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13-Limb Development.pdf

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Department
Biology
Course
Biology 3338A
Professor
Sashko Damjanovski
Semester
Fall

Description
1 •  Limbs  come  a▯er  body  plan   •  In  vertebrates  form  2  pairs  of  limbs   •  Limbs  take  body  axis  with  it;  don’t  neccesarily  have  le▯  right     •  Limbs  start  as  limb  bud   •  Limb  bud  come  out  of  side,  take  with  it  body  axisà  as  limb  grows  s▯ll  constain   body  axisà  proximal  dis▯nal  instead  of  le▯  right  (how  close  you  are  to  body)   •  These  limbs  are  coming  out  due  to  boundaries  of  hox  gene  exression   •  Basic  sturcture  of  limb  is  same  in  all  animals   •  Stylopod  is  most  proximal,  middle  is  zeugopos,  autopod  is  most  distal   •  Limbs  form  in  limb  field   •  Cells  migra▯ng  in  from  differetn  placesà  mst  important    mytoomoes  from  somite   (gives  rise  to  muscle),and  lat  plate  meso  (gives  rise  to  skeleton)   •  Also  going  to  be  nc  migra▯ng  in   2 •  Hix  genes  found  in  most  embryos   •  Give  pos▯onal  info  in  embryos   3 •  Have  embryo  undergo  gastr,  neural  happens   •  Most  important  gradient  are  RA  (ant  to  post;  higher  in  post)à  within  gradient,   cells  have  pos▯iotning  info   •  Ra  interacts  with  hox  genes   •  Hox  gens  are  found  within  somtes  goning  from  ant  to  post   •  Different  animals  respond  to  gradient  in  different  ways  to  specify  different   boundaries   •  Chicks  have  longer  neck;  higher  domain  of  hox  gene   •  Mouse  have  longer  throac;  higher  domanin  of  hox  gene   •  Boundaries  of  hox  gene  specify  different  regions  in  body   4 •  Don’t  memorize   5 •  Binds to DNA; birth defects •  When you gave it, totally different effects •  Timing of Hox genes crucial to development 7 •  Grow  limb  buds;  associated  with  FGF-­‐10  expression;  expressed  in  lateral  plate   mesoderm   •  A)  Check  embryo  stained  for  FGF-­‐10;  tons  of  FGF-­‐10  in  head,  can  see  FGF-­‐10   expressed  in  lateral  plate  mesoderm  in  2  regions  that  will  give  rise  to  limbs   •  Take  FGF-­‐10  and  transplant  him,  can  induce  another  pair  of  limbs   •  Can  induce  another  limb  bud  with  more  FGF-­‐10   8 •  Somites  anterior  to  posterior:  hox  gene  expression,  is  boundary  somewhere,  get   limb  fields  forming   •  Another  transcrip▯on  factor  called  Tbx;  along  with  hox;  responsible  for  FGF-­‐10   expression  in  these  region,  FGF-­‐10  expression  now  limbs  can  form   •  Tbx  by  itself  wont  do  anything   •  FGF-­‐10  will  signal,  cause  expression  of  other  FGFs  in  ectoderm   •  Requires  wnts  in  ectoderm   •  Somites,  Hox  genes  and  ret  acid,  turn  on  tbx,  fgf-­‐10,  will  turn  on  fgf8  in  ectoderm.   This  requires  wnts,     •  FGF-­‐8  feedsback,  cause  limb  to  grow   •  Order  of  things  is  importnant   •  Get  cell  movement  from  lateral  plate  meso   •  Lpmà  meso  that  segments  follwing  neurala▯on;  comes  way  a▯er  somite   forma▯on   •  Start  moving  into  limb   •  Fgf10  singals  to  ectoderem  to  turn  on  fgf  8   •  Wnt  is  needed   9 •  Different  tbx  transcrip▯on  factors  found  at  hindlimb  and  forelimb   •  2  places  on  body  axis,  get  limb  buds  forming,  start  expressing  fgf-­‐10   •  Different  tbx  proteins   •  Cervical  thoracic  boundary,  tbx5  boundary,  limb  growing  from  this  will  be   forelimb(wing  etc)   •  Hindlimb,  tbx4,  turn  on  fgf-­‐10,  leg  in  chick  etc   •  Mix  these  proteins,  FGF-­‐10,  under  influence  of  tbx4  and  tbx5,  get  mixed  limb   10 •  Apical  ectodermal  ridge  (AER);  important   •  Limb  bud  coming  out  of  body  axis,  along  ridge,  cells  are  thicker,  border  between   ventral  and  dorsal  side  of  limb;  this  thickening  is  called  AER   •  Cells  with  FGF-­‐10  prolifera▯ng  and  signaling  FGF-­‐10,  this  growing  ridge  goes  into   AER   •  Cells  expressing  FGF-­‐10  now  called  progressing  zone   •  Wnts  now  signaling  back  FGF8,  feedback  of  FGF8  maintain  progress  zone  in   prolifera▯ng  state   •  Mesenchymal  cells  from  lateral  plate,  secre▯ng  FGF  10,  secrete  back  FGF8;   progress  zones  happy,  priflera▯ng  zone  happy,  limb  grows  distally   •  Growing  limb  has  progress  zone,  came  from  lateral  plate  mesoderm,  secre▯ng   FGF-­‐10,  as  cells  leave  progress  zone,  give  rise  to  proximal  part  of  limb   •  Need  AER  and  FGF8  to  feed  back   •  Cells  first  mving  secrete  fgf  10;  also  prolifera▯on     11 •  AER  importance;  secretes  FGF8  back     •  Remove  it,  stops  immediately   •  Remove  it  late,  get  part  of  hand  then  stop  etc   •  AER  maintain  prolifera▯ng  state   •  Add  extra  AER;  aucment  growth,  get  longer  limbs  and  duplica▯on  in  anterior   posterior  axis;  duplica▯ng  posterior   •  Change  mesencyhmal  cells;  take  forelimb  and  remove  progress  zone,  replace  with   leg  mesenchyme,  change  it  from  wing  to  leg   •  Posi▯onal  informa▯on  in  progress  zone;  s▯ll  under  proper  tbx  informa▯on   •  Has  to
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