DNA METHYLATION AND GENOME IMPRINTING IN THE ZEBRAFISH, DANIO-RERIO -SOME EVOLUTIONARY RAMIFICATIONS

Although methylation has been recognized as an important component in a number of developmental processes in mammals, in zebrafish almost no thing is known about this epigenetic modification. This is despite the fact that the zebrafish is becoming increasingly popular as a develop mental model system. The little work that has been done on methylation and development in fish concerns genomic imprinting. In mammals, impr inting results in an inability to reproduce parthenogenetically becaus e a genetic contribution from both parents is necessary to successfull y complete development. However, this is not true of zebrafish, and a number of the theories that have been presented to explain the evoluti on of imprinting are not consistent with imprinting in these fish. A n ew model is presented that discusses some of the potential evolutionar y ramifications of methylation and imprinting and that leads to the su ggestion that imprinting may actually be a simple genetic mechanism to enhance the efficient evolution of both individual genetic loci and c ombinations of loci with related functions, without risking the popula tion as a whole. This model can accommodate all of the information kno wn about imprinting, including its broad phylogenetic range, imprintin g by both males and females, and the diverse nature of the genes that are known to be imprinted.