• Occurs just prior to implantation 
  
  
• Embryo breaks through ZP 
  
  
• Likely due to proteases secreted by blastocyst 
  
  
• Sometimes inability to hatch is reason for infertility; while the causes remain unknown this could be due to an altered zona pellucida or to the absence of essential protease for zona digestion 
  
  
• Often assisted hatching is done in vitro during IVF procedures 
  
  
• In contrast, in mutant mouse embryos that lack ZP1, the zona pellucida is very weak and the embryos hatch prematurely causing developmental problems (Rankin et al, 1999. Development 126: 3847-3855). 
  
  
  

  

This information was provided by Professor Danton H. O'Day - Univerisity of Toronto at Mississauga - Canada. Unless otherwise stated the information and graphics that are presented within this embryology section are the sole property of Danton H. O'Day, copyright 1998(c), 1999(c), 2000(c), 2001(c), 2002(c).

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