title: Molecular and ultrastuctural changes of rat pre-implantation  embryos during two-cell developmental arrest.
abstract: BACKGROUND
  Rat pre-implantation embryos often suffer 2-cell stage developmental arrest and fail to progress further under in-vitro conditions.
  
  
  OBJECTIVE
  In order to understand underlying mechanism leading to 2-cell arrest, we investigated the molecular changes, culture conditions and subcellular changes.
  
  
  METHODS
  Gene expression in in-vivo developed 2-cell embryos (in-vivo), in- vitro developed 2-cell embryos (in-vitro), and in-vitro 2-cell arrested embryos (arrested) were investigated using microarrays and real-time PCR. Ultra-structural changes were determined using electron microscopy.
  
  
  RESULTS
  Gene expression was similar between in-vivo and in-vitro embryos. Over 2400 genes changed in arrested embryos compared to in-vivo and in-vitro embryos. The mRNAs encoding proteins involved in translation were elevated in arrested embryos. In-vivo and in-vitro embryos highly expressed genes that were involved in cell cycle, and protein catabolic process compared to arrested embryos. Gene expression data suggested subcellular changes associated with 2-cell block. Transmission electron microscopy showed that in-vivo embryos had healthy subcellular structure, whereas arrested embryos did not have a nuclear membrane, contained small mitochondria and autophagic vacuoles. Furthermore, gene expression data was used for the optimization of culture media conditions to obtain better in-vitro embryonic development. Comparison of five and 20 % oxygen in culture resulted in two times more blastocyst formation with 5 % oxygen.
  
  
  CONCLUSIONS
  These results showed that although all experimental groups appeared morphologically similar, arrested embryos had ultra-structural and molecular changes associated with oxidative stress and apoptosis. In-vitro culture under low oxygen and media additives reduced 2-cell block in rat embryos.
authors.forename: Cansu
authors.initials: C
authors.lastname: Agca
authors.forename: Yuksel
authors.initials: Y
authors.lastname: Agca
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D002453:Cell Cycle / Q000235:genetics; D003470:Culture Media; D004622:Embryo, Mammalian / Q000378:metabolism* / Q000648:ultrastructure; D047108:Embryonic Development / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D018384:Oxidative Stress; D051381:Rats
chemical_list: D003470:Culture Media