Identification and characterization of a novel axon guidance receptor in the eye-specific visual projection

Correct functioning of the nervous system critically depends on the formation of the precise neuronal network. In mammals with binocular vision, axons of retinal ganglion cells from the right and left eyes project to different domains of the lateral geniculate nucleus in the thalamus (Retinogeniculate projection). The eye-specific visual projection provides the anatomical basis for disparity-based stereopsis (perception of depth). However, the molecular mechanism that regulates the eye-specific visual projection is not well understood. Nell2 (neural epidermal growth factor (EGF)-like-like 2) is an extracellular glycoprotein that is predominantly expressed in the nervous system. Our lab has previously shown that Nell2 acts as an inhibitory axon guidance molecule in establishment of the eye-specific retinogeniculate projection. The current work aims to identify and functionally characterize the receptor molecule that transduces Nell2-mediated signaling in retinal ganglion cells. By using immunohistochemistry, we found that the receptor tyrosine kinase Ros1, which is known to bind the Nell2, is expressed in developing chick retinal ganglion cells., suggesting that Ros1 may act as a receptor for Nell2 in the visual projection. We are currently generating gene knock-down constructs for Ros1, which will be used in in vitro and in vivo axon guidance assays. We expect that this project will elucidate the function of Nell2-Ros1 interaction in establishment of the eye-specific retinogeniculate projection

Identification and characterization of a novel axon guidance receptor in the eye-specific visual projection

Correct functioning of the nervous system critically depends on the formation of the precise neuronal network. In mammals with binocular vision, axons of the retinal ganglion cells from the right and left eyes project to different domains of the lateral geniculate nucleus in the thalamus (Retinogeniculate projection). The eye-specific visual projection provides the anatomical basis for disparity-based stereopsis (perception of depth). However, the molecular mechanism that regulated the eye-specific visual projection is not well understood. Nell2 (neural epidermal growth factor (EGF)-like-like 2) is an extracellular glycoprotein that is predominantly expressed in the nervous system. Our lab has previously shown that Nell2 acts as an inhibitory axon guidance molecule in the establishment of the eye-specific retinogeniculate projection. The current wor aims to identify and functionally characterize the receptor molecule that transduces Nell2-mediated signaling in retinal ganglion cells. By using immunohistochemistry, we found that the receptor tyrosine kinase Ros1, which is known to bind to Nell2, is expressed in developing chick retinal ganglion cells, suggesting that Ros1 may act as a receptor for Nell2 in the visual projection, We are currently generating gene known-down constructs for Ros1, which will be used in in vitro and in vivo axon guidance assays. We expect that this project will elucidate the function of Nell2-Ros1 interaction in establishment of the eye-specific retinogeniculate projection

Identification and characterization of a novel axon guidance receptor in the layer-specific visual projection

Correct functioning of the nervous system critically depends on the formation of the precise neuronal network. In the vertebrate visual system, axons of retinal ganglion cells project to the specific layers on the target regions in the brain, such as the lateral geniculate nucleus in the thalamus and the superior colliculus/tectum in the midbrain. In mammals, the layer-specific visual projection provides the anatomical basis for disparity-based stereopsis (perception of depth). Our previous studies have provided evidence that Nell2 (Neural epidermal growth factor (EGF)-like-like 2), an extracellular glycoprotein predominantly expressed in the nervous system, acts as an inhibitory guidance molecule for retinal axons in establishment of the layer-specific visual projection. A crucial question at the next step is how Nell2 is recognized by retinal axons and how downstream signals are mediated. However, the receptor(s) for Nell2 has not been identified in retinal axons. The current work aims to identify and functionally characterize the receptor(s) that transduces Nell2-mediated signaling in retinal axons. By using immunohistochemistry, we have recently found that the receptor tyrosine kinase Ros1, which is known to bind to Nell2 in the testis, is expressed in developing chick retinal ganglion cells, suggesting that Ros1 may act as a receptor for Nell2 in the visual system. To analyze the function of Ros1 in the visual projection, we have designed and generated DNA oligonucleotides that encode pre-micro-RNA (pre-miRNA) sequences against Ros1 cDNA. The pre-miRNA sequences will be introduced into and stably expressed in the developing retina, by using the Tol2 transposon system and in vivo electroporation, and effects of Nell2 knockdown on the layer-specific visual projection will be analyzed by axon tracing. We expect that this project will elucidate the function of Nell2-Ros1 interaction in the layer-specific visual projection and provide novel insights into the molecular mechanisms of neuronal network formation