Pituitary Tumor Transforming Gene 1 Orchestrates Gene Regulatory Variation in Mouse Ventral Midbrain During Aging.

Yujuan Gui,Mélanie H Thomas,Shlomo Melmed,Michel Mittelbronn,Rashi Halder,Cuiqi Zhou,Mona Karout,Thomas Sauter,Pierre Garcia,Heike Kollmus,Alessandro Michelucci,Rudi Balling,Lasse Sinkkonen,Manuel Buttini,Klaus Schughart,Robert W Williams,Joseph H Nadeau

doi:10.3389/fgene.2020.566734

Abstract

Dopaminergic neurons in the midbrain are of particular interest due to their role in diseases such as Parkinson’s disease and schizophrenia. Genetic variation between individuals can affect the integrity and function of dopaminergic neurons but the DNA variants and molecular cascades modulating dopaminergic neurons and other cells types of ventral midbrain remain poorly defined. Three genetically diverse inbred mouse strains – C57BL/6J, A/J, and DBA/2J – differ significantly in their genomes (∼7 million variants), motor and cognitive behavior, and susceptibility to neurotoxins. To further dissect the underlying molecular networks responsible for these variable phenotypes, we generated RNA-seq and ChIP-seq data from ventral midbrains of the 3 mouse strains. We defined 1000–1200 transcripts that are differentially expressed among them. These widespread differences may be due to altered activity or expression of upstream transcription factors. Interestingly, transcription factors were significantly underrepresented among the differentially expressed genes, and only one transcription factor, Pttg1, showed significant differences between all three strains. The changes in Pttg1 expression were accompanied by consistent alterations in histone H3 lysine 4 trimethylation at Pttg1 transcription start site. The ventral midbrain transcriptome of 3-month-old C57BL/6J congenic Pttg1–/– mutants was only modestly altered, but shifted toward that of A/J and DBA/2J in 9-month-old mice. Principle component analysis (PCA) identified the genes underlying the transcriptome shift and deconvolution of these bulk RNA-seq changes using midbrain single cell RNA-seq data suggested that the changes were occurring in several different cell types, including neurons, oligodendrocytes, and astrocytes. Taken together, our results show that Pttg1 contributes to gene regulatory variation between mouse strains and influences mouse midbrain transcriptome during aging.

Highlights

Two populations of dopaminergic neurons (DAns) in ventral midbrain are of translational interest
A principle component analysis (PCA) of RNA-seq data could clearly separate the samples according to strain of origin (Figure 1B), suggesting significant differences exist at the transcriptomic level between ventral midbrains
Pituitary Tumor Transforming Gene 1 (Pttg1) appears to play a role in development or maintenance of central nervous system, and our results indicate its possible involvement in genetic control of midbrain cell types

Summary

Introduction

Two populations of dopaminergic neurons (DAns) in ventral midbrain are of translational interest. One group resides in substantia nigra (SN) controlling motor function, while the other is in ventral tegmental area (VTA) and associated with cognitive function (Vogt Weisenhorn et al, 2016). Many human phenotypes, such as differences in motor learning (PearsonFuhrhop et al, 2013) or in disease susceptibility to schizophrenia and Parkinson’s disease (PD), are linked to DAns and modulated by genetic variation regulating dopaminergic circuits (Gao and Hong, 2011; Avramopoulos, 2018). Peripheral master regulators such as transcription factors (TFs) with tens to hundreds of target genes could be mediating a lot of gene regulatory variation through trans-effects while their own expression is altered by local cis-variants

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