MCDB 4650 Imprinting and Gene Silencing

1. MCDB 4650Imprinting and Gene Silencing

2. Genetics of mouse Igf2 gene deletions Igf2 encodes an insulin-like growth factor that stimulates growth of the placenta, which allows embryos to grow larger. Mouse embryos homozygous for a deletion of the Igf2 gene (Igf2∆/Igf2∆) have very small placentas and the fetuses do not survive. When a heterozygous Igf2∆/+ male is mated to a normal female (Igf2+) mouse, the resulting Igf2∆/+ embryos also die as above. From these data alone, you could conclude that Igf2∆ is A) a dominant mutation B) a gain-of-function mutation C) a haploinsufficient mutation D) (a) and (b) E) (a) and (c)

3. However, if a heterozygous Igf2∆/+ female mouse mates with an Igf2+ male, the resulting Igf2∆/+ embryos develop normally. This result together with the previous one suggest that A) Igf2∆ is not a dominant mutation. B) The Igf2 gene is imprinted in males. C) The Igf2 gene is imprinted in females. D) (A) and (B). E) (A) and (C).

4. How many copies of a parentally imprinted gene are functional in an embryo whose parents are both wild-type? A) 0 B) 1 C) 2

5. The human heritable disorder Prader-Willi syndrome (obesity, mild mental retardation, short stature) results from a deletion of a locus on one end of the paternal copy of chromosome 15. This locus must include a gene that is imprinted in A) females. B) males.

6. Back to the mouse . . . The mouse H19 gene is linked to Igf2 on chromosome 7. When a heterozygous H19∆/+ female is mated to a normal male (H19+) mouse, the resulting H19∆/+ embryos resemble androgenetic embryos: the placenta is overgrown and the embryos die at the somitogenesis stage. However, when an H19∆/+ male mates with an H19+ female, the resulting H19∆/+ embryos develop normally. These results indicate that the H19 gene is imprinted A) in females. B) in males.

7. The text states that H19 is a non-coding gene of unknown function. Recent work has shown that its transcript is the precursor of several miRNAs. miRNAs generally A) activate gene expression by acting at promoters to stimulate transcription. B) repress gene expression by acting at promoters to inhibit transcription. C) activate gene expression by binding to mRNA and enhancing translation. D) repress gene expression by binding to mRNA and inhibiting translation.

8. The mouse Igfr gene encodes a receptor protein that binds to IGF-2 and degrades it. What would you predict about imprinting of the Igfr gene? A) It is imprinted in females. B) It is imprinted in males. C) It is probably not imprinted.

9. The following gynogenetic mouse embryos (diploid, with 2 maternal genomes) were constructed by injection of a second maternal pronucleus of the genotype shown into normal embryos from which the male pronucleus had been removed. One of these embryos developed normally. Which one would you predict? A) Igf2(+) H19(+) Igf2(+,imprinting blocked) H19(∆) B) Igf2(+) H19(+) Igf2(+, imprinting blocked) H19(+) C) Igf2(+) H19(+) Igf2(∆) H19(+) D) Igf2(+) H19(+) Igf2(+) H19(+) Hint: Think about the states of these two genes in a normal embryo. Does one of these gynogenetic embryos mimic that state?

10. As drawn in the figure, which side of the cytosine pyrimidine ring forms hydrogen bonds in base pairing, and which side can be methylated? A) H-bonds on the right, methylation on the right. B) H-bonds on the right, methylation on the left. C) H-bonds on the left, methylation on the right. D) H-bonds on the left, methylation on the left.

11. You are studying a new mouse growth factor, IGF-6, which normally acts to limit growth of the placenta during pregnancy, and you find that it is imprinted. Based on your reading about imprinting, would you expect it to be imprinted in: a) females b) males