invertebrate models Flashcards
(113 cards)
1
Q
why are sea urchins used as invertebrate models?
A
they produce a large number of embryos
they are easy to manipulate genetically
we can change their genes to study their effect on development
2
Q
what are echinoderms?
A
organisms with a spiny skin such as sea urchins
they are a type of deuterostome
3
Q
how do protostomes and deuterostomes develop differently?
A
in protostomes the blastopore formed in gastrulation forms the mouth and the anus forms after
but in deuterostomes the blastopore forms the anus and the head forms later
4
Q
why are sea urchin embryos useful in the lab?
A
they develop quickly and in large numbers
they are easy to grow
they have developmental markers so their development is easy to monitor
5
Q
what is the mosaic model of development?
A
there is a hidden pattern in the fertilised eggs that when the cell divides different genes go into different cells which changes the cell to its fate
6
Q
what is the regulative development theory of development?
A
when cells divide they communicate and interact to form different cell types
7
Q
what is the structure of a fertilised sea urchin egg?
A
there is an animal pole and a vegetal pole
the animal pole gives rise to the ectoderm
the vegetal pole gives rise to the mesoderm and endoderm
8
Q
what experiment performed by Driesh disproved the mosaic model of development?
A
he removed a cell from the blastomere and separated it into 2 and it developed into a complete larvae
this disproves the mosaic model because the cell would’ve only had half the genes so wouldn’t have developed correctly
9
Q
what experiment showed that there is cytoplasmic determinance in sea urchin embryos?
A
he split a blastomere cell into 4 and it formed complete larvae
he split a cell into 8 (vegetal and animal poles separated) and the larvae were incomplete
10
Q
what are genetic models?
A
model organisms where the genes within the genome can be altered to study their effect on development
11
Q
what are the 2 main genetic models used in labs?
A
C. elegans (worms) and drosophila melanogaster (flies)
12
Q
how are mutant phenotypes produced?
A
scientists disrupt the gene in heterozygotic animals and breed them to produce homozygous animals with 2 mutated chromosomes
13
Q
why are C. elegans and drosophila used for research?
A
they are easy to breed, small, produce large batches of embryos, have a short generation time, have sequenced genomes that are easy to analyse
14
Q
what is the life cycle of C. elegans?
A
the fertilised egg undergoes cleavages and hatches to form a young worm
the worm undergoes moulting and is sexually mature after 72 hours
15
Q
how do C. elegans reproduce?
A
they are hermaphrodites meaning they have both female and male reproductive organs
they first develop as a male and then produce oocytes
they use their own sperm to fertilise the oocytes
16
Q
how can the cell fate of C. elegans be modified?
A
the first cleavage of the zygote is asymmetric and fixed
cells can be manipulated to change their fate using Par 2 and 3 proteins that control cell cleavage
17
Q
what is apoptosis used for in humans?
A
forming reproductive organs in males and females
removing skin between digits in the embryo
maturation of the immune system
18
Q
what is the RNA interface in C. elegans?
A
a mechanism that can cause downregulation of gene activity
double stranded RNA triggers a biochemical process that degrades specific mRNAs blocking gene expression after transcription
19
Q
what is the mechanism of RNA interface?
A
- double stranded RNA is taken up by the cells
- RNA is cut up into short interfering RNA (siRNA) by the enzyme dicer
- siRNA is loaded into a protein complex called RISC
- the RNA guides RISC to specific mRNA and cuts it up so the gene can’t be expressed
20
Q
how is RNA interference used in humans?
A
drugs to treat high cholesterol and genetic mutations that cause protein overproduction
21
Q
what did Thomas Hunt Morgan discover about genes?
A
that genes are found on chromosomes and they are the basis of hereditary (passing down characteristics to offspring)
22
Q
how are drosophila used in research?
A
they are used for reverse genetics to study the importance of specific genes in development
used in forward genetics to understand mutations
23
Q
what is forward genetics?
A
when you mutate a specific gene that you know the function of to find out what mutation causes a specific phenotype
24
Q
what is reverse genetics?
