Induced CREB activity is a hallmark of long-term memory, but the full repertoire of CREB transcriptional targets required specifically for memory is not known in any system. To obtain a more complete ...picture of the mechanisms involved in memory, we combined memory training with genome-wide transcriptional analysis of C. elegans CREB mutants. This approach identified 757 significant CREB/memory-induced targets and confirmed the involvement of known memory genes from other organisms, but also suggested new mechanisms and novel components that may be conserved through mammals. CREB mediates distinct basal and memory transcriptional programs at least partially through spatial restriction of CREB activity: basal targets are regulated primarily in nonneuronal tissues, while memory targets are enriched for neuronal expression, emanating from CREB activity in AIM neurons. This suite of novel memory-associated genes will provide a platform for the discovery of orthologous mammalian long-term memory components.
The axons of Olfactory Sensory Neurons (OSNs) project to reproducible target locations within the Olfactory Bulb (OB), converting odorant experience into a spatial map of neural activity. We ...characterized the initial targeting of OSN axons in the zebrafish, a model system suitable for studying axonal targeting early in development. In this system the initial targets of OSN axons are a small number of distinct, individually identifiable neuropilar regions called protoglomeruli. Previously, Olfactory Marker Protein-expressing and TRPC2-expressing classes of OSNs were shown to project to specific, non-overlapping sets of protoglomeruli, indicating that particular subsets of OSNs project to specific protoglomerular targets. We set out to map the relationship between the classical Odorant Receptor (OR) an OSN chooses to express and the protoglomerulus its axon targets.
A panel of BACs were recombineered so that the axons of OSNs choosing to express modified ORs were fluorescently labeled. Axon projections were followed into the olfactory bulb to determine the protoglomeruli in which they terminated.
RNA-seq demonstrates that OSNs express a surprisingly wide variety of ORs and Trace Amine Associated Receptors (TAARs) very early when sensory axons are arriving in the bulb. Only a single OR is expressed in any given OSN even at these early developmental times. We used a BAC expression technique to map the trajectories of OSNs expressing specific odorant receptors. ORs can be divided into three clades based upon their sequence similarities. OSNs expressing ORs from two of these clades project to the CZ protoglomerulus, while OSNs expressing ORs from the third clade project to the DZ protoglomerulus. In contrast, OSNs expressing a particular TAAR project to multiple protoglomeruli. Neither OR choice nor axonal targeting are related to the position an OSN occupies within the olfactory pit.
Our results demonstrate that it is not the choice of a particular OR, but of one from a category of ORs, that is related to initial OSN target location within the olfactory bulb. These choices are not related to OSN position within the olfactory epithelium.
Insulin/insulin-like growth factor signalling (IIS) is a critical regulator of an organism's most important biological decisions from growth, development, and metabolism to reproduction and ...longevity. It primarily does so through the activity of the DAF-16 transcription factor (forkhead box O (FOXO) homologue), whose global targets were identified in Caenorhabditis elegans using whole-worm transcriptional analyses more than a decade ago. IIS and FOXO also regulate important neuronal and adult behavioural phenotypes, such as the maintenance of memory and axon regeneration with age, in both mammals and C. elegans, but the neuron-specific IIS/FOXO targets that regulate these functions are still unknown. By isolating adult C. elegans neurons for transcriptional profiling, we identified both the wild-type and IIS/FOXO mutant adult neuronal transcriptomes for the first time. IIS/FOXO neuron-specific targets are distinct from canonical IIS/FOXO-regulated longevity and metabolism targets, and are required for extended memory in IIS daf-2 mutants. The activity of the forkhead transcription factor FKH-9 in neurons is required for the ability of daf-2 mutants to regenerate axons with age, and its activity in non-neuronal tissues is required for the long lifespan of daf-2 mutants. Together, neuron-specific and canonical IIS/FOXO-regulated targets enable the coordinated extension of neuronal activities, metabolism, and longevity under low-insulin signalling conditions.
