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Cell and Developmental biology > Patterning invertebrate embryos > Flashcards

Patterning invertebrate embryos Flashcards

1
Q

How do you identify genes involved in the developmental process?

A

use of forward genetics
mutation > gene > protein > function
use of mutagenesis to create random mutations in the genome
inbreed the mutant gemone
use phenotype analysis to find the function of the gene
clone the gene to find molcule identity
analyse the function of the gene product

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2
Q

what are the cleavage divisions of drosophila (30, 70, 90, 2hrs, 3hrs

A

30 - fusion of sperm and egg nuclei
70 - nuclear division creating the synctium
90 - nuclei migrate to the periphery of cytoplasm
2 hrs - synctial blastoderm forms
3hrs - cellular blastoderm forms

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3
Q

how do you recognise the anterior end of a drosophila egg?

A

micropyle - a nipple shaped sturcture in the tough external coat surrounding the egg

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4
Q

where do sperm enter the drosphila egg?

A

the micropyle

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5
Q

what occurs after fertilisation and fusion of nuclei in drosophila?

A

a series of mitotic divisions

no cleavage of cytoplasm and no formation of cell membrane to separate nuclei

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6
Q

what forms after 12 nuclear division in drosophila development?

A

formation of the synctium, approx 6000 nuclei present in the cytoplasm

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7
Q

what does formation of the synctium in drosophila allow?

A

allows large molecules to to diffuse between nuclei during the first 3hrs of development

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8
Q

what happens at synctial stage of drosphila?

A

small no of nuclei move to the posterior end and become surrounded by the cell membrane to form pole cells

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9
Q

What do pole cells in drosophila do?

A

pole cells give rise to germ cells from which gametes develop

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10
Q

what happens after 9 nuclear divisions in drosophila?

A

nuclei move to the periphery to form the synctial blastoderm

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11
Q

what is the synctial blastoderm in drosophila development?

A

a superficial layer of nuclei and cytoplasm which surrounds a central mass of yolky cytoplasm, membranes grow in from the surface to enclose the nuclei and form cells

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12
Q

what does the blastoderm in drosophila give rise to?

A

somatic cells of the embryo

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13
Q

what are the three germ layers?

A

ectoderm, endoderm, mesoderm

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14
Q

where is the mesoderm located in drosophila?

A

in the ventral region

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15
Q

what is the future midgut derived from in drosophila?

A

2 regions of the prospective endoderm

1 at anterior and one at posterior end of the embryo

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16
Q

when do drosophila endodermal and mesodermal tissues move to their future positions?

A

during gastrulation, this leaves the ectoderm as the outer layer

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17
Q

when does gastrulation start in drosophila?

A

3hrs after fertilisation

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18
Q

how is the the future mesoderm of drosophila formed?
how is it internalised?
what does it eventually give rise to?

A

at ventral region it invaginates to form a furrow along the ventral midline
internalised by formation of a mesoderm tube where the cells separate from the surface layer of the tube and migrate under the ectoderm to internal locations
later gives rise to muscle and other connective tissues

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19
Q

what does each germ layer become?

A

a unit of lineage, once cells have been specified to one fate they all of its descendants will adopt this fate

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20
Q

where in insects does the main nerve chord lie?

A

ventrally

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21
Q

in drosohila after the invagination of the mesoderm, what is formed?

A

the nervous system

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22
Q

how is the nervous system of drosophila formed?

A

ectodermal cells in the ventral region leave the surface individually and form a layer of prospective neural cells between the mesoderm and the outer ectoderm

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23
Q

how and when is the gut formed in drosophila?

A

at the same time as nervous system formation , 2 tubular invaginations develop at the future posterior and anterior midgut. they grow inward toward each other and fuse to form the endoderm of the midgut.
the ectoderm is dragged inward behinds the tubular invaginations to form the foregut and hindgut

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24
Q

what does the outer ectoderm develop into in drosophila?

A

the epidermis, ectoderm continues to divide during gastrulation but the mesoderm does not

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25
Q

when does germ band extension occur in drosophila?

A

during gastrulation, the central body of the blastoderm undergoes extension along the antero-posterior axis

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26
Q

what happens to mesoderm cells and the epidermis after gastrulation is complete in drosophila?

A

mesoderm begin to divide again

epidermis 2 times more and then secrete a thin cuticle of protein and polysaccharide chitin

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27
Q

what does germ band extension in drosophila drive?

A

drives posterior regions round the posterior end and onto the dorsal side

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28
Q

what happens to the germband after embryonic development is completed?

A

it retracts

29
Q

when are the first external signs of segmentation in drosophila seen?

A

as germ band extension occurs

30
Q

what mark parasegments externally in drosophila?

A

evenly spaced grooves

31
Q

how many parasegments are there in drosophila and what do they show?

A

14, 3 to mouth parts of the head, 3 to the thoracic region and 8 to the abdomen

32
Q

what is the telson?

A

the posterior end of larva

33
Q

how many segments are there between the head and telson?

A

3 thoracic and 8 abdomen

34
Q

what are dendrites?

