L4 Drosophila, Setting Up the Body Axes (Imported from Quizlet)

A/P axis consists of what ...?

A head, a tail, a thorax and abdominal region are formed

The thorax and abdomen are ______

Segregated

D/V axis consists of ...?

4 regions need to be defined, the ventral most mesoderm, ventral ectoderm, dorsal ectoderm and aminoserosa (an embryonic tissue)

Who used the screens identified the genes that control this?

Nusslein-Volhard and Weischaus

The many anteroposterior patterning genes in drosophila can be broadly grouped into a ______

Hierarchy

What do the initial maternal gradients result in expression of?

Gap genes that define different regions in the embryo

What do gap genes lead to?

Periodic expression of the pair-rule genes which specify the para-segments and foreshadow segmentation of the larva

The segmentation genes elaborate what?

Patterning within each para-segment

Patterning of these segments happens when and what does this mean is essential?

The embryo has cellularised, so cell-to-cell signalling is essential to coordinate this patterning process

A final group of genes are the homeotic selector genes, what do they do?

Determine the identity

Results from these screens pointed out what?

That the genes form a logical hierarchy

Using AP patterning as an example

Initial symmetry is broken under the control of a set of maternal genes

These are genes that are required in the mother -> a maternal gene like for instance bicoid are present in the gradient, in this case a high concentration at the anterior that falls when you move backwards

What do these gradients lead to expression of?

Zygotic gap genes in discrete bands across the embryo, thereby defining regions in the developing embryo -> the gap genes lead to expression of the next set of genes: the pair rule genes

The pair-rule genes set up what?

The para segments which will foreshadow the actual segments of the larva

The patterning within each segment is set up by another layer in the hierarchy known as ...?

The segmentation genes

If patterning needs to be coordinated at this stage cell-to-cell communication needs to take place across ______, they use _____ ______ ______

Membranes, specialised signalling pathways

At this point about 14 segments are produced, but they are all more or less identical, the final set of genes do what?

Give the segments their precise character, these are the homeotic selector genes

What does the mother provide?

The initial information to set up the two main perpendicular axes

What does the formation of the two main perpendicular axes require the action of?

Maternal genes -> genes that need to be present in the genome of the mother

Identified by specially adapted ____ ____ where homozygous mutant mothers were ______ for defects in ____ of their _______

Genetic screen, screened, all, progeny

The perpendicular axes is set up by genes who's activity are ___ needed in the zygote itself rather these genes need to be _____ and _____ in the mother

Not, present, functional

The A/P axis is set up by _ classes of ______ genes

3, maternal

What are the 3 relatively independent systems at work setting up the A/P axis?

Anterior-bicoid, posterior, terminal

How were the independent systems defined?

By mutations that led to the corresponding defects either in anterior, posterior or terminal structures in the larva

Bicoid was the first example of what?

A morphogen

The existence of morphogens has been postulated by theoretical biologists to explain what?

How patterning could occur in an embryo

What is a morphogen?

A molecule the emanates from a specific region and is present in a concentration gradient and that specifies the fate of each cell along this gradient

A morphogen should be able to induce what?

More than one fate

A morphogen forms a _____ ____ across the A/P axis of the _______ embryo, its ____ is localised at the ______ end of the egg

Protein gradient, syncytial, RNA, anterior

Bicoid is a ______ _____, it switches on different genes at different ______ _______

Transcription factor, threshold concentrations

Bicoid can only function like a morphogen because ...?

Egg is a syncytial

As predicted, bicoid form a protein gradient, ____ concentration at anterior and _____ concentration at posterior

High, low

The protein gradient is formed because ...?

The RNA for bicoid is concentrated at the anterior end of the egg

The drosophila embryo is a syncytium thus there are __ ____ _______ that prevent the movement of this protein and is why this _______ ______ can function as a _______

No cell membranes, transcription factor, morphogen

What are Nanos and Caudal required for?

Proper formation of the posterior segments under the influence of Oskar

What is the role of Nanos?

Preventing hunchback translation in the posterior of the egg

______ is also important for posterior patterning

Caudal

Bicoid protein has a second role in addition to transcription, what is this role?

Preventing anterior caudal mRNA translation

Nanos is an important gene in the posterior, like bicoid its RNA is tightly localised -> this RNA is stuck to the _____ end of the _____ (this occurs under the influence of a protein called Oskar)

Posterior, oocyte

Nanos RNA is translated into what and what does this do?

Nanos protein, this protein forms a gradient that runs opposite to the bicoid gradient with high concentration in the posterior and low concentration in the anterior

Nanos prevents ...?

Posterior expression of hunchback

Bicoid prevents ...?

Anterior expression of caudal

The final A/P patterning system is required only for both extreme ends of the embryo, what is it mediated by?

Torso signal

Where is the torso receptor present?

