Non-muscle myosin IIB plays a major role in applying force on the nucleus to facilitate nuclear translocation through tight spaces during 3D invasive migration, while non-muscle myosin IIA is critical for generating force during active protrusion.

To understand the mechanisms of neuronal Zn2+ homeostasis better, experimental data obtained from cultured cortical neurons were used to inform a series of increasingly complex computational models. Total metals (inductively coupled plasma-mass spectrometry), resting metallothionein, 65Zn2+ uptake and release, and intracellular free Zn2+ levels using ZnAF-2F were determined before and after neurons were exposed to increased Zn2+, either with or without the addition of a Zn2+ ionophore (pyrithione) or metal chelators [EDTA, clioquinol (CQ), and N, N, N′, N′-tetrakis(2-pyridylmethyl)ethylenediamine]. Three models were tested for the ability to match intracellular free Zn2+ transients and total Zn2+ content observed under these conditions. Only a model that incorporated a muffler with high affinity for Zn2+, trafficking Zn2+ to intracellular storage sites, was able to reproduce the experimental results, both qualitatively and quantitatively. This “muffler model” estimated the resting intracellular free Zn2+ concentration to be 1.07 nM. If metallothionein were to function as the exclusive cytosolic Zn2+ muffler, the muffler model predicts that the cellular concentration required to match experimental data is greater than the measured resting concentration of metallothionein. Thus Zn2+ buffering in resting cultured neurons requires additional high-affinity cytosolic metal binding moieties. Added CQ, as low as 1 μM, was shown to selectively increase Zn2+ influx. Simulations reproduced these data by modeling CQ as an ionophore. We conclude that maintenance of neuronal Zn2+ homeostasis, when challenged with Zn2+ loads, relies heavily on the function of a high-affinity muffler, the characteristics of which can be effectively studied with computational models.

No abstract

Alterations in the processing of the amyloid precursor protein (APP) lead to familial Alzheimer's disease (AD). AD patients exhibit increased seizure susceptibility and alterations in their EEGs, which suggests that APP and its metabolites may modulate neuronal networks. Here we demonstrate that transgenic mice overexpressing APP intracellular domain (AICD) and its binding partner Fe65 exhibit abnormal spiking events and a susceptibility to induced seizures. These abnormalities are not observed in PDAPP(D664A) mice, which express high Aβ levels but harbor a mutation in the APP intracellular domain. These data suggest that alterations in the levels of AICD contributes to network dysfunction in AD.