Bio-objects as "boundary crawlers:" the case of microRNAs

microRNAs (miRNAs), short RNAs of 21-25 nucleotides, are implied in gene expression and regulation, in biological processes and in human pathologies including cancer. Since miRNAs of plant origin can survive digestion and cooking and enter in animal (including human) sera and tissues, their intervention in mammalian gene expression and regulation might be expected. Mouse experimental feeding, in fact, showed that a miRNA class (MIR168a) is involved in accumulation of the low-density lipoprotein (LDL), the major cholesterol-carrying lipoprotein of human plasma. Considering LDL's role in atherosclerosis, a negative influence of miRNAs from food origin on our health may be expected. Here we concentrate on the miRNAs' capability to cross inter-kingdom boundaries through the diet and acting as a "boundary crawler." The boundary between plant and human is presented under a new perspective, where a new intimate relationship between two genomes - mammalian and plant - belonging to quite different kingdoms is proposed. The food's role as molecule carrier in our health is also discussed. miRNAs, finally, are presented as an example of "bio-objects" with impact on both medical and cultural issues.