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Download A Hierarchy of Genes Establish the Anterior-Posterior Axis
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A Hierarchy of Genes Establish the Anterior-Posterior Axis Maternal-effect genes Gap genes Pair-rule genes Segment polarity genes Selector genes 1 Maternal–Effect Genes Maternal genes. First Polarize the Embryo. mRNA and protein are deposit by Nurse cells. 3 gene groups: Anterior, Posterior, Terminal. Anterior group: Bicoid, Hunchback. Posterior group: Nanos, Caudal. Terminal group: Torso. Anterior Group – Bicoid (Head and Thorax) 2 A riboprotein complex transports it on microtubules to the anterior pole through a special sequence in the 3’ UTR of the mRNA. Translation happens only after fertilization. Bicoid is a transcription factor and acts as a morphogen. Two functions: translation repression (mRNA translation inhibitor) and transcriptional activation (transcription factor). Anterior Group - Hunchback A transcription factor activating anterior specifying gap and pair-rule genes as a morphogen. Two forms: maternal mRNA deposited in the oocyte homogenously and zygotic form activated after fertilization by Bicoid in the anterior part of the embryo. The maternal mRNA is inhibited in the posterior side by Nanos. Posterior Group – Nanos (Abdomen) 3 A riboprotein complex transports it on microtubules to the posterior pole through a special sequence in the 3’ UTR of the mRNA. Translation happens only after fertilization. Nanos acts as a morphogen. Functions as translational repressor (mRNA translation inhibitor). Terminal Group – Torso (Acron, Telson) Specifies the ends structures. Torso is a receptor tyrosine kinase – uniformly distributed throughout the egg plasma membrane. The ligand is released after fertilization, and is localized at the ends of the fertilized egg. After fertilization 4 Gap Genes The first zygotic genes in the A/P axis. Are expressed in broad domains. Their expression is controlled by maternal genes and by reciprocal interactions between them. Control the expression of downstream A/P genes – the Pair-rule genes . Pair-Rule Genes 5 Are the first periodic genes and define 14 parasegments. Each is expressed in seven stripes either odd or paired. The primary pair-rule genes expression pattern (e.g. eve) is determined by maternal and gap genes as well as reciprocal interactions between themselves. The secondary pair-rule gene expression (e.g ftz) is mostly established by the primary pair-rule gene pattern. Pair-Rule gene Regulation Even-skipped Red 6 Blue מעבודת ההכנה לתרגיל – 3 התפתחות מוקדמת בדרוזופילה bicoidהינו גן אימהי בעל תפקיד מכריע ביצירת הציר קדמי/אחורי )(A/P בעובר דרוזופילה מתפתח. תאר/י וצייר/י כיצד יראה עובר הדרוזופילה )ביחס ל (w.tבכל מקרה: Wild-type embryo A = Acron H = Head T = Thorax Ab = Abdomen Te = Telson Tail .1כאשר חלה מוטציה והעובר חסר הגן .(bcd - ) bicoid Head Wild-type embryo .2כאשר mRNA bicoidמוזרק לחלק קדמי ) (Anteriorשל ביצית לא מופרית .bcd - .3כאשר חלבון Bicoidמוזרק לחלק אמצעי של ביצית מופרית .bcd - .5כאשר mRNA bicoidמוזרק לחלק אחורי ) (Posteriorשל ביצית לא מופרית . .w.t 7 .10עובר חסר אחד מגני ה - Gapכיצד תיראה הלרווה?. Kruppel mutant .11עובר חסר אחד מגני ה ) Pair-ruleלדוגמא –fushi tarazu המופיע בפאראסגמנטים זוגיים( .כיצד יראה העובר? fushi tarazu mutant 8
