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I can’t wait to grow up!
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Laugh now
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The fruit fly body plan is self-assembled in 24 hours
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How is the body plan specified? Egg ---> animal in 24 hours!
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Eric Wieschaus and Christiane Nüsslein-Volhard used genetics to identify proteins that set up the embryonic body plan
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The molecular genetics of pattern formation in candy corn The wild-type pattern Anterior Posterior
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We collected a series of mutants affecting the body plan Wild-type Anterior group Gap gene Posterior group Morphogenesis defects
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The wild-type body is segmented and each segment has a unique identity and thus produces distinctive structures
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Wieschaus and Nüsslein-Volhard removed single genes and looked for effects on the body plan
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Wildtype larva bicoid mutant bicoid mutants have no head!! Gilbert Fig. 9.13
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Remember that cleavage starts without cell division in Drosophila
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= bicoid mRNA= nanos mRNA
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Increasing Bicoid concentration Head Tail Bicoid accumulates in a gradient
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A gradient of the bicoid transcription factor turns on different genes at different "thresholds"
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These “bicoid target genes” are known as the gap genes Hunchback Kruppel Knirps Expression pattern of proteins ecoded by gap genes
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Hunchback Kruppel
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Gap gene mutants are missing different regions of the body
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Wildtype Krüppelhunchback knirps
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Hunchback Kruppel
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Alberts Chapter 8 title page
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So, in summary so far… Maternal Determinants Zygotic Gap Genes Zygotic Pair-rule Genes
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Figure 9.8(1) Model of Drosophila Anterior-Posterior Pattern Formation
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Isn’t life wonderful, beautiful and incredible!
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Ed Lewis was far ahead of his time
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who’s
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Wildtype Antennapedia mutant
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Wildtype Ubx mutant T2 A2 T3 and A1 take on a 2nd thoracic identity T2
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Wildtype Ubx abdA AbdB triple mutant T2 T3 A1 A8 T2 All segments take on a 2nd thoracic identity
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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
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Figure 9.28 Homeotic Gene Expression in Drosophila
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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
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Lewis hypothesized that the duplication and diversification of homeotic master regulators underlies the evolution of an increasingly complex body plan
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The human body is also built up from reiterated units with different identities along the A/P axis
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As we’ll see later, mammals also have homeotic genes expressed at different places along the A/P axis
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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.
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