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SUMMARY:Developmental Constraints? Why blind cavefish still have eye at em
 bryonic stage - Yoshiyuki Yamamoto (University College London)
DTSTART:20140514T120000Z
DTEND:20140514T130000Z
UID:TALK51671@talks.cam.ac.uk
CONTACT:Jeremy Solly
DESCRIPTION:Many organisms lost their eye after living in a darkness envir
 onment. Recent data suggested that the losing eye is a result of natural s
 election instead of genetic drift. Therefore\, the losing eye could have s
 ome advantageous effects for living in a darkness environment. Interesting
 ly\, most of blind vertebrate (could be all of them) have small vestigial 
 eye. The blind animals had developed eye at embryonic stage\, but it was d
 egenerated at later stage. Why have they started building their eye that d
 estroyed at later stage? \nAstyanax mexicanus has a surface dwelling eyed 
 population and several cave dwelling eyeless populations. The cavefish pop
 ulations also have started to develop eye structures similar as other blin
 d vertebrate. At embryonic stage\, the cavefish have developed small eye a
 nlagen comparing with eyed surface population and the small eye anlagen ha
 ve degenerated by apoptosis at later stage. Astyanax mexicanus is a good e
 xperimental model system for tackling the issue of why blind animal still 
 have eye. \nRx3 is a transcription factor containing a homeobox domain and
  is expressed at future eye field of anterior neural plate for initiating 
 eye development in vertebrate. Homozygous mutants of Rx3 fail to form eye 
 anlagen at embryonic stage and completely lost the eye tissues. We have is
 olated a fragment of rx3 gene from Astyanax mexicanus and compare the sequ
 ences and expression pattern among different populations of Astyanax. The 
 cording sequences of rx3 are identical among three Astyanax populations. H
 owever\, the expression patterns and amount during embryonic development a
 re different at each population. One of cavefish population\, Tinija have 
 extremely small rx3 expression domain at future eye field comparing with t
 he expression domain of eyed surface fish. Another cavefish population\, P
 achon have slightly small expression domain of rx3\, and interestingly\, t
 he expression intensity is very weak in the eye field comparing with eyed 
 surface and Tinija cavefish populations. Cell transplantation experiments 
 confirmed the reduction of the expression intensity in Pachon cavefish cou
 ld be controlled by cell-autonomous manner. \nThese observations indicate 
 having large eye anlagen in Astyanax is probably less favored in the cave 
 environment. However\, why have they developed small eye anlagen instead o
 f getting ride of the whole eye anlagen\, like a rx3 mutant? In zebrafish\
 , rx3 homozygous mutant have malformation of telencephalon and jaw structu
 re. Losing eye at early embryonic stage could have deleterious effect in t
 he head\, and it has not been selected during evolution. This phenomenon c
 ould be one of developmental constraints that a limitation on phenotypic v
 ariability caused by dynamics of the developmental system.\n
LOCATION:Part II Lecture Theatre\, Department of Zoology
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