Drosophila Body plan

Question 1

What can be used as a readout for Drosophila segment identity and number?

Answer 1

denticle belts = cuticle productions, stereotypical and segment-specific

Question 2

What screen did Christiane Nüsslein-Volhard and Eric Wieschaus do and what was the result?
What method did they use to visualize deletions?

Answer 2

mutagenesis screen looking for defect in embryonic segmentation

saturation screen = mutagenized the genome until they got multiple alleles for each mutant

identified 15 loci that regulate segment number and polarity
also identified mutants that affect AP axis formation

polytene chromosomes to visualize deletions because they result in specific patterns

Question 3

Which are the 3 classes of segmentation mutants and what are their characteristics? Name 2 genes for each class.

Answer 3

segment polarity mutants = denticles are duplicated in a mirror image (gooseberry, patch)
pair-rule = even or odd segments are missing (even-skipped, odd-skipped)
gap = blocks of segments are missing (Krüppel, knirps)

Question 4

How were the genes important for segmentation ordered into hierarchy?

Answer 4

epistasis analysis

Question 5

How can you visualize gene products (mRNA and proteins) in situ?

Answer 5

old: autoradiographic exposure (up to 40 days!)

mRNA: in situ hybridization with dioxigenin-labeled RNA probe, which is then visualized with anti-dioxigenin AB coupled to a pigment producing enzyme

proteins: antibody staining (primary and secondary AB)

Question 6

What is the difference in expression pattern of segmentation and axis patterning genes?

Answer 6

segmentation genes are expressed in segmental patterns

axis patterning genes are expressed in gradients

Question 7

What was the “elegant” way to explain the regularity of patterns of gene expression and what actually happens?

Answer 7

Turing models for modelling, but not that simple

actually: regulated by cis-regulatory elements which read out morphogen concentration (above treshold = triggers target gene expression)

Question 8

What is segmentation?

Answer 8

visible morphogenetic process
determined by gene products acting before the segments become visible
gradients of maternal information are converted into discrete domains of gene expression

Question 9

In what order are segmentation genes acting?

Answer 9

maternal -> gap -> pair-rule -> segment polarity