Bevington 6 Phenotype & differentiation

Question 1

differentiate:

Answer 1

multi-cellular with the ability of the cells to differentiate into cells with specialised functions (tissue types and organs)

Question 2

Embryonic stem cells:

Answer 2

: cells at this stage can differentiate into many different fates or lineages

Question 3

Connective tissue cells:

Answer 3

Fibroblasts

Question 4

Embryogenesis

Answer 4

in Eumetazoa “true animals”
Zygote
Blastula
Blastocoel

Question 5

Transit Amplifying Cells

Answer 5

Serve as an Intermediate Step Between Stem Cells & Terminally Differentiated: daughters committed to differentiation, limited series of more rapid divisions before completing process.

Question 6

Terminal differentiation

Answer 6

Many highly differentiated human cell types (e.g. neurones & skeletal muscle) cells are arrested in terminally differentiated state “G0” i.e. effectively stuck at the start of G1

Question 7

Limb regeneration:

Answer 7

in the salamander Ambystoma mexicanum (the axolotl).
• Amputation without scarring
• Full regeneration of the limb occurs
= BUR full regeneration occurs through LIMITED dedifferentiation of cells to form progenitor cells NOT from utilisation of resident stem cells

Question 8

Determining phenotype:

Answer 8

• Depend on the muscle cell’s environment (i.e the fact that it’s surrounded by other muscle cells in a muscle)? de-differentiate into a poorly defined fibroblast-like cell
• OR
• set of genes that is expressed (or not expressed) in a particular cell (or the the intensity of their expression) “locked” in some way? “committed” in some way to muscle lineage
• BOTH

Question 9

Myotubes

Answer 9

synthetic muscle cells
occasionally “twitch” but do not differentiate into fully developed muscle
Limited Differentiation/ De-differentition
Even in vivo the phenotype of an animal cell is not constant
Skin fibroblasts

Question 10

Environment of cells affects differentiation

x2

Answer 10

1 Soluble “factors”:
• Vitamin derivatives (e.g. Retinoic acid)
• Hormones (e.g. Insulin)
• Cytokine proteins released from other cells (e.g. Interleukins)
2 Extracellular matrix

Question 11

Cellular PHENOTYPE:

Answer 11

conglomerate of multiple cellular processes involving gene & protein expression results in elaboration of cell’s particular morphology & function

• Genome
• Transcriptome
• Proteome

Question 12

COMMITMENT to cell lineage

Answer 12

1) Genetic mutation of somatic cells
- Somatic Hypermutation
- Activation-induced deaminase (AID)
2) Epigenetics
- Methylation of Cytosine bases in the DNA double helix.

Question 13

Somatic Hypermutation:

Genetic mutation of somatic cells

Answer 13

Rapid Mutation of DNA Nucleotide Sequences in B Lymphocytes => Novel Antigen Recognition Sites Variable (V) Regions of Antibody Proteins (Immunoglobulins)
Each clone of B cells has differentiated to produce only one mutant variant of an antibody protein molecule.

Question 14

Activation-induced deaminase (AID) :

Genetic mutation of somatic cells

Answer 14

subsequent repair of the DNA as in Cell Biology Lecture 4) drives the process of mutation

Question 15

Methylation of Cytosine bases in the DNA double helix.

Epigenetics

Answer 15

Vertebrates: only occurs on certain cytosines in sequence CG.
& other mechanisms, strongly represses expression of certain genes => passed on to progeny cells

Question 16

Nucleosomes

Answer 16

DNA in chromatin packaged in units
DNA double helix wrapped around core of histone proteins
Multi-cellular eukaryotic organisms: “memory” of a cell’s differentiation state (i.e the set of genes that can be read and expressed), depends in part on the structure of the histones on which the DNA is packaged

Question 17

Example of

BACTERIA DIFFERENTIATION

Answer 17

Caulobacter crescentus, a Gram-negative bacterium that is used as a model organism owing to its unusually complex developmental cycle