APPL, theDrosophilaMember of the APP-Family, Exhibits Differential Trafficking and Processing in CNS Neurons

Abstract

The Drosophila Appl gene encodes a transmembrane protein that is expressed exclusively in neurons. Amino acid comparisons show that APPL protein is a member of the amyloid precursor protein (APP)-like family of proteins. Similar to mammalian APP-family proteins, APPL is synthesized as a transmembrane holoprotein and cleaved to release a large secreted amino-terminal domain. Using immunocytochemical methods, we have analyzed the distribution of APPL in the Drosophila CNS. Surprisingly, although APPL is present in all neuronal cell bodies, the neurophil shows sterotypic differential distribution. Double-labeling experiments with different neuronal markers were used to distinguish between APPL associated with neuronal processes or extracellular matrix. The distribution of APPL protein produced from transgenes encoding wild-type (APPL), secretion-defective (APPLsd), and constitutively secreted (APPLs) forms was analyzed in an Appl-deficient background to determine which APPL form is associated with different neuropil regions. We found that APPLsd protein is enriched where APPL immunoreactivity coincides with neuronal processes. In contrast, APPLs preferentially localizes to those parts of the neuropil that show a diffuse APPL signal that rarely colocalizes with processes, and thus seems to be a component of the extracellular matrix. These data indicate that proteolytic cleavage and trafficking of APPL is differentially regulated in different neuronal populations. Through metamorphosis, APPL is especially abundant in growing axons and in areas where synapses are forming. Interestingly, in adult brains, APPL protein is enriched in the mushroom bodies and to a lesser extent in the central complex, structures involved in learning and memory.

Drosophila homolog of APP-BP1 (dAPP-BP1) interacts antagonistically with APPL during Drosophila development

“…were mouse anti-Armadillo (N27A1, 1:50, Iowa Hybridoma Bank), rat anti-elav (7E8A10, 1:500, Iowa Hybridoma Bank), rabbit anti-b-gal (1:1000, Sigma), mouse anti-GFP (1:200, Sigma), rat anti-Ci (2A1, 1:3), 38 rabbit anti-Cul1 (1:250, Zymed), rabbit anti-cleaved (activated) caspase 3 (1:50, Cell Signaling Technology), rabbit anti-phospho-histone H3 (1:500, Upstate Biotechnology), rabbit anti-APPL (Ab952, 1:500), 21 and mouse anti-Myc (1:200, Roche). Secondary antibodies coupled to the appropriate fluorophore (FITC, Cy3, or Cy5; Jackson Immunoresearch Laboratories) were diluted to 1:200 in wash solution.…”

“…20 Different forms of Drosophila APPL protein are enriched in different areas of the brain. 21 Deletion of the Appl gene does not cause obvious defects in adult brain morphology. 20 However, loss-and gain-of-function studies have revealed a role for APPL in synapse differentiation and axonal transport.…”

Amyloid Protein Precursor Stimulates Excitatory Amino Acid Transport

“…APP is expressed at relatively high levels in the central nervous system of diverse species (6,7). Multiple APP isoforms are derived from a single gene by alternative splicing (see Ref.…”

Modeling Amyloid Diseases in Fruit Fly Drosophila Melanogaster

“…This indicates functional conservatism between Drosophila Appl and human АРР [Luo et al, 1992]. Many researches specify the key role of Appl in formation and maintenance of synapses in Drosophila [Ashley et al, 2005;Torroja et al, 1996]. Experiments by definition of Appl localization have shown significant Appl enrichment in growing axons and synaptic www.intechopen.com structures and participation of Appl in formation and differentiations of synapses in neuromuscular junctions of larvae [Torroja et al, 1996[Torroja et al, , 1999b.…”

“…Many researches specify the key role of Appl in formation and maintenance of synapses in Drosophila [Ashley et al, 2005;Torroja et al, 1996]. Experiments by definition of Appl localization have shown significant Appl enrichment in growing axons and synaptic www.intechopen.com structures and participation of Appl in formation and differentiations of synapses in neuromuscular junctions of larvae [Torroja et al, 1996[Torroja et al, , 1999b. The overexpression both Appl, and human АРР caused disturbance of axon transport [Gunawardena and Goldstein, 2001;Torroja et al, 1999a].…”