Abstract article: Science communication is highly important in present-day society. But mere factual information transfer does not suffice for enhancing public understanding of scientific results, theories, and concepts. In this paper we compare science communication among experts with communication from experts to laypeople, to better understand the role of metaphors in constructing understanding of abstract scientific concepts. As a case study, we analyze specialist and non-specialist scientific articles on epigenetics, the study of heritable changes in gene expression not altering DNA sequence. The results of our analysis show that there is no substantial difference between the two types of articles in frequency of metaphors and in their content. However, the function of the metaphors is different: the figurative aspect of metaphors is employed for public understanding but plays no role in specialist scientific articles. We outline the implications of these results for current philosophical debates on scientific understanding and public understanding of science: (1) metaphors are tools for rendering theoretical concepts intelligible, for both expert and lay audiences; (2) expert and public understanding differ in degree rather than in kind; (3) conveying understanding crucially involves skills: metaphors in this context do not so much add knowledge as enhance relevant conceptual reasoning abilities.