Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints

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. CONCLUSION: 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

Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints

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. Conclusion: 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

Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints-3

H the UPT82 antiserum. Mo = morula. Bl = blastocyst. B. Time course of Dnmt1s expression during preimplantation development in embryos derived from crosses between wild-type (+/+) female mice and homozygous (V/V) male mice. Inset is bright-field image of immunostained 1-cell embryo. C. Time courses of Dnmt1s expression during preimplantation development in embryos derived from crosses between heterozygous (V/+) female mice and homozygous (V/V) male mice. The 4-cell and 8-cell embryos in the top row show primarily nuclear Dnmt1s staining whereas 4-cell and 8-cell embryos in the botton row show little or no nuclear Dnmt1s. All seven 2-cell, three out of seven 4-cell and six out of 13 8-cell embryos showed nuclear staining. Bar, 20 μm.<p><b>Copyright information:</b></p><p>Taken from "Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints"</p><p>http://www.biomedcentral.com/1471-213X/8/9</p><p>BMC Developmental Biology 2008;8():9-9.</p><p>Published online 25 Jan 2008</p><p>PMCID:PMC2266903.</p><p></p

Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints-1

F development. MII = MII oocytes; 1 = 1-cell; 2 = 2-cell; 4 = 4-cell; 8 = 8-cell; Bl = blastocyst. Sample sizes: 105 wild-type MII oocytes; 105 1-cell embryos; 110 2-cell embryos; 110 4-cell embryos; 110 8-cell embryos; 120 blastocysts. B. Relative stability of oocyte-derived Dnmt1o and Dnmt1s proteins from homozygous mice during preimplantation development to the 8-cell stage. Sample sizes: 22 MII oocytes; 21 8-cell embryos. The blot was first probed with UPT82, stripped and then reprobed with UPTC21. The assay was repeated, and nearly identical results were obtained (data not shown). C. Relative levels of maintenance methyltransferase activity (MA) per oocyte. MA is expressed as [H]methyl group incorporation into the synthetic template poly(dIdC). Oocyte genotype is the genotype of the diploid precursor of the analyzed MII oocyte. The assay was performed on three separate occasions (1–3). The background measurement is the cpm in sample containing poly(dIdC) and S-adenosyl methionine, but no oocyte extract. Dnmt1o MA/Total MA was calculated as [(– background) – (– background)]/(– background), expressed as a percentage.<p><b>Copyright information:</b></p><p>Taken from "Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints"</p><p>http://www.biomedcentral.com/1471-213X/8/9</p><p>BMC Developmental Biology 2008;8():9-9.</p><p>Published online 25 Jan 2008</p><p>PMCID:PMC2266903.</p><p></p

Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints-2

UPT82 antiserum. Intracellular DNA was detected with DAPI. B. Immunostaining of MII oocytes and pronuclear-stage embryos of different genotypes with the UPT82 antiserum. PN3 and PN4 refer to pronuclear stage 3 and 4 as defined by morphologic criteria [17]. Insets are bright-field images of immunostained embryos. C. Immunostaining of pronuclear-stage embryos with the UPTC21 antiserum to detect the abundant Dnmt1o protein. Genotype abbreviations are the same as in the legends to Figures 1 and 2. Bar, 20 μm.<p><b>Copyright information:</b></p><p>Taken from "Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints"</p><p>http://www.biomedcentral.com/1471-213X/8/9</p><p>BMC Developmental Biology 2008;8():9-9.</p><p>Published online 25 Jan 2008</p><p>PMCID:PMC2266903.</p><p></p

Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints-5

Hted, the PCNA binding domain (PBD) and targeting sequence (TS) that have been implicated in targeting Dnmt1 to replication foci [18,29]. The black rectangles identify the positions of the mouse Dnmt1s amino acid sequences used to immunize a rabbit to produce the UPT82 antiserum or to immunize a chicken to produce the UPTC21 antiserum [6]. B. Immunoblots showing expression of Dnmt1s protein in oocytes from various mouse lines. The upper and lower blots were probed with the UPT82 antiserum. + refers to wild-type oocytes; refers to homozygous mutant oocytes from the strain [6]; refers to homozygous mutant oocytes from the strain; refers to oocytes from hemizygous transgenic mice. Sample sizes for the upper blot: 100 wild-type GV oocytes; 120 wild-type MII oocytes; 25 oocytes; 60 oocytes. Sample sizes for the lower blot: 105 wild-type MII oocytes; 40 oocytes. C. Expression of Dnmt1o protein in wild-type, and oocytes. The same blot shown in panel B was probed with UPTC21.<p><b>Copyright information:</b></p><p>Taken from "Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints"</p><p>http://www.biomedcentral.com/1471-213X/8/9</p><p>BMC Developmental Biology 2008;8():9-9.</p><p>Published online 25 Jan 2008</p><p>PMCID:PMC2266903.</p><p></p

Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints-4

Oocytes of the transgenic mouse line. ZP3 = 6.6-kb mouse zona pellucida 3 gene promoter [23]. Dnmt1s = full-length Dnmt1s cDNA containing coding sequence for N-terminal Anti-Xpress epitope tag. BGH = bovine growth hormone polyadenylation and transcription termination sequence. B. Summary of bisulfite genomic sequencing of two normally imprinted genes in mice of various genotypes. alleles were analyzed in a DNA sample isolated from an E13.5 embryo derived from a cross between a homozygous female and a Cast-7 male. , alleles were analyzed in DNA samples isolated either from an E13.5 embryo (Embryo #4) or from an adult (Adult #1) derived from crosses between a , female and a Cast-7 male. C. Analysis of and gene expression in mice of various genotypes. Allele-specific expression of was determined by restriction endonuclease digestion of RT-PCR products. Allele-specific expression of was determined by SnuPE assay. Lanes 1–4: , E13.5 embryos, Embryo #1 through Embryo #4. Lane 5–6: embryos. Lanes 7–10: , adults, Adult #1 through Adult #4. Lane 11: inbred Cast-7. Lane 12: inbred FVB/N. Lane 13: F1 hybrid from cross between an FVB/N female mouse and a Cast-7 male mouse.<p><b>Copyright information:</b></p><p>Taken from "Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints"</p><p>http://www.biomedcentral.com/1471-213X/8/9</p><p>BMC Developmental Biology 2008;8():9-9.</p><p>Published online 25 Jan 2008</p><p>PMCID:PMC2266903.</p><p></p

Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints-0

Ion development. Dnmt1o is localized in the nucleus of blastomeres of 8-cell embryos. Dnmt1o is not found in the pronuclei. B. The middle row of schematics depicts the pattern of maternal Dnmt1s protein expression in the early stages of preimplantation development. Dnmt1s is not found in the pronuclei. C. The bottom row of schematics depicts the pattern of zygotic Dnmt1s protein expression during preimplantation development. Dnmt1s is evident in nuclei of many stages, including in blastomeres of 8-cell embryos.<p><b>Copyright information:</b></p><p>Taken from "Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints"</p><p>http://www.biomedcentral.com/1471-213X/8/9</p><p>BMC Developmental Biology 2008;8():9-9.</p><p>Published online 25 Jan 2008</p><p>PMCID:PMC2266903.</p><p></p

Interspecies chimera between primate embryonic stem cells and mouse embryos: Monkey ESCs engraft into mouse embryos, but not post-implantation fetuses

AbstractUnequivocal evidence for pluripotency in which embryonic stem cells contribute to chimeric offspring has yet to be demonstrated in human or nonhuman primates (NHPs). Here, rhesus and baboons ESCs were investigated in interspecific mouse chimera generated by aggregation or blastocyst injection. Aggregation chimera produced mouse blastocysts with GFP-nhpESCs at the inner cell mass (ICM), and embryo transfers (ETs) generated dimly-fluorescencing abnormal fetuses. Direct injection of GFP-nhpESCs into blastocysts produced normal non-GFP-fluorescencing fetuses. Injected chimera showed >70% loss of GFP-nhpESCs after 21h culture. Outgrowths of all chimeric blastocysts established distinct but separate mouse- and NHP-ESC colonies. Extensive endogenous autofluorescence compromised anti-GFP detection and PCR analysis did not detect nhpESCs in fetuses. NhpESCs localize to the ICM in chimera and generate pregnancies. Because primate ESCs do not engraft post-implantation, and also because endogenous autofluorescence results in misleading positive signals, interspecific chimera assays for pluripotency with primate stem cells is unreliable with the currently available ESCs. Testing primate ESCs reprogrammed into even more naïve states in these inter-specific chimera assays will be an important future endeavor