Drosophila Flashcards
What is a holometabolous life cycle?
The insect undergoes complete metamorphosis. The larval forms look completely different than the adults
What is hemimetabolous life cycle?
The insect undergoes incomplete metamorphosis. The larval form looks like a mini adult
Do flies have a holometabolous or hemimetabolous life cycle?
Holometabolous
What effects do the nurse and follicle cells have on the embryo during oogenesis?
The nurse and follicle cells determine the egg and embryo axes by producing oskar and bicoid mRNA. The follicle cells also produce paracrine and juxtacrine signals
What type of yolk distribution do fly eggs have?
Centrolecithal
What type of cleavage do flies have?
Superficial. Karyokinesis occurs without cytokinesis, so the embryo is syncytial
What happens for the first 11 divisions?
Karyokinesis without cytokinesis
What happens after the 9th division?
The nuclei migrate to the outer cytoplasm of the embryo
What happens at the 12 division?
The nuclei are segregated into individual cells and form the cellular blastoderm
How does the cellular blastoderm form?
Microtubules grow from the outer cytoplasm towards the yolk, and actin filaments pinch off the new cells
What three proteins work to cause the midblastula transition?
Smaug, Zelda, and cyclin regulators
What does Smaug do? Where does it come from?
Accumulates over time and destroys maternal mRNA. Is a maternal signal
What does Zelda do? Where does it come from?
Regulates transcription by allowing the chromatin to unwind for transcription to occur. Is a maternal signal
What do cyclin regulators do?
Regulate how long each cell division takes
Where does gastrulation occur?
The ventral furrow
What is the ventral furrow?
An invagination of future mesoderm cells that eventually closes to form a tube
Where does the endoderm tissue come from during gastrulation?
Anterior and posterior pockets
Where is the neural ectoderm during gastrulation?
Surrounding the ventral furrow
How does the germ band expand over the posterior end of the embryo?
Convergent extension
How are the different segments of the larva created during gastrulation?
Convergent extension of the germ band over the posterior end of the embryo, which then contracts back to its original position and leaves the segments together in the correct places
What are the segments found on a fly larvae?
8 abdominal segments (A1-A8), 3 thoracic segments (T1-T3) and 3 head segments
How do the germ cells get inside the embryo?
Invagination of endoderm tissue
What are imaginal disks?
Discs of tissue in the larva that give rise to corresponding adult features
How does syncytial specification work?
Cytoplasmic signals with different locations in the cytoplasm as a gradient
What 3 maternal signals establish the anterior-posterior axis in the oocyte?
Bicoid, oskar, nanos
What 5 maternal signals establish the dorsal-ventral axis in the oocyte?
Gurken, torpedo, pipe, nudel, dorsal
Where does Gurken come from?
Synthesized by the oocyte
What does Gurken do?
Leaves the egg cell and binds to Torpedo on the neighbouring follicle cells to tell them to create a reciprocal signal back to the egg
What do the follicle cells tell the oocyte to do when receiving signalling by Gurken?
Tells the oocyte to make Par1 to anchor microtubules
How does anchoring the microtubules contribute to positioning of the anterior-posterior axis?
It allows the microtubules to grow in a particular orientation, with the minus end growing out as the oocyte expands anteriorly
Does bicoid bind to kinesin or dynein? Which way does it go?
Dynein, goes to the anterior end
Does oskar bind to kinesin or dynein? Which way does it go?
Kinesin, goes to the posterior end
What does oskar do?
Gets translated into a protein at the posterior end of the cell where it holds on to nanos mRNA
What is the function of bicoid and nanos?
Transcription factors
Where is the nucleus of the oocyte going as the cell grows? What is it doing?
The nucleus is moving anteriorly, and still making Gurken as it moves
What does Gurken do as the nucleus is moving anteriorly?
Diffuses into the dorsal follicle cells and shuts off transcription of Pipe
Where is Pipe expressed? What does it do?
Expressed in the ventral follicle cells. It turns on Dorsal transcription
What does Dorsal do?
Is a transcription factor activated by Pipe signalling, and it stays near the ventral side and creates a ventral phenotype. It activates Twist and Snail and surppresses Dpp
What does Twist do?
Specifies mesoderm cells on the ventral side
What does Snail do?
Suppresses non-mesoderm genes in the ventral side
What does Dpp do?
Specifies dorsal ectoderm through BMP signalling
Why is BMP being expressed on the dorsal side in insects?
The nervous system is ventral in insects, and where there’s BMP there is no neural ectoderm
What is a gene hierarchy?
Step by step progression of which genes are activated from general to specific
What is the gene hierarchy in fly embryos?
Maternal effects -> GAP genes -> pair rule genes -> segment polarity genes
What does bicoid do?
Transcription factor that shuts off posterior related genes in the anterior end of the embryo. Activates hunchback and inhibits nanos and caudal
What does nanos do?
Transcription factor that shuts off anterior related genes in the posterior end of the embryo. Activates caudal and inhibits bicoid and hunchback
Where is torso expressed and what is it doing?
Expressed in the centre of the embryo and creates torso-like features
What do GAP genes specify? What happens if one is mutated?
Large areas of the embryo. Mutation leads to the loss of large regions of the body
What causes the expression pattern of the GAP genes?
The maternal effect
Where is kruppel expressed? What is it doing?
Expressed in the centre of the embryo. It inhibits Giant
Where is Giant expressed? What is it doing?
The anterior and posterior ends of the embryo. It inhibits Kruppel
How do we get clean boundaries of gene expression for the GAP genes?
They inhibit each other, so only one or the other can be expressed in a region
What do the pair-rule genes specify? What happens if one is mutated?
They divide into periodic segments and are expressed in every second fragment. Mutations result in the loss of every second fragment
What are the two pair-rule genes?
Fushi tarazu and even-skipped
What determines the expression pattern of the pair-rule genes?
Expression patterns of the GAP genes, especially where and how they overlap
Which two stripes are inhibited by Giant?
2 and 5
What do segment polarity genes do? What happens if one is mutated?
They give polarity to each segment. Each segment will have defects if one is mutated
What determines the expression pattern of the segment polarity genes?
The expression pattern of the pair-rule genes
What products do segment polarity genes produce, in general?
Parts of the Wnt and Hedgehog signalling pathways
Do gene expression parasegments line up with the actual segments on the embryo?
Not completely, but there is overlap
What establishes the boundaries of the parasegments?
A positive feedback loop between engrailed, wingless, and hedgehog
Where is wingless expressed? What does it do?
Where both fushi tarazu and even-skipped are absent. It’s a paracrine signal that activates the Wnt pathway and turns on engrailed and hedgehog in nearby cells
Where is engrailed expressed? What does it do?
Where either fushi tarazu or even-skipped is expressed. It’s a transcription factor that turns on hedgehog
Where are both wingless and engrailed expressed?
Boundaries of the parasegments
