Endocrine Abstracts

Background: 5-Cytosine methylation of DNA is a means of encoding epigenetic information. In the testis, the generation of de novo methylation is conducted by the enzymes DNMT3a and 3b and the co-enzyme DNMT3L. Epigenetic marks made to the DNA of germ cells are important as a potential means of trans-generational carriage of environmental information. In fetal life, germ cell demethylation and remethylation are important physiological events and these overlap with key changes in germ cell differentiation (loss of pluripotency), but whether this is coincidental or not is unknown. This study characterised expression of the DNMT3s.

Methods: DNMT 3a, 3b and 3L were co-localised with the germ cell markers Oct4 and VASA using immunofluorescence in fetal testes from the rat (17.5 and 21.5 days post conception (dpc)), marmoset (98 and 110 dpc) and human (gestation weeks 14 and 19) to determine changes in expression related to age and to germ cell differentiation status.

Results: DNMT3a and 3b are expressed in some but not all germ cells of the fetal testis across all the species examined. DNMT3a is expressed in fewer pluripotent Oct4+ cells than DNMT3b. The proportion of Oct4+ germ cells expressing DNMT3b increased in the rat, marmoset and human from dpc 17.5 to 21.5, 98 to 110 and gestational weeks 14 to 19 respectively. Ongoing studies are characterising DNMT3L expression and identifying if there is a relationship between DNMT3 expression and germ cell differentiation.

Discussion: We show that DNA methytransferase enzymes are present in fetal germ cells across multiple species, including primates, at the protein level. The potential manipulation of DNA methylation by environmental stimuli is a mechanism by which life style and pathogen exposure could impact upon the health of subsequent generations. The presence of DNMTs in fetal germ cells demonstrates a means by which de novo cytosine methylation can be induced.

Declaration of funding: This work was supported by the UK Medical Research Council (grant number G33253).