Biologia do Desenvolvimento

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Biologia  do  Desenvolvimento	
Estabelecimento  dos  Eixos  Corporais	
Prof.  Pedro  Vale  de  Azevedo  Brito	
Drosophila	
Determinação  do  Eixo  Antero-­‐‑Posterior	
Drosophila	
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Diferentes  fatores  de  sinalização  transitam  livremente  pela  blastoderme  sincicial	
Determinação  do  Eixo  Antero-­‐‑Posterior	
Drosophila	
!
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The Origins of Anterior-Posterior Polarity!
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The Maternal Effect Genes!
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Embryological evidence of polarity regulation by oocyte cytoplasm!
A  polaridade  é  definida  por  fatores  maternos  localizados  diferencialmente  no  ovo  
de  Drosophila	
Dois  mensageiros  maternos  são  essenciais  na  determinação  do  eixo  antero-­‐‑posterior	
bicoid	
 nanos	
O  mRNA  das  duas  
proteínas  é  expresso  
após  a  fertilização	
Determinação  do  Eixo  Antero-­‐‑Posterior	
Drosophila	
!
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Determinação  do  Eixo  Antero-­‐‑Posterior	
Drosophila	
Padrão  de  expressão  de  nanos	
Determinação  do  Eixo  Antero-­‐‑Posterior	
Drosophila	
Interações  inibitórias	
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-­‐‑Altos  níveis  de  bicoid  ou  nanos,  
inibema  expressão  de  hunchback	
	
-­‐‑  Altos  nívie  de  bicoid  inibem  a  
expressão  de  caudal	
Anfíbios	
Xenopus Laevis 
Anfíbios	
 O  Trabalho  de  Hans  Spemann  e  Hilde  Mangold	
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Em  1903...	
Conclusão:  o  núcleo  das  células  é  idêntico  e  capaz  de  originar  um  indivíduo  completo	
Anfíbios	
 O  Trabalho  de  Hans  Spemann  e  Hilde  Mangold	
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Com  ovos  de  Salamandra...	
Apenas  o  blastômero  que  ficou  com  o  cinza  
crescente  é  capaz  de  originar  uma  larva  
completa	
Qual  a  importância  da  região  do  
cinza  crescente?	
Anfíbios	
 O  Trabalho  de  Hans  Spemann  e  Hilde  Mangold	
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Na  gástrula  tardia  o  destino  das  
células  já  encontra-­‐‑se  especificado	
Anfíbios	
 O  Trabalho  de  Hans  Spemann  e  Hilde  Mangold	
Apenas  uma  região  do  embrião  de  anfíbios  é  auto-­‐‑indutora	
Organizador  =  indutor  primário  =  organizador  de  Spemann  e  Mangold	
!
Hans Spemann and Hilde Mangold: Primary Embryonic Induction!
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Anfíbios	
 O  Trabalho  de  Hans  Spemann  e  Hilde  Mangold	
Questões  levantadas  pelo  experimento  de  Spemann  e  Mangold	
-­‐‑O  que  torna  o  lábio  dorsal  do  blastóporo  diferente  de  qualquer  outra  região  do  
embrião?	
	
-­‐‑Que  fatores  estão  sendo  secretados  pelo  organizador  e  diferenciando  o  tubo  neural,  
estabelecendo  o  eixo  antero-­‐‑posterior  e  dorso-­‐‑ventral?	
	
-­‐‑Como  diferentes  partes  do  tubo  neural  se  diferenciam?	
Anfíbios	
 Como  é  formado  o  organizador?	
Células  presentes  no  local  certo  e  no  momento  certo.	
!
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The Mechanisms of Axis Formation in Amphibians!
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Dois  sinais  se  encontram:	
Anfíbios	
 Como  é  formado  o  organizador?	
Células  presentes  no  local  certo  e  no  momento  certo.	
!
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The Mechanisms of Axis Formation in Amphibians!
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Experiência  de  Nieukoop  e  Nakamura	
Anfíbios	
 Como  é  formado  o  organizador?	
Como  é  determinada  a  porção  dorsal  do  embrião?	
!
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Concentração  de  β-­‐‑catenina	
Rotação  cortical  desloca  
Dsh  para  porção  dorsal	
Wnt11  desloca  
através  de  cinesinas  
para  a  porção  dorsal	
Dsh  e  Wnt11  inibem  
destruição  de  β–catenina  
por  GSK3	
Anfíbios	
 Como  é  formado  o  organizador?	
!
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Outros  fatores  determinam  a  diferenciação  do  organizador	
VegT  e  Vg1  são  fatores  
maternos  localizados  
no  polo  vegetal	
Juntamente  com  β–
catenina  eles  
estimulam  a  
produção  de  genes  
do  tipo  nodal	
Anfíbios	
 Destino  do  organizador	
As  células  do  organizador  contribuem  para  quatro  tipos  celulares:	
	
