Neuronal migration during development and the amyloid precursor protein

Abstract

The Amyloid Precursor Protein (APP) is the source of amyloid peptides that accumulate in Alzheimer’s Disease. However, members of the APP family are strongly expressed in the developing nervous systems of invertebrates and vertebrates, where they regulate neuronal guidance, synaptic remodeling, and injury responses. In contrast to mammals, insects express only one APP ortholog (APPL), simplifying investigations into its normal functions. Recent studies have shown that APPL regulates neuronal migration in the developing insect nervous system, analogous to the roles ascribed to APP family proteins in the mammalian cortex. The comparative simplicity of insect systems offers new opportunities for deciphering the signaling mechanisms by which this enigmatic class of proteins contributes to the formation and function of the nervous system.

Pitfalls of using confocal-microscopy based automated quantification of synaptic complexes in honeybee mushroom bodies (response to Peng and Yang 2016)

“…Most importantly, however, the results on age-related changes in MG bouton densities reported by Peng and Yang 17 largely contrast with several earlier studies including serial EM analyses 10 , 11 , 13 showing that mature honeybee foragers have lower MB-calyx MG densities than younger bees (pruning effect). This discrepancy with earlier studies was also pointed out by Fahrbach and Van Nest 16 , but is largely ignored in the study by Peng and Yang 17 . In summary, we suggest that in the light of the serious methodological flaws outlined above the results by Peng and Yang on both maturation under normal conditions and after insecticide treatment should be viewed as preliminary and potentially flawed rather than conclusive.…”

“… 10 confirmed the size of projection neuron synaptic boutons in olfactory and visual subregions of the MB calyx of the honeybee using serial electron-microscopy based 3D reconstructions. However, fluorescent background staining and partly irregular shapes of olfactory and visual MG may further complicate quantitative confocal microscopy based measurements of synapsin-positive MG boutons 16 , 19 . Furthermore, as the laser energy at high confocal magnification is focused on a small volume, this may easily result in substantial bleaching of fluorophores within a small tissue block, especially when obtaining large 3D image stacks.…”

“…All of these studies used anti-synapsin labeling of relatively large presynaptic boutons of MG in the MB calyx, which, in some studies, was combined with f-actin phalloidin labeling of postsynaptic compartments or quantitative 3D serial electron microscopy analyses 10 . A recent review by Fahrbach and Van Nest 16 provides a most comprehensive summary of these studies addressing possible links between brain plasticity and behavioral flexibility in social honeybees.…”

A possible structural correlate of learning performance on a colour discrimination task in the brain of the bumblebee

“…Synaptic plasticity is considered to be a basis for learning and memory [ 5 – 7 ]. However, how synaptic structures relate to individual learning differences is not known [ 8 ].…”

“…Identification of microglomeruli via immunolabelling has shown that age, age-dependent behavioural changes, temperature during pre-adult development, developmental changes and foraging activities of various social Hymenoptera lead to synaptic organizational and structural changes within the mushroom body calyces [ 8 , 21 – 24 ]. Recent work also showed that establishment of long-term memory is accompanied by changes in microglomerular density within the mushroom body of the insect brain, but this has only been examined for olfactory learning [ 25 , 26 ].…”