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SUMMARY:Evolution of color and motion vision - Claude Desplan- NYU Biology
DTSTART:20160114T160000Z
DTEND:20160114T170000Z
UID:TALK63197@talks.cam.ac.uk
CONTACT:Sarah Harrison
DESCRIPTION:Like the human retina\, the Drosophila retina contains randoml
 y distributed color photoreceptor cells that are defined by the expression
  of different color sensitive Rhodopsins.  In Drosophila\, two types of in
 dividual unit eyes (ommatidia) are specified by stochastic expression of t
 he transcription factor Spineless. This decision is controlled by a two-st
 ep process: First\, each allele of spineless randomly makes a cell-intrins
 ic ON/OFF expression decision governed by global activation coupled with s
 tochastic repression. When the expression decisions disagree (one allele O
 N and one allele OFF)\, interchromosal communication coordinates expressio
 n state between the two alleles. This effect does not depend on chromosoma
 l pairing or endogenous spineless chromosomal position but instead require
 s specific DNA elements to mediate regulatory interactions. This mechanism
  couples stochastic repression with interallelic coordination and contrast
 s starkly with the noisy activation mechanisms seen in bacteria\, and the 
 mono-allelic\, stochastic activation mechanisms observed in the mouse olfa
 ctory and human color vision systems.\n	Many vertebrate and invertebrate e
 yes also have retinal mosaics that contain different stochastically specif
 ied types of photoreceptors.  At least one group\, the butterflies\, make 
 a three-way stochastic choice between three ommatidial types.  However\, i
 t remains unclear how much of the regulatory network that specifies photor
 eceptor subtypes is retained or has evolved in other insects\, and whether
  they use stochastic Spineless expression to diversify their sometimes mor
 e complex retinal mosaics.  We will present evidence that a conserved regu
 latory code defines and expands photoreceptor subtypes between flies (Dros
 ophila) and butterflies (Papilio xuthus and Vanessa cardui).  We used CRIS
 PR/Cas9 to knock out Spineless in butterflies and provide functional evide
 nce that there is deep evolutionary conservation of stochastic patterning 
 mechanisms.  Furthermore\, butterflies have two R7 photoreceptors that all
 ow for the specification of three types of ommatidia instead of two. This 
 in turn allowed for the evolution and deployment of additional opsins\, te
 trachromacy\, and improved color vision\, important features of butterfly 
 life history and ecology.  Our extensive knowledge of patterning in the Dr
 osophila visual system applies to other groups\, and adaptation for specif
 ic visual requirements can occur through modification of this network.\n	T
 here are other instances where instead\, the animal has sacrificed its col
 or vision in order to improve its ability to track flying prey or females.
  The most dramatic example is the ‘love spot’ observed in males of sev
 eral dipteran species. For instance\, in the dorso-frontal region of the M
 usca (house fly) male eye\, which faces the flying female being chased\, R
 7 cells are transformed from color detectors into motion sensitive photore
 ceptors. This completely disrupts color vision but adds a seventh ‘outer
 ’ photoreceptor that improves the ability of the male to track the femal
 e. This R7 now expresses the broad spectrum Rh1 instead of a UV opsin\; it
  also projects to the lamina part of the optic lobe where motion is proces
 sed instead of reaching directly into the medulla where R7 normally compar
 es its output with R8 for color discrimination.  We have shown that this d
 rastic change in wiring pattern is due to loss of expression of the runt g
 ene in R7. We suggest that similar changes occur in both males and females
  of ‘killer’ flies that rely on in-flight chases of other insects. \n	
 Therefore\, these two examples in the insect world illustrate the flexibil
 ity of the visual system to adapt to specific circumstances that fit the l
 ifestyle of the animal. These changes rely on molecular variations that ca
 n be explained in simple evolutionary steps.\n
LOCATION:Hodgkin Huxley Seminar Room\, Physiology Building\, Downing Site
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