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Flashcards in Lecture 6 Deck (33):
1

What are the four main stages of the drosophila life cycle?

The adult form, the embryonic form, the larval form and the pupa form
9 days are taken to complete the lifecycle

2

Where does oogenesis occur in drosophila?

In the ovary of the female drosophila which has 16-20 ovarioles made of anterior germarium and posterior vitellarium

3

What makes up the germarium in the ovarioles of the drosophila?

Germ line stem cells

4

What makes up the vitellarium in the ovarioles of drosophila?

A chain of developing egg chambers

5

What makes up a mature egg chamber?

A mature oocyte, 15 nurse cells and a large number of follicle cells

6

How does oogenesis occur in the drosophila?

Stem cells in the germarium divide to give rise to one stem call and one cystoblast
The cystoblast then undergoes 4 rounds of mitotic division with incomplete cytokinesis giving rise to a syncytial cyst of 16 cells
One of the 16 cystocytes which is connected to 4 neighbouring cells undergoes meiosis to form the oocyte while the remaining cystoblasts go on to form nurse cells

7

What connects all the 16 cells of the syncytial cyst?

Ring canals which forms cytoplasmic bridges from arrested mitotic cleavage furrows
There is also microtubule-based fusome which runs between the all of the ring canals
This forces the cells to divide in a specific known pattern

8

How can the fusome indicate which cystoblast is most likely to give rise to the oocyte?

The cystoblast which contains the most of the fusome is typically the one which goes on to become the oocyte

9

What is the function of nurse cells in drosophila?

The produce mRNAs and proteins into the oocyte which are moved by motor proteins along the fusome and throguh ring canals to establish the maternal factors in the oocyte

10

What is the fusome made of?

Continuous elements of the endoplasmic recticulum and cytoskeletal proteins including polarized microtubules which have their minus ends restricted to the future oocyte

11

Where does the fusome come from?

It is a product of the asymmetric cell division which forms the cystoblast

12

What is the function of the fusome?

It controls the microtubule driven localization of the oocyte fate as it marks the anterior of the oocyte

12

What is the function of the fusome?

It controls the microtubule driven localization of the oocyte fate as it marks the anterior of the oocyte

13

How are nurse cells aided in their function of mass producing mRNAs and proteins for the oocyte?

They become polytene increasing the rate of transcript accumulation

14

How do nurse cells become polytene?

When multiple rounds of replication produce many sister chromatids that remain synapsed together

15

What cells other than nurse cells are associated with the drosophila egg?

1000 small follicle cells which are mesodermal and pass nutrients from the haemolymph into the developing egg and lay down the vitelline membrane and the egg shell or chorion

16

What happens to the mRNA when it is placed inside the oocyte?

It is relocalised based on the oocyte cytoskeleton, this process helps to set up the body axis before sperm has even entered the egg

17

How does fertilization of the oocyte in drosophila occur?

The sperm are stored in the seminal receptacle of the female and the eggs are fertilized in the uterus, where the sperm enters the egg through the micropyle, a small anterior protrusion

18

Why is there no block to polyspermy in drosophila?

The huge sperm structures blocks anything else from entering

19

What occurs in the first 10 nuclear divisions of a drosophila egg?

They are very rapid with each division taking 10 minutes there is no G1 or G2 phase
There is no cytoplasmic division resulting in the formation of a syncytium
From this point division will get progressively slow

20

What are energids and how are they formed?

At about the 9th division the nuclei in the syncytium of the drosophila will move out from the center to the surface forming the syncytial blastoderm
The nuclei and their surrounding island of microtubules and microfilaments are called energids

21

How many nuclei formed in the syncytial phase of drosophila development are not used in the embryo proper?

About 200 nuclei remain in the centre of the yolk and do not contribute to the embryo proper

22

How and when are the pole cells formed in drosophila development?

In the beginning of cycle 9 about 5 nuclei reach the posterior pole of the egg so they can from the pole cells which will be the future germ cells
They are also the first cells to become covered by a cell membrane
The pole plasm which becomes incorporated into posterior cells that form around the nuclei controls germ cell determination through polar granules

23

What is the mid blastula transition in drosophila?

After 13 divisions mitotic synchrony is lost, transcription increases and the normal G1 and G2 phases of the cell cycle are establshed and all non-germ cells are delineated

24

What is the difference between syncytial blastoderm and the cellular blastoderm?

After all peripheral cells have been delineated and covered in a cell membrane the syncytial blastoderm is now referred to as the cellular blastoderm

25

What is contained inside a polar granule?

Proteisn such as oskar, vasa, staufen and tudor, mRNAs for oskar, mitochondrial coded ribosomal RNA and polysomes

26

How does gastrulation proceed in the drosophila?

Gastrulation begins soon after the mid blastula transition when 1000 ventral cells express twist and snail causing the cellular blastoderm invaginate ventrally and elongate to form the germ band
There is an invagination in the anterior and posterior end which meet and fuse together to form the gut

27

What are the features of the first instar larva of drosophila?

Hatches about 22 hours after fertilization
Has a spatially patterned cuticle with anterior mouthparts and segmentally repeated ventral dentricle bands

28

What is pupation with regards to drosophila?

A phase about 120 hours after fertilization where the larva stop eating and the external cuticle hardens to become the puparium

29

What occurs during the metamorphosis phase of drosophila?

Over the four days after pupation begins larval tissues degenerate within the puparium and form new adult tissues
Most of the increasingly polyploid larval tissues die and are replaced by nests of diplid cells which remained undifferentiaited during larval growth

30

What are the undifferentiated groups of cells in the drosophila which serve as precursosrs to the adult system?

Imaginal disc (9 pairs plus a central genital disc) form cuticular structures of the adult (wings, leg, head etc)
Abdominal histoblasts which are segmentally repeated structures which give rise to the adult abdomen
Imaginal nests clustered within each larval organ to give rise to adult organs like salivary glands

31

What does the imaginal disc do during metamorphosis?

The undifferentiated cells proliferate further and differentiate under the influence of moulting hormone 20-hydroxyecdysone and change shape evertign the disc to form the adult structure

32

What is transdetermination?

When an imaginal disc cells in drosophila differentiate into inappropriate structures