CHARACTERIZATION AND DEVELOPMENTAL ANALYSIS OF PBX1 IN ZEBRAFISH by TEOH PICK HAR Thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy

Pbx genes are TALE class homeodomain transcription factors. They play diverse and important roles in organogenesis. To date, four Pbx members have been identified in vertebrate. The objectives of this study were to characterize and analyze the developmental functions of zebrafish pbx members. It is hoped that the information gained from this model system will facilitate in the understanding of human organogenesis. Zebrafish pbx genes, in particular pbx1, were cloned and characterized in this study. It displays strong homology to mammalian Pbx1 and clustered together in the phylogenetic analysis. The encoded protein of pbx1 exhibited similar identity of mammalian Pbx1 in the DNA binding domain. RT-PCR of adult zebrafish organs showed high level expression in the brain, swim bladder, muscle and spleen. Following that, in vivo analyses of pbx1 expression during embryonic development were performed by in situ hybridization. pbx1 transcript was detected in three separate domains. The most significant area of expression is at the central nervous system, similar to mammalian Pbx1. The second domain is at the posterior pharyngