EPIGENETICS: WHERE NATURE AND NURTURE COLLIDE  

Epigenetics is a broad term that refers to a pattern of gene expression in animals not caused by mutation as most people think of mutation.  Rather, epigenetic alterations can be the result of DNA methylation, histone modification or conformational changes in chromatin; collectively referred to as epimutations, which are far more likely to occur in animals than changes in base pairs.  This presentation will focus on DNA methylation and potential implications in aquaculture.

With all deference to friends and colleagues working in the area of genetics, epigenetics begins with nutrition, specifically 1-carbon (1-C) metabolism and the synthesis of methyl groups.  1-C metabolism involves dietary essential nutrients methionine, riboflavin (vitamin B2), folic acid (vitamin B9), choline, pyridoxine (vitamin B6) and vitamin B12.  Inadequate dietary intakes of these nutrients impacts 1-C metabolism and DNA methylation.  Given adequate supply of methyl groups, DNA methylation does not proceed in a random fashion.  Attachment of methyl groups is specific to nucleotides and to genes.  Further, once methylated, these patterns are considered heritable, that is, they are passed on to future generations.  The contemporary definition of epigenetics is "stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence".  Regulation of gene expression does not stop at DNA methylation, but also includes RNA (micro-, small-, long noncoding- and messengerRNA) molecules.  Epigenetic alterations have been linked to most of the major human diseases and to a wide range of developmental and reproductive abnormalities.

Stress induces changes in DNA methylation patterns, thus in gene expression patterns.  Most of these alterations studied to date are not considered advantageous alterations.  How many times have we seen particular groups of aquatic animals that just do not do well, do not thrive, do not grow to their genetic potential, produce fewer offspring, or are more susceptible to disease?  Early life history stresses significantly influence methylation patterns in humans, and they probably influence methylation patterns in aquaculture species.  The stressors identified to date include availability of food both in utero and post partum, deficiency of specific nutrients involved in 1-C metabolism, and psychosocial stressors.  The effects of these stressors include increased susceptibility to disease, poor growth, neurological abnormalities, and altered reproductive success.  This is an area where interdisciplinary groups of scientists need to coalesce and aggressively pursue new avenues of research; a more basic research line with potentially significant benefits back to practical production of aquaculture species.