AS.020.151 Chapter Notes - Chapter 14: Polarity In Embryogenesis, Cell Potency, Blastocyst
12 Jun 2018
School
Department
Course
14.1 Development Involves Distinct but Overlapping
Processes
Development- the%process%by%which%an%organism%undergoes%a%series%of%changes%
that%lead%to%the%forms%characterizing%its%life%cycle
Four%processes%of%development:
Determination:%fate%of%cell%decided
1)
Differentiation:%realization%of%fate
2)
Morphogenesis:%cells%move%to%locations
3)
Growth:%cells%divide%and%grow%in%size%and%number
4)
Differentiated%plant cells%can%be%totipotent->%induced%to%produce%any%cell%type%
of%the%plant
Differentiated%animal cells%are%totipotent->%nuclear%transplant%experiments,%
one%cell%induced%to%produce%all%cell%types
Stem5cells-undifferentiated,%rapidly%dividing%cells%in%clusters%in%plant%
meristems
Multipotent5stem5cells- in%mammals,%in%most%tissues%(especially%frequent%
replacement- skin,%blood)
Pluripotent cells%in%blastocyst%embryonic%stage->%ability%to%form%all%cells%in%
body
14.2 Changes in Gene Expression Underlie Cell
Differentiation in Development
Cell5fate determined%by:
Cytoplasmic5segregation- asymmetrical%distribution%of%cytoplasmic%
factors%in%the%cell
1)
Cytoplasmic5determinants- transcription%factors%that%promote%
differential%gene%expression
2)
Axes%of%body%plan%develop%early
Polarity- having%a%top%(animal%pole)%and%bottom%(vegetal%pole)
Can%lead%to%determination%early%in%development
Transcriptional5controls->%controls%of%gene%expression%in%differentiation
All%cells%have%same%DNA,%differentiated%cells%have%different%mRNAs
Induction- signaling%events%in%the%developing%embryo%
Cells%influence%one%another's%fates%through%chemical%signals%and%pathways
Different%amounts%of%inductive%signals->%differences%in%gene%expression
14.3 Spatial Differences in Gene Expression Lead to
Morphogenesis
Pattern5formation-the%process%that%results%in%the%spatial%organization%of%
tissues
Spatial%differences%depend%on:
-Cells%in%body%must%be%self-aware%of%location
-Cells%must%activate%appropriate%gene%expression
-Apoptosis%(programmed%cell%death)%is%important->%many%appear%and%
disappear
Expression%key%in%fingers%and%toes%(remove%webbing)
French5Flag5model-cells%can%form%blue/white/red
-Which%color%depends%on%concentration%of%morphogen%
-Concentration%gradient%signals%each%cell's%position
Sonic5hedgehog- morphogen%secreted%by%cells%in%the%limb%bud
-Makes%a%gradient%on%cells%that%will%form%limbs
-Determines%posterior-anterior%index%(pinky%to%thumb)
-Thumb->%little%Shh
-Pinky->%a%lot%of%Shh
Pattern5formation in%drosophila%(fruit%fly)-already%occurs%24%h%after%
fertilization
-Segments%of%body%begin%to%appear%early%(fates%already%determined)
-Morphogens%diffuse%easily%in%the%embryo
-Genes%involved
Maternal5effect5genes- set%up%the%major%axes%(anterior–posterior%
and%dorsal–ventral)%of%the%egg
○
Segmentation5genes- determine%the%boundaries%and%polarity%of%
each%of%the%segments
○
Hox5genes- determine%what%organ%will%be%made%at%a%given%location
○
14.4 Changes in Gene Expression Pathways Underlie the
Evolution of Development
Principles%of%evo-devo:
Many%animals%share%molecular%mechanisms%for%morphogenesis%and%
pattern%formation
•
Molecular%pathways%act%independently-modularity5
•
Changes%in%location%and%timing%of%expression%of%genes->%important%in%
evolution
•
Development->%morphology;%morphological%evolution%exists%by%
modification%of%existing%pathways
•
Modularity- also%allows%timing%of%events%to%act%independently-> heterochrony
Heterotopy-altered%spatial%expression%pattern
14.5 Developmental Genes Contribute to Species
Evolution but Also Pose Constraints
Evolutionary%innovations->%modifications%of%previously%existing%structures%
(wings)
Two%ways%developmental%genes%constrain%evolution:
Nearly%all%evolutionary%innovations%are%modifications%of%existing%
structures
1)
The%genes%that%control%development%are%highly%conserved%(change%slowly%
over%course%of%evolution)
2)
Genes,%Development%and%Evolution%(Ch.%14)
Thursday, December 14, 2017
6:25 PM
14.1 Development Involves Distinct but Overlapping
Processes
Development- the%process%by%which%an%organism%undergoes%a%series%of%changes%
that%lead%to%the%forms%characterizing%its%life%cycle
Four%processes%of%development:
Determination:%fate%of%cell%decided1)
Differentiation:%realization%of%fate2)
