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LIFE114 Developmental Biology > Mechanisms of Development > Flashcards

Mechanisms of Development Flashcards

1
Q

What are the two different ways in which cytoplasmic components may separate during cell division?

A

Asymmetrically and symmetrically.

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2
Q

Describe how pre-implantation genetic diagnosis (PGD) works?

A

One cell is removed for genotyping, if it is normal then the rest of the embryo is transferred to the uterus for normal development.

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3
Q

At what stage does compaction occur?

A

8 cell stage, transforms us from behaving like single-celled organisms to metazoan.

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4
Q

What follows compaction?

A

The first differentiation event - cells on the surface of the embryo become TROPHECTODERM CELLS, a form of epithelium.

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5
Q

What does compaction lead to the fomation of?

A

The blastocyst, which is what implants into the wall of the uterus.

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6
Q

What is a blastocyst made up of?

A

Trophectodermal cells and the inner cell mass.

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7
Q

What do trophectodermal cells eventually become?

A

The placenta.

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8
Q

What does the inner cell mass become?

A

The growing child.

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9
Q

Compaction involves cell adhesion. Which CAM is necessary for this?

A

E-cadherin.

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10
Q

How does E-cadherin bind cells together?

A

E-cadherin on one cell binds to e-cadherin on another - these are trans-membrane proteins and exist across the cell membrane.

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11
Q

What does e-cadherin bind to inside cells?

A

E-cadherin binds to beta-catenin inside cells.

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12
Q

What are the two roles of beta-catenin within cells?

A

Beta-catenin binds to the actin cytoskeleton (aids cell structure and polarisation).
Beta-catenin is a part of a signalling pathway; binds to TCF/LEF and this complex acts as a transcription factor, regulates gene expression.

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13
Q

Name the three ways in which signals are passed between cells.

A

Diffusion through the inter-cellular space.
Direct cell-cell contact.
Passage through inter-cellular junctions.

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14
Q

Signals from one cell can induce changes in adjacent cell populations - for example, how is this useful in C.elegans?

A

The Anchor cell instructs a program of development in the underlying vulval cells in C. elegans.

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15
Q

Describe how vulval development occurs in C. elegans.

A

Anchor cell (Ac) expresses LIN-3. LIN-3 induces vulval precursor cells (VPCs) at close range, which adopt 1/2/3 degree fates. VPC closest to anchor cells signals to 2 degree cells instructing them NOT to generate the CENTRAL VULVAL LINEAGES - lateral inhibition. Only VPCs in a position to recieve info will become vulval cells (1 and 2) - 6 VPCs.

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16
Q

What determines if a cell will respond to signalling?

A

Molecular composition.

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17
Q

Define competence.

A

An actively acquired condition which may change over time - it is NOT a passive state within the cell.

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18
Q

Give an example of a gene that acts as a ‘master’ competence factor.

A

Pax6 - mutations in Pax6 cause aniridia (partial or complete loss of the iris).

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19
Q

What does over expression of eyeless (or the human orthologue Pax6) result in?

A

Ectopic eyes that are morphologically normal.

20
Q

What is Pax6, essentially?

A

A transcription factor that changes patterns of gene expression, providing the conditions for cells to respond to various inducers of eye morphogenesis.

21
Q

What is the term used to describe the facets found in compound fly eyes?

A

Ommatidia

22
Q

What does a stereotypical facet within a fly eye consist of?

A 
Core of 8 photoreceptor cells (R1-R8)
4 cone cells
Pigment cells
1 sensory bristle
The number of cells/their identities/functions within each ommatidia is invariant.
23
Q

Which cell is responsible for the series of inductive steps used to specify the cells of the ommatidium?

A

The R8 cell.

24
Q

How do the cells R1-7 become specified within the ommatidium, in relation to R8?

A

R7 - cell-cell contact with R8.

R1-R6 - diffusable signals from R8.

25
Q

Which signal is LIN-3 from C. elegans evolutionarily related to in Drosophila?

A

Evolutionarily related to Boss - both encode proteins related to mammalian epidermal growth factor (EGF).

26
Q

How does cell-cell signalling influence patterning within C.elegans eyes?

A

R8 cell prevents its neighbours from becoming R8 cells by secreting an inhibitory molecule, limiting R8 cell fate to one cell - LATERAL INHIBITION.

27
Q

Where does ommatidia formation start?

A

In the morphogenetic furrow. Behind this, cells differentiate to become regularly spaced ommatidia.

28
Q

What does the ‘French Flag Model’ of cell positioning suggest?

A

Explains how identical cells can adopt a pattern irrespective of how many there are. Relies upon ability of diffusible substances to induce different EFFECTS at different CONCENTRATIONS.

29
Q

What type of molecule provides positional information?

A

Morphogens

30
Q

What must a substance be capable of to be classed as a morphogen?

A

Capable of directly activating cells at a DISTANCE, and must produce CONCENTRATION-DEPENDENT responses in receptive cells.

31
Q

Define INDUCTION.

A

Instructive cell interaction between adjacent cell populations (often in contact, usually produces a few responses).

32
Q

Define COMPETENCE.

A

Ability to respond to a specific inductive signal.

33
Q

Why is LATERAL INHIBITION important in development?

A

Can give rise to spacing patterns when cells produce an inhibitor that prevents formation of similar structures in area adjacent to them.

34
Q

Why are SPATIAL SIGNALS important in development?

A

Act over a LONG SPATIAL RANGE, inducer/responder aren’t always in contact, effect of inducer depends on its concentration.

35
Q

What accounts for the diversity of different cell types?

A

Not all genes expressed in every cell - subsets of genes that are expressed (RNA/protein) will differ, subset expressed confers unique properties to the cell.

36
Q

How many protein coding genes are there in the human genome?

A

23,000

37
Q

How does regulation of gene expression control heterogeneity?

A

Determines which genes are expressed where, when and at what level - they in turn determine cell function.

38
Q

What can lead to ‘hidden’ diversity in proteins?

A

Alternative splicing - can generate many different isoforms, creating a large potential for heterogeneity.

39
Q

Is it exons or introns that encode proteins?

A

Exons; introns are removed in the primary transcript.

40
Q

How many different isoforms can a single gene make?

A

Up to 28,016 (minor differences)

41
Q

What is responsible for transcriptional regulation?

A

DNA-binding proteins - bind DNA in sequence specific manner, act as transcriptional activators and repressors.

42
Q

What are enhancer elements required for?

A

Gene expression.

43
Q

What are enhancer elements bound by?

A

Bound by more than one transcription factor.

44
Q

Why is a single transcription factor able to induce expression of many genes?

A

Many (often functionally related genes) share the same REGULATORY SEQUENCES.

45
Q

What are homeotic gene?

A

Master control genes that confer identity to individual segments of an organism.

LIFE114 Developmental Biology (5 decks)

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