A
when you know the sequence of a gene and you mutate it to find its function
25
what is saturation screening?
screening to see all the genes involved in a specific phenotype
26
what has saturation screening allowed us to do?
understand how genes control the plan of our body
identify new genes and cell to cell signalling pathways
27
what is the life cycle of drosophila?
the fertilised egg undergoes cleavages and gastrulation to form an embryo
the embryo hatches after around 24 hours to form a larvae
the larvae goes through 3 instar before it malts its cuticle to grow and form a pupa
the pupa undergoes metamorphosis to form an adult fly
28
when do drosophila reach sexual maturity and how long do they live for?
reach sexual maturity at around 9 days
live for around 140 days
29
what are instar?
larvae development stages
30
what happens to drosophila during cleavage?
after fertilisation the nucleus starts to divide and form a syncytium
the nuclei move to the edges of the cell forming a syncytial blastoderm
pole cells start to separate off from the other cells and form the germline of the fly
a cellular blastoderm forms
31
what is a syncytium?
a large cell with multiple nuclei
32
what is the germline?
a series of germ cells that will develop into sperm or egg cells
33
what happens to drosophila during gastrulation?
the mesoderm invaginates into the membrane and the cells move to the ventral side pushing tissue to the anterior end to form a germband extension
the germband retracts and moves to form segmentation
34
what do the germ layers form in drosophila?
the ectoderm forms the epidermis and nervous system
the endoderm forms the gut
the mesoderm forms the muscle
35
why do drosophila larvae have to hatch?
when the larvae can't grow any further (due to the cuticle surrounding it
36
what happens to drosophila during metamorphosis?
populations of cells in the larvae called imaginal disks grow quickly to form structure such as the eyes, mouth, legs and wings
stem cells at the tup of reproductive organisms divide to form germ cells
37
what is the role of the denticles at the anterior end of drosophila?
to climb over food
to check it is in the right polarity
38
how is the body axes of drosophila set up within the egg?
the head, tail, thorax and abdominal cavity form along the anterior-posterior axes
the thorax and abdomen are segmented
along the ventral-dorsal axes the ventral mesoderm, ventral ectoderm, dorsal ectoderm and amnioserosa form
39
what is the amnioserosa?
a tissue that supports the development of the embryo
(like a placenta for humans)
40
what is an initial maternal gradient?
the distribution of a morphogen in a concentration gradient across the embryo that sets up the body plan
41
what is a morphogen?
a signalling molecule that diffuses from a localised source to form a concentration gradient over a developing tissue
it influences the fate of cells depending on their distance from the source and therefore the concentration of the morphogen
42
what are GAP genes and what do they cause?
genes that define different regions in the embryo
they cause periodic expression of pair-rule genes
43
what are pair-rule genes?
genes that create a segmental pattern that leads to segmentation in the larvae
44
what are segmentation genes?
genes that give each segment of the embryo an anterior and posterior pattern
45
when does patterning of the segments in the embryo happen and why is this important?
after the cell has cellularised (when each nucleus has its own cell membrane and all the cells are separate)
this allows cell to cell signalling to coordinate the patterning process
46
what are homeotic selector (HOX) genes?
genes that give rise to wings and other structures along the anterior-posterior axes
47
what are maternal genes?
genes from the mother's genome that provide the initial information needed to set up the body axes of the embryo
there are 3: bicoid, nanos and torso signal
48
what is the role of bicoid maternal gene and what does the bicoid mutant look like?
it patterns the anterior end of the embryo
the bicoid mutant has 2 back ends because the anterior end doesn't form
49
what is the structure of bicoid?
it is a nuclear protein and it forms a protein gradient from the anterior (highest) to posterior end because its RNS is localised by the mother at the anterior end of the egg
50
how does bicoid form the anterior end and how can it work as a morphogen?
it influences different genes at different threshold concentrations
when the threshold is met the gene will be expressed or suppressed
it acts as a morphogen because the egg is in syncytium so it can diffuse across
51
what is the role of nanos maternal gene and what does the nanos mutant look like?
nanos is required for patterning the posterior end of the embryo
the mutant has a normal anterior end but the posterior end is missing some sections
52
how does nanos work to pattern the posterior end?
it forms a concentration gradient from the posterior (highest) to anterior end because its RNA is localised by the mother at the posterior end of the egg
it acts on hunchback gene to supress its translation and expression at the posterior end
53
what is the role of torso signal maternal gene and what does the torso mutant look like?
torso signal is required for patterning the terminal regions (head and tail) of the embryo
the mutant has deformed head and tail
54
how does torso signalling work to pattern the anterior and posterior extremities?
torso receptor is present on the membrane of the whole egg
a protein called trunk protein can only form when the ligand trunk is released from torso receptors
a protease called torso-like releases trunk and it is only present at the ends of the eff
trunk protein forms when the receptor is activated by the protease and that causes patterning
55
how is the dorsal-ventral axes patterned?
