Project description:Caulobacter crescentus is a model for the bacterial cell cycle which culminates in asymmetric cell division, yet little is known about the absolute levels of protein synthesis of the cellular parts needed to complete the cell cycle. Here we utilize ribosome profiling to provide absolute measurements of mRNA translation in C. crescentus, providing an important resource with quantitative genome-wide measurements of protein output across individual genes. Analysis of protein synthesis rates revealed ∼4.5% of cellular protein synthesis is for genes related to vitamin B12 import (btuB) and B12-independent methionine biosynthesis (metE) when grown in common growth media lacking B12 While its facultative B12 lifestyle provides a fitness advantage in the absence of B12, we find that it provides a fitness disadvantage of the cells in the presence of B12, potentially explaining why many Caulobacter species have lost the metE gene and become obligates for B12IMPORTANCECaulobacter crescentus is a model system of the bacterial cell cycle culminating in asymmetric cell division, with each daughter cell inheriting a distinct set of proteins. While a genetic network of master transcription factors coordinates the cell cycle timing of transcription for nearly 20% of Caulobacter genes, we lack knowledge of how many of each protein "part" encoded in the genome are synthesized. Therefore, to determine the absolute production rates across the genome, we performed ribosome profiling, providing, for the first time, a quantitative resource with measurements of each protein "part" needed to generate daughter cells. This resource furthers the goal of a systems-level understanding of the genetic network controlling asymmetric cell division. To highlight the utility of this data set, we probe the protein synthesis cost of a B12 utilization pathway and provide new insights into Caulobacter's adaptation to its natural environments.
Project description:Microarrays revolutionized biological research by enabling gene expression comparisons on a transcriptome-wide scale. Microarrays, however, do not estimate absolute expression level accurately. At present, high throughput sequencing is emerging as an alternative methodology for transcriptome studies. Although free of many limitations imposed by microarray design, its potential to estimate absolute transcript levels is unknown. In this study, we evaluate relative accuracy of microarrays and transcriptome sequencing (RNA-Seq) using third methodology: proteomics. We find that RNA-Seq provides a better estimate of absolute expression levels. We first determined whether we could reproduce the agreement between mRNA expression estimates measured by microarrays and by RNA-Seq reported in other studies. For this purpose, we collected mRNA expression data in two independent cerebellar samples, each containing pooled mRNA from 5 adult human individuals, using both methodologies. Next, to test whether biological variation among samples would substantially reduce correlation strength, we compared expression levels determined by RNA-Seq in two pooled samples to the microarray data obtained from different individuals. For this purpose we used expression measurements obtained using Affymetrix Exon Arrays in 5 individual adult human cerebellar samples, none of which were included in the two pooled samples. Further, since technical and stochastic variation are extremely unlikely to result in better correlation between mRNA and protein expression measurements, we argue that the technology resulting in better correlation must provide more accurate measurements.
Project description:Digestion with restriction enzymes is a classical approach for probing DNA accessibility in chromatin. It allows to monitor both the cut and the uncut fraction and thereby the determination of accessibility or occupancy (= 1- accessibility) in absolute terms as the percentage of cut or uncut out of the total molecules. The here presented protocol takes this classical approach to the genome-wide level. After exhaustive restriction enzyme digestion of chromatin, DNA is purified, sheared and converted into libraries for high throughput sequencing. Bioinformatic analysis counts DNA fragments cut by the restriction enzyme as well as DNA ends generated by restriction enzyme digest and derives thereof the fraction of accessible DNA. This straight forward principle is technically challenged as preparation and sequencing of the libraries leads to biased scoring of DNA fragments with ends generated by restriction enzymes versus by shearing. Our protocol includes two orthogonal approaches to correct for this bias, the “corrected cut-uncut” and the “cut-all cut” method, so that accurate measurements of absolute accessibility/occupancy at restriction sites throughout a genome are possible. The protocol is presented for the example of S. cerevisiae chromatin but may be adapted for any other species.
Project description:Background:Vitamin B12 deficiency causes a number of neurological features including cognitive and psychiatric disturbances, gait instability, neuropathy, and autonomic dysfunction. Clinical recognition of B12 deficiency in neurodegenerative disorders is more challenging because it causes defects that overlap with expected disease progression. We sought to determine whether B12 levels at the time of diagnosis in patients with Parkinson's disease (PD) differed from those in patients with other neurodegenerative disorders. Methods:We performed a cross-sectional analysis of B12 levels obtained around the time of diagnosis in patients with PD, Multiple System Atrophy (MSA), Dementia with Lewy Bodies (DLB), Alzheimer's disease (AD), Progressive Supranuclear Palsy (PSP), Frontotemporal Dementia (FTD), or Mild Cognitive Impairment (MCI). We also evaluated the rate of B12 decline in PD, AD, and MCI. Results:In multivariable analysis adjusted for age, sex, and B12 supplementation, we found that B12 levels were significantly lower at time of diagnosis in patients with PD than in patients with PSP, FTD, and DLB. In PD, AD, and MCI, the rate of B12 decline ranged from -?17 to -?47?pg/ml/year, much greater than that reported for the elderly population. Conclusions:Further studies are needed to determine whether comorbid B12 deficiency affects progression of these disorders.
Project description:Our two main aims were 1) to isolate age-related changes in gene expression in queens of the eusocial bumble bee, Bombus terrestris; and 2) to determine whether experimentally increasing the costs of reproduction (by removing eggs) caused changes in age-related gene expression in these queens. To address these aims we extracted RNA from three key tissues (brain, fat body and ovary) from queens at two time points (10% and 60% mortality phases). Each of these queens had experienced one of two treatments: an egg removal (R) treatment (to increase the costs of reproduction) and an egg removal and replacement (C) treatment (to control for the effects of disturbance caused by egg removal).