C. elegans orthologs MUT-7/CeWRN-1 of Werner syndrome protein regulate neuronal plasticity

Caenorhabditis elegans expresses human Werner syndrome protein (WRN) orthologs as two distinct proteins: MUT-7, with a 3′−5′ exonuclease domain, and CeWRN-1, with helicase domains. How these domains cooperate remains unclear. Here, we demonstrate the different contributions of MUT-7 and CeWRN-1 to 22G small interfering RNA (siRNA) synthesis and the plasticity of neuronal signaling. MUT-7 acts specifically in the cytoplasm to promote siRNA biogenesis and in the nucleus to associate with CeWRN-1. The import of siRNA by the nuclear Argonaute NRDE-3 promotes the loading of the heterochromatin-binding protein HP1 homolog HPL-2 onto specific loci. This heterochromatin complex represses the gene expression of the guanylyl cyclase ODR-1 to direct olfactory plasticity in C. elegans. Our findings suggest that the exonuclease and helicase domains of human WRN may act in concert to promote RNA-dependent loading into a heterochromatin complex, and the failure of this entire process reduces plasticity in postmitotic neurons.

Plasticity and modulation of olfactory circuits in insects

Olfactory circuits change structurally and physiologically during development and adult life. This allows insects to respond to olfactory cues in an appropriate and adaptive way according to their physiological and behavioral state, and to adapt to their specific abiotic and biotic natural environment. We highlight here findings on olfactory plasticity and modulation in various model and non-model insects with an emphasis on moths and social Hymenoptera. Different categories of plasticity occur in the olfactory systems of insects. One type relates to the reproductive or feeding state, as well as to adult age. Another type of plasticity is context-dependent and includes influences of the immediate sensory and abiotic environment, but also environmental conditions during postembryonic development, periods of adult behavioral maturation, and short- and long-term sensory experience. Finally, plasticity in olfactory circuits is linked to associative learning and memory formation. The vast majority of the available literature summarized here deals with plasticity in primary and secondary olfactory brain centers, but also peripheral modulation is treated. The described molecular, physiological, and structural neuronal changes occur under the influence of neuromodulators such as biogenic amines, neuropeptides, and hormones, but the mechanisms through which they act are only beginning to be analyzed.

Specific anosmia in humans and animals: Environmental and genetic influences

Olfaction plays a very important role across the lifespan of most mammalian species, including humans. Being the oldest, chemical communication is one of the least understood forms of communication due in part to the difficulty of detecting and measuring the chemicals in a sample. The ability to detect chemicals in the environment serves many functions. Individuals with specific anosmia, or “odor blindness”, have significantly increased olfactory thresholds to particular odorants though they show normal general olfactory acuity. Hereby we review research on specific anosmia in humans, factors that may affect individual variation in olfaction as well as animal models of specific anosmia. Variability in sensitivity to odorants is influenced by genotype, age, gender, individual olfactory experience and environmental cues. Large data pile from human and animal studies suggests that not all factors are determined yet. The possibility of induction of olfactory sensitivity to biologically relevant chemical cues is discussed. Olfactory plasticity determines the adaptability of the species to the environment. Mechanisms that underlie the induction of sensitivity to the odorants still to be elucidated.