Presenilins play prominent roles in the molecular pathogenesis of Alzheimer's disease and during embryo development. We have isolated a zebrafish presenilin orthologue (pre2), which shows a high degree of sequence identity to the human PS2 protein. Zebrafish pre2 is maternally and ubiquitously expressed during early embryo development, whereas Pre2 protein expression is initiated between 6 and 12 hours post fertilisation (hpf), suggesting strict regulation of pre2 translation. pre2 expression is especially high in neural-crest-derived melanocytes.