Insect Oogenesis; Development Of The Drosophila Body Plan Flashcards
What do network circuits (a kernel) consist of?
Regulatory genes (encoding transcription factors)
What are kernels?
They are GRNs for a given developmental function not used elsewhere in development. Is a precise set of inactions between genes that have a particular developmental function that doesn’t occur elsewhere
GRNs have ‘recursive wiring’ what does this mean?
Products of many genes are required for the function of the kernel
What will interference of any one kernel gene do?
Will destroy the function of the entire kernel and have severe developmental consequences. So once evolved they tend not to change (so once they have evolved they tend to be stable during evolution
Kernels can be highly conserved during evolution. Give an example
. The same gene are being transcribed in early gastrulation in sea urchins and starfish
. These organisms diverged at least 500m years ago, so that circuit has not changed since then
. The developmental kernel has not changed over that time
What is oogenesis?
Egg formation
What is spermatogenesis?
Sperm formation
What are the features of the mature ovum?
. Storage molecules ‘yolk’ containing a lipoprotein ‘vitellin’ (the nutrient component)
. Membranes and associated structures involved in the fertilisation reaction (results in fertilisation membrane). Very important, often when the sperm fertilised the egg it swells and stops any more sperm penetrating
. Mitochondria, ribosomes, stored mRNA
Describe what happens in oogenesis (creating an egg)
. The primary oxygen (ovum or egg) is diploid and through meiosis forms a haploid cell, the mature ovum
. Vitelligenesis May occur through a lengthened prophase of meiosis (May be months-Years
. The oocyte increases enormously in size and the reduction division may be delayed until after its growth phase
What are the three categories of oogenesis categorised by the relationship of the oocyte to other cell?
. Solitary
. Follicular
. Nutrimentary
What are the two types of oogenesis categories as categorised by the synthetic pathway for the stored yolk in the cytoplasm?
. Autosynthetic oogenesis
. Heterosynthesis oogenesis
Describe solitary oogenesis
The egg cell is floating around on its own and it is not associated with any other cells.
No follicle cells or muse cells.
Is associated with W covering of somatic cells
Describe follicular oogenesis
The germ cell becomes associated with the diploid somatic cells, provide a outer layer from the germ cell (protection)
Describe follicular oogenesis in insects (locusts)
Locusts have panoistic ovaries (with follicle cells) and oocyte develop within ovaries. So, the eggs are actually produced in structures called ovarioles which are closely associated with follicle cells
Describe an oviduct
Where the egg cells move down from the ovaries where they are formed
Describe the ovipositor
Point that the female will stick into the soil and lay her eggs
See middle of page 73
…
Describe nutrimentary oogenesis
Oocyte associated with sister nurse cells which supply it with nutrients. There is an outer layer of somatic follicle cells in an egg chamber
What kind of development do drosophila ovary show? What happens in this type of development?
Polytropic meroistic development- pogo is divide into oocyte and nurse cells
What do nurse cells pass to the egg? How do they pass these?
RNAs and nutrients between them. Passed using cytoplasmic bridges
See middle page 74
…
What is autosynthesis used in? How can it be demonstrated?
. The synthesis of yolk and other stored materials by the oocyte itself
. Uptake of low molecular weight precursors of yolk- amino acid and carbohydrates
. Sometimes observed in solitary oogenesis in polychaetes
. Can be demonstrated by labelling of precursors with radioactive tritium
When is heterosynthesis used?
. Synthesis of yolk proteins by other, non-germ cells (so doesn’t develop them themselves)
. Characterised by uptake if the yolk-precursor protein vitellogenin, later stored as vitellin
What evidence is there for heterosynthesis?
. From electron microscopy showing characteristic vesicle formation at the cell surface
. Electrophoresis showing proteins identical to the yolk protein in the body fluid
. Immunological demonstration of yolk protein-like proteins in the body fluid
Are most follicular and nutrimentary oocytes Autosynthetic or heterosynthetic?
Most follicular and nutrimentary oocytes are heterosynthetic (take in high precursors)
What is Vitellogenin? What is it converted to and by what?
Is a high MW protein transported to theoocyte bed converted to vitellin
Explain the ‘masked mRNA’ hypothesis
. During oogenesis the oocyte accumulates stores RNA, some of which is ribosomal
- much of the RNA is mRNA which stores developmental information
- the mRNA is ‘masked’- only available for protein synthesis after fertilisation because there are associated proteins that’s stop it from being translated
Picture at bottom page 75
…
Explain the development of the body plan in drosophila
They have too much yolk so only the nucleus can did use. Then as the yolk is used up as development occurs the other cells can divide outside of the embryo, they then go through the process of gastrulation- formation of the gut and germ layers. Embryo gets divided into smaller and smaller segments- segmentation (different body zones). All the processes take 9 days to get a fully formed fly.
See bottom page 76
…
