animal physiology and development insects – 4 jcs lecture outcome: by the end of this lecture...
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Animal Physiology and Development Insects – 4 JCS
Lecture Outcome:
By the end of this lecture student should have:
a) Become aware of the role of the imaginal discs in imaginal development.
b) Understood the evidence for their determined state as a result of transplantation experiments.
c) Appreciated how the determination becomes more specific as larval development progresses and the discs grow and how this can be determined using mitotic recombination..
d) Understood the concept and evidence of compartments.
e) Followed the development of one imaginal disc – the wing disc.
JCS 6/11/02
Location of imaginal discs within the larva
Transplant experiments – discs into meta-morphosing larvae give rise to specific adult parts in the abdomen of the hosts
Transplantation of cut pieces of discs into meta-morphosing larval hosts shows that in mature disc each part is determined. Note: that the discs are folded and the distal parts are central
Wing disc Leg disc
The study of disc development is very much the investigation of how this occurs.
For developmental biologists the nice thing about imaginal discs is that they are discrete developmental fields and easily manipulated.
Relationship between disc structure/ determination and final adult structure of the wing and the leg.
Determination state is stable – persists on extended culture of discs in female abdomens…
..but change of disc from one disc to another
type can occur – Transdetermination.
Marking a single cell and its mitotic descendants by creating a genetic change (mitotic recombination) using X-rays
The clone is visible because the cell from which the clones originates is made homozygous for recessive mutants which colour the cuticle or facets of the eye
or the affect shape/number of bristles and hairs.
How mitotic clones are poroduced with X-rays
Minute+/Minute- cells grow slowly compared to wild type
Homozygous Minute- cells die.
Wild-type cells thus grow to become very large clones in a Minute+/Minute- organism
Large clones can show restrictions – i.e. cells and their descendants are restricted to compartments by compartment boundaries
Minute+
clone
Note how the large ‘Minute’ clones readily define the compartment border
engrailed mutation affects the wing (see below). Gene is expressed in every segment of the early embryo and
then is maintained throughout disc development.
engrailed is a segment polarity gene. It
Leg disc - gene expression patterns and eversion
Wing disc – dorso-ventral compartments and eversion