Cell Adhesion Molecules

Proper formation of synapses in the developing nervous system is critical to the expected function and behavior of an adult organism. Neurons must project neurites, in the form of axons or dendrites, to target areas to complete synaptic circuits. The biochemical tool that cells use to interact with the external environment and direct the guidance of developing neurites are guidance receptors. One such guidance receptor that is extensively studied to uncover its roles in developmental disorders and disease is DSCAM (Down-Syndrome Cell Adhesion Molecule). To better understand the role of DSCAM in humans, a fly homolog Dscam1 was extensively characterized in the giant fiber system (GFS) of Drosophila to further explore its roles in axon guidance, synapse formation, and synapse function. The UAS-Gal4 system was used to alter the protein levels of Dscam1 within the giant fiber interneurons (GFs). A UAS-RNAi construct against Dscam1 was used to knockdown translation of all possible isoforms within the GFs. A UAS-Dscam1(TM2) construct was used to overexpress a single isoform of Dscam1 that is specifically trafficked to the axons. Confocal microscopy was used to determine the morphological changes associated with dysregulated Dscam1 levels. Visualization via fluorescent markers was accomplished of both pre- and post-synaptic cells, the GFs and tergotrochanteral motorneurons (TTMns), respectively, and synapse interface was determined as colocalization of the two cells. Additionally, the functional components of the GF-TTMn synapse, both gap-junctions, and presynaptic chemical active zones were tagged via fluorescent antibodies and quantified.

Neuronal cell adhesion molecules of L1 family play a critical role in proper nervous system development. Various mutations on human L1-CAM that lead to severe
neurodevelopmental disorders like retardation, spasticity etc. termed under L1 syndrome. The vertebrr their roles in axon pathfinding, neurite extension and cell migration, howeverate L1CAM and its homolog in Drosophila, neuroglian (nrg) have been well studied fo, much less is known about the mechanisms by which they fine tune synaptic connectivity to control the development and maintenance of synaptic connections within neuronal circuits. Here we characterized the essential role of nrg in regulating synaptic structure and function in vivo in a well characterized Drosophila central synapse model neuron, the Giant Fiber (GF) system. Previous studies from our lab revealed that the phosphorylation status of the tyrosine in the Ankyrin binding FIGQY motif in the intracellular domain of Nrg iscrucial for synapse formation of the GF to Tergo-Trochanteral Motor neuron (TTMn) synapse in the GF circuit.
The present work provided us with novel insights into the role of Nrg-Ank interaction in regulating Nrg function during synapse formation and maintenance. By
utilizing a sophisticated Pacman based genomic rescue strategy we have shown that
dynamic regulation of the Neuroglian–Ankyrin interaction is required to coordinate
transsynaptic development in the GF–TTMn synapse. In contrast, the strength of Ankyrin binding directly controls the balance between synapse formation and maintenance at the NMJ.
Human L1 pathological mutations affect different biological processes distinctively
and thus their proper characterization in vivo is essential to understand L1CAM function.
By utilizing nrg14;P[nrg180ΔFIGQY] mutants that have exclusive synaptic defects and the previously characterized nrg849 allele that affected both GF guidance and synaptic function, we were able to analyze pathological L1CAM missense mutations with respect to their effects on guidance and synapse formation in vivo. We found that the human pathological H210Q, R184Q and Y1070C, but not the E309K and L120V L1CAM mutations affect outside-in signaling via the FIGQY Ankyrin binding domain which is required for synapse formation and not for axon guidance while L1CAM homophilic binding and signaling via the ERM motif is essential for axon guidance in Drosophila.

Tumor cells interact with basement membrane collagen at the site of extravasation through distinct cellular receptors, including the α2β1 and α3β1integrins. These receptors are known to be differentially expressed in metastatic tumors, relative to the normal cells, depending on tumor type and stage of progression. The binding sites within type IV collagen for the α2β1 andα3β1 integrins have been identified. Since both of the integinspecific sequences possess at least one glycosylated Hyl residue, we questioned whether glycosylation could modulate integrin binding. Triple-helical peptides with and without Lys substituted by glycosylated Hyl for Lys543 and Lys540 from the human a1(IV)531-543 gene sequence (α3β integrin-specific) and Lys393 from the human a1(IV)382-393 gene sequence (α2β1 integrin-specific) were synthesized and utilized in the present study.