The LIM-homeodomain (LIM-HD) family of transcription factors is well known for its functions during several developmental processes including cell fate specification, cell migration and axon ...guidance, and its members play fundamental roles in hippocampal development. The hippocampus is a structure that displays striking activity dependent plasticity. We examined whether LIM-HD genes and their co-factors are regulated during kainic acid induced seizure in the adult rat hippocampus as well as in early postnatal rats, when the hippocampal circuitry is not fully developed. We report a distinct and field-specific regulation of LIM-HD genes Lhx1, Lhx2, and Lhx9, LIM-only gene Lmo4, and cofactor Clim1a in the adult hippocampus after seizure induction. In contrast none of these genes displayed altered levels upon induction of seizure in postnatal animals. Our results provide evidence of temporal and spatial seizure mediated regulation of LIM-HD family members and suggest that LIM-HD gene function may be involved in activity dependent plasticity in the adult hippocampus.
Understanding the molecular basis underlying aging is critical if we are to fully understand how and why we age—and possibly how to delay the aging process. Up until now, most longevity pathways were ...discovered in invertebrates because of their short lifespans and availability of genetic tools. Now, Reichwald et al. and Valenzano et al. independently provide a reference genome for the short-lived African turquoise killifish, establishing its role as a vertebrate system for aging research.
Understanding the molecular basis underlying aging is critical if we are to fully understand how and why we age—and possibly how to delay the aging process. Up until now, most longevity pathways were discovered in invertebrates because of their short lifespans and availability of genetic tools. Now, Reichwald et al. and Valenzano et al. independently provide a reference genome for the short-lived African turquoise killifish, establishing its role as a vertebrate system for aging research.
Aging is a risk factor for chronic diseases, and identifying targets for intervention is a goal of the aging field. Burkewitz et al. now describe a mechanism that mediates the specific role for AMPK ...in longevity, whereby its activity in neurons modulates metabolism and mitochondrial integrity in peripheral tissues.
Aging is a risk factor for chronic diseases and identifying targets for intervention is a goal of the aging field. Burkewitz et al. now describe a mechanism that mediates the specific role for AMPK in longevity, whereby its activity in neurons modulates metabolism and mitochondrial integrity in peripheral tissues.
The thalamocortical tract is the primary source of sensory information to the cerebral cortex, but the mechanisms regulating its pathfinding are not completely understood. LIM-homeodomain (LIM–HD) ...gene
Lhx2 has been proposed to participate in a combinatorial “code” to regulate dorsal thalamic patterning and also the topography of thalamocortical projections. Here, we report that
Lhx2−/− embryos exhibit a gross disruption in the
early development of the thalamocortical tract, such that thalamic axons are unable to enter the ventral telencephalon. A possible cause for this deficit is a severe reduction of “pioneer” cells in the mutant ventral telencephalon that constitutes a putative mechanism for guiding the entry of the thalamocortical tract into this structure
in vivo.
However,
in vitro, the thalamocortical tract is able to enter the ventral telencephalon, and this permitted an examination of whether thalamocortical topography is normal in the
Lhx2 mutant. Contrary to hypotheses that proposed a cell-autonomous role for Lhx2 in the thalamus,
Lhx2−/− thalamic explants generate a normal topography of projections in control ventral telencephalic preparations. This is consistent with our findings of normal patterning of the
Lhx2 mutant dorsal thalamus using a wide array of markers. In the reverse experiment, however, control thalamic explants display aberrant topography in
Lhx2−/− telencephalic preparations. This perturbation is restricted to projections from caudal thalamic explants, while rostral and middle explants project normally.
Thus Lhx2 is required for multiple steps in thalamocortical tract pathfinding, but these functions appear localized in the ventral telencephalon rather than in the dorsal thalamic neurons. Furthermore, the absence of Lhx2 in the ventral telencephalon selectively disrupts a subset of thalamic axon topography, indicating a specific rather than a general perturbation of cues in this structure.
Olfactory sensory neurons expressing particular olfactory receptors project to specific reproducible locations within the bulb. The axonal guidance cues that organize this precise projection pattern ...are only beginning to be identified. To aid in their identification and characterization, we generated a transgenic zebrafish line, OR111-7:IRES:Gal4, in which a small subset of olfactory sensory neurons is labeled. Most sensory neurons expressing the OR111-7 transgene project to a specific location within the bulb, the central zone protoglomerulus, while a smaller number project to the lateral glomerulus 1 protoglomerulus. Inhibiting Netrin/DCC (deleted in colorectal cancer) signaling perturbs the ability of OR111-7-expressing axons to enter the olfactory bulb and alters their patterns of termination within the bulb. The Netrin receptor DCC is expressed in olfactory sensory neurons around the time that they elaborate their axons, netrin1a is expressed near the medial-most margin of the olfactory bulb, and netrin1b is expressed within the ventral region of the bulb. Loss of Netrin/DCC signaling components causes some OR111-7-expressing sensory axons to wander posteriorly after exiting the olfactory pit, away from netrin-expressing areas in the bulb. OR111-7-expressing axons that enter the bulb target the central zone less precisely than normal, spreading away from netrin-expressing regions. These pathfinding errors can be corrected by the reexpression of DCC within OR111-7 transgene-expressing neurons in DCC morphant embryos. These findings implicate Netrins as the only known attractants for olfactory sensory neurons, first drawing OR111-7-expressing axons into the bulb and then into the ventromedially positioned central zone protoglomerulus.
