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bio 333- developmental biology > lec 10- segmentation in Drosophila > Flashcards

lec 10- segmentation in Drosophila Flashcards

1
Q

what genes do gap genes activate?

A

pair-rule genes

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2
Q

what do pair-rule genes define?

A

para segments

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3
Q

what do the segmentation genes define?

A

segments into the developing embryo

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4
Q

what are pair-rule genes?

A

transcription factors

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5
Q

what do pair rule genes divide the embryo into?

A

repeated stripes just before cellularization

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6
Q

how many bands does one pair-rule gene have?

A

7

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7
Q

what are the two pair rule genes that create the 14 parasegments in the embryo?

A

even-skipped and fushi tarazu

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8
Q

after the parasegments are formed, what occurs?

A

segmentation, pair rule genes activate the transcription of segmentation genes

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9
Q

what are parasegments?

A

repeating units that form along the AP axis, and are also offset from segments

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10
Q

what does the anterior region of a parasegment line up with?

A

with the posterior region of one segment and the anterior of the next

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11
Q

does the segmentation pattern carry over into the fly?

A

yes, resulting in the development of specific appendages like wings or legs which develop on specific segments only

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12
Q

how is each stripe of a pair rule gene regulated?

A

by different combinations of maternal effect and gap genes

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13
Q

how are pair rule stripes formed?

A

they form via a combination of gene product accumulation in the stripes and loss in the intervening regions

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14
Q

where are stripes established and how are the inter stripe regions made?

A

-they are established in areas where gene expression continues or is increased
-while in the inter stripe regions, gene expression is repressed and pre-existing gene products are degraded

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15
Q

how is the expression of even skipped regulated by bicoid, hunchback, giant, and kruppel?

A

-bicoid and hunchback activate the even skipped gene in a broad domain
-giant and kruppel are repressors which define the boundaries of the even skipped stripe

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16
Q

can giant and kruppel still repress a even skipped stripe when bicoid and hunchback are still present?

A

yes, they overtake

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17
Q

how are the anterior and posterior portions of the even skipped stripe determined?

A

-anterior is determined by the threshold concentration of giant gene
-posterior is determined by the threshold concentration of the kruppel gene

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18
Q

what do the regulatory regions of pair rule genes contain?

A

different modules

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19
Q

what does each module do?

A

controls gene expression in different regions of the embryo

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20
Q

what does each module have different combinations of binding sites for?

A

transcription factors

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21
Q

how is the positioning of the stripes determined?

A

by the binding of activators and repressors to module binding sites

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22
Q

how does gene expression occur with respect to activators?

A

it occurs when the number of activators are above a threshold concentration

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23
Q

how is transcription stopped with respect to repressors?

A

binding of repressors above a threshold level prevents transcription

24
Q

what does the ability of a gene to respond to threshold levels of a transcription factor depend on?

A

the presence of high and low affinity sites for proteins in that regulatory region

25
Q

what activates segmentation genes?

A

pair rule genes

26
Q

what happens during segmentation?

A

the positions of parasegment become fixed and the boundaries of the segments that are visible in the larval epidermis become established

27
Q

what are the bristles on the ventral epidermis called?

A

denticles

28
Q

do denticles occur in the posterior region?

A

no, only in the anterior as stripes

29
Q

what does the larval denticle pattern depend on?

A

the correct establishment and maintenance of the embryonic parasegment boundaries

30
Q

what due mutations in segmentation genes cause?

A

they alter the denticle pattern in larvae, an example of a mutation is hedgehog which loses the naked region of each segment

31
Q

what is a compartment?

A

a region in which all the cells are made up of descendants of cells that were present when the compartment was set up, no other cells present

32
Q

when parasegments are set up, what do the cells at the anterior form?

A

a compartment

33
Q

what do the cells in the parasegment compartment follow?

A

cell lineage restriction

34
Q

what is cell lineage restriction?

A

cells do not move across the boundary into adjacent parasegments

35
Q

what do the parasegment compartment cells express?

A

transcription factors called engrailed

36
Q

what activates the expression of engrailed?

A

fushi-tarazu and even skipped

37
Q

what does engrailed do?

A

changes the properties of cells so they do not mix with the cells of adjacent compartments and it confers a posterior segment identity

38
Q

are engrailed selector genes?

A

yes

39
Q

what is a selector gene?

A

a gene whose activity causes cells to adopt a particular fate

40
Q

to maintain the posterior character of segment, what must engrailed do?

A

be expressed throughout development

41
Q

which genes control the signals sent between cells that set up parasegment boundaries?

A

engrailed, hedgehog, wingless

42
Q

what are hedgehog and wingless genes?

A

secreted signalling molecules

43
Q

what establishes the expression of wingless and engrailed in cells?

A

pair rule genes

44
Q

what does engrailed activate the expression of ?

A

hedgehog

45
Q

where are the engrailed, hedgehog, and wingless genes located in a parasegment?

A

-engrailed and hedgehog is located at the anterior, engrailed is activated by fushi tarazu and even skipped
-wingless Is located at the posterior, activated by the expression of the pair rule gene sloppy paired and no fushi tarazu or even skipped is present

46
Q

what are the 4 steps to maintaining segmentation boundaries

A
  1. wingless protein is secreted from cells expressing wingless gene and it diffuses to neighbouring cells
  2. secreted wingless protein signals to the cells expressing engrailed and hedgehog, maintaining their expression in those cells
    3.the hedgehog protein is secreted, and diffuses to adjacent cells
  3. hedgehog signals maintain wingless expression in cells at the posterior of the adjacent parasegment
47
Q

what happens in the Wnt/B-catenin signalling pathway when no Wnt is present?

A
  1. B-catenin is bound by a destruction complex of proteins in the cytoplasm
  2. kinases in the complex phosphorylate B-catenin which targets it for degredation via the proteasome
  3. with no B-catenin in the nucleus, co-repressors bind to the transcription factors and prevent transcription
48
Q

what happens in the Wnt/B-catenin signalling pathway when Wnt is present?

A
  1. Wnt binds to the receptor frizzled and activates the pathway
  2. Dishevelled and kinases of the destruction complex are recruited to the receptors where they are prevented from forming B-catenin destruction complex
  3. B-catenin accumulates and enters the nucleus where it displaces the co-repressors and activates transcription of target genes
49
Q

what happens in the hedgehog signalling pathway when no hedgehog is present?

A
  1. Patched receptor inhibits Smoothened
  2. When Smoothened is inhibited, it binds to a complex of proteins that includes the transcription factor cubitus interruptus (Ci)
  3. Ci also forms a complex with another protein in the cytoplasm called suppressor of fused or Su(fu)
  4. Ci in the complex associated with Smoothened is phosphorylated by several protein kinases
  5. Phosphorylated Ci is cleaved forming a truncated protein that enters the nucleus and represses hedgehog target genes
50
Q

what happens in the hedgehog signalling pathway when hedgehog is present?

A
  1. The hedgehog receptor Patched no longer inhibits Smoothened
  2. Ci is released from both complexes
  3. it enters the nucleus and activates gene transcription
51
Q

what do the hedgehog signals maintain?

A

wingless expression in cells at the posterior

52
Q

what do wingless signals maintain?

A

engrailed and hedgehog, expression in cells at the anterior

53
Q

where is the expression of patched located?

A

on the cells adjacent to the ones that produce hedgehog and engrailed

54
Q

where is the expression for frizzled (the receptor for wingless) located?

A

in all the cells

55
Q

do the hedgehog and wingless signalling molecules diffuse from the cell and form gradients along the AP axis?

A

yes

56
Q

what does the gradient formed by hedgehog and wingless provide?

A

it provides cells with the signals they need to acquire their identities

57
Q

when the hedgehog, wingless, and engrailed protein signalling pathways are intact what happens? what happens when wingless is missing due to mutation?

A

-compartment boundary is established
-loss of parasegment boundary due to no expression of hedgehog or engrailed

bio 333- developmental biology (11 decks)

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