Transgene expression in the Nop-tTA driver line is not inherently restricted to the entorhinal cortex

Abstract

The entorhinal cortex (EC) plays a central role in episodic memory and is among the earliest sites of neurodegeneration and neurofibrillary tangle formation in Alzheimer's disease. Given its importance in memory and dementia, the ability to selectively modulate gene expression or neuronal function in the EC is of widespread interest. To this end, several recent studies have taken advantage of a transgenic line in which the tetracycline transactivator (tTA) was placed under control of the neuropsin (Nop) promoter to limit transgene expression within the medial EC and pre-/parasubiculum. Although the utility of this driver is contingent on its spatial specificity, no detailed neuroanatomical analysis of its expression has yet been conducted. We therefore undertook a systematic analysis of Nop-tTA expression using a lacZ reporter and have made the complete set of histological sections available through the Rodent Brain Workbench tTA atlas, www.rbwb.org. Our findings confirm that the highest density of tTA expression is found in the EC and pre-/parasubiculum, but also reveal considerable expression in several other cortical areas. Promiscuous transgene expression may account for the appearance of pathological protein aggregates outside of the EC in mouse models of Alzheimer's disease using this driver, as we find considerable overlap between sites of delayed amyloid deposition and regions with sparse (β-galactosidase reporter labeling. While different tet-responsive lines can display individual expression characteristics, our results suggest caution when designing experiments that depend on precise localization of gene products controlled by the Nop-tTA or other spatially restrictive transgenic drivers.

Prion-like mechanisms in Alzheimer disease

“…The mice developed tauopathy initially in the entorhinal cortex, as expected, but with passing time the abnormalities successively emerged in axonally connected brain areas (de Calignon et al, 2012; Liu et al, 2012). Subsequent studies have found that the tau transgene is weakly expressed in other brain regions, which could influence the pattern of lesion progression (Yetman et al, 2016). However, when considered in light of the orderly neuroanatomic localization of tau lesions in interconnected brain regions in AD (Saper et al, 1987; Arnold et al, 1991; Braak and Braak, 1995), the experiments in mouse models implicate neuronal transport and cytotic mechanisms in the propagation of tau seeds within the nervous system.…”

Prions and Protein Assemblies that Convey Biological Information in Health and Disease

“…However, while in situ analysis suggested this mouse model only expresses the transgene in the entorhinal cortex (de Calignon et al, 2012), analysis by qPCR of laser-captured dentate gyrus granule cells detected human tau mRNA (Liu et al, 2012). Further, recent work based on tet-induced LacZ expression now indicates that over time the neuropsin promoter activates gene expression fairly widely, including the hippocampus (Yetman et al, 2015). This casts some doubt on the use of this model to definitively test for trans-synaptic propagation.…”

Propagation of Aß pathology: hypotheses, discoveries, and yet unresolved questions from experimental and human brain studies

“…Human mutated APP and human mutated tau tg mice have been crossed to study the interaction of Aβ and tau pathologies [100]. Neurofibrillary tangles are initially found in the entorhinal cortex in tg mice expressing P301L human tau predominantly in that area (rTgTauEC) [135]. With age, tau pathology progresses along connections.…”