Body Plans Development Flashcards
What is morphogenesis
Process by which an organism or structure develops into a 3D form (like in embryogenesis)
Name the 3 axes of an embryo body plan
Antero posterior - head (anterior) to tail (posterior)
Dorso ventral - dorsal (back) to ventral (belly)
Left- right axis - 2 lateral sides of embryo
Where is the neural tube located
At the dorsal side (back)
What has to occur for body plans to develop
Cell distance into a blastocyst from an embryo
What 2 cells present in blastocysts
Trophoblast - cells for structure support
Embryoblast - cells that form embryo
What determines type of signalling and how readily it binds to receptors in cell signalling during development
Genes the embryo possesses
What are morphogens
Growth factors that control the position of cell types
They repress or induce gene expression depending on concentration
Give major examples of morphogens
SHH (hedgehog signal)
Wnt
RA (retanoic acid)
How does morphogens from source to sink change to induce different gene expression
Source = most morphogen and then it diffuses in lower conc. the lower conc areas might have different genes expressed
Which protein morphogen in flies is famous for activating transcription of ANTERIOR STRUCTURES
Bicoid protein
Which morphogen in flies opposes bicoid in antero posterior polarity by suppressing translation closer to ANTERIOR
Nanos
Why is diffusion of morphogens easier in flies
Due to it being one egg and not having to go through cellularised tissue
How do homeobox genes use morphogens to switch on genes at different areas
Morphogen concentration eg high could allow gene expression at anterior
At low conc it allows gene expression at posterior
Name the 4 ways morphogenic signals pass cellular tissues
1- restricted diffusion model
2- planar transcytosis model
3- lipoprotein transfer model
3- cytoneme model
Explain the restricted diffusion model of how morphogens can diffuse
They can bind to carbohydrates on the cell surface when secreted and diffuse along the surfaces of cells
Explain planar transcytosis
Morphogens pass directly via cytoplasm of cells across
Explain lipoprotein morphogen transfer
When secreted lipoproteins can bind and allow movement across cell surface down gradient
Explain cytoneme model of morphogen diffusion
Morphogens using cytonemes (cell extensions) to move long distances
Name the 2 sources of morphogens in embryo (where they are high in conc) and what they form
1- AVE: anterior visceral endoderm - morphogens used to produce anterior end
2- the NODE - patterns the whole of the embryo including the anterior in sync with AVE
How do the node and the anterior visceral endoderm (AVE) have large conc of morphogens
That’s where the cells that release them are located
What can disruption of sources such as the Node have on the embryo (give SHH as example)
Can affect body plan of the embryo due to no gene expression in areas
Eg if disruption to shh the embryo can develop with no eyes or tail
What side in left right axis formation undergoes cell signalling through morphogens
Left side
How is the node important for left right asymmetry
Node releases morphogens such as RA and SHH which are wafted to left side of body to activate gene expression to form eg organ tissues
How are morphogens directed in left right axis formation
Cilia on node cells waft to left side to get more gene expression
What are PITX homeobox genes for
Development of organs and skeletal muscle
Which morphogen on the left side is activated by node morphogen release on left side
Nodal TGF morphogen
What does nodal tgf morphogen do when activated by node morphogens on left side
Activate pitX genes which allow for organ development
How does dosage of pitX allow for organ asymmetry in the body
Higher conc areas will have different genes meaning different organs formed to low conc areas
What in left right axial formation prevents signalling morphogens on right side
SHH sonic hedgehog
What would happen if nodal signalling was on the right side
Organs would be reversed
What would happen if nodal signalling was on both sides
There would be 2 left sides (left isomerism)
What would happen if nodal signalling happened on neither side of body
Right isomerism (2 right sides of the body)
How were frogs manipulated to see the effects of left right axis formation and signalling in embryo
Frog was dissected and the part where the node was was taken out and transplanted into another frog
It was rotated by 180• and this showed organs reversed in the frog embryo
= shows structure and orientation is dependant on nodal signalling
Which gene knockout meant that instead of asymmetrical lung lobes, mice had 2 left lobes (left isomerism)
Lefty 1 / SHH gene - important for left side cell signalling (stops signalling on right) as pitX was found on both sides of lungs when it was knocked out = left isomerism
Which genes famously are related to antero posterior axial formation
Hox genes / homeobox genes - found laterally across the human body aswell as flies (head to tail)
Name the 3 main morphogens which affect homeobox genes in anterior posterior axes
Wnt - specific to anterior gene expression
RA(retanoic acid) - mid brain gene expression
FGF - caudal / tail region
What would happen if hox 6 genes where ribs are were expresssed at the tail for example eg due to disruption on morphogen signalling
Ribs would grow at the tail
Which morphogen is in high conc at dorsal region (back)
Wnt
Which morphogen is at the ventral region at high conc
SHH
What does sHH and wnt polarity in dorsal ventral axial formation cause
Different genes expressed which specify different neurones in the brain
By activating different homeobox genes
What is the proximal and distal axis in terms of limbs such as the arms
Proximal is shoulder
Distal is the digits
What is the anterior and posterior axis in the limbs
Anterior is what makes pinky distinct from posterior thumb
Apart from proximal and distal and posterior and anterior in limbs, what other 2 axis are there
Front or back of the hand which is distinct
Left or right hand axis
Which morphogens are important in proximal and distal axis from shoulder to digits
RA and FGF
Which place on the limb has the most RA and the least FGF
Most RA = shoulder
Least FGF = shoulder
(Most FGF in digits)
What type of genes do RA and FGF in the limbs affect expression of
Hox genes in the limbs
Which centre is important for outgrowth of the limbs
Apical ectodermal ridge (AER)
What happens if the apical ectodermal ridge is removed or duplicated
If removed no limb is grown
If duplicated it causes limb duplication
What doesn’t the apical ectodermal ridge determine
Which limb is grown
What is the most important morphogen in limb outgrowth
FGF (highest in the digits)
Which morphogen is important in anterior posterior axis of the limbs (pinky to thumb) patterning
SHH
Where is shh highest and lowest in the anterior posterior of the limb
Highest in the anterior (pinky)
Lowest in the posterior (thumb)
Which centre is SHH on at the posterior of the limb
Zone of polarising activity (zpa)
How does thalidomide alter the expression of morphogens like FGF and SHH
By disrupting the apical ectodermal ridge
And zone of polarising activity (zpa)
How else apart form disrupting the AER and ZPA does thalidomide disregulate SHH and FGF signalling
By degradation of the transcription factor called sall4