A

smooth outgrowth from the epidermis showing the segments

35
Q

what happens after the third instar (shed of cuticle) in larva?

A

they become pupa, the metamorphosis into fly form occues

36
Q

how are suitable informative developmental mutations found?

A

v rare
induce random muts into a large no of individuals
and screen systematically for developmental defects

37
Q

how do maternal effect mutations effect embryos?

A

the mutations are present in the mother but do not affect her appearance of physiology, they have profound effects on development of progeny independent to the father

38
Q

what does maternal factors in drosophila do?

A

guide earliest stages of development

50 maternal genes involved in setting up 2 axes and basic molecular frame work

39
Q

3 classes of maternal genes that specifies regional differences in drosophila eggs

A

ones that affect only anterior
ones that affect only posterior
ones that effect both terminal regions

40
Q

what does bicoid mutation in the anterior end of drosophila result in?

A

reduction of head, thoracic features and in some cases replacement with posterior end

41
Q

what does nanos mutation in the posterior end of drosophila result in?

A

loss of the abdominal region which leads to a smaller than normal larva

42
Q

where is biciod mRNA located?

A

anteriorly

43
Q

what do female flies that dont express bicoid produce?

A

embryos with no proper head or thorax

44
Q

what do nanos and caudal control?

A

posterior patterning of flies, nanos located at posterior end and translated after fertilisation, this suppresses the hunchback gene

45
Q

what creates positional information?

A

opposing gradients of maternal gene products

46
Q

what determines the dorsal ventral axis?

A

toll receptor activation

47
Q

what creates the intracellular gradient from ventral to dorsal in flies?

A

dorsal protein entering the nuclei of the synctial blastoderm

48
Q

what divides the dorsal ventral axis into 4 distinct regions?

A

dorsal transcription factor gradient

49
Q

what does the ventral ectoderm become?

A

neuroectoderm which gives rise to the nervous system and ventral epidermis

50
Q

how is the dorsal gradient acheived?

A

differing binding affinity

most ventral end has the highest intracellular conc of dorsal

51
Q

what activates dorsal to enter the nucleus and trigger transcription?

A

toll signalling

52
Q

what controls segmentation in drosophila?

A

a hierarchy of gene expression

53
Q

gap genes are the first to be expressed where? and what do they code for?

A

expressed along antero-posterior axis and code for transcription factors

54
Q

what is gap gene expression triggered by?

A

gradient of bicoid proteins

55
Q

how do gap genes act?

A

in combination with other transcription factors, short lived proteins only extend slightly beyond region of expression in which overlaps sharpen the domains of diff regions

56
Q

how do bicoid genes target hunchback expression?

A

in a concentration dependent manner
bicoid induces expression of hunchbacck over most of the anterior half of the embryo
hunchback is only switched on when bicoid is of a certain treshold
hunchback expression extends posteriorly as so does bicoid protein above treshhold conc

57
Q

when is Kruppel expressed?

A

above a certain threshold (low conc) of hunchback

58
Q

what acts as a morphagen to other gap genes?

A

hunchback

59
Q

how are gap genes expressed?

A

in transverse stripes which depend on control genes being sensitive to diff concs of hunchback

60
Q

where does the gradient of hunchback locate Kruppel?

A

in the centre of the embryo - when bicoid isnt present, hunchback conc is low so kruppel is seen anteriorly, when hunchback conc is high, kruppel is shown at the posterior end of the embryo

61
Q

how are larval segments made up?

A

posterior region of one parasegment and anterior of the next, initially parasegments are similar to one another but soon have their own identity

62
Q

how is the expression of even skipped stripe 2 defined?

A

pair rule genes are expressed in stripes
mutations effect alternate segments
striped pattern is present before cells are formed

63
Q

how are the 14 parasegments created?

A
  1. production of local combination gap gene transcription factors
  2. activation of each pair rule gene in 7 transverse stripes along antero posterior axis
  3. pair rule gene expression defines 14 parasegments each pair rule gene is expressed in alternate parasegments
    segments have their own polarity
64
Q

what happens in the absence of hedgehog?

A

in the absence of hedgehog, membrane protein patched inhibits membrane protein smoothened
so transcription factor Cubitus interruptus is held in the cytoplasm in 2 protein complexes
1. associated with smoothened 2. associated with protein suppressor of fused
Ci in smoothened is phosphorylated by several protein kinases which leads to the cleavage of Ci and formation of truncated protein CiRep
CiRep enters the nucleus as a repressor of the hedgehog target gene

65
Q

what happens in the presence of hedgehog?

A

it binds to patched and lifts the inhibition of smoothened to block production of CiRep
Ci is release from both complexes in the cytoplasm to then enter the nucleus and act as a gene activator
the genes activated include - wingless, decapentapleigic and engrailed
wingless and hedgehog define compartment boundary

66
Q

what do Homeobox genes provide?

A

identity of body segments (hox genes)

67
Q

what make sup the hom-c complex?

A

hox genes organised into 2 gene clusters of gene complexes

68
Q

what does the homeobox DNA motif encode?

A

part of the DNA binding sites of hox genes

Cell and Developmental biology (13 decks)

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