| Summary: | 5-hydroxymethyl-cytosine (5-hmc) is a cytosine modification that is relatively abundant in mammalian pre-implantation
embryos and embryonic stem cells (Esc) derived from mammalian blastocysts. Recent observations imply that both
5-hmc and Tet1/2/3 proteins, catalyzing the conversion of 5-methyl-cytosine to 5-hmc, may play an important role in
self renewal and differentiation of Escs. here we assessed the distribution of 5-hmc in zebrafish and chick embryos
and found that, unlike in mammals, 5-hmc is immunochemically undetectable in these systems before the onset of
organogenesis. In addition, Tet1/2/3 transcripts are either low or undetectable at corresponding stages of zebrafish
development. however, 5-hmc is enriched in later zebrafish and chick embryos and exhibits tissue-specific distribution in adult zebrafish. Our findings show that 5-hmc enrichment of non-committed cells is not a universal feature of vertebrate development and give insights both into evolution of embryonic pluripotency and the potential role of 5-hmc in its regulation.
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