along the dorsal-ventral axes there is a receptor called toll and a ligand called spatzle that are present all across the embryo
an enzyme called pipe activates the spatzle ligand and is only found on the ventral side
when spatzle is activated it binds to toll producing a dorsal protein that forms a gradient across the nucleus from the ventral (highest) to dorsal end
56
why is the protein called dorsal?
the mutant has no ventral side (only dorsal)
57
what is an ovariole?
a string of cells that are each in a different stage of development
it is found in the ovary of female drosophila
a cell at the posterior end of the ovariole will form the oocyte of the offspring
58
how does the mother determine the formation of the anterior-posterior axis?
the polarity of the ovariole is transmitted into the egg and determines the axis
59
how is the dorsal-ventral axis determined in the embryo?
the nucleus is in an asymmetrical position within the oocyte
the oocyte moves from the posterior to the anterior end during development
the side of the cell that the nucleus ends up in is the dorsal side
60
what sets up the anterior-posterior axes within the oocyte?
a cell to cell signalling molecule called gurken that is transmitted from the nucleus to the follicle cells
in the follicle it binds to a receptor called torpedo to make the oocyte posterior
61
how does dorsal protein work to pattern the dorsal-ventral axes?
promotors of genes that are required for patterning are activated by different concentrations of dorsal protein
so different genes are expressed along the the axes
62
what is the role of snail gene and where is it expressed?
it forms the mesoderm
it has a low affinity for dorsal binding sites so it is expressed where there is high levels of dorsal protein
63
what is the role of rhomboid gene and where is it expressed?
it forms the neuroectoderm
it has a high affinity for dorsal binding sites so is expressed where there are low levels of dorsal protein on either side of the mesoderm
64
how do snail and rhomboid interact?
rhomboid is supressed by snail
snail also acts as a transcription factor
65
what happens when there is a low level of nuclear dorsal protein?
only rhomboid is expressed because it binds to rhomboid promotor
66
what happens when there is a high level of nuclear dorsal protein?
snail is expressed
dorsal protein binds to promotors for both genes but snail inhibits rhomboid
67
what is the role of Dpp and what is it called in vertebrates?
sets up a signalling pathway on the dorsal side of the embryo
it is called BMP
68
what happens when HOX genes are mutated and what are the 2 mutants?
the fly has one structure replaced with another
bithorax mutants have 2 sets of wings (legs replaced with wings)
antennapedia mutants have legs instead of antenna
69
what 2 HOX complexes are found in drosophila?
bithorax and antennapedia
70
how are HOX genes expressed?
in a specific order from anterior to posterior end
the order determines the spatial and timing of the expression of other genes
71
why do vertebrates have 4 HOX genes?
there has been 4 genome duplications between proteomes and vertebrates
72
what is the role of the bithorax complex and what are the mutants?
it diversifies the posterior segments
mutants have a normal T1 segment but all the others look the same
73
what is the role of GAP genes and how are they expressed?
they create a combinatory code that defines different regions in the embryo
they are expressed by hunchback and bicoid
74
how do GAP genes express pair-rule genes?
they cause the pair-rule genes Ftz and Eve to be expressed in a striped pattern
the stripes are coded for individually by enhancers that cause the expression of certain combinations of GAP genes
75
how do pair-rule genes cause segmentation?
Ftz and Eve switch on a transcription factor called engrailed that is expressed in the posterior boundary
76
what is the role of the transcription factor engrailed?
it forms 14 stripes from the 7 stripes formed by Ftz and Eve because it responds to both genes
77
which 2 signalling proteins are expressed at the same time as engrailed and where?
wingless (Wg) and hedgehog (Hh)
they are expressed in adjacent cells
78
how are wingless and hedgehog transported?
by a signalling pathway because the embryo has cellularised (cells separate into individual cells)
79
how is wingless expressed and how does it effect other signalling molecules?
expression of wingless is activated by hedgehog
wingless activates the expression of engrailed and hedgehog creating a positive feedback loop
80
why are wingless and hedgehog considered protein signals?
they act across cell boundaries and have to be actively transported out of cells
81
what happens if activity of wingless and hedgehog are reduced or increased?
reduced activity leads to defects
increased activity leads to cancer
82
why are drosophila used to study neurogenesis?
