title: Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints.
abstract: BACKGROUND
  Identical DNA methylation differences between maternal and paternal alleles in gametes and adults suggest that the inheritance of genomic imprints is strictly due to the embryonic maintenance of DNA methylation. Such maintenance would occur in association with every cycle of DNA replication, including those of preimplantation embryos.
  
  
  RESULTS
  The expression of the somatic form of the Dnmt1 cytosine methyltransferase (Dnmt1s) was examined in cleavage-stage preimplantation mouse embryos. Low concentrations of Dnmt1s are found in 1-, 2-, 4-, and 8-cell embryos, as well as in morulae and blastocysts. Dnmt1s is present in the cytoplasm at all stages, and in the nuclei of all stages except the 1-cell, pronuclear-stage embryo. The related oocyte-derived Dnmt1o protein is also present in nuclei of 8-cell embryos, along with embryo-synthesized Dnmt1s. Dnmt1s protein expressed in 1-cell and 2-cell embryos is derived from the oocyte, whereas the embryo synthesizes its own Dnmt1s from the 2-cell stage onward.
  
  
  CONCLUSIONS
  These observations suggest that Dnmt1s provides maintenance methyltransferase activity for the inheritance of methylation imprints in the early mouse embryo. Moreover, the ability of Dnmt1o and Dnmt1s proteins synthesized at the same time to substitute for one another's maintenance function, but the lack of functional interchange between oocyte- and embryo-synthesized Dnmt1 proteins, suggests that the developmental source is the critical determinant of Dnmt1 function during preimplantation development.
authors.affiliation: Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA. ccirio@yahoo.com
authors.forename: M Cecilia
authors.initials: MC
authors.lastname: Cirio
authors.forename: Sarayu
authors.initials: S
authors.lastname: Ratnam
authors.forename: Feng
authors.initials: F
authors.lastname: Ding
authors.forename: Bonnie
authors.initials: B
authors.lastname: Reinhart
authors.forename: Chris
authors.initials: C
authors.lastname: Navara
authors.forename: J Richard
authors.initials: JR
authors.lastname: Chaillet
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000201:enzymology*; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000096:biosynthesis*; D019175:DNA Methylation; D005260:Female; D015870:Gene Expression; D018392:Genomic Imprinting; D015151:Immunoblotting; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D009865:Oocytes / Q000201:enzymology; D011247:Pregnancy
chemical_list: D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619381:Dnmt1 protein, mouse