DSCAM AND SIDEKICK PROTEINS DIRECT LAMINA-SPECIFIC SYNAPTIC CONNECTIONS

Dscam

• Down syndrome cell adhesion molecule
• Transmembrane protein related to IgSF
• Related to Down's Syndrome

SIDEKICK

• Cell adhesion molecule
• Immunoglobilin, Fibronectin, PDZ

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METHODS

• Chick embryos utilized
• Reagents
• Histology
• Gene transfer in ovo

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NON-OVERLAPPING SUBSETS OF NEURONS

• Double label in situ hybridization

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ANTIBODIES USED FOR IMMUNOSTAINING

• Localize Dscam and Sidekick proteins
• Study follows convention of 5 levels of IPL
• Dscam/S5, DscamL/S1;S2;S4
• Sidekick-1/S4;S2, Sidekick-2/S2;S4

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HOMOPHILIC ADHESION

• Green and red aggregates show homophilic binding
• Untransfected cells did not aggregate

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HETEROPHILIC ADHESION NOT PRESENT

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DECREASE DSCAM AND SIDEKICK

• Interfering RNAs
• Retroviral vectors to infect retina

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MARKERS FOR RGC SUBSETS

• Dscam R-cadherin
• Sidekick-1 cadherin-7
• Sidekick-2+ calbindin

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DEFASCICULATED

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DSCAMS SIDEKICKS SUFFICIENT FOR LAMINATION IN IPL

• PiggyBac system used to transpose desired gene sequence
• GFP alone processes evenly distributed
• Dscam diverted sublamina to S5
• Sidekick-1 and Sidekick-2 diverted sublamina to S-2 and S-4
• Dscams and Sidekicks sufficient to bias IPL lamination

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SUMMARY

• Dscams and Sidekicks help establish 4 parallel pathways in IPL
• Homophilic adhesion
• Specify sublamina layers in IPL