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Developmental, Stem Cell & Regenerative biology > Lecture 12 - Drosophila - setting up the body axis > Flashcards

Lecture 12 - Drosophila - setting up the body axis Flashcards

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1
Q

What parts of the body are formed through the development of the A/P axis?

A
  • a head, a tail, a thorax and abdominal region are formed
  • the thorax & abdomen are SEGMENTED
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2
Q

What 4 regions are formed through the development of D/V axis?

A
  • the ventral most mesoderm
  • the ventral ectoderm
  • dorsal ectoderm
  • aminoserosa (an extra embryonic tissue)
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3
Q

What is the initial expression of genes that result in the expression of GAP genes that define different regions in the embryo?

A

initial maternal gradient (maternal genes)

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4
Q

Where does the expression of maternal genes occur?

A

occurs in syncytium - multiple nucleus in one cytoplasm

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5
Q

What does the expression of GAP genes lead to?

A

GAP gene expression leads to the periodic expression of the Pair-Rule gene.

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6
Q

What do the GAP genes do?

A

divide the embryo

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7
Q

What does a mutation in GAP genes lead to?

A

loss of an area in embryo

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8
Q

What does the Pair-Rule gene do?

A
  • continue to refine the body - these specify the so called ‘para-segments’ and foreshadow segmentation of the larva
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9
Q

What follows the Pair-Rule gene?

A

the segmentation genes

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10
Q

What does the segmentation genes do?

A
  • elaborate patterning within each para-segment
  • patterning of these segments happens when the embryo has cellularised.
  • so cell-to-cell signaling is essential to coordinate this patterning process
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11
Q

What follows segmentation genes?

A

homeotic seletion genes

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12
Q

What do homeotic selector genes do?

A

determine segment identity

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13
Q

Where does the cascade (initiated by maternal genes) occur?

A

Occurs in syncytium - multiple nuclei in one cytoplasm (NOT IN THE ZYGOTE ITSELF)

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14
Q

Where are the maternal genes located?

A

mother - genes that need to be present in the genome of the mother to provide the initial information

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15
Q

How were initial mother genes identified?

A

identified by specially adapted genetic screens where homozygous mutant mothers were screened for defects in all their progeny

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16
Q

What are the 3 relatively independent classes of maternal genes that set up the A/P axis?

A
  • anterior
  • posterior
  • terminal system
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17
Q

How were the 3 classes of maternal genes defined?

A

these were defined by mutations that led to the corresponding defects either in anterior, posterior or terminal structures in the larva

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18
Q

A mutation in what gene leads to a defect in anterior?

A

Bicoid - an example of a MORPHOGEN

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19
Q

What is a morphogen?

A

a molecule that emanates (originates) from a specific region and is present in a concentration gradient.
- a morphogen should be able to induce more than one fate

20
Q

What type of gradient does Bicoid form?

A

a protein gradient across the A/P axis of the syncytial embryo

21
Q

Where is RNA of Bicoid localised in the egg?

A

at the anterior

22
Q

Where is Bicoid transcribed?

A

transcribed at the anterior and diffuses towards the posterior

23
Q

What is Bicoid?

A

GENE - transcription factor - switches on different genes at different THRESHOLD CONCENTRATIONS
- Bicoid can only function like a morphogen, because the egg is a syncytium
- UNUSUAL as a morphogen, as it is a transcription factor

24
Q

What gene acts on the anterior?

A

Bicoid

25
Q

What gene acts on the posterior?

A

Nanos

26
Q

What is the role of Nanos?

A
  • preventing Hunchback translation in the posterior of the egg
27
Q

Where does Nanos travel from?

A
  • from posterior to anterior (creating posterior gradient)
  • this create a lot of the anterior & posterior pattern
28
Q

What does the Torso signal do?

A

specifies the extreme ends of the egg

29
Q

Where is the Torso receptor present?

A

everywhere on the outside of the egg

30
Q

What binds to the Torso receptor?

A

Trunk protein

31
Q

What is required to release the ligand ‘Trunk Protein’, which is attached to the ‘Torso receptors’?

A

the protease ‘Torso-like’

32
Q

Where is the protease ‘Torso-like’ located?

A

only present at the poles - leading to torso activation only at the poles

33
Q

Describe the basic principles of cell-cell signalling

A
  • ligand can’t cross membrane
  • attaches to receptor
  • ligand changes structure (depending on signalling pathway)
  • activation of transcription factor
  • leads to action in cell
34
Q

What is the receptor on the outside of the egg that determines D/V polarity?

A

Toll

35
Q

What is the ligand that attaches to Toll, which is involved in creating D/V polarity?

A

Spatzle

36
Q

What is the localised enzyme which creates an active ligand on ventral side?

A

Pipe

37
Q

What is Dorsal?

A

a protein and transcription factor that moves into the nuclei on the ventral side (nuclear localisation)

38
Q

What side does ‘Dorsal’ the protein act on?

A

ventral
- high levels of Dorsal on ventral side
- low levels of Dorsal on dorsal side

39
Q

What does differing levels of Dorsal on the ventral & dorsal side create?

A

creates a gradient of the Dorsal protein in nuclei

40
Q

How is Dorsal activated?

A

via nuclear localisation

41
Q

Why is toll activated only on the ventral side?

A

Toll is activated on ventral side cos PIPE is only found on that side (pipe only on ventral side of egg)

42
Q

What is a summary of the creation of D/V polarity?

A

PIPE (enzyme) - only ventral side
Spatzle (ligand) - everywhere
Toll (receptor) - everywhere
Dorsal (protein) - nuclei on ventral side

Pipe activates spatzle which activates toll which activates Dorsal

43
Q

How does the polarity in the oocyte needed to form A/P axis come about?

A

polarity of the ovaries is somehow transmitted to the egg - this occurs through nuclear positioning.

the side where the nucleus is closer to, is the side where the dorsal side develops

44
Q

What is the one cell-cell singal that is required to set up BOTH anterio-posterior and dorso-ventral axes?

A

Gurken

45
Q

Where does Gurken come from?

A

nucleus

Developmental, Stem Cell & Regenerative biology (15 decks)

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