D104 Lecture 5.docx

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Biological Sciences
Ken Cho

D104 Lecture 5 • review session for midterm exam on jan 21 Monday 4-6 pm Rm 4201 Nat Sci II Increasing the bicoid copy number results in a coordinate shift in the domain of Hb expression • changing the concentration (maternal effect genes control the expression of gap genes) of bicoid changes the expression of hunchback hunchback activates and represses Kruppel genes • Kruppel expressed in the middle part of the embryo • Hunchback acts as a morphogen to control the expression of Kruppel • Once Kruppel increases in concentration, Hb repressed Kruppel expression in the anterior region of the embryo (zygotic Hb gene) • Hb protein was controlled by using the bicoid mutant (Hb comes from the maternal)— bicoid absent in this case so not as much Hb o Hb fails to suppress Kruppel expression in the anterior portion b/c Hb never reached the original threshold (vs. left box comparison) • Gap gene control the expression of another gap gene Mutual regulation of gap gene expression • One gap gene controlling the expression of another gap gene causes mutually exclusive domains • Gap genes control the pair rule genes and the pair rule genes control the segment polarity genes Segment vs. parasegment reading pg. 66-70, 81-86 • parasegment: segment at cellular blastoderm stage (much earlier stage) • segment: actual segment in adult flies • talk about parasegments when talk about gene expression • Yellow box=odd numbered genes (pair-rule genes) • white box =even numbered genes (other parasegment genes) • embryo has 14 parasegments Mutant phenotypes of pair-rule genes • embryo ends up with only 7 parasegments in mutants vs. 14 parasegments in normal embryo • focus on even-skipped today Pair-rule gene expression • Which mutation is this : even skipped (purple disappeared) o without the dotted lines, it could be Krupple Primary and secondary pair-rule genes • pair rule genes controlled by gap genes and also materal effect genes The eve promoter contains “independent” regulatory modules for “individual” stripes • yellow regions = regulatory regions/genes to control eve gene • distinct regions that control spatial expression in the embryo Stripe 2 element controls expression in parasegment 3 Multiple gap genes regulate eve stripe 2 • as go down to posterior end, bicoid expression decreases • giant (gap gene) • notice the different curves (relationships) eve stripe 2 element • 2 stripe is parasegment 3: in this region, bicoid and hunchback are expressed (stripe 2 element)—they activate stripe 2 eve stripe 2 element etc • what transcriptional factors present in surrounding environment of stripe 2 eve? o hunchback, giant, bicoid  giant represses gene expression eve stripe 2 element etc 3 • no bicoid • hunchback present • Kruppel present (functions as a repressor to silence the eve strip 2 element) • the only region that stripe 2 element is activated is when they are in parasegment 3 Clicker question: What would happen to the expression of eve stripe 2 if you managed to express Kr protein throughout the embryo? No expression (b/c would act as a repressor) Segment polarity genes • denticles: anterior part of segment • posterior part of segment is missing denticles (naked) nd • 2 box (on right), posterior segment has failed and anterior segment takes its place (two anterior segmen
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