Chapter 9 - Axis specification in Drosophila

• Drosophila genetics is the groundwork for _______________l genetics

• 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

• Insects tend to undergo ________________- cleavage occurs at _____ of the egg

• In contrast to other creatures, insects form nuclei, then ____ ________

Fig. 9.1

Drosophila1. Cleavage

1 7

10

• Mitotic divisions #1-#9 - duplicate _____ (8 min/division)

• Mitotic division #10 – nuclei _______ to rim

Termed a __________ _______

• Mitotic division #11-14 – progressively

_________divisions

Fig. 9.3

Drosophila1. Cleavage

14• Mitotic divisions #14 – cells created with each nuclei to create the _______ _____________

Note – each nuclei has a _________ of cytoskeletal proteins

Nucleistaun

Tubulinstain

Egg plasma membrane _____ between nuclei to create individual _____

Cycle 11-14- ______ ___________- nuclear division slows and __________ increases

2. Gastrulation Ventral Dorsal

Ventral furrow(from mesoderm)

It becomes the ventral tube

Segments

3 _____

8 _________

Head

Fig. 9.6

Fig. 9.7

2. Gastrulation

Establishment of anterior-posterior polarity-

a. _______________- in specific region of

egg

b. _____-among 1st gene transcribed in embryo

c. ______ – result in 7 bands

d. ____________ – result in 14 segments

Gene family

Fig. 9.8

Examples

bicoid____

caudel

fushi tarazu______

Kruppel_________

_______wingless

Protein gradients rule the day

2. Gastrulation

Active during creation of _________________

Fig. 9.10

_____ mRNA injected in anterior

_______ mRNA injected, localize to posterior

Hunchback (diffuse)Caudel (diffuse)

Bicoid prevents ____ mRNA _____________Nanos prevents_________ mRNA ___________

a. Maternal effect genes

Oocyte ________

Syncytial Blastoderm _______

Mechanism

Anterior

Posterior

a. Maternal effect genes

Fig. 9.11

______mRNA

_____ mRNA

Caudel and hunchback mRNA

What if we mess up the ______gradient?

Bicoid- mutant

Wild-type

Two ____

Inject bicoid into:

Anterior

Wild-typeBicoid-/- Bicoid-/-

Middle Posterior

_________ Head in ____

Two ____

Thus, bicoid specifies _______ development

a. Maternal effect genes

Fig. 9.14

How does nanos specify __________?Answer- By preventing _________ translation

Anterior (no nanos)

MechanismIn anterior, ________ binds 3’UTR (untranslated region) of hunchback mRNA, and mRNA is polyadenylated and translated

In posterior, nanos prevents _____________, and thus prevents ____________

Posterior (with nanos)

Fig. 9.16

2. Gastrulation Segmentation genes

Two steps in Drosophila development

Bicoid, nanos, hunchback, caudel, etc.

a. __________ ________ genes

____________ genes

b. Gap genes c. ________ genes

d. Segment polarity genes

Specification DeterminationEgg(Cell fate is flexible) (Cell fate is determined)

Maternal effect genes activate ____ genes, which activate _________ genes, which activate ________________ genes

Segmentation genes

establish ___________ Gap Pair-rule Segment polarity

Fig. 9.19

a. Gap Genes

• Gap genes respond to ________ _______ proteins

• Gap proteins interact to define specific________ of embryo

• Four major gap proteins- _______, ________, ________, _______

•These are all _____________ proteins- activate or repress ______________

Fig. 9.21

Gap

hunchback

giant

kruppel

knirps

Fig. 9.21

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

Pair-rule

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

Fig. 9.22

This ________ is only active in stripe #1

b. Pair-rule genes

Different concentrations of ____ proteins determine _________ gene expression

c. _________ __________ genes

Pair-rule Segment polarity

Segment polarity genes act once cells are _______

_____________________

Maternal, gap and pair-rule genes operate ______ cells

are formed

14

Fig. 9.1

c. Segment polarity genes

Segment polarity genes encode proteins that make up ________ and __________ signal transduction pathways

One cell produces ________

The adjacent cell produces ________

Wingless and hedgehog activate expression of _________ indirectly

Fig. 9.25

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-

Chromosome 3

1. The _____ of these genes on the chromosome matches order of ______________ expression2. _____________ are regulated by all gene products expressed ___________ to it

Two amazing features

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