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  • Title: Adult mice cloned from migrating primordial germ cells.
    Author: Yamazaki Y, Low EW, Marikawa Y, Iwahashi K, Bartolomei MS, McCarrey JR, Yanagimachi R.
    Journal: Proc Natl Acad Sci U S A; 2005 Aug 09; 102(32):11361-6. PubMed ID: 16055553.
    Abstract:
    We previously reported that the genomes of gonadal germ cells at 11.5-19.5 days postcoitum (dpc) are incompetent to support full-term development of cloned mouse embryos. In this study, we performed nuclear transfer using primordial germ cells (PGCs) from earlier stages at 8.5-10.5 dpc. When PGC nuclei at 8.5, 9.5, and 10.5 dpc were transferred into enucleated oocytes, seven cloned embryos developed into full-term offspring. Of these, five, all derived from 8.5- or 9.5-dpc PGCs, developed into healthy adults with normal fertility. Of the remaining two offspring derived from 10.5-dpc PGCs, one died shortly after birth, and the other showed slight growth retardation but subsequently developed into a fertile adult. We examined allele-specific methylation at the imprinted H19 and Snrpn loci in 9.5- to 11.5-dpc PGCs. Although the beginning of methylation erasure was evident on the H19 paternal allele at 9.5 dpc, most PGCs did not demonstrate significant erasure of paternal allele-specific methylation until 10.5 dpc. Maternal allele-specific methylation was largely erased from Snrpn by 10.5 dpc. By 11.5 dpc, the majority of PGCs showed nearly complete or complete erasure of allele-specific methylation in both H19 and Snrpn. These results demonstrate that at least some genomic imprints remain largely intact in 8.5- to 9.5-dpc PGCs and then undergo erasure at approximately 10.5 dpc as the PGCs enter the genital ridges. Thus, migrating PGCs at 8.5-9.5 dpc can be successfully used as donors for nuclear transfer, whereas gonadal PGCs at 11.5 dpc and later are incompetent to support full-term development.
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