During development, sensory neurons in the olfactory epithelium extend axons into the olfactory bulb. The earliest axons to enter the bulb terminate onto distinct neuropilar condensations called ...protoglomeruli. Protoglomeruli are thought to segregate into individual glomeruli later in development. The three day old larval zebrafish olfactory bulb contains 12 stereotyped, identifiable protoglomeruli, rendering it a good system to investigate mechanisms of initial axonal targeting in the bulb. In this thesis, I describe the generation of transgenic zebrafish lines in which neurons expressing odorant receptors along with the olfactory marker protein (OMP), V2R vomeronasal receptors along with the transient receptor potential channel2 (TRPC2) or the odorant receptor OR111-7 are selectively labeled. OMP and TRPC2 expressing neurons innervate multiple, non-overlapping protoglomeruli. Transgenic neurons expressing OR111-7:IRES:Gal4; UAS:Citrine transgenes primarily target a single protoglomerulus, the central zone, allowing the investigation of mechanisms directing axonal navigation to an individual protoglomerulus. Using this transgenic line, I show for the first time in any system that netrin/DCC signaling is required to guide olfactory sensory axons to a specific location within the olfactory bulb. Interestingly, I find that the central zone protoglomerulus is innervated by neurons expressing related odorant receptors of the OR111 subfamily. Upon replacing the coding sequence of OR111-7 in the OR111-7:IRES:Gal4 transgenic construct with RFP, axons continue to target the central zone, suggesting that the OR111-7 is not required for the protoglomerular targeting of transgene expressing axons. Rather, it is likely that the transgenic construct is selectively expressed in neurons destined to target the central zone. Based on these observations, I propose a model hypothesizing that the zebrafish olfactory epithelium consists of distinct neuronal subsets. Each subset innervates a specific protoglomerulus and is restricted to express a predetermined set of odorant receptors and axon guidance receptors, which mediate the navigation of axons to particular protoglomeruli. These studies have laid the groundwork for future investigations into the mechanisms of axonal targeting to protoglomeruli in the larval zebrafish olfactory bulb.
Fibroblast growth factors (FGF) receptors FgfR1, FgfR2 and FgfR3 are differentially regulated during oligodendrocyte (OL) maturation in vitro: FgfR3 is expressed by OL progenitors whereas FgfR2 is ...expressed by differentiated OLs Mol Cell Neurosci 1996;7:263-275, and we have recently shown that FgfR3 is required for the timely differentiation of OLs in vivo J Neurosci 2003;23:883-894. Here we have used in situ hybridization to investigate the expression patterns of FgfR1-3 and compare them to the putative OL progenitor markers Olig2, Pdgfralpha and Plp/dm20 as a function of development in vivo, in particular at sites of OL specification, migration or differentiation in the mouse forebrain and cerebellum. We show that at early stages FgfR1-3 expression overlaps with that of Olig2 in the embryonic ventricular zone of the lateral and medial ganglionic eminences. Further, a scattered population of cells expressing FgfR3 (but not FgfR1 or FgfR2) in the ventral telencephalon appear to arise from the ventricular zone, and at later stages are found more dorsally in the cortex, in an overall pattern similar to Olig2 and/or Pdgfralpha. Postnatal expression of FgfR2 increases with age, more prominently in specific regions, including the cortical and cerebellar white matter and optic nerve. Thus, the differential expression pattern of FgfR2 and FgfR3 observed in vivo suggests that their expression is developmentally regulated in a manner consistent with the pattern of their expression in culture. These data provide further insights into role of FgfRs in OL development, and they emphasize that these receptors are positioned both spatially and temporally to impact OL generation in vivo.
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