CSB349H1 Lecture Notes - Lecture 14: Embryonic Stem Cell, Neural Cell Adhesion Molecule, Cell Adhesion Molecule
14 May 2018
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Lecture 14(a): Heterokaryons & Nuclear Transfer
Early Mammalian Development:
• Zygote undergoes cellular division to generate a blastocyst
o Blastocyst has an inner cell mass: consists of pluripotent embryonic stem cells
§ ESCs are capable of giving rise to three germ layers
Nuclear Reprogramming:
• Nuclear reprogramming is the phenomenon when DNA experiences a whole genome-wide
demethylation – there are two nuclear reprogramming events
1. Zygote Formation:
§ Methylation marks on both maternal and paternal DNA will be demethylated
• Imprinted genes are not be demethylated – required for premature
development
2. Primordial Germ Cells (PGCs):
§ PGCs have the potential to give rise to gametes (egg/sperm) – full
demethylation even will occur within these cells, including the imprinted marks
ð A specialized machinery is present in zygotes and primordial germ cells that are capable of
inducing a nuclear reprogramming event
o Differentiated somatic cells can reprogrammed when their nucleus is inserted into an
enucleated egg; this process is known as a nuclear transplant
Heterokaryon:
• Fusion of two distinct somatic cell to form a single cell that contains two different nuclei in a
common cytoplasm is called a heterokaryon
o Two nuclei are distinct and variable from each other; their level of differentiation is
usually different
§ Nuclei that is
less
differentiated will have the ‘upper hand’ and can lead to:
a) Inactivation of the
more
differentiated nuclei which is associated
with chromosomal loss (ploidy reduction)
b) Transmit factors that make the
more differentiated
nuclei change
expression patterns
Trans-Acting Factors Stimulate Gene Expression:
• Stable heterokaryon generated by fusing a human fibroblast nuclei + mouse muscle nuclei
o NCAM – cell adhesion molecule that is present in muscle cells but not fibroblast
• Staining human NCAM with an antibody:
o Fibroblast began to express NCAM (muscle marker) after fusion with muscle cell
ð Human fibroblast cells were reprogrammed to express muscle-specific cells (i.e. NCAM)
Antibody
staining is
recognizing
human
NCAM
Document Summary
Early mammalian development: zygote undergoes cellular division to generate a blastocyst, blastocyst has an inner cell mass: consists of pluripotent embryonic stem cells. Escs are capable of giving rise to three germ layers. Nuclear reprogramming: nuclear reprogramming is the phenomenon when dna experiences a whole genome-wide demethylation there are two nuclear reprogramming events, zygote formation: Methylation marks on both maternal and paternal dna will be demethylated. Imprinted genes are not be demethylated required for premature development: primordial germ cells (pgcs): Pgcs have the potential to give rise to gametes (egg/sperm) full demethylation even will occur within these cells, including the imprinted marks. Nuclei that is less differentiated will have the upper hand" and can lead to: inactivation of the more differentiated nuclei which is associated with chromosomal loss (ploidy reduction, transmit factors that make the more differentiated nuclei change. Human fibroblast cells were reprogrammed to express muscle-specific cells (i. e. ncam)
