13/ drosophila patterning the embryo Flashcards
how is mesoderm made
- different levels of nuclear dorsal lead to dif genes being expressed
- promotors on snail gene has low affinity dorsal binding sites so are only expressed when a high number of nuclear dorsal are present
- make mesoderm
how is neuroectoderm made
- rhumboid has high affinity dorsal binding sites in its promotor and is repressed by snail
- expressed laterally on both sides of mesoderm
- make neuroectoderm
what is Dpp
- ligand that sets up a second signalling centre on the dorsal side of the embryo in the dorsal ectoderm
- in drosophila
what is bone morphogenetic protein bmp
- ligand that sets up a second signalling centre on the dorsal side of the embryo in the dorsal ectoderm
- in vertebrates
gap genes: how are they activated, what is a primary target, what does this do, what do gap genes create, what does this do
- a/p gradients of bicoid and nanos activate a number of genes encoding transcription factors - gap genes
- primary target is hunchback gene, which together w bicoid sets up expression of other gap genes
- cap genes create a combinatory code that defines dif regions in embryo
pair rule expression, whats responsible, even and odd segments names
- gap genes
- even skipped/ eve
- fushi tatazu/ ftz
- each stripe is a unique gap gene combo
why are pair rule gene expression stripes known as para segments
- pair rule gene segments slightly shifted relative to visible segments
- eg anterior of even skipped stripe forms posterior of a larval segment
what does the segmentation gene elaborate the pair rule pattern into
a segmental pattern
what switches on engrailed, how many stripes does it express, do engrailed positive cells form the anterior or posterior boundary of the segment
- high levels of ftz or eve
- 14, forms 14 identical segments
- posterior
what 2 other signalling genes are expressed adjacent to engrailed En, how are they expressed, can they act across cell boundaries
- wingless Wg
- hedgehog Hh
- first under influence of pair rule genes
- then as a result of feedback loop: wg maintained by hh
- and en and hh by wg
- yes
what does inappropriate expression of wnt (wg in drosophila) and hh in humans lead to
- wnt - colon cancer
- hh - basal cell carcinoma
what gene specifies identities of identical segments, what types of mutations discovered these genes
- homeotic selector genes - HOX genes
- homeotic mutations - one structure is replaced by another:
- bithorax - 4 wings
- antennapedia - antenna turned into legs
how are hox genes dif in drosophila compared to most organisms
- most organisms hox genes are a single complex - hox complex
- in drosophila its broken into 2 pieces
what does the order of hox genes in the genome reflect
- spatial and timing of expression
- 3’ first and most anterior (head), 5’ last and most posterior
what is the bithorax complex responsible for
diversification of posterior segments
which genes are cell-cell signals and which are tfs
- cell-cell: wg, hh
- tfs: hunchback, en, ftz, eve
how many homeotic gene complexes do mammals have
4