Morphogenesis:%cells%move%to%locations3)
Growth:%cells%divide%and%grow%in%size%and%number4)
Differentiated%plant cells%can%be%totipotent->%induced%to%produce%any%cell%type%
of%the%plant
Differentiated%animal cells%are%totipotent->%nuclear%transplant%experiments,%
one%cell%induced%to%produce%all%cell%types
Stem5cells-undifferentiated,%rapidly%dividing%cells%in%clusters%in%plant%
meristems
Multipotent5stem5cells- in%mammals,%in%most%tissues%(especially%frequent%
replacement- skin,%blood)
Pluripotent cells%in%blastocyst%embryonic%stage->%ability%to%form%all%cells%in%
body
14.2 Changes in Gene Expression Underlie Cell
Differentiation in Development
Cell5fate determined%by:
Cytoplasmic5segregation- asymmetrical%distribution%of%cytoplasmic%
factors%in%the%cell
1)
Cytoplasmic5determinants- transcription%factors%that%promote%
differential%gene%expression
2)
Axes%of%body%plan%develop%early
Polarity- having%a%top%(animal%pole)%and%bottom%(vegetal%pole)
Can%lead%to%determination%early%in%development
Transcriptional5controls->%controls%of%gene%expression%in%differentiation
All%cells%have%same%DNA,%differentiated%cells%have%different%mRNAs
Induction- signaling%events%in%the%developing%embryo%
Cells%influence%one%another's%fates%through%chemical%signals%and%pathways
Different%amounts%of%inductive%signals->%differences%in%gene%expression
14.3 Spatial Differences in Gene Expression Lead to
Morphogenesis
Pattern5formation-the%process%that%results%in%the%spatial%organization%of%
tissues
Spatial%differences%depend%on:
-Cells%in%body%must%be%self-aware%of%location
-Cells%must%activate%appropriate%gene%expression
-Apoptosis%(programmed%cell%death)%is%important->%many%appear%and%
disappear
Expression%key%in%fingers%and%toes%(remove%webbing)
French5Flag5model-cells%can%form%blue/white/red
-Which%color%depends%on%concentration%of%morphogen%
-Concentration%gradient%signals%each%cell's%position
Sonic5hedgehog- morphogen%secreted%by%cells%in%the%limb%bud
-Makes%a%gradient%on%cells%that%will%form%limbs
-Determines%posterior-anterior%index%(pinky%to%thumb)
-Thumb->%little%Shh
-Pinky->%a%lot%of%Shh
Pattern5formation in%drosophila%(fruit%fly)-already%occurs%24%h%after%
fertilization
-Segments%of%body%begin%to%appear%early%(fates%already%determined)
-Morphogens%diffuse%easily%in%the%embryo
-Genes%involved
Maternal5effect5genes- set%up%the%major%axes%(anterior–posterior%
and%dorsal–ventral)%of%the%egg
○
Segmentation5genes- determine%the%boundaries%and%polarity%of%
each%of%the%segments
○
Hox5genes- determine%what%organ%will%be%made%at%a%given%location
○
14.4 Changes in Gene Expression Pathways Underlie the
Evolution of Development
Principles%of%evo-devo:
Many%animals%share%molecular%mechanisms%for%morphogenesis%and%
pattern%formation
•
Molecular%pathways%act%independently-modularity5
•
Changes%in%location%and%timing%of%expression%of%genes->%important%in%
evolution
•
Development->%morphology;%morphological%evolution%exists%by%
modification%of%existing%pathways
•
Modularity- also%allows%timing%of%events%to%act%independently-> heterochrony
Heterotopy-altered%spatial%expression%pattern
14.5 Developmental Genes Contribute to Species
Evolution but Also Pose Constraints
Evolutionary%innovations->%modifications%of%previously%existing%structures%
(wings)
Two%ways%developmental%genes%constrain%evolution:
Nearly%all%evolutionary%innovations%are%modifications%of%existing%
structures
1)
The%genes%that%control%development%are%highly%conserved%(change%slowly%
over%course%of%evolution)
2)
Genes,%Development%and%Evolution%(Ch.%14)
Thursday, December 14, 2017
6:25 PM
14.1 Development Involves Distinct but Overlapping
Processes
Development- the%process%by%which%an%organism%undergoes%a%series%of%changes%
that%lead%to%the%forms%characterizing%its%life%cycle
Four%processes%of%development:
Determination:%fate%of%cell%decided1)
Differentiation:%realization%of%fate2)
Morphogenesis:%cells%move%to%locations3)
Growth:%cells%divide%and%grow%in%size%and%number4)
Differentiated%plant cells%can%be%totipotent->%induced%to%produce%any%cell%type%
of%the%plant
Differentiated%animal cells%are%totipotent->%nuclear%transplant%experiments,%
one%cell%induced%to%produce%all%cell%types
Stem5cells-undifferentiated,%rapidly%dividing%cells%in%clusters%in%plant%
meristems