their development is very similar to vertebrates
83
where does the neural tube develop in drosophila and vertebrates and what does this show?
in drosophila it forms on the ventral side
in vertebrates it forms on the dorsal side
this shows there has been a dorsal-ventral rotation during evolution
84
what is the role of BMP in vertebrates?
it patterns the ventral side
85
what happens to cells in the neuroectoderm of drosophila?
some cells become neurones and others remain ectodermal epithelial cells
86
what is a neuroblast and how does it form?
a neural stem cell that gives rise to neurons and glial cells
it is selected from a group of cells called a proneural cluster by lateral inhibition
87
what is the role of proneural genes and the Achaeate-Scute complex?
they roughly position where a neuron should form
88
what happens to cells within the proneural cluster?
they interact to decide which cell forms the neuronal precursor and which cells remain as epithelia
they do this through the notch/delta cell signalling pathway
89
what is delta?
a transmembrane ligand that binds to the notch receptor within the cell membrane
cells can only signal to other adjacent cells
90
how does the Achaete-Scute complex and delta interact?
achaete-scute proteins promote expression of delta
delta binds to notch receptors activating them causing downregulation of Achaet-scute proteins
91
what happens if there is high levels of Achaete-scute expression?
neural genes are activated causing the cell to develop into a neuron
92
what happens if notch is blocked or activated?
if it is blocked all the cells take on a neuronal identity
if it is activated all cells revert back to epithelial identity
93
what happens to the neuroblast after it has been selected?
it will generate a number of neurons and glial cells through asymmetric cell division
then it drops down into the embryo
94
what is the role of the bazooka (Par 3) gene?
it marks the epithelial side of the cells in the epidermis giving them an apical-basal polarity
95
what is the role of Insc/Pins protein?
it forms a complex with the bazooka gene that directs the localisation of certain RNA on the opposite side of the cell
the complex orients the mitotic spindle that determines the plane of division in the cells
96
what is the role of numb protein
it causes the cell to become neuronal by inhibiting notch to promote neuronal development
97
why does the cell have to divide asymmetrically?
so cell components can be correctly distributed to form a neuroblast and ganglion cell
the ganglion cell divides to form neurons and glia
98
how do vertebrates carry out neurogenesis?
stem cells in the embryo's cerebral cortex divide and the nucleus moves to the ventral side of the cell
at the ventral side the cell divides asymmetrically so one cell forms a neuron and the other forms a stem cell
99
what is phylogeny?
how organisms are classified based on their common ancestors
100
what causes differences in our morphologies?
changes in expression of a common set of developmental genes
101
how can we analyse molecular sequences to study phylogeny?
comparing the amino acid, mRNA or DNA sequence of proteins to see how similar they are
use blast protein sequence software to identify similar protein sequences
102
what are query and alignment proteins in blast sequencing?
the query protein is the protein that we input
the alignment proteins are proteins with similar sequences to the query protein
103
what does it mean if 2 proteins have a similar sequence?
they have evolved from the same common ancestor and have similar molecular functions
104
how many fibroblast growth factors (Fgfs) do vertebrates have and how many clusters can they be grouped into?
vertebrates have 22 grouped into 4 clusters based on their protein sequences
105
how do different Fgfs arise?
by gene duplication which can be changes in ploidy (copies of the genome) or local duplications of one region of the genome
106
what are paralogues?
new copies of genes in the same genome
107
what happens to the genes after genome duplication?
the genes are redundant at first (multiple genes have the same role)
over time mutations can cause gene loss of neurofunctionalisation
108
what is neofunctionalization and what causes it?
when the function of a gene changes
this can be due to the pattern of expression changing during development
the coding sequence of the protein changing by mutations
109
how many copies of HOX genes do vertebrates have?
vertebrates have 4 copies so they have been duplicated twice because drosophila only have 2
110
what happens if you change the expression of HOX genes?
it changes the segmental identity of the embryo
111
what are the roles of HOXc5 and HOXc6?
HOXc5 is involved with cervical vertebrate identity (neck)
HOXc6 is involved with thoracic vertebrate identity (chest)
they are expressed in the somites and tell the cells which vertebrae to form
112
what are Ubx and Dlx in drosophila?
Ubx is a gene that regulates the number of limbs a (legs and wings) the fly has
Dlx is a gene that specifies leg development
113
how do Ubx and Dlx interact in drosophila?
Ubx blocks Dlx expression in the abdomen to stop legs forming
