In JoVE (1)

Other Publications (4)

Articles by Onkar S. Dhande in JoVE

Other articles by Onkar S. Dhande on PubMed

Bone Morphogenetic Proteins, Eye Patterning, and Retinocollicular Map Formation in the Mouse

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Jul, 2008  |  Pubmed ID: 18614674

Patterning events during early eye formation determine retinal cell fate and can dictate the behavior of retinal ganglion cell (RGC) axons as they navigate toward central brain targets. The temporally and spatially regulated expression of bone morphogenetic proteins (BMPs) and their receptors in the retina are thought to play a key role in this process, initiating gene expression cascades that distinguish different regions of the retina, particularly along the dorsoventral axis. Here, we examine the role of BMP and a potential downstream effector, EphB, in retinotopic map formation in the lateral geniculate nucleus (LGN) and superior colliculus (SC). RGC axon behaviors during retinotopic map formation in wild-type mice are compared with those in several strains of mice with engineered defects of BMP and EphB signaling. Normal RGC axon sorting produces axon order in the optic tract that reflects the dorsoventral position of the parent RGCs in the eye. A dramatic consequence of disrupting BMP signaling is a missorting of RGC axons as they exit the optic chiasm. This sorting is not dependent on EphB. When BMP signaling in the developing eye is genetically modified, RGC order in the optic tract and targeting in the LGN and SC are correspondingly disrupted. These experiments show that BMP signaling regulates dorsoventral RGC cell fate, RGC axon behavior in the ascending optic tract, and retinotopic map formation in the LGN and SC through mechanisms that are in part distinct from EphB signaling in the LGN and SC.

Development of Single Retinofugal Axon Arbors in Normal and β2 Knock-out Mice

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Mar, 2011  |  Pubmed ID: 21368050

The maturation of retinal ganglion cell (RGC) axon projections in the dorsal lateral geniculate nucleus (dLGN) and the superior colliculus (SC) relies on both molecular and activity-dependent mechanisms. Despite the increasing popularity of the mouse as a mammalian visual system model, little is known in this species about the normal development of individual RGC axon arbors or the role of activity in this process. We used a novel in vivo single RGC labeling technique to quantitatively characterize the elaboration and refinement of RGC axon arbors in the dLGN and SC in wild-type (WT) and β2-nicotinic acetylcholine receptors mutant (β2(-/-)) mice, which have perturbed retinal waves, during the developmental period when eye-specific lamination and retinotopic refinement occurs. Our results suggest that eye-specific segregation and retinotopic refinement in WT mice are not the result of refinement of richly exuberant arbors but rather the elaboration of arbors prepositioned in the proper location combined with the elimination of inappropriately targeted sparse branches. We found that retinocollicular arbors mature ∼1 week earlier than retinogeniculate arbors, although RGC axons reach the dLGN and SC at roughly the same age. We also observed striking differences between contralateral and ipsilateral RGC axon arbors in the SC but not in the LGN. These data suggest a strong influence of target specific cues during arbor maturation. In β2(-/-) mice, we found that retinofugal single axon arbors are well ramified but enlarged, particularly in the SC, indicating that activity-dependent visual map development occurs through the refinement of individual RGC arbors.

Role of Adenylate Cyclase 1 in Retinofugal Map Development

The Journal of Comparative Neurology. Nov, 2011  |  Pubmed ID: 22102330

The development of topographic maps of the sensory periphery is sensitive to the disruption of adenylate cyclase 1 (AC1) signaling. AC1 catalyzes the production of cAMP in a Ca(2+) /calmodulin dependent manner, and AC1 mutant mice (AC1(-/-) ) have disordered visual and somatotopic maps. However, the broad expression of AC1 in the brain and the promiscuous nature of cAMP signaling have frustrated attempts to determine the underlying mechanism for AC1-dependent map development. In the mammalian visual system, the initial coarse targeting of retinal ganglion cell (RGC) projections to the superior colliculus (SC) and lateral geniculate nucleus (LGN) is guided by molecular cues, while the subsequent refinement of these crude projections occurs via an activity-dependent process that depends on spontaneous retinal waves. Here, we show that AC1(-/-) mice have normal retinal waves but disrupted map refinement. We demonstrate that AC1 is required for the emergence of dense and focused termination zones and elimination of inaccurately targeted collaterals at the level of individual retinofugal arbors. Conditional deletion of AC1 in the retina recapitulates map defects, indicating that the locus of map disruptions in the SC and dorsal LGN of AC1(-/-) mice is presynaptic. Last, map defects in mice without AC1 and disrupted retinal waves (AC1(-/-) ;β2(-/-) double KO mice) are no worse than those lacking only β2(-/-) , but loss of AC1 occludes map recovery in β2(-/-) mice during the second postnatal week. These results suggest that AC1 in RGC axons mediates the development of retinotopy and eye-specific segregation in the SC and dorsal LGN. J. Comp. Neurol., 2011. © 2011 Wiley-Liss, Inc.

Visualization and Manipulation of Neural Activity in the Developing Vertebrate Nervous System

Frontiers in Molecular Neuroscience. 2011  |  Pubmed ID: 22121343

Neural activity during vertebrate development has been unambiguously shown to play a critical role in sculpting circuit formation and function. Patterned neural activity in various parts of the developing nervous system is thought to modulate neurite outgrowth, axon targeting, and synapse refinement. The nature and role of patterned neural activity during development has been classically studied with in vitro preparations using pharmacological manipulations. In this review we discuss newly available and developing molecular-genetic tools for the visualization and manipulation of neural activity patterns specifically during development.

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