Asymmetric cell division

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The two strategies that become different from their neighbours
Induced to become different by their neighbours, or daughter cells are born different
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Define induction
The process by which a signal from one cell or group of cells influences the development of another cell or group of cells
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An example of induction
The development of the optic vesicle induces the overlying ectoderm to differentiate and form the lens placode
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Another example of induction
the development of the ***** in C. elegans
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What is the ***** of C. elegans
The external reproductive organs in the hermaphrodite and connects with the uterus
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How many cells does it develop from, how many in the adult
develops from three cells out of 6 precursors, in the adult there is 22.
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Which three cells does it derive from, and what happens to the others?
P5-P7 form the *****. P3,4 and 8 form the epidermis.
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Explain how the ***** is induced.
A diffusible signal secreted from the anchor cell above p6. P5 and p7 percieve a lower concentration of diffusable signal and respond by adopting the secondary fate.
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How does p6 reinforce these cell fate descisions?
Direct cell-to-cell inhibition of it's neighbours.
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What is the result of lateral inhibiton. What is the protien and the receptor
It stops them from becoming p6 as well. The protien is a member of the notch family acting on Lin-12
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What is the anchor cell's secreted product?
The protein of the lin-3 gene. Which acts on the Let-23 gene
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What stops p3, p4 and 8 becoming *****?
inhibitory signals from the epidermis, and not enough signal from the anchor cell
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An example of long range induction
The spemann organiser induces neural tissue from the adjacent ectoderm
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An example of cell-to-cell diffusion induction
the retina secretes FGF to induce the lens, the anchor cell secretes epidermal growth factor like protien to induce p6
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Example of direct contact inducton
The delta protien on P6 binds to the notch protein on P5 and P7 to prevent them becoming P6 cells in the c.elegans *****.
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Define asymmetric cell division
the process by which one cell divides to give two daughters with differing identities or fates
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How does asymmetric cell division come about?
Unequal segregation of determinants and cytoplasic factors
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An example of cells that divide asymmetrically
Drosophila neuroblasts - the stem cells that develop neuronal cells in the drosophila CNS
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Describe asymmetric cell division in drosophila neuroblasts
a single neuroblast is specified in the neuroepithelum. it delaminates from the neuroectoderm, and divides assymetrically to give a NB and a smaller ganglion mother cell
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What happens to the NB then
it continues to divide in a stem cell manner.
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What happens to the GMC
It divides once to form two neurons
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What proteins segregate to the apical end of the NB
Bazooka (Par3), Par6, Atypical Protein Kinase C.
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What proteins are segregated to the basal end of the NB
Miranda, Prospero, Numb, Prospero mRNA
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How does the c.elegans zygote divide asymmetrically
creates a large anterior AB cell and a small posterior P cell, which has stem-cell like properties and generates the germ line
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How does it acheive this assymetric germ lineage
P granules segregate - they are teh cytoplasmic determinant of germ cell fate.
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What protein complexes form in the anterior>
Par3, Bazooka, Par6, aPKC.
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What proteins assemble in the posterior (the future germ cell)
Par1, par2.
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What is an important concept in asymmetric cell division
the orientation of the mitotic spindle.
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Another example of asymmetric division - and why they're a good model
The development of drosophila sensory organs, they have only our cells.
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What are the four cells?
1 hair cell, 1 socket cell, one sheath cell, 1 sensory neuron.
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Describe the asymmetric division from the sensory organ precursor
SOP into IIA and IIB. IIA into socket cell and hair cell. IIb into sheath cell and sensory neuron.
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What determines the fate of IIb and IIa
Numb protein localised at the cortex is asymmetrically segregated into IIb
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What is the function of Numb in IIb
antagonises signalling by the Notch protein, a cell surface receptor. So delta can't bind and effect cell fate choice
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Then what happens in IIa
Numb is resynthesised and, like IIb, the numb is segregated in one side.
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what do the numb containing cells form?
Hair cells (iia) and sensory neuron (iib)
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What happens if numb is not segregated
they all become sensory neurons
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What happens if numb is repressed
notch activity in all cells means they all become socket cells
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Where does asymmetric cell division happen in the mammalian cortex
in the proliferative ventricular zone, to form adult neural stem cells.
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What are the two protiens that get segregated in adult neural stem cells
numb and notch - numb posteriorly, notch anteriorly
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Card 2


Define induction


The process by which a signal from one cell or group of cells influences the development of another cell or group of cells

Card 3


An example of induction


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Card 4


Another example of induction


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Card 5


What is the ***** of C. elegans


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