design-analysis-temperature-preference-behavior-its-circadian-rhythm

Design and Analysis of Temperature Preference Behavior and its Circadian Rhythm in <em>Drosophila</em>

The circadian clock regulates many aspects of life, including sleep, locomotor activity, and body temperature (BTR) rhythms1,2. We recently identified a ...

Cincinnati Childrens Hospital Medical Center

The organization of neural progenitors in the developing mammalian neuroepithelium is marked by cadherin-based adherens junctions. Whereas RhoA, a founding member of the small Rho GTPase family, has been shown to play important roles in epithelial adherens junctions, its physiological roles in neural development remain uncertain due to the lack of specific loss-of-function studies. Here, we show that RhoA protein accumulates at adherens junctions in the developing mouse brain and colocalizes to the cadherin-catenin complex. Conditional deletion of RhoA in midbrain and forebrain neural progenitors using Wnt1-Cre and Foxg1-Cre mice, respectively, disrupts apical adherens junctions and causes massive dysplasia of the brain. Furthermore, RhoA-deficient neural progenitor cells exhibit accelerated proliferation, reduction of cell- cycle exit, and increased expression of downstream target genes of the hedgehog pathway. Consequently, both lines of conditional RhoA-deficient embryos exhibit expansion of neural progenitor cells and exencephaly-like protrusions. These results demonstrate a critical role of RhoA in the maintenance of apical adherens junctions and the regulation of neural progenitor proliferation in the developing mammalian brain.

Loss of RhoA in neural progenitor cells causes the disruption of adherens junctions and hyperproliferation.

Different types of sensory neurons in the dorsal root ganglia project axons to the spinal cord to convey peripheral information to the central nervous system. Whereas most proprioceptive axons enter the spinal cord medially, cutaneous axons typically do so laterally. Because heavily myelinated proprioceptive axons project to the ventral spinal cord, proprioceptive axons and their associated oligodendrocytes avoid the superficial dorsal horn. However, it remains unclear whether their exclusion from the superficial dorsal horn is an important aspect of neural circuitry. Here we show that a mouse null mutation of Sema6d results in ectopic placement of the shafts of proprioceptive axons and their associated oligodendrocytes in the superficial dorsal horn, disrupting its synaptic organization. Anatomical and electrophysiological analyses show that proper axon positioning does not seem to be required for sensory afferent connectivity with motor neurons. Furthermore, ablation of oligodendrocytes from Sema6d mutants reveals that ectopic oligodendrocytes, but not proprioceptive axons, inhibit synapse formation in Sema6d mutants. Our findings provide new insights into the relationship between oligodendrocytes and synapse formation in vivo, which might be an important element in controlling the development of neural wiring in the central nervous system.

Ectopic myelinating oligodendrocytes in the dorsal spinal cord as a consequence of altered semaphorin 6D signaling inhibit synapse formation.

RhoA, a member of the Rho family small GTPases, has been shown to play important roles in axon guidance. However, to date, the physiological function of RhoA in axon guidance events in vivo has not been determined genetically in animals. Here we show that RhoA mRNA is strongly expressed by sensory neurons in the developing mouse dorsal root ganglia (DRG). We have deleted RhoA in sensory neurons of the DRG using RhoA-floxed mice under the Wnt1-Cre driver in which Cre is strongly expressed in sensory neurons. Peripheral projections of sensory neurons appear normal and there are no detectable defects in the central projections of either cutaneous or proprioceptive sensory neurons in RhoA(f/f); Wnt1-Cre mice. Furthermore, a co-culture assay using DRG explants from RhoA(f/f); Wnt1-Cre embryos, and 293T cells expressing semaphorin3A (Sema3A) reveals that RhoA is not required for Sema3A-mediated axonal repulsion of sensory neurons. Expression of RhoC, a closely related family member, is increased in RhoA-deficient sensory neurons and may play a compensatory role in this context. Taken together, these genetic studies demonstrate that RhoA is dispensable for peripheral and central projections of sensory neurons in the DRG.

RhoA is dispensable for axon guidance of sensory neurons in the mouse dorsal root ganglia.

