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BO3101 Test 2 - Coggle Diagram
BO3101 Test 2
lecture 3: cellular diversity
evolution of multicellularity
evolved 17x, only 3 gave risea
advantages: large size & division promote effiicient acquisition of & processing of food, efficient locomotion
animals arised from unicellular choanoflagellates
all share collagen, epithelia w/tight junctions, signaling pathways, cluster of HOX genes
volvocales(algae) as model
w true multicellularity
2 cell types
somatic & germ
somatic cells die, germ cells contribute to next gen
problems= conflict of interest & propagation requires small units
problems solved= unicellular stage of propagation, early separation of germ line & control
cell division:
s-phase= synthesis of DNA
M-PHASE= mitosis
G-phase= gap inbetween
august weismann= differntiation v distribution of nuclear determinants---> frog embryos
differences between cells epigenetic= permits cloning (exception= DNA arrangements in antibody producing cells)
phenotypic plasticity= environment can affect phenotype
progenitor cell= no self-renewal
pluripotent ES cells can give rise to all cell types and form complete organism
morphogenesis= generation of form due to cell shape changes or programmed cell death= cytoskeleton proteins, cell surface & extracellular matrix molecules, death factors
lineage decisions occur in several steps:
specification
allignment of cell fae, still flexible in response to external signals
determination
stable assignment of cell fate, inherited by daughter cells
differentiation
cell stops dividing & adopts specialized phenotype
fate established by fate mapping
potential established by exposing cells to diff environment
genes encoding bHLH TFs control muscle differentiation( MyoD & Myf5 & myogenin)
Myo D & myf5= determination
myogenin= differentiation
field specific selector genes
Pax6 (eyeless in Drosophila) activates genes in eye development
also in mammals
needed for retina and eye lens
epigenetic inheritance
mechanisms
stabilisation of state by +ve feedback
DNA methylation
modifications of histones
leads to chromatin modifications=inactivation by formation of heterochromatin
overexpression of 4 TFs can reprogram cells
induced pluripotent s cells
lecture 5: development vertebrate models
early development in Xenopus
egg w maternal deposits mRNAs, proteins, yolk
sperm entry determines dorsal (opposite sperm entry point)
cleavage divsions subdivide fertilized egg
blastocoel develops
gastrulation
external tissues internalized via blastopore & gut forms
dorsal blastopre lip forms notochord
3 germ layers can be dinstinguished
neural induction: dorsal blastopore lip induces neural plate in overlying ectoderm
neurulation: neural plate folds to form neural tube
neural tube gives rise to CNS
ectoderm forms epidermis & placodes (precursors of sensory irgans)
neural crest: originate in region of neural fold fusion
trunk neural crest gives rise to pigment cells, sensory neurons, glial cells & endocrine cells
cranial neural crest form connective & skeletal tissues
the chick
amniote development modified due to adaptations to terrestrial development: extraembryonic membranes (4)
allantois: gas exchange
chorion: gas exchange
amnion: water balance
yolk sac: nutrition
yolk rich eggs, development confined to 1 side of yolk
early development
cleavage incomplete (meroblastic)
blastodisc forms w epiblast & hypoblast
hypoblast forms extraembryonic membrane
gastrulation proceeds by ingression of cells
ingressed cells form embryonic endoderm & mesoderm
Hensen's node (dorsal blastopore lip, organizer) forms notochord
regresses from anterior to posterior
anteroposterior progression of development
as model organism
pros
eggs easily accessible
large embryos
overexpression & knockdown of genes by electroporation
cons
genetic screens difficult ( large, long life cycle)
no trageted gene knockout by homologous recombination
organogenesis: subdivision of mesoderm
axial, paraxial, intermediary, lateral plate
paraxial becomes somites
somites: dermatome, myotome, sclerotome (migrate to notochord & form anlagen)
mesoderm forms notochord, dermis, muscles, skeleton, circulatory & urogenital
Xenpus as Model Organism:
large no eggs
egg laying inducible by hormone injection
embryos easily accessible & amenable to grafting
transgenic frogs
Pros:
v large genome
pseudotetraploid (genetics difficult)
Cons:
Zebrafish:
development similar to frogs but diff due to large yolk
pros
lots of eggs
laying & spawning can be induced by controlled mating
short life cycle
embryos eaily accessible, transparent & amenable to microinjection
mutants available
many transgenic reporter lines
cons
small eggs (grafting hard)
teleost fish gene duplicated: redundant gene pairs
cleavage in mammals
eggs v small
no yolk cause placenta provides nutrients
holoblastic cleavage & diff from chick
inner & outer cells diff during compaction
blastocyst forms w inner cell mass & trophoblast
trophoblast forms placenta
inner cell mass forms embryo & epiblast & hypoblast
formation of placenta
blastocyst implants in uterus
trophoblast cell divides
supplied by maternal blood vessels
embryonic allantois forms umbilical cord
mouse
embryo assumes cup shape before gastrulation
similar to chick
as model
pros
small & short life cycle
trageted gene knockout by homologous recombination
close to humans
cons
development in uterus difficult to observe
embryonic grafting not possible
lecture 2: gene regulation
development requires: zygote, cleavage, blastula, gastrula
morphogenesis: shaping the embryo
differential gene expression:
2 steps
transcription of DNA to mRNA
translation of mRNA into protein
In eukaryotes
transcription of DNA to pre-mRNA in nucleus
splicing
export of mRNA to cytoplasm
translation of mRNA to protein in ribosome
mechanisms
regulation or RNA processing
diff splicing of RNA can generate diff mRNAs/proteins
some genes have many exons that can be combined diff
regulation of translation by binding of proteins to 3' UTR of mRNA e.g. regulation of caudal mRNA by Bicoid protein in Drosophila
regulation of translation by binding of microRNAs to 3' UTR of mRNA e.g. regulation of lin-14 mRNA by lin-4 miRNA in C.Elegans
regulation of gene transcription
promoter & operator function in cis: cis-regulatory genes
regulatory gene encoding repressor function in trans
similar in eukaryotes but
complex cis-regulatory elements
exon-intron structure requires RNA splicing
genes transcribed
when specififc transcription factors bind enhancers
when basal transcriptional apparatus bind to promotor
TFs are proteins
DNA binding domain (6-15 nucleotides)
may regulate more than 1 gene
its activation allows coordinated activation of gene battery
cis-regulatory genes complex
diff enhancers for diff expression domains
each enhancer has several TF binding sites
segmentation in Drosophila
mutagenesis screen
maternal effect genes affect antero-posterior axis formation
gap genes specify large sections of body regions
pair rule genes pattern 2 segment units
segmentation genes pattern individual segments
every stripe regulated by own enhancer