L13: drosophila- zygotic patterning

what do snail gene promotors make

mesoderm

what do rhomboid gene promotors make

neuroectoderm

how are snail genes expressed

low affinity dorsal binding sites: only expressed with high level of nuclear dorsal

how are rhomboid genes expressed

high dorsal binding sites but repressed by snail

where are rhomboid gene promotors expressed

laterally on both sides of mesoderm

what gene is expressed at low levels of nuclear dorsal

rhomboid

what gene is expressed at high levels of nuclear dorsal

snail, also interferes with rhomboid expression

what gene is present in the dorsal ectoderm

decapentaplegic (Dpp)

what is Dpp conserved at in vertibrates

bone morphogenetic protein (BMP)

what 4 domains are formed along the D/V axis

D → V

amnioserosa → dorsal ectoderm → neuroectoderm → mesoderm

what are gap genes

genes encoding transcription factors

create a combinatory code that defines different regions in the embryo

what 2 gap genes set up the expression of other gap genes

hunchback + bicoid

what gap genes are responsible for striped pair rule expression

even skipped (eve) + fushi tarazu (ftz)

how are individual stripes generated in pair-rule expression

specific combinations of gap genes

what are pair rule expression stripes known as

parasegments

how do pair-rule gene expression stripes relate to visible segments

slightly shifted, anterior part of eve expression stripe formed posterior of larval segment

how is engrailed switched on

high levels of Ftz or Eve

what is engrailed expression described to be

14 striped

how are wingless and hedgehog induced

first under the influence of the pair rule genes + then due to a feedback loop

describe the feedback loop between wingless + hedgehog

hedgehog maintains wingless + wingless maintains hedgehog + engrailed

where do Wg + Hh act

across cell boundaries

what occurs due to reduced or aberrant activity of Wg + Hh

variety of congenital defects

what results from inappropriate activation of Wg

colon cancer

what results from innapropriate activation of Hh

basal cell carcinoma

how many segments are formed along the A/P axis

14

what specifies the identity of the 14 identical segments

hox genes / homeotic selector genes

what are homeotic mutations

one structure is replaced with another

how are hox genes organised

usually in a single complex

(split into 2 in drosophila)

how many hox complexes are in vertebrates

4

what 3 genes make up the bithorax complex

Ubx, abd-A, abd-B

what happens when Ubx, abd-A, + abd-B are absent

most segments take on T2 fate

(T1, T2 → T2, A9)

what happens when only Ubx is present

most abdominal segments take on A1 fate

(T1, T2, T3, A1 → A1, A9)

what happens when only Ubx + abd-A are present

A5 to A8 take on A4 fate

(T1, T2, …, A3, A4 → A4, A9)

what happens when only abd-A + abd-B are present

T3 to A1 take on T2 fate

(T1, T2 → T2, A2, …, A8)