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

Disc growth from clonal analysis

Very early induction of Minute clones

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

Signalling to derive compartments and specify the determination of the wing.

Leg disc - gene expression patterns and eversion

Wing disc – dorso-ventral compartments and eversion

From oogenesis to the imago