BIPN 144 – Spring 2015 Ethan Bier Week 5 Handout 1. Localized Determinants & Neural Specification 1. CENTRAL NERVOUS SYSTEM: NB FORMATION *Review: NBs are central nervous system (CNS) precursor cells with stem cell-‐like lineage (able to regenerate itself after cell division)  Give rise to another NB+ GMC  The GMC (ganglion mother cell) gives rise to 2 neurons What is a localized determinant? *Review: Lateral inhibition (Notch signaling) determines what cells become NBs & the NB delaminates so that it resides beneath the epidermis Page 1 of 5 BIPN 144 – Spring 2015 Ethan Bier How do localized determinants play a role in NB formation of the CNS? 2. PERIPHERAL NERVOUS SYSTEM: SENSORY ORGAN PRECURSORS (SOPs) SOPs are peripheral nervous system (PNS) sensory organ precursors that go through defined lineages (not stem cell-‐like)  Give rise to neurons and non-‐neuronal support cells What are the 3 sensory organ precursors (SOPs) of the PNS? • MD= Multiple Dendrite (Touch & Pain Receptors) o Have multiple dendrites coming out of the cell body o Dendrites are sensitive to physical distortion (touch, pain, heat) o Single SOP gives rise to single neuron • ES= External Sensory Organs (Innervated Hairs) o Innervated hairs detect brushing up against objects o Single SOP gives rise to 4 cell types: hair cell, Socket cell, glial cell, neuron • CHO= Chordotonal Organs (Stretch Receptors) o Ligament cell holds the cell body of the neuron fixed o Sheath is connected to the cap cell o Dendrite is pulled by cap cell & sends signal to neuron Page 2 of 5 BIPN 144 – Spring 2015 Ethan Bier What factor determines whether an SOP becomes an ES or CHO organ? What two mutants prove this? Diagram the cell lineage of an ES organ. IIa & IIb cells form an __________________________________ IIa has the same potential to become a IIb cell and make a neuron (does not mean they are equal) How does Numb function to bias Notch signaling in the secondary precursor cells? 2. Eye Development & Cellular Interactions 1. EYE DEVELOPMENT • 20-‐40 cells in eye imaginal discdivides to ~50,000 cells in larval stage • Hh activates Dpp in cells anterior to Hh expressing cells • Dpp activates Hh with a delay creates propagating positive feedback loop o Morphogenetic furrow moves across the eye disc • Each facet has 8 photoreceptors o R8 makes Boss (signal/ligand that activates Sevenless receptor in other cells) o R7 is sensitive to UV light Page 3 of 5 BIPN 144 – Spring 2015 Ethan Bier 2. MOSAIC ANALYSIS: Sevenless & Boss (I will explain in section!) -‐Sevenless (Sev) is expressed in many photoreceptor cells So how do we know in which cell does it function? -‐Mosaics allows us to analyze this by using an organism with cells that have different genotypes (A facet contains R1-‐R8 photoreceptor cells a mosaic fly eye can have a facet where some photoreceptor cells have a gene mutation and others don’t) • Use x-‐ray irradiation to induce mitotic recombination in flies heterozygous (+/-‐) for Sev gene (one good copy and one bad copy) o End up with cells that may be (+/+) and (-‐/-‐) o The bad copy of the gene is also associated with a pigment mutation (so we can tell which cells are mutant mutants will be a different color) • Look only at normal facets (that contain all 8 photoreceptors)  see which cells can be mutant for Sev but still form a normal facet In one experiment the following sets of cells were found to be mutant for Sev in clusters that had an R7 cell. From these data, which cell(s) require Sev function? 1.) R1, R2 2.) R1, R3, R4 3.) R6, R8 4.) R5, R6 5.) R5, R8 6.) R4, R6 7.) R1-‐R6, R8 In another experiment the following sets of cells were found to be mutant for Bride of Sevenless (Boss) in clusters that had an R7 cell. From these data, which cell(s) require Boss function? 1.) R1, R2 2.) R3, R5 3.) R1, R3, R7 4.) R5, R6 5.) R1, R2, R3 6.) R1-‐R7 7.) R7 Page 4 of 5 BIPN 144 – Spring 2015 Ethan Bier 3. BOSS-SEVENLESS SIGNALING PATHWAY • Sevenless is a ____________________________________(RTK) • Boss is a signal/ligand that is expressed in R8 cells Describe the steps of the Boss-Sevenless signaling pathway How does phosphorylation of Yan and Pnt contribute to the R7 cell fate? _____________________ is the TF that determines R7 cell fate (needs to be active to form R7) It is controlled by: • Yan= • Pnt= Unphosphorylated Phosphorylated by MAPK* Yan: Pnt: Yan: Pnt: Page 5 of 5