicle marker, not only increases vesicle secretion from cells, but has also a positive effect on lentiviral transduction efficiency. Moreover, it was shown that expression of CD9 on the viral envelope in absence of viral glycoproteins was sufficient for the transduction of mammalian cells. In this study, we investigate the effect of CD9 and folate receptor alpha, a GPI-anchored protein, on biosynthesis and transduction efficiency of vesicles carrying lentiviral vectors. We demonstrate that neither CD9 nor FRα nor the combination of both were able to mediate a significant transduction of therapeutic vesicles carrying lentiviral RNA. Further studies are required to identify endogenous mammalian proteins that can be used for pseudotyping of viral envelopes to improve viral targeting without inducing immune responses.

Cln5 represents a new type of cysteine-based S-depalmitoylase linked to neurodegeneration.

Genetic CLN5 variants are associated with childhood neurodegeneration and Alzheimer's disease; however, the molecular function of ceroid lipofuscinosis neuronal protein 5 (Cln5) is unknown. We solved the Cln5 crystal structure and identified a region homologous to the catalytic domain of members of the N1pC/P60 superfamily of papain-like enzymes. However, we observed no protease activity for Cln5; and instead, we discovered that Cln5 and structurally related PPPDE1 and PPPDE2 have efficient cysteine palmitoyl thioesterase (S-depalmitoylation) activity using fluorescent substrates. Mutational analysis revealed that the predicted catalytic residues histidine-166 and cysteine-280 are critical for Cln5 thioesterase activity, uncovering a new cysteine-based catalytic mechanism for S-depalmitoylation enzymes. Last, we found that Cln5-deficient neuronal progenitor cells showed reduced thioesterase activity, confirming live cell function of Cln5 in setting S-depalmitoylation levels. Our results provide new insight into the function of Cln5, emphasize the importance of S-depalmitoylation in neuronal homeostasis, and disclose a new, unexpected enzymatic function for the N1pC/P60 superfamily of proteins.

Layer-specific integration of locomotion and sensory information in mouse barrel cortex.

During navigation, rodents continually sample the environment with their whiskers. How locomotion modulates neuronal activity in somatosensory cortex, and how it is integrated with whisker-touch remains unclear. Here, we compared neuronal activity in layer 2/3 (L2/3) and L5 of barrel cortex using calcium imaging in mice running in a tactile virtual reality. Both layers increase their activity during running and concomitant whisking, in the absence of touch. Fewer neurons are modulated by whisking alone. Whereas L5 neurons respond transiently to wall-touch during running, L2/3 neurons show sustained activity. Consistently, neurons encoding running-with-touch are more abundant in L2/3 and they encode the run-speed better during touch. Few neurons across layers were also sensitive to abrupt perturbations of tactile flow during running. In summary, locomotion significantly enhances barrel cortex activity across layers with L5 neurons mainly reporting changes in touch conditions and L2/3 neurons continually integrating tactile stimuli with running.