2008 Annual Science Report
Massachusetts Institute of Technology Reporting | JUL 2007 – JUN 2008
Requirements for the Development and Maintenance of Complex Life
Our work on jellyfish Aurelia involves examination of neural and sensory development and developmental genetics in all three developmental stages (planula, polyp and medusa), using a range of techniques TEM, confocal microscopy combined with in situ hybridization and antibody studies. These permit a three-dimensional understanding of neural morphology and developmental process as well as the loci of gene expression in that developmental context.
1) We documented two sensory systems in the planula larva: A lateral system, presumptively associated with mechano-sensation and locomotion, develops first; and an “apical” sensory system, likely associated with larval settlement, appears at the end of larval development. These sensory structures express distinct sets of neural peptides and may be evolutionary precursors to posterior sensory structures, e.g. ears/lateral line, and anterior, e.g. olofactory/ adenohypophyseal, in Bilateria suggesting a range of testable hypotheses.
2) We documented the de novo development of polyp nervous system. Following settlement the entire planuula endoderm and nervous system is lost, in a process involving markers for cell death (caspase). A new polyp nervous system then develops, apparently from cells that migrate form the ectoderm – multiple nervous systems develop in through cnidarian life-history.
3) Expression studies of the rhopalia, the sense organ bearing features of the medusa, demonstrate that genes involved in sensory cell differentiation in bilaterians are also involved in differentiation of these sense organs and subsets of sensory cell types within them. Neural and sensory gene homologues studied include, Brain, sine oculis, optix, eyes absent and Otx. Of the many detailed aspects of this work, the expression of Otx homologues in association with the neural connectivity of statocyst and eye, may be the most striking as it suggests a developmental role similar to that of the bilaterian homologue expressed in brain area associated with integration of sensory information from the eye and ear.
PROJECT INVESTIGATORS:David Jacobs
RELATED OBJECTIVES:Objective 3.2
Origins and evolution of functional biomolecules
Foundations of complex life