Multipotent5stem5cells- in%mammals,%in%most%tissues%(especially%frequent%
replacement- skin,%blood)
Pluripotent cells%in%blastocyst%embryonic%stage->%ability%to%form%all%cells%in%
body
14.2 Changes in Gene Expression Underlie Cell
Differentiation in Development
Cell5fate determined%by:
Cytoplasmic5segregation- asymmetrical%distribution%of%cytoplasmic%
factors%in%the%cell
1)
Cytoplasmic5determinants- transcription%factors%that%promote%
differential%gene%expression
2)
Axes%of%body%plan%develop%early
Polarity- having%a%top%(animal%pole)%and%bottom%(vegetal%pole)
Can%lead%to%determination%early%in%development
Transcriptional5controls->%controls%of%gene%expression%in%differentiation
All%cells%have%same%DNA,%differentiated%cells%have%different%mRNAs
Induction- signaling%events%in%the%developing%embryo%
Cells%influence%one%another's%fates%through%chemical%signals%and%pathways
Different%amounts%of%inductive%signals->%differences%in%gene%expression
14.3 Spatial Differences in Gene Expression Lead to
Morphogenesis
Pattern5formation-the%process%that%results%in%the%spatial%organization%of%
tissues
Spatial%differences%depend%on:
-Cells%in%body%must%be%self-aware%of%location
-Cells%must%activate%appropriate%gene%expression
-Apoptosis%(programmed%cell%death)%is%important->%many%appear%and%
disappear
Expression%key%in%fingers%and%toes%(remove%webbing)
French5Flag5model-cells%can%form%blue/white/red
-Which%color%depends%on%concentration%of%morphogen%
-Concentration%gradient%signals%each%cell's%position
Sonic5hedgehog- morphogen%secreted%by%cells%in%the%limb%bud
-Makes%a%gradient%on%cells%that%will%form%limbs
-Determines%posterior-anterior%index%(pinky%to%thumb)
-Thumb->%little%Shh
-Pinky->%a%lot%of%Shh
Pattern5formation in%drosophila%(fruit%fly)-already%occurs%24%h%after%
fertilization
-Segments%of%body%begin%to%appear%early%(fates%already%determined)
-Morphogens%diffuse%easily%in%the%embryo
-Genes%involved
Maternal5effect5genes- set%up%the%major%axes%(anterior–posterior%
and%dorsal–ventral)%of%the%egg
○
Segmentation5genes- determine%the%boundaries%and%polarity%of%
each%of%the%segments
○
Hox5genes- determine%what%organ%will%be%made%at%a%given%location
○
14.4 Changes in Gene Expression Pathways Underlie the
Evolution of Development
Principles%of%evo-devo:
Many%animals%share%molecular%mechanisms%for%morphogenesis%and%
pattern%formation
•
Molecular%pathways%act%independently-modularity5
•
Changes%in%location%and%timing%of%expression%of%genes->%important%in%
evolution
•
Development->%morphology;%morphological%evolution%exists%by%
modification%of%existing%pathways
•
Modularity- also%allows%timing%of%events%to%act%independently-> heterochrony
Heterotopy-altered%spatial%expression%pattern
14.5 Developmental Genes Contribute to Species
Evolution but Also Pose Constraints
Evolutionary%innovations->%modifications%of%previously%existing%structures%
(wings)
Two%ways%developmental%genes%constrain%evolution:
Nearly%all%evolutionary%innovations%are%modifications%of%existing%
structures
1)
The%genes%that%control%development%are%highly%conserved%(change%slowly%
over%course%of%evolution)
2)
Genes,%Development%and%Evolution%(Ch.%14)
Thursday, December 14, 2017 6:25 PM
Document Summary
Development- the process by which an organism undergoes a series of changes that lead to the forms characterizing its life cycle. Growth: cells divide and grow in size and number. Differentiated plant cells can be totipotent-> induced to produce any cell type of the plant. Differentiated animal cells are totipotent-> nuclear transplant experiments, one cell induced to produce all cell types. Stem cells- undifferentiated, rapidly dividing cells in clusters in plant meristems. Multipotent stem cells- in mammals, in most tissues (especially frequent replacement- skin, blood) Pluripotent cells in blastocyst embryonic stage-> ability to form all cells in body. Cytoplasmic segregation- asymmetrical distribution of cytoplasmic factors in the cell. Cytoplasmic determinants- transcription factors that promote differential gene expression. Polarity- having a top (animal pole) and bottom (vegetal pole) Transcriptional controls-> controls of gene expression in differentiation. All cells have same dna, differentiated cells have different mrnas. Cells influence one another"s fates through chemical signals and pathways.
