I can’t wait to grow up!

Laugh now

The fruit fly body plan is self-assembled in 24 hours

How is the body plan specified? Egg ---> animal in 24 hours!

Eric Wieschaus and Christiane Nüsslein-Volhard used genetics to identify proteins that set up the embryonic body plan

The molecular genetics of pattern formation in candy corn The wild-type pattern Anterior Posterior

We collected a series of mutants affecting the body plan Wild-type Anterior group Gap gene Posterior group Morphogenesis defects

The wild-type body is segmented and each segment has a unique identity and thus produces distinctive structures

Wieschaus and Nüsslein-Volhard removed single genes and looked for effects on the body plan

Wildtype larva bicoid mutant bicoid mutants have no head!! Gilbert Fig. 9.13

Remember that cleavage starts without cell division in Drosophila

= bicoid mRNA= nanos mRNA

Increasing Bicoid concentration Head Tail Bicoid accumulates in a gradient

A gradient of the bicoid transcription factor turns on different genes at different "thresholds"

These “bicoid target genes” are known as the gap genes Hunchback Kruppel Knirps Expression pattern of proteins ecoded by gap genes

Hunchback Kruppel

Gap gene mutants are missing different regions of the body

Wildtype Krüppelhunchback knirps

Hunchback Kruppel

Alberts Chapter 8 title page

So, in summary so far… Maternal Determinants Zygotic Gap Genes Zygotic Pair-rule Genes

Figure 9.8(1) Model of Drosophila Anterior-Posterior Pattern Formation

Isn’t life wonderful, beautiful and incredible!

Ed Lewis was far ahead of his time

who’s

Wildtype Antennapedia mutant

Wildtype Ubx mutant T2 A2 T3 and A1 take on a 2nd thoracic identity T2

Wildtype Ubx abdA AbdB triple mutant T2 T3 A1 A8 T2 All segments take on a 2nd thoracic identity

Is Ubx is expressed at the right time and place to make in T3 different from T2? Yes! Ubx is expressed in T3 and A1

Figure 9.28 Homeotic Gene Expression in Drosophila

Ultrabithorax, abdA, and AbdB normally repress expression of the“leg gene” Distalless in the abdominal segments Distalless in wild-typeDistalless in triple mutant T1 T2 T3 abdomen

Lewis hypothesized that the duplication and diversification of homeotic master regulators underlies the evolution of an increasingly complex body plan

The human body is also built up from reiterated units with different identities along the A/P axis

As we’ll see later, mammals also have homeotic genes expressed at different places along the A/P axis

DELTA mutant cells can be rescued by wild type neighbors. Therefore, DELTA must be the SIGNAL. NOTCH mutant cells cannot be rescued by wild type neighbors. Therefore, NOTCH must be the Receptor.