Everywhere

Where is trunk protein (which can form the ligand) present?

Everywhere

Where is the protease torso-like which is required to realise the ligand present?

Only at the poles

Where is the torso signal coming from?

Outside the actual embryo

The torso signal is only activated at the ______ and _____ poles

Anterior, posterior

The receptor protein is called _____ and is expressed on the outside of the embryo -> expressed ______ on the membrane of the egg and projects into a small space between the egg and viteline membrane

Torso, everywhere

What is the small space between the egg and viteline membrane called?

Periviteline space

This torso receptor can bind a ligand named _____

Trunk

Trunk is localised in the viteline membrane, ____ _____ the embryo

All around

The ligand needs to be proteolytically cleaved in order to function, what is the name and location of the protein that does this?

Torso-like, it's localised at the poles of the egg

Localised production of active ligand ensures that the torso receptor is only what?

Activated at the tips

A little bit of active trunk is produced at the pole and this is captured by the receptor that are nearest to the source, what does this lead to?

An activation gradient

In order for cells to communicate in many cases they use signals that cannot pass through _____, these signals are received by special _______ proteins, _______

Membranes, transmembrane, receptors

On the outside they bind to a signal which is often referred to as the ...?

Ligand

Upon binding, the ______ changes its state (can be in a variety of ways) and this will have effects inside the cell -> often leads to activation of a ______ _____ this enters the nucleus where it will act to change the transcription of target genes

Receptor, transcription factor

There is only a limited set of cell signalling pathways, what does the colour relate to?

The type of protein

The receptor "toll" is found ...?

Everywhere

The ligand "spätzle" is found ...?

Everywhere

The second perpendicular axis is known as ...?

Dorsoventral patterning

Dorsoventral patterning generated under the influence through the ____ _______

Toll receptor

What does localised enzyme "pipe" create?

Active ligand on ventral side

_______ ______ of "dorsal" protein on ventral side

Nuclear localisation

Dorsal is required for what?

To make ventral

The activity of the receptor leads to the _____ _____ of a _______ factor named ______

Nuclear localisation, transcription, dorsal

Polarity of the ovariole is transmitted to ...?

The egg

Eggs are formed from ...?

Stem cells at the tip of the germarium

The daughter cell divides _ times and forms clusters of __ connected cells, called a _____

4, 16, cyst

One of these cyst cells will become the actual _____, the other 15 cells are _____ cells that will produce ____, ____ and _____ _____ for the egg

Oocyte, nurse, protein, RNA, other materials

The cyst is surrounded by what and what do they provide?

Follicle cells that provide important signals to the oocyte -> together they form an egg chamber

Each egg chamber is connected to the next via a ...?

Set of stalk cells

The eggs form a string where the oldest are at one end and the youngest at the other end, these ovariole strings are therefore _____ _____ in the A/P direction and this ______ _______ is transferred to the _______

Polar structures, polarity information, oocyte

Signals from older egg chamber induce what?

Stalk cells

The oocyte adheres to stalk cells and what does this do?

Places the oocyte at the posterior end of the egg chamber

The stalk signals to the ______ _____

Follicle cells

If the stalk cells signal to the follicle cells and this signal coincides with a gurken signal from the oocyte, what will happen?

They will become posterior follicle cells

If there is no Turkmen signal what will happen?

They will become anterior follicle cells

What is gurken related to?

Vertebrate transforming growth factor alpha (TGF-α) a member of the epidermal growth factor (EGF) family

The posterior follicle cells are different from the anterior follicle cells, why?

The posterior follicle cells get a signal from both the stalk and the oocyte but the anterior follicle cells only get one signal

What is the result of the signal from the posterior follicle cells?

The microtubules re-arrange with their positive ends towards the end of the oocyte, their negative end to their anterior

Microtubules form a ...?

Cellular skeleton

Microtubules also function as transport highways, what do these do?

Guide transport motors and cargo

Kinesin moves to which end?

Positive

Dunein moves to which end?

Negative

What does Oskar form?

An anchor for Nanos RNA

These motors are used by bicoid RNA by being transported to the ______ end and Oskar RNA to the ______ end

Anterior, posterior

Oskar is made into a ______ that does what?

Protein that localises nanos RNA at the posterior

What is another consequence of the signal from the posterior follicle cells and the rearrangement of the cytoskeleton?

The nucleus repositions itself to an anterior corner, it locally expresses the same gurken signal that induces the A/P axis formation but the signal makes dorsal follicle cells different from ventral ones which leads to ventral specific deposition of "pipe"

The nucleus also responds to the _______ microtubules and gets pushed to one corner of the ______

Orientated, oocyte

The nucleus produces a localised ____ that encodes for _____ ____ that creates a _____ _____ to the nearby _____ cells

RNA, gurken protein, localised signal, follicle

Gurken is setting up both ____ and _____ axes

A/P, D/V