RhoA is a key regulator of cytoskeletal dynamics with a variety of effects on cellular processes. Loss of RhoA in neural progenitor cells disrupts adherens junctions and causes disorganization of the neuroepithelium in the developing nervous system. However, it remains essentially unknown how the loss of RhoA physiologically affects neural circuit formation. Here we show that proper neuroepithelial organization maintained by RhoA GTPase in both the ventral and dorsal spinal cord is critical for left-right locomotor behavior. We examined the roles of RhoA in the ventral and dorsal spinal cord by deleting the gene in neural progenitors using Olig2-Cre and Wnt1-Cre mice, respectively. RhoA-deleted neural progenitors in both mutants exhibit defects in the formation of apical adherens junctions and disorganization of the neuroepithelium. Consequently, the ventricular zone and lumen of the dysplastic region are lost, causing the left and right sides of the gray matter to be directly connected. Furthermore, the dysplastic region lacks ephrinB3 expression at the midline that is required for preventing EphA4-expressing corticospinal neurons and spinal interneurons from crossing the midline. As a result, aberrant neuronal projections are observed in that region. Finally, both RhoA mutants develop a rabbit-like hopping gait. These results demonstrate that RhoA functions to maintain neuroepithelial structures in the developing spinal cord and that proper organization of the neuroepithelium is required for appropriate left-right motor behavior.

Left-right locomotor circuitry depends on RhoA-driven organization of the neuroepithelium in the developing spinal cord.

Temperature sensation has a strong impact on animal behavior and is necessary for animals to avoid exposure to harmful temperatures. It is now well known that thermoTRP (transient receptor potential) channels in thermosensory neurons detect a variable range of temperature stimuli. However, little is known about how a range of temperature information is relayed and integrated in the neural circuits. Here, we show novel temperature integration between two warm inputs via Drosophila TRPA channels, TRPA1 and Pyrexia (Pyx). The internal AC (anterior cell) thermosensory neurons, which express TRPA1, detect warm temperatures and mediate temperature preference behavior. We found that the AC neurons were activated twice when subjected to increasing temperatures. The first response was at ∼25°C via TRPA1 channel, which is expressed in the AC neurons. The second response was at ∼27°C via the second antennal segments, indicating that the second antennal segments are involved in the detection of warm temperatures. Further analysis reveals that pyx-Gal4-expressing neurons have synapses on the AC neurons and that mutation of pyx eliminates the second response of the AC neurons. These data suggest that AC neurons integrate both their own TRPA1-dependent temperature responses and a Pyx-dependent temperature response from the second antennal segments. Our data reveal the first identification of temperature integration, which combines warm temperature information from peripheral to central neurons and provides the possibility that temperature integration is involved in the plasticity of behavioral outputs.

Temperature integration at the AC thermosensory neurons in Drosophila.

In mammalian spinal cord, group Ia proprioceptive afferents form selective monosynaptic connections with a select group of motor pool targets. The extent to which sensory recognition of motor neurons contributes to the selectivity of sensory-motor connections remains unclear. We show here that proprioceptive sensory afferents that express PlexinD1 avoid forming monosynaptic connections with neurons in Sema3E(+) motor pools yet are able to form direct connections with neurons in Sema3E(off) motor pools. Anatomical and electrophysiological analysis of mice in which Sema3E-PlexinD1 signaling has been deregulated or inactivated genetically reveals that repellent signaling underlies aspects of the specificity of monosynaptic sensory-motor connectivity in these reflex arcs. A semaphorin-based system of motor neuron recognition and repulsion therefore contributes to the formation of specific sensory-motor connections in mammalian spinal cord.

Article	Year
Loss of RhoA in neural progenitor cells causes the disruption of adherens junctions and hyperproliferation. Proceedings of the National Academy of Sciences of the United States of America\| PubMed ID: 21502507	2011
Ectopic myelinating oligodendrocytes in the dorsal spinal cord as a consequence of altered semaphorin 6D signaling inhibit synapse formation. Development (Cambridge, England)\| PubMed ID: 21831918	2011
RhoA is dispensable for axon guidance of sensory neurons in the mouse dorsal root ganglia. Frontiers in molecular neuroscience\| PubMed ID: 22661927	2012
Left-right locomotor circuitry depends on RhoA-driven organization of the neuroepithelium in the developing spinal cord. The Journal of neuroscience : the official journal of the Society for Neuroscience\| PubMed ID: 22836272	2012
Temperature integration at the AC thermosensory neurons in Drosophila. The Journal of neuroscience : the official journal of the Society for Neuroscience\| PubMed ID: 23325228	2013
Specificity of monosynaptic sensory-motor connections imposed by repellent Sema3E-PlexinD1 signaling. Cell reports\| PubMed ID: 24210822	2013

Jennifer R. Leslie

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