title: Differences in gene expression between first and third trimester human placenta: a microarray study.
abstract: BACKGROUND
  The human placenta is a rapidly developing organ that undergoes structural and functional changes throughout the pregnancy. Our objectives were to investigate the differences in global gene expression profile, the expression of imprinted genes and the effect of smoking in first and third trimester normal human placentas.
  
  
  METHODS
  Placental samples were collected from 21 women with uncomplicated pregnancies delivered at term and 16 healthy women undergoing termination of pregnancy at 9-12 weeks gestation. Placental gene expression profile was evaluated by Human Genome Survey Microarray v.2.0 (Applied Biosystems) and real-time polymerase chain reaction.
  
  
  RESULTS
  Almost 25% of the genes spotted on the array (n = 7519) were differentially expressed between first and third trimester placentas. Genes regulating biological processes involved in cell proliferation, cell differentiation and angiogenesis were up-regulated in the first trimester; whereas cell surface receptor mediated signal transduction, G-protein mediated signalling, ion transport, neuronal activities and chemosensory perception were up-regulated in the third trimester. Pathway analysis showed that brain and placenta might share common developmental routes. Principal component analysis based on the expression of 17 imprinted genes showed a clear separation of first and third trimester placentas, indicating that epigenetic modifications occur throughout pregnancy. In smokers, a set of genes encoding oxidoreductases were differentially expressed in both trimesters.
  
  
  CONCLUSIONS
  Differences in global gene expression profile between first and third trimester human placenta reflect temporal changes in placental structure and function. Epigenetic rearrangements in the human placenta seem to occur across gestation, indicating the importance of environmental influence in the developing feto-placental unit.
authors.affiliation: Department of Obstetrics and Gynecology, Akershus University Hospital, Lørenskog, Norway. Vasilis.Sitras@ahus.no
authors.forename: Vasilis
authors.initials: V
authors.lastname: Sitras
authors.forename: Christopher
authors.initials: C
authors.lastname: Fenton
authors.forename: Ruth
authors.initials: R
authors.lastname: Paulssen
authors.forename: Åse
authors.initials: Å
authors.lastname: Vårtun
authors.forename: G
authors.initials: G
authors.lastname: Acharya
mesh_terms: D000328:Adult; D044127:Epigenesis, Genetic / Q000502:physiology*; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D020411:Oligonucleotide Array Sequence Analysis; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy / Q000378:metabolism*; D011257:Pregnancy Proteins / Q000096:biosynthesis*; D011261:Pregnancy Trimester, First / Q000378:metabolism*; D011263:Pregnancy Trimester, Third / Q000378:metabolism*
chemical_list: D011257:Pregnancy Proteins