Genes & Development

Question 1

Development is controlled at both…?

Answer 1

Transcriptional and translational levels

Question 2

The expression of cap proteins is controlled by…?

Answer 2

Nuclear transcription and translation of the cytoplasmic RNA

Question 3

Genomic equivalence

Answer 3

• All somatic cells are mitotic descendants of the fertilized egg. Each somatic nucleus has the same set of genes (DNA packed in chromosomes) as the fertilized egg
• No information is lost from the cell nuclei: genome is identical in every cell (some exception like immune cells)
• Cellular differentiation occurs despite each cell having equivalent genomes (differential gene expression)

Question 4

1952 Briggs & King (Rana pipiens)

Answer 4

first successful transplant of living nuclei in multicellular organism. Transplantation of blastula nuclei into enucleated eggs that developed into an embryo.

Question 5

1962 Gurdon (Xenopus)

Answer 5

nuclei from tadpole (juvenile) intestinal epithelial cells into enucleated eggs that developed into tadpoles

Question 6

1997 Wilmut

Answer 6

nuclei from adult animal (mammary gland) used to successfully clone Dolly the sheep by cell fusion (enucleated egg + mammary gland cell)

Question 7

Proteins involved in chromatin remodeling

Answer 7

Histone components and modifications (acetylation, methylation):
-hypermethylation of H3 in cloned embryos compared to normal fertilized embryos

DNA methylation status (imprinting, X-chromosome inactivation tissue-specific gene activation):

• abberrant methylation patterns in cloned embryos
• dysregulation of methylates (in time and space)

Chromatin remodeling complexes: ATPases capable of DNA translocation

Transcription factors: DNA-binding proteins that activate or press gene transcription

Repressive chromatin proteins: proteins recruited to chromatin by interaction with sequence-specific transcription factors or methylated DNA. Promoting folding into repressed (heterochromatin) state.

Question 8

Nuclear reprogramming

Answer 8

• somatic cell nucleus is transcriptionally active whereas the pronuclei of a fertilized egg are not
• all of the epigenetic changes that created the somatic cells need to be “erased” so that the state of the chromatin of the transplanted nucleus is more like egg and sperm pronuclei
• following normal fertilization there is time limit for reprogramming pronuclei. The process needs to be completed before activation of zygotic gene transcription begins
• reprogramming is probably incomplete in most embryos derived from SCNT resulting in death during development or shortly after birth

Question 9

pluripotent

Answer 9

capable of many things

Question 10

totempotent

Answer 10

capable of all things

Question 11

traditional SCNT

Answer 11

remove oocyte haploid nucleus prior to SCNT

Question 12

Triploid method

Answer 12

leave oocyte nucleus after SCNT