Chapter 9 - Axis specification in Drosophila

1. Chapter 9 - Axis specification in Drosophila • Drosophila genetics is the groundwork for _______________lgenetics • Cheap, easy to breed and maintain • Drosophila geneticists take pride in being __________, in ___________ information and being Mac users. • Problems- fairly complex, non-transparent Fig. 8.1

2. 1. Cleavage Drosophila • Insects tend to undergo ________________- cleavage occurs at _____ of the egg • In contrast to other creatures, insects form nuclei, then____ ________ Termed a __________ _______ • Mitotic divisions • #1-#9 - duplicate _____ (8 min/division) 1 7 • Mitotic division • #10 – nuclei _______ to rim • Mitotic division • #11-14 – progressively _________divisions 10 Fig. 9.1

3. 1. Cleavage Drosophila 14 Note – each nuclei has a _________ of cytoskeletal proteins • Mitotic divisions • #14 – cells created with each nuclei to create the _______ _____________ Nuclei staun Tubulin stain Egg plasma membrane _____ between nuclei to create individual _____ Cycle 11-14- ______ ___________- nuclear division slows and __________ increases Fig. 9.3

4. 2. Gastrulation Ventral Dorsal Ventral furrow (from mesoderm) Fig. 9.6 Segments Head 3 _____ 8 _________ Fig. 9.7 It becomes the ventral tube

5. 2. Gastrulation Establishment of anterior-posterior polarity- Protein gradients rule the day Gene family Examples a. _______________- in specific region of egg bicoid ____ caudel b. _____-among 1st gene transcribed in embryo Kruppel _________ c. ______ – result in 7 bands fushi tarazu ______ d. ____________ – result in 14 segments _______ wingless Fig. 9.8

6. 2. Gastrulation a. Maternal effect genes Active during creation of _________________ _______mRNA injected, localize to posterior _____mRNA injected in anterior Caudel (diffuse) Hunchback (diffuse) Fig. 9.10 Bicoid prevents ____ mRNA _____________ Nanos prevents_________ mRNA ___________

7. a. Maternal effect genes Mechanism Oocyte ________ Anterior Caudel and hunchback mRNA _____ mRNA ______mRNA Syncytial Blastoderm _______ Posterior Fig. 9.11

8. a. Maternal effect genes What if we mess up the ______gradient? Inject bicoid into: Wild-type Bicoid- mutant Bicoid-/- Bicoid-/- Wild-type Anterior Middle Posterior Head in ____ Two ____ _________ Thus, bicoidspecifies _______ development Two ____ Fig. 9.14

9. How does nanos specify __________? Answer- By preventing _________ translation Mechanism In anterior, ________ binds 3’UTR (untranslated region) of hunchback mRNA, and mRNA is polyadenylated and translated Anterior (no nanos) Posterior (with nanos) In posterior, nanos prevents _____________, and thus prevents ____________ Fig. 9.16

10. 2. Gastrulation Segmentation genes Gap Pair-rule Segment polarity • __________ • ________ genes ____________ genes Egg Specification Determination Bicoid, nanos, hunchback, caudel, etc. b. Gap genes c. ________ genes d. Segment polarity genes Two steps in Drosophila development (Cell fate is flexible) (Cell fate is determined) Maternal effect genes activate ____ genes, which activate _________ genes, which activate ________________ genes Fig. 9.19 Segmentation genes establish ___________

11. a. Gap Genes Gap hunchback • Gap genes respond to ________ _______ proteins • Gap proteins interact to define specific________ of embryo • Four major gap proteins- _______, ________, ________, _______ • These are all _____________ proteins- activate or repress ______________ giant kruppel knirps Fig. 9.21

12. b. Pair-rule genes • Gap genes activate and repress ___________ genes in ________ stripe, resulting in ________ stripes • Three major pair-rule proteins- ______, _____________, ______ • These are all ____________ proteins- activate or repress transcription • Cells in each ______________contains • a unique ______ of pair rule genes expression unlike any other parasegment Fig. 9.21 Pair-rule

13. b. Pair-rule genes Pair-rule Why do we observe expression of pair-rule proteins in ______________ segment? Answer- pair-rule genes use different ________ elements Example- even-skipped (a pair-rule gene) has several _______, but only one is _________ in a given stripe Different concentrations of ____ proteins determine _________ gene expression This ________ is only active in stripe #1 Fig. 9.22

14. c. _________ __________ genes Maternal, gap and pair-rule genes operate______ cells are formed Pair-rule Segment polarity _____________________ 14 Segment polarity genes act once cells are _______ Fig. 9.1

15. c. Segment polarity genes Segment polarity genes encode proteins that make up ________ and __________ signal transduction pathways One cell produces ________ The adjacent cell produces ________ Fig. 9.25 Wingless and hedgehog activate expression of _________ indirectly

16. 2. Gastrulation _______ _______ genes Responsible for directing structure formation of each segment • These genes are clustered on chromosome 3 in the ________ • ___________ (also called Hom-C) in two regions- • The _______________ complex- • The ________________ complex- Two amazing features 1. The _____ of these genes on the chromosome matches order of ______________ expression Chromosome 3 2. _____________ are regulated by all gene products expressed ___________ to it

17. What about ______________ polarity?? • This occurs _______cells are created (post syncytial blastoderm) • ______ ( a transcription factor) gradient is established • Dorsal is found throughout syncytial blastoderm, but only in _______ of ______cells How does this occur? By a very complex pathway involving _____ and __________ proteins ( and a host of other proteins) Organs form at the ___________ of dorsal-ventral and ____________ regions of gene expression