Recently, scientists constructed a transgene that expresses a mutant form of Drosophila histone H3 inwhich lysine 27 in the histone tail was changed to methionine (H3K27M). Expression of the H3K27Mtransgene results in aberrant development of fruit fliesbecause of inappropriate expression of many differentgenes. Explain this finding.

Recently, scientists constructed a transgene that expresses a mutant form of Drosophila histone H3 inwhich lysine 27 in the histone tail was changed to methionine (H3K27M). Expression of the H3K27Mtransgene results in aberrant development of fruit fliesbecause of inappropriate expression of many differentgenes. Explain this finding.

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter29: Transcription And The Regulation Of Gene Expression

Section: Chapter Questions

Problem 7P

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Researchers know that Fru-M controls male sexualbehavior in Drosophila because inappropriate Fru-Mexpression in females causes them to behave likemales: Such females display male behaviors that areoriented toward other females.a. Describe a fru mutation that could cause the expression of Fru-M in females.b. Describe a transgene construct that scientistscould generate and insert into Drosophila femalesthat would have the same effect as the mutant youdescribed in (a).
Drosophila geneticists have isolated many mutationsthat modify position-effect variegation. Dominantsuppressors of variegation [Su(var)s] cause less frequent inactivation of genes brought near heterochromatin by chromosome rearrangements, whiledominant enhancers of variegation [E(var)s] causemore frequent inactivation of such genes.a. What effects would each of these two kinds of mutations have on position-effect variegation of thewhite gene in Drosophila (that is, would the eyesbe more red or more white)?b. Assuming that these Su(var) and E(var) mutationsare loss-of-function (null) alleles in the corresponding genes, what kinds of proteins do youthink these genes might encode?
Let’s suppose an X-linked gene in mice exists as two alleles, whichwe will call B and b. X-chromosome inactivation, a process inwhich one X chromosome is turned off, occurs in the somatic cellsof female mammals . Allele B encodes an mRNA that is 900 nucleotides long, whereas allele b contains a small deletion that shortens the mRNA to a length of 825 nucleotides.Draw the expected Northern blot that will be obtained usingmRNA isolated from somatic tissue of the followingmice:Lane 1. mRNA from an XbY male mouseLane 2. mRNA from an XbXb female mouseLane 3. mRNA from an XBXb female mouse.Note: The sample taken from the female mouse is not from aclone of cells. It is from a tissue sample, like the one shown.
The TBX20 transcription factor is important for the developmentof heart tissue. Deletion of the Tbx20 gene in mice results in poorheart development and the death of mice well before birth. Tobetter understand how TBX20 regulates heart development ata genetic level, Sakabe et al. (2012. Hum. Mol. Genet. 21:2194–2204) performed a transcriptome analysis in which they comparedthe levels of all mRNAs between heart cells from wild-typemice and mice with Tbx20 deleted. This study concluded that TBX20 acts as an activator ofsome genes but a repressor of other genes in cardiac tissue.How might a single transcription factor have oppositeeffects on the transcription of different genes?
Researchers have exploited Minute mutations in orderto study the phenotypes associated with recessive lethal mutations (l−) that decrease the rate of cell divisionand thus make only very tiny homozygous mutant clones that are difficult to analyze. Many differentstrains of Drosophila carry dominant loss-of-functionMinute (M) mutations in a variety of genes encodingribosomal protein subunits. The M genes are haploinsufficient; flies with only one wild-type M+ gene copyhave a slower pace of cell division, and thus prolongeddevelopment and subtle morphological abnormalities.To circumvent the tiny clone problem, researchersgenerate GFP-marked homozygous l−/ l− clones thatare also M+/ M+, in flies that are l−/ l+ and M−/ M+.The loss of the Minute mutation only in cells withinthe clone gives the l−/ l− cells a growth advantageover their neighbors, enabling the mutant clone togrow large enough to study. Diagram chromosomesthat could be used to generate such clones
The Wnt planar polarity signaling pathway nor-mally ensures that each wing cell in Drosophila has a sin-gle hair. Overexpression of the Frizzled gene from a heat-shock promoter (hs-Fz) causes multiple hairs to grow frommany cells (Figure Q15–5A). This phenotype is suppressedif hs-Fz is combined with a heterozygous deletion (DshΔ)of the Dishevelled gene (Figure Q15–5B). Do these resultsallow you to order the action of Frizzled and Dishevelledin the signaling pathway? If so, what is the order? Explainyour reasoning
In the Fast Forward Box Visualizing X ChromosomeInactivation in Transgenic Mice, suppose the investigators had looked at the expression of green and red fluorescent protein in early mouse embryos, when theembryos have fewer than 500 cells. What patterns wouldthey likely have observed? (Assume that the transgenesmake gene product this early in development.)
Each year in the United States, there are over 230,000 newcases of prostate cancer and almost 28,000 deaths. A 3.8-Mbregion on chromosome 8 (8q24), called a gene desert, has genes but contains enhancer sequences that potentiallyconfer significant risks for prostate cancer. One particular enhancerallele, which is known to be associated with an elevated risk forprostate cancer, physically interacts with the promoter region ofthe nearby MYC gene and facilitates its upregulation. Overexpressionof MYC, which encodes a cell-cycle regulatory protein, isobserved in multiple types of cancer (see Chapter 24). The riskallele has a frequency of 49 percent in men of European descentand 81 percent in men of African ancestry. Most of the differentialMYC activity associated with the risk allele occurs during prenataldevelopment, raising the possibility that testing for this alleleearly in life can be used to identify those in the African-Americanpopulation who are at very high risk for prostate…
What would be the most likely effect of inhibiting the translation of hunchback mRNA throughout a Drosophila embryo?
Based on Figure 14-14 and the features of ultraconservedelements, what would you predict you’d observe if youinjected a reporter-gene construct of the rat ortholog ofthe ISL1 ultraconserved element into fertilized mouseoocytes and examined reporter gene expression in thedeveloping embryo?
The Saccharomyces cerevisiae nuclear gene ARG8encodes an enzyme that catalyzes a key step in biosynthesis of the amino acid arginine. This protein isnormally synthesized on cytoplasmic ribosomes, butthen is transported into mitochondria, where the enzyme conducts its functions. In 1996, T. D. Fox andhis colleagues constructed a strain of yeast in which agene encoding the Arg8 protein was itself moved intomitochondria, where functional protein could besynthesized on mitochondrial ribosomes.a. How could these investigators move the ARG8gene from the nucleus into the mitochondria, whilepermitting the synthesis of active enzyme? In whatways would the investigators need to alter theARG8 gene to allow it to function in the mitochondria instead of in the nucleus?b. Why might these researchers have wished to movethe ARG8 gene into mitochondria in the firstplace?
In a mutant mouse, it was discovered that a gene "W" is moved from its original chromosomal locus to the telomere region, where chromatin is packed into heterochromatin. Given what we have learned about eukaryotic gene regulation, can you speculate how the expression of gene W in the new mouse line would be changed as compare to the normal mouse? Question 18 options: elevated in the mutant mouse than in the wild-type mouse. cannot be determined. reduced in the mutant mouse than in the wild-type mouse. no change in the mutant mouse as compared to the wild-type mouse.