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EMBRYO SQ 5-6 FULL.doc

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Department
Biology
Course
BIOL 303
Professor
Dragana Miskovic
Semester
Summer

Description
Lecture 5-6, half of 7 Study Questions 1. What determines patterning during early Drosophila development? - Patterning determined by Body segmentation that are established by release of morphogens o Create gradient that provide cell w/ precise 3D positioning AND developmental info - Interaction b/w egg and follicular cells in ovary > influence location of maternal determinants 2. When are A-P and D-V axes specified during Drosophila development? How is this different (or not) from C. elegans (or Sea urchin) early development? - Anterior-Posterior Axis o Unchanged after fertilization o Border cells contribute in oocyte o Specified during oogenesis (before fertilization) - Dorsal-Ventral Axis o Specified during oogenesis - C. elegans o Anterior-poster = specified by site sperm entry (sperm pronucleus = posterior) o Dorsal-ventral axis specified by AB p cell - Sea Urchin o AP axis specified by animal-vegetal axis before fertilization o DV axis specified after fertilization 3. What are the differences between two different types of blastoderm formed sequentially during early Drosophila development? - Syncytial blastoderm – peripheral nuclei w/ same cytoplasm, no cell membranes, formed at 9 cell divisin th - Cellular blastoderm – nuclei separated by membranes, formed at 13 cell division 4. Define germ band (in respect to germ layers and function). - Germ band = collection of cells along ventral midline that includes all cells that will form trunk of embryo o Made of ectoderm and mesoderm o Retraction, dorsal closure controlled by AMNIOSEROSA 5. What are the types of genes involved in determination of anterior-posterior axis (anterior-posterior pattern formation) in Drosophila? - Maternal egg polarity genes: o Bicoid, hunchback regulate anterior structures o Nanos and caudal regulate posterior structures 6. The graph and picture below show the distribution of the bicoid protein during the early Drosophila development. Is bicoid protein acting as a transcription or translation factor at this point? Explain your reasoning. What does it control (expression of which proteins)? - Bicoid protein controls expression of caudal protein from maternal mRNA (translation factor) - Bicoid protein entered nuclei = transcription factor > regulate gene expression of anterior embryo hunchback protein 7. Where are bicoid and nanos mRNAs produced during Drosophila oogenesis and where are they localized in the early embryo? - Nanos and bicoid mRNA secreted by ovarian nurse cell o Bicoid localized in anterior embryo (BA) o Nanos localized in posterior embryo (NP) 8. You isolate embryos laid by a female Drosophila that lacks both copies of the bicoid gene (homozygous mutant). Describe (in 1-3 sentences or with a clearly labeled diagram) what would be the spatial distribution of caudal protein that is made from the corresponding maternal caudal mRNA in these mutant embryos at the syncytial blastoderm stage. Explain in additional 1-3 sentences how and why this distribution is different from that seen in normal embryos. - Translation of caudal protein mRNA not repressed = translation in anterior embryo = spatial distribution in anterior and posterior areas o Caudal protein activate transcription of genes in anterior nuclei = no head or thorax, acron region formed, and another telson forms instead - Distribution different b/c bicoid protein in anterior embryo acts as translation factor preventing caudal protein from being made in anterior part o Allows transcription of gap genes (hunchback) for anterior which forms acron, telson, 9. Thinking question (possible bonus): You inject synthetic bicoid mRNA into the middle of the egg laid by female homozygous mutant for a bicoid. Describe (in 1-3 sentences or with a clearly labeled diagram), what do you expect to be the spatial distribution of caudal protein at the syncytial blastoderm stage that is made from the corresponding maternal caudal mRNA in these embryos. Explain how this distribution is achieved in additional 1-3 sentences. - Translation of bicoid mRNA into bicoid protein repress translation of caudal protein in the middle so caudal protein will be isolated to posterior and anterior end resulting in 2 telson distal regions and a head/thorax in middle 10.What are the major posterior determinants in an early Drosophila development? - Nanos protein and scaffold protein 11.What is the terminal embryonic determinant in an early Drosophila development? What is the consequence in the homozygous mutant for this protein? - Terminal embryonic determinant = torso-like protein o Homozygous Mutation for this protein = no activation of terminal gap genes or torso protein kinase = missing acron, telson 12.Compare syncytial with autonomous and conditional cell specifications in respect to interactions between cells (be careful here, it’s somewhat a tricky question). - Autonomous spec
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