BIO305 GENE EXPRESSION AND GENOME ANALYSIS
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1st SEMESTER 2021/22 FINAL EXAMINATION
Undergraduate – Year 4
BIO305
GENE EXPRESSION AND GENOME ANALYSIS
Section A
Question A1
BTG3-associated nuclear protein (BANP) activates transcription from CpG island (CGI) promoter. Figure A below shows change in the RNA levels of BANP-bound genes across the degradation time course of BANP. ΔExon, ΔIntron, and Δs4U indicate changes in exonic, intronic, and SLAM-seq signals, respectively. Briefly explain why the change in exonic signal is different from others. (10 marks) Figures B and C indicate examples of BANP target genes that are consistent (B) or differ (C) between ES cells and neurons. Briefly explain ChIP-seq and RNA-seq methods and discuss how you could uncover the potential underlying mechanism(s) of these results. (15 marks)
Question A2
Enhancer sequence diverges extensively during evolution but the function could be conserved. Figures A and B below indicate comparison of GFP expression pattern at 48 hpf for four stable transgenic zebrafish lines harboring candidate eISL enhancers from sponge, human, mouse, and fish. The whole animal (A) as well as the close-up of lateral views (B) from insets numbered 1 and 2 in (A) are shown. Briefly explain function of enhancer and how above eISL enhancers with little sequence homology could drive similar gene expression in zebrafish. (12.5 marks) Sponge has simple body without neurons but the eISL enhancer directs gene expression in zebrafish’s brain. Based on this observation, briefly discuss the potential underlying mechanism of complex body plan. (12.5 marks)
Section B
Question B1
Enhancer release and retargeting (ERR) could be potential mechanism to activate genes associated with various diseases. Figure A below shows a heat map denoting the change in expression of oncogene promoters (OPs) and oncogene-neighboring promoters (ONPs) measured after repressing ONPs. Briefly discuss why ERR appears to occur with only some of the tested ONP-OP pairs. (12.5 marks) Figure B indicates RNA expression levels of CLPTM1L (ONP) and TERT (OP) in wild type (WT) versus KI-CLPTM1Lp cells. CTCF binding motif near the transcriptional start site of CLPTM1L was mutated in KI-CLPTM1Lp cells. Briefly explain CTCF and the specific roles for ERR to activate TERT. (12.5 marks)
Question B2
CRISPR adenine base editor can inactivate PCSK9 by disrupting splice donor at the exon-intron boundary. A figure below shows the editing of splice-site adenine base (arrow) in primary human hepatocytes transfected by adenine base editor and gRNA with the protospacer sequence (black box). Explain the outcomes of editing in detail. (15 marks) Briefly discuss use of base editing to modify gene function in comparison to standard nuclease editing. (10 marks)
Section C
Question C1
Lungfish genome contains a large number of transposable elements (TEs). Figure A below shows Kimura substitution level (%) for each copy of TE against its consensus sequence. DNA, LINE, LTR, and SINE TEs are indicated by blue, green, orange, and purple, respectively. Briefly explain the mechanism of LINE transposition and expansion history of the TEs in lungfish genome. (12.5 marks) Figure B indicates relationship between the copy number and expression level of DNA, LINE, LTR, SINE, and unknow TEs in gonad, brain and liver of lungfish. The expression was estimated for each TE family using poly (A)-enriched RNA-seq data. Briefly discuss about activities of the TEs in lungfish genome. (12.5 marks)
Question C2
RNA binding protein, Neuro-oncological ventral antigen 1 (Nova1) represents one of the few protein-coding differences between modern human and archaic hominin genomes. Figure A below shows numbers of differential splicing events of different types from comparisons between two different cortical organoids at early and late stages of maturation. These cortical organoids were derived from human iPS cell lines with NOVA1 human variant (NOVA1Hu/Hu), homozygous reintroduction of the NOVA1 archaic variant (NOVA1Ar/Ar), and NOVA1 knock-out allele (NOVA1Ko/Ko). Based on these results, briefly explain alternative splicing and the functions of NOVA1. (12.5 marks). Figure B indicates heatmap of the interaction between two synaptic proteins (listed at right) in NOVA1Hu/Hu and NOVA1Ar/Ar cortical organoids. Briefly discuss the underlying mechanism of these results. (12.5 marks)
Section D
Question D1
Mammalian DICER generates two isoform proteins (Dicer and aviD) by the alternative splicing. Figure A below shows Dicer and aviD mRNAs in stem and differentiated cells from small intestine, skin, and hippocampus. Briefly explain the methods to distinguish stem and differentiated cells and the results of Fig. A. (15 marks) Figure B indicates percentage of Zika virus-infected stem cells measured 4 days after infection on organoid with the indicated genotype at the bottom. Briefly discuss the functions of Dicer and aviD for antiviral pathway in stem cells. (10 marks)
Question D2
Histone H1 folds arrays of nucleosomes to more compact chromatin structures. Figure A below shows the difference of type 1-3 chromatins based on the histone H1 to H3 ratio. Figure B shows linear genome browser views of H3K27me3 (top two tracks) and H3K36me2 (bottom two tracks) ChIP-seq signals in wild type (black) and triple-H1-knockout (H1cTKO, red) CD8+ splenic T cells. Chromatin types are annotated as type 1 (black), type 2 (blue) or type 3 (red). Explain general roles of H3K27me3 as well as H3K36me2 and predict which genes in Fig. B (a-e) would be dysregulated for the transcription in H1cTKO cells. (12.5 marks) Figure C indicates change in H1 occupancy, as determined by the percent change in the normalized H1 to H3 ratio between unstimulated and stimulated CD8+ T cells, as a function of the change in gene expression between the two conditions. Figure D indicates number of B cells, CD4+ and CD8+ T cells in spleens of wild type (grey) and H1cTKO (red) mice. Briefly discuss the underlying mechanism of results in Figs. C and D. (12.5 marks)
2023-01-03