Zoo 470 Spring 2015 Unit 11 Anterior Posterior A P Axis Specification in Drosophila Key Terms Syncytial blastoderm cellular blastoderm cellularization Maternal polarity centers segmentation genes denticle band nanos bicoid torso Nurse cell oskar hunchback caudal pumilio Gap gene pair rule gene segment polarity gene even skipped eve fushi tarazu ftz wingless engrailed armadillo catenin hedgehog patched smoothened germ band extension cellular rosette non muscle myosin ventral furrow apical constriction homeotic gene homeobox homeodomain antennapedia General notes a We will be covering much of the material on anterior posterior patterning in flies Because it is significantly more complicated than A P patterning we will NOT be covering dorsoventral patterning or most of the terminal system in lecture This is a tactical decision due to a vast amounts of material and molecular detail and b less direct connection to molecular mechanisms in vertebrates b Although we will be covering much of the material on anterior posterior patterning in flies we will intentionally cover this material at a level that is somewhat more basic than the presentation in your text Focus on the learning objectives and level of presentation in lecture for your exam preparation c Although we will cover things basically as they are presented in your text an A P axis by the numbers handout will likely be produced to aid your study Learning Objectives By the end of this unit you should be able to 1 Explain how the early mitoses in the fly embryo allow for the establishment of simple gradients of proteins to be established after fertilization 2 Explain how denticle bands were used as the basis for genetic screens to identify maternal effect and zygotic mutants that affect A P patterning 3 Provide evidence from classic experiments to show that there are maternal polarizing centers at the anterior and posterior ends of the early fly embryo 4 List the major maternal effect genes that are responsible for polarizing the zygote 5 Explain how key maternal mRNAs are provided to the oocyte how they localize once inside the oocyte and the cytoskeletal system responsible for their transport 6 Outline the levels of genetic control of anterior posterior patterning in the embryo as a flow chart explaining the main role of maternal genes gap genes pair rule genes segment polarity genes and homeotic genes 7 Explain how bicoid functions to establish anterior fates how the distributions of bicoid mRNA and protein in normal fly oocytes and zygotes are important for this process and how the bicoid protein gradient affects zygotic hunchback transcription as well as translation of caudal mRNA 8 Explain how nanos functions in the posterior how the distributions of nanos mRNA and protein in normal fly oocytes and zygotes are important for this process and how the nanos protein gradient affects the translation of hunchback mRNA via pumilio 9 Explain the basic actions of the gap pair rule and segment polarity genes at what approximate stage of development each class of gene acts and how these classes of genes interact with one another and maternal genes in a general way 10 Describe the basic expression pattern of a typical gap gene what happens when one is mutated and what sorts of proteins they encode 11 Describe the basic expression pattern of a typical pair rule gene how the domains of expression of pair rule genes relate to one another what type of protein each encodes and what happens when one is mutated 12 Explain in a general sense how gap proteins regulate expression of pair rule genes 13 Describe the basic expression pattern of a typical segment polarity gene what happens when one is mutated and in a general way how are the levels of pair rule gene products regulate where segment polarity genes are expressed 14 Explain why cellularization requires cell cell signaling in the later embryo and how reciprocal wingless Wnt and hedgehog signaling is involved in establishing segmental boundaries 15 Describe what morphogenetic movements characterize gastrulation and what set of cells are internalized through these movements 16 Describe a homeotic mutation the types of proteins encoded by homeotic genes and explain how are their regions of expression relate to their position on the chromosome Reading assignment Gilbert 9e Ch 6 pp 201 213 218 235 OR Gilbert 10e Ch 6 pp Ch 6 pp 179 186 194 204 204 213