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BIO230 > Development of multicellular organisms > Flashcards

Development of multicellular organisms Flashcards

1
Q

multicellular development requires

A
  1. morphogenesis- generation of tissue shapes that form organ and bodies
  2. cell differentiation- generation of different cell types in tissues
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2
Q

epidermis composition

A
  • epithelial tissue of the skin
  • keratinized squames
  • stem cells –> granular and prickle cell layers
  • basal cell layer
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3
Q

dermis composition

A
  • connective tissue of the skin
  • basal lamina (specialized ECM)
  • connective tissue of the dermis
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4
Q

embryogenesis

A

starts at fertilization and ends before birth

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5
Q

animal embryogenesis begins with

A

the blastocyst

- undergoes minimal morphogenesis and cell differentiation

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6
Q

morphogenesis requires

A
  • internalization of cells
  • elongation of the embryo
  • fine re-positioning of the cells
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7
Q

internalization of cells

A
  • happens during gastrulation (formation of gut tube)
  • cells start crawling over the inner surface
  • endoderm beginning to invaginate
  • cavity formation
  • future mouth and anus formed
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8
Q

mechanisms of cell internalization

A
  1. ingression/delamination
    - individual cells separate from the early outer epithelium
    - epithelial to mesenchymal transition (EMT- specialized to less specialized)
    - EMT are dangerous during cancer progression
  2. invagination/involution
    - intact epithelial sheets move inside the embryo
    - microtubules elongate, causing cells to become columnar
    - apical actin-filament bundles contract, narrowing the cells at their apices
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9
Q

mechanisms of embryo elongation

A
  1. convergent extension
    - converge towards center and elongate lengthwise
  2. cell division and cell shape change
    - orientation regulated by the orientation of cellulose microfibrils and driven by turgor pressure
    - vertical orientation stops cells from growing vertically (short + wide)
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10
Q

mechanisms of cell positioning

A
  1. migration of the whole cell
    - later born neurons migrate to higher cortical layers
  2. migration of a cell extension
    - attractant (netrin) binds to growth cone expressing receptor (DCC) on a commissural neuron
    - growth cone expressing receptor (Roundabout, decreases netrin responsiveness and repels growth cone) for slit and semaphorin repellents
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11
Q

main mechanisms of cell differentiation

A

asymmetric- sister cells born different

symmetric- sister cells become different as result of environmental influences

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12
Q

asymmetric cell division

A
  • partitions cell fate determinants to define the germline and other tissues
  • requires asymmetric determinants and proper spindle alignment
  • incorrect spindle alignment –> symmetrical cell division
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13
Q

extrinsic mechanisms of cell differentiation

A
  1. direct lateral inhibition
    - cells begin equal, cells that gain an advantage differentiate and inhibit their neighbours from differentiating
    - Notch signalling
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14
Q

three general rules for cell regeneration

A
  1. some tissues contain the same cells for the life of the organism, but the molecular components turn over
    - typically cells with very specialized architecture
  2. other tissues renew their cells rapidly
    - typically cells exposed to harsh environments or activities
  3. other tissues are between these extremes
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15
Q

specialized architecture of auditory hair cells in the organ of Corti

A

see lec 6 slide 3

  • supporting cell
  • outer hair cells
  • tectorial membrane (mass of ECM)
  • stereocilia
  • inner hair cells
  • basilar membrane
  • nerve fibers
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16
Q

how the stereocilia work

A

1 hair cell : 4 stereocilia

  • one stereocilia touches the membrane
  • sound causes vibration causing the stereocilia to tilt
  • tethers pull open ion channels on neighbouring stereocilia initiating a nerve impulse
17
Q

pulse-chase experiment

A
  • cells exposed to a radiolabeled leucine for a short time
  • take up labeled AA and incorporate it into newly synthesized proteins for a short period of time
  • leucine is detected but will gradually be lost (destroyed by pigment cells)
18
Q

stem cell

A
  • not terminally differentiated
  • can divide without limit
  • daughters can remain a stem cell or differentiate
19
Q

stem cell mechanisms

A
  1. controlling fates of stem cell daughters
  2. dividing slowly for long term preservation
  3. supported by local environment (their niche)
20
Q

controlling fates of stem cell daughters

A
  1. divisional asymmetry
    - one daughter receives factors promoting stemness and the other promoting differentiation
    - drawback: lost stem cells cannot be restored
  2. environmental asymmetry
    - environment promotes either stemness or differentiation
    - stem cell numbers can be increased by having both daughters enter the environment promoting stemness
21
Q

stem cells divide slowly for their LT preservation

A

protects the cell from

  • mutations associated with cell division
  • telomere depletion associated with cell division

large numbers of cells are needed to renew differentiated cell populations

  • one cell kept safe
  • one cell changes to a transit amplifying cell
22
Q

stem cells are supported by a local environment

A

in skin cells, the basal lamina provides a niche for the stem cells
- after detaching from the basal lamina, the cells differentiate through a linear sequence of cell types

23
Q

identifying blood stem cells and progeny

A
  • cells separated by arbitrary differences (i.e. cell surface markers)
  • the population that saves the mouse has stem cell activity

OR

  • homogenize mouse bone marrow to release single cells
  • expose to fluorescent antivodies recognizing specific cell surface molecules
  • isolate using Fluorescence-Activated Cell Sorting
  • isotonic fluid is made to be -ve
  • negatively charged cell = fluorescence; positive = no fluorescence
24
Q

how are blood stem cells maintained

A

through itneractions with stromal cells in the bone marrow

- stromal cell provides a niche for the blood stem cells

25
Q

medical uses of stem cells

A
  • blood stem cells to treat leukemia

IF IMMUNE REJECTION HAPPENS

  • careful tissue matching and immunosuppressive drugs used
  • patient’s own stem cells can be used after sorting if a cancer arises
26
Q

can cells of a different tissue be used to make stem cells for treatment

A
  • done in experiments, not for humans

- could avoid immune rejection but cancer development is a problem should cell differentiation go out of control

27
Q

ways to avoid immune rejection of ES cells

A
  1. somatic cell nuclear transfer- use a nucleus from one of the patient’s own cells and transfer it into an unfertilized egg to develop an embryo to harvest ES cells
  2. treat some of the patient’s own cells with factors that generate ES cells –> oct3/4, Sox2, Myc and Klf4 (TFs) can convert differentiated cells into cells with ES characteristics

BIO230 (4 decks)

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