CSB329H1 Lecture Notes - Lecture 4: Homeobox, Spermatogenesis, Meiosis
9 May 2018
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Department
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Professor
Lecture 4(a): Neural Stem Cells, Drosophila
ð Neural stem cells were historically called neuroblasts
o Neuroblasts have self-renewal abilities, and their daughter
cells are capable of differentiating into neurons
Key Points:
• Generation of diverse cell types with specialized functions is mediated through the
differentiation of stem cells
o Stem cells requires: ECM, support cells and signaling
• Epigenetic:
o Heritable, and reversible modifications to DNA and histones that affect chromatin
structure that result in changes in gene expression; that do not involve changed to DNA
sequences
• Epigenome:
o Differentiation of stem cell-derived daughter cells is achieved by transient alteration
to the ‘epigenome’
§ i.e. sperm production and the degree of methylation
(initial stages of spermatogenesis, the genome is completely hypo-methylated)
o Dynamic transitional changes to the epigenome occur throughout the developmental
history of differentiated cells
§ Epigenetic changes are require to “turn-off stemness” in daughter cells and
“turn-on genes” required for lineage specification/commitment
• ‘stemness’ is the state in which the epigenome where self-renewal is
favored over differentiation
Epigenetic Changes to
Promote
Transcription
Activation:
• H3K4m3 (histone 3, lysine 4, tri-methylation)
• H3K28ac (histone 3, lysine 28, acetylation) => destroys the + charge; opens up DNA
Epigenetic Changes to
Promote
Transcription
Repression:
• H3K9me3 (histone 3, lysine 9, tri-methylation) => piRNA and PIWI protein in Planaria
• H3K27m3 (histone 3, lysine 28, tri-methylation)
ð Methylation is often associated with the repressing transcription – because transcription
active genes are hypo-methylated
Drosophila Life Cycle:
• 24 hours post fertilization at 25°C – will take 9-10 days for the drosophila to become an adult
o Neural stem cells form during embryonic stage 9-11 derived from the neural
ectodermal cells (Neuroectoderm)
Document Summary
Neural stem cells were historically called neuroblasts: neuroblasts have self-renewal abilities, and their daughter cells are capable of differentiating into neurons. Epigenetic changes are require to turn-off stemness in daughter cells and. Stemness" is the state in which the epigenome where self-renewal is favored over differentiation. Epigenetic changes to promote transcription activation: h3k4m3 (histone 3, lysine 4, tri-methylation, h3k28ac (histone 3, lysine 28, acetylation) => destroys the + charge; opens up dna. Epigenetic changes to promote transcription repression: h3k9me3 (histone 3, lysine 9, tri-methylation) => pirna and piwi protein in planaria, h3k27m3 (histone 3, lysine 28, tri-methylation) Methylation is often associated with the repressing transcription because transcription active genes are hypo-methylated. Drosophila life cycle: 24 hours post fertilization at 25 c will take 9-10 days for the drosophila to become an adult, neural stem cells form during embryonic stage 9-11 derived from the neural ectodermal cells (neuroectoderm)
