Abstract
PRESENILIN 2 (PSEN2) is one of the genes mutated in early onset familial Alzheimer’s disease (EOfAD). PSEN2 shares significant amino acid sequence identity with another EOfAD-related gene PRESENILIN 1 (PSEN1), and partial functional redundancy is seen between these two genes. However, the complete range of functions of PSEN1 and PSEN2 is not yet understood. In this study, we performed targeted mutagenesis of the zebrafish psen2 gene to generate a premature termination codon close downstream of the translation start with the intention of creating a null mutation. Homozygotes for this mutation, psen2S4Ter, are viable and fertile, and adults do not show any gross psen2-dependent pigmentation defects, arguing against significant loss of γ-secretase activity. Also, assessment of the numbers of Dorsal Longitudinal Ascending (DoLA) interneurons that are responsive to psen2 but not psen1 activity during embryogenesis did not reveal decreased psen2 function. Transcripts containing the S4Ter mutation show no evidence of destabilization by nonsense-mediated decay. Forced expression in zebrafish embryos of fusions of psen2S4Ter 5’ mRNA sequences with sequence encoding enhanced green fluorescent protein (EGFP) indicated that the psen2S4Ter mutation permits utilization of cryptic, novel downstream translation start codons. These likely initiate translation of N-terminally truncated Psen2 proteins lacking late endosomal/lysosomal localization sequences and that obey the “reading frame preservation rule” of PRESENILIN EOfAD mutations. Transcriptome analysis of entire brains from a 6-month-old family of wild type, heterozygous and homozygous psen2S4Ter female siblings revealed profoundly dominant effects on gene expression likely indicating changes in ribosomal, mitochondrial, and anion transport functions.
Highlights
IntroductionTranscriptome analysis of a dominant psen mutation in zebrafish supported by an Adelaide Scholarship International scholarship from the University of Adelaide
To predict what changes in molecular/cellular processes might be reflected by the differential expression of genes, enrichment analyses were conducted using the Hallmark, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) gene sets defined in the MSigDB database (38)
We found that the RNA-seq data indicated considerable ribosomal RNA content, presumably due to somewhat inefficient depletion of zebrafish rRNA from samples, using a human genome-based rRNA depletion kit
Summary
Transcriptome analysis of a dominant psen mutation in zebrafish supported by an Adelaide Scholarship International scholarship from the University of Adelaide. ML and SP are employees of the University of Adelaide. No funding body played any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript
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