How does a fertilized 1-cell egg become a complex organism with billions of different cells (like us)?

         

   

human  body  as  drawn  by  Leonardo  Da  vinci    

Recipe  to  make  an  animal  from  a  fertilized  egg:  1.    Make  more  cells  (cell  division)  2.    Make  many  KINDS  of  cells  starting  from  1  cell  (differentiate  -­‐  nerve  cell,  blood  cell,  skin  cell,  hair  cell,  muscle  cell  etc.)  3.    Make  the  cells  form  tissues  and  organs  at  the  right  time  and  place    (morphogenesis,  organogenesis)  4.  Make  the  various  tissues  and  organs  connect  and  function  together  in  synergy    to  make  a  living  animal  !    How  do  we  study  these  questions?  We  use  “Model  Organisms”  such  as  the  worm,  C.  elegans  or  the  common  aquarium  fish,  zebrafish.    Why  do  we  use  “model  organisms”?        Because  they  are  simple,  grow  fast  in  laboratory  conditions,  and  are  easy  to  manipulate  and  observe.    Its  easy  to  do  experiments  with  them  (especially  if  they  don’t  talk  back  to  you  !)    What  kinds  of  experiments  can  you  do  with  these  animals?  -­‐You  can  study  the  functions  of  genes:  genetics  and  genomics  -­‐You  can  observe  cells  and  tissues  form  as  they  happen  in  real  time  in  a  living  animal,  especially  if  parts  are  “labeled”  with  a  visible  marker,  which  emits  light  of  a  certain  wavelength:  cell  &  developmental  biology  -­‐You  can  manipulate  them  in  various  ways:  treat  with  specific  substances  (chemicals  or  mutagens):  chemical  genetics  -­‐You  can  physically  manipulate  them  and  see  the  outcome:  mechanobiology  -­‐You  can  see  how  cells  or  tissues  grow  back  after  injury:    Stem  cells  &  regeneration  

Human egg cell (not to scale)

   

    What will you see today?  1)  We  did  an  experiment  to  determine  the  effect  of  alcohol  on  developing  fish  embryos.    We  treated  eggs  at  4  hours  after  fertilization  with  2.4  %  alcohol  for  3  hours,  and  then  removed  the  alcohol  and  grew  the  embryos  in  normal  egg  water  (water  with  some  salts).    As  controls  we  left  the  embryo  in  egg  water  throughout.        Which panel has the treated fish? Spot the differences and tell us.

     2)  Worms  with  neurons  labeled  with  a  green  fluorescent  protein.          We  will  visualize  different  tissues/organs  such  as  neurons  in  living  animals  with  a  powerful  technique  of  genetic  engineering  that  utilizes  a  green  fluorescent  protein  (GFP)  that  was  originally  discovered  in  a  jellyfish.        

heart

brain blood

C. elegans larva

Fish facts: freshwater fish, vertebrate like humans, 70% genes similar to humans; 1 mm diameter egg, 3 months to become adult, rudiments of all organs in place by 24 hours ! Clear body for first day or so.

Worm facts: Grows on compost has ~ 1000 cells, 1 mm long as adult, small genome size (1/30 of humans), takes 3-4 days to become an adult . Clear body, easy to see cells.  

Normal zebrafish embryo at 24 h