Brigidi Flashcards
Chromatin:
the mass of DNA and proteins that
comprises a chromosome.
Solenoid:
packed nucleosomes + DNA as a 30nm
fiber of chromatin from helical winding of ≥5 strands.
Nucleosome: .
146 bp of DNA wrapped 1.76x
around a histone octamer.
Histone octamer:
two H2A-H2B dimers and a
H3-H4 tetramer
Histones:
5 major families – H2A, H2B, H3, H4 (core
histones), H1/H5 (linker histones). Each subunit’s amine
tails project away from the nucleosome core and can be
epigenetically modified (e.g. acetylation, methylation, and
phosphorylation)
Euchromatin vs. Heterochromatin:
the former is less condensed, localized to chromosome
“arms”, and rich with accessible genes. The latter is highly condensed, located at centromeres
or telomeres, enriched for repetitive sequences and paucity of genes
Epigenetic processes:
1) Signals that trigger the
the establishment of
an epigenetic mark.
(e.g. neuronal activity)
2) Epigenetic initiators that
define the location of a
mark in the genome,
and determine which
genes to activate or
repress (e.g.
transcription factors)
3) Signals that maintain
the epigenetic mark
(e.g. the histone code)
Signal Transduction
Opening of NMDA receptors or L-type Calcium
channels leads to the influx of CALCIUM
Elevated calcium is sensed by calmodulin and
triggers a biochemical cascade involving
autophosphorylation of calcium/calmodulin kinase
(CaMKII) at T286
CaMKII phosphorylates AMPAR subunits, increasing
AMPAR-mediated excitatory post-synaptic current
during LTP, and phosphorylates TARPs leading to
increased AMPAR numbers at the synapse (early LTP)
Elevated calcium also leads to activation of
adenylyl cyclase, leading to increased cAMP and
activation of PKA.
PKA translocates to the nucleus with MAPK and
phosphorylates cAMP response element-binding
protein-1 (CREB).
CREB-1 binds to the CREB response element (CRE)
in the promoter of target genes.
CRCT1
Distal synaptic activity can trigger CREB-dependent
gene activation by nuclear shuttling of CRTC1
CRTC1 is constitutively expressed and
localized to the cytosol through an
association with scaffolding proteins.
De-phosphorylation of CRTC1 dissolves
its anchorage and translocation to the
nucleus where it binds CREB and recruits
it to CREs along with transcriptional
machinery.
Local activation of ≈10-15 synapses >100μm
from the nucleus using glutamate uncaging
triggers the translocation of CRTC1 from
the proximity of those synapses to the
nucleus.
CRTC1 trafficking requires active transport,
Calcium flux through L-type VGCCs, and
NMDA receptors.
Distal synapses can trigger gene activation
through synapse-to-nucleus translocation of CRTC1!
The H3K27ac histone modification is strongly
indicative of…
The H3K27ac histone modification is strongly
indicative of open and accessible chromatin
and suggests the presence of an enhancer
Experiment Q
Expression of luciferase driven by the Nptx2 promoter is highest when enhancers that exhibited increased activity-dependent K3K27ac marks are inserted upstream.
Increasing H3K27ac marks directly correlate with expression levels of nearby genes.