-­‐‑  Endoderme  da  faringe	
-­‐‑  Mesoderme  da  cabeça	
-­‐‑  Notocorda	
-­‐‑  Lábio  dorsal  do  blastóporo	
Anfíbios	
 Propriedades  do  organizador	
1-­‐‑  Habilidade  de  se  auto  diferenciar  em  mesoderme  dorsal	
	
2-­‐‑  Capacidade  de  transformar  o  mesoderme  circundante  em  mesoderme  paraxial  
(somitos),  ao  invés  de  mesoderme  ventral	
	
3-­‐‑  Capacidade  de  induzir  a  formação  do  tubo  neural	
	
4-­‐‑  Capacidade  de  iniciar  os  movimentos  da  Gastrulação	
Gallus gallus 
Aves	
Aves	
 Estabelecimento  de  Eixos  e  do  Organizador	
O  Papel  da  Gravidade	
!
Axis Formation in the Chick Embryo!
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The role of pH in forming the dorsal-ventral axis!
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The role of gravity in forming the anterior-posterior axis!
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&'!,%9!IAAD>9!!
O  Ovo  se  desloca  por  20  horas  ao  longo  do  oviduto  da  galinha,  girando  
15  vezes  por  hora	
Determinantesmaternos  mais  leves  concentram-­‐‑se  em  um  dos  lados  da  
blastoderme,  onde  terá  início  a  formação  da  linha  primitiva	
Aves	
 Estabelecimento  de  Eixos  e  do  Organizador	
Não  sabemos  o  que  especifica  uma  porção  da  região  marginal  como  posterior,  já  
que,  caso  isoladas,  todas  as  porções  são  capazes  de  iniciar  a  gastrulação	
Aparentemente...	
-­‐‑  Toda  porção  marginal  produz  Wnt8c,  capaz  de  induzir  β-­‐‑catenina	
-­‐‑  A  porção  marginal  posterior  produz  Vg1	
-­‐‑  Wnt8c  juntamente  com  Vg1  induzem  a  expressão  de  nodal	
As  células  do  hipoblasto  primitivo  produzem  Cerberus  um  antagonista  de  nodal	
!
!
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Aves	
 Estabelecimento  do  nó  de  Hensen	
O  Nó  de  Hensen  é  formado  pelas  células  anteriores  da  foice  de  Koller  	
Aves	
 Funções  do  nó  de  Hensen	
É  equivalente  ao  lábio  dorsal  do  blastóporo  em  mamíferos  porque:	
	
-­‐‑Suas  células  originam  a  notocorda	
	
-­‐‑É  capaz  de  induzir  um  segundo  eixo  quando  transplantado  para  outra  gástrula	
	
-­‐‑Expressa  os  mesmos  fatores  que  o  organizador  de  Spemann	
!
!
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Mus musculus 
Mamíferos	
Mamíferos	
1)  BMP4  originado  do  trofoblasto  induz  a  produção  de  Wnt3a  e  Nodal  no  Epiblasto	
2)  Placa  precordal  produz  Lefty-­‐‑1  e  Cerberus,  antagonistas  de  Wnt3a  e  Nodal	
3)  Wnt3a  estimula  a  produção  de  Brachyury  apenas  no  epiblasto  posterior	
Mamíferos	
1)  Quando  o  nó  é  formado  ele  começa  a  secretar  Chordin	
2)  A  notocorda  secreta  Noggin	
Esses  dois  sinais  são  inibidos  na  região  da  placa  precordal