Molecular - gap genes etc

Question 1

Timeline

Answer 1

Nuclei divide and distribute around cell, but still one cell. 1.25 hrs = 128 nuclei, 2hrs 1500, 2.5 = 5000 - Cellular blastoderm, then cellularization/division.

Question 2

Between fertilization and cellularization what is happening?

Answer 2

2.5hrs for maternal effect gradient to be read, requires cascade of transcription factors.

Question 3

Maternal effect genes

Answer 3

Nanos at post., bicoid at ant (concentration gradients). Hunchback and caudal throughout, but hunchback repressed by nanos and caudal repressed by bicoid.

Question 4

What helps anchoring?

Answer 4

exuperantia for bicoid, oskar tudor and vasa for nanos

Question 5

Third maternal genes set

Answer 5

Terminal group including torso develops structures at both extremes (antennae, anus)

Question 6

Second set: Gap genes

Answer 6

Some of first embryonic genes to be expressed. They are TFs. Mutations result in gaps in segmentation. More complicated gradients.

Question 7

Examples of gap genes

Answer 7

Tailless, huckebein, buttonhead, empty spiracles, kruppel

Question 8

How are gap genes turned on?

Answer 8

Respond to bicoid, caudal, hunchback, torso, and others, which are binding to the promotor regions of the gap genes.

Question 9

Gap gene regulation

Answer 9

Affected by enhancers and enhancer synergy. Ex. 2 enhancers are important in the expression of each of hunchback, knirps and kruppel

Question 10

Pair-rule genes

Answer 10

Found in alternating parasegments, post half of one future segment and anterior half of next (ie offset). This is post-cellular blastoderm expression. They respond to the gap genes.

Question 11

Examples of pair-rule genes

Answer 11

Even-skipped and fushi-tarazu

Question 12

How is even-skipped set up?

Answer 12

Coding region with enhancer elements up (3, 2+7) and downstream (4+6, 1 and 5). Each affects a stripe or two

Question 13

Even-skipped expression experiment

Answer 13

Formed constructs with response elements in front of lacZ which causes blue precipitate so we can see where that response element is activated normally. Different elements are individually responsible for one to two stripes.

Question 14

Even-skipped and gap genes

Answer 14

Activated by hunchback, inhibited by kruppel, giant and knirps. Eve is expressed where [inhibitors] is lowest

Question 15

Even-skipped 2nd stripe

Answer 15

Hunchback binds on top, kruppel and giant on bottom of enhancer. Each stripe is a sum of the competition of the activators and repressors for the response elements.

Question 16

Promotors of pair-rule genes

Answer 16

Complex - different activators or repressors bind to the enhancers around the promotor, so very regulated. Determines which stripe is expressed where

Question 17

Penultimate set - segment polarity genes

Answer 17

Set up the polarity of the parasegment. Ant end will have high hedgehog and the post end with have high wingless. Positive feedback loop b/w these two gives post. polarity to segment

Question 18

Engrailed

Answer 18

Segment polarity gene. Engrailed is activated by high levels of even-skip or fushi tarazu; it is a TF and induces hedgehog.

Question 19

Hedgehog

Answer 19

Induced by engrailed. Activates cells anterior to it (which are in fact the post end of the next parasegment) and bind to patched there.

Question 20

Wingless

Answer 20

wingless is never expressed if neither eve or ftz at high []. Wingless is secreted, binds frizzled, which starts engrailed expression and induces hedgehog.

Question 21

Final set - homeotic genes

Answer 21

Determine differentiation pattern. Identified by phenotype from a mutation in these. Code for TF which activate cascades of genes

Question 22

How do we identify homeotic genes?

Answer 22

Look at homeobox (60 aa), highly conserved

Question 23

Homeotic complexes in drosophila

Answer 23

Two clusters of genes on same chromosomes: Antennapedia (lab, pb, Dfd, scr, Antp) and Bithorax (Ubx, abdA, AbdB)

Question 24

Homeotic gene expressions

Answer 24

Position in the genome matches expression in embryo, spatially and temporally. Results from reading the concentrations of other genes.

Question 25

Homeotic genes and evolution

Answer 25

First appeared pre-cambrian. Humans and drosophila very similar, line up closely. Humans have had gene duplications (4 sets). More complex animals have more homeotic genes.

Question 26

Flowers and hox genes

Answer 26

4 different Whorl genes. Whorl 1 = A genes, sepals; Whorl 2 = A and B genes, petals; Whorl 3 = B and C genes; Whorl 4 = C genes, ovaries