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BIOL 202 > Lecture 29 > Flashcards

Lecture 29 Flashcards

1
Q

general development of drosophila

A

within 1 day becomes multicellular, then at 9 days become full drosophila

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2
Q

describe 2 stages of cell division of drosophila

A
  1. NUCLEAR DIVISION
  2. CELLULARIZATION
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3
Q

what happens during drosophila nuclear division?

A

replicate DNA and divide many many times, then nuclei migrate to PM

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4
Q

what happens during drosophila cellularization?

A

individual nuclei are enclosed in PM to form cells

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5
Q

describe the genes used in drosophila development

A

at beginning: only using mRNA from mother (cytoplasmic inheritance) so there is no transcription

later: transcription of embryo’s own mRNA (mendelian inheritance)

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6
Q

2h to 10h to adult stages of drosophila

A

2h: embryo has defined anterior, posterior, back, and front regions

10h: body divided into 14 segments

adult: each segment forms specific structures

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7
Q

what was the heidelberg screen?

A

forward genetic screen to identify genes required for Drosophila embryo organization

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8
Q

2 types of genes investigated in heidelberg screen?

A
  1. maternal genes
  2. zygotic genes
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9
Q

what is the purpose of the screen for maternal genes?

A

find the mutations in the mother that prevent her offspring from completing embryonic development –> i.e. what mRNAs from cytoplasmic inheritance are required for development?

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10
Q

what are maternal-effect genes?

A

genes whose phenotype are determined by maternal genotype

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11
Q

experiment to find maternal-effect genes

A

paternal genotype doesn’t matter: if it carries mutation, offspring are normal

only maternal genotype matters: if it carries mutation, offspring are mutant

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12
Q

what is the purpose of the screen for zygotic genes?

A

find the genes from embryo that are required for embryonic development

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13
Q

what is drosophila development regulated by?

A

cascade of TFs that turn on genes

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14
Q

5 genes involved in drosophila development

A
  1. egg-polarity genes (maternal-effect genes)
  2. gap genes
  3. pair-rule genes
  4. segment-polarity genes
  5. homeotic genes
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15
Q

what is the role of the maternal-effect genes?

A

establish anterior-posterior axis

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16
Q

2 maternal-effect genes

A
  1. Bicoid
  2. Nanos
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17
Q

what is the role of bicoid?

A

form anterior axis

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18
Q

bicoid mutants

A

lack anterior structures (head, thoracic segments)

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19
Q

how does bicoid work?

A

concentration gradient: high [bicoid] at anterior end, low [bicoid] at posterior end

tells nucleus how far cell is from the front of organism

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20
Q

how is the bicoid concentration gradient formed? (3 steps)

A
  1. bicoid mRNA from mother localizes at anterior of embryo
  2. bicoid protein translated at anterior
  3. bicoid protein diffuses toward posterior
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21
Q

bicoid is _______ and ________ to form anterior structures

A

bicoid is REQUIRED and SUFFICIENT to form anterior structures

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22
Q

how do we know that bicoid is sufficient to form anterior structures?

A

inject bicoid mRNA –> anterior structures form

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23
Q

what is the role of nanos?

A

form posterior structures

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24
Q

what happens to nanos mutants?

A

lack posterior abdominal structures

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25
Q

how is the nanos concentration gradient formed?

A
  1. nanos mRNA from mother localizes at posterior of embryo
  2. nanos protein translated at posterior
  3. nanos protein diffuses towards anterior
26
Q

role of nanos

A

inhibits translation of maternal HUNCHBACK mRNA

27
Q

where is hunchback mRNA localized?

A

uniformly-spread thru embryo

28
Q

describe the inhibition of hunchback by nanos

A

nanos is found in high [ ] at posterior and low [ ] at anterior –> since hunchback is uniformly-distributed, it gets inhibited by nanos so there is low [hunchback] at posterior and high [ ] at anterior

29
Q

what is the role of gap genes?

A

translate maternal anterior-posterior gradients into subdomains

30
Q

what is an example of a gap gene?

A

hunchback

31
Q

how many gap genes are there? what type of proteins do they encode?

A

9

all encode TFs

32
Q

what regulates gap genes? how?

A

regulated by maternal-effect genes, TRANSCRIPTIONALLY

33
Q

what happens to gap gene mutants?

A

large gaps in the body due to loss of several consecutive segments

34
Q

how does bicoid affect hunchback transcription?

A

hunchback promoter has 3 bicoid binding sites to activate hunchback expression at anterior (where there’s high [bicoid])

35
Q

role of pair-rule genes?

A

make 7 pairs of segments –> make 14 segments

36
Q

what happens to pair-rule gene mutants?

A

absence of every other segment

37
Q

how many pair-rule genes are there? what type of proteins are they?

A

8

all TFs

38
Q

how are pair-rule genes expressed?

A

each gene is expressed in 7 stripes (stripes at diff positions depending on gene)

39
Q

2 examples of pair-rule genes?

A

Eve and Ftz

40
Q

what happens if you mutate Eve

A

7 stripes will be lost, but not the other stripes in each pair bc those are determined by Ftz

41
Q

what does Eve mean?

A

Even-skipped

42
Q

what regulates pair-rule gene expression?

A

maternal effect and gap genes

43
Q

in Eve stripe 2, what is the relative expression of hunchback, bicoid, and two gap genes (giant and kruppel)?

A

high expression of Eve

since at anterior, high [hunchback] and medium [bicoid]

low [giant and kruppel]

44
Q

describe the activation of eve in specific stripes

A

eve gene has different enhancers to regulate eve expression in diff stripes (ex. stripe 2 has its own enhancer, stripe 3,7 share an enhancer, stripe 4,6 share an enhancer, etc.)

each enhancer has diff arrangements of binding sites for maternal-effect and gap genes to regulate expression

45
Q

which genes are eve activators? how many binding sites do they each have?

A

bicoid - 5 binding sites
hunchback - 1 binding site

46
Q

which genes are eve repressors? how many binding sites do they each have?

A

kruppel - 3 binding sites
giant - 3 binding sites

47
Q

when are segment-polarity genes expressed?

A

once cellularization has occurred

48
Q

what is the purpose of segment-polarity genes? (2)

A

to encode components of cell-cell signaling pathways (Hedgehog and Wingless) and define anterior/posterior within each segment

49
Q

3 examples of proteins encoded by segment-polarity genes?

A
  1. secreted proteins
  2. membrane receptors
  3. TFs
50
Q

what genes control segment polarity genes?

A

pair-rule genes

51
Q

what happens to segment polarity gene mutants?

A

half of each segment is mirrored (lose defined anterior vs posterior)

52
Q

what is the purpose of homeotic genes?

A

determine the function of each stripe

53
Q

what happens to homeotic gene mutants?

A

drosophila lack a certain structure which is replaced by another structure normally found on other body segments –> HOMEOTIC TRANSFORMATION

54
Q

2 examples of homeotic mutants

A
  1. Ultrabithorax - second thorax and set of wings
  2. Antennapedia - leg instead of antenna
55
Q

what are the homeotic genes called?

A

hox genes

56
Q

how many hox genes are there?

A

8

57
Q

what do hox genes encode?

A

homeo-domain family TFs

58
Q

where are hox genes expressed?

A

expressed in specific segments and there is some overlap btwn segments

59
Q

what control hox gene expression?

A

gap gene and pair-rule gene products

60
Q
A

BIOL 202 (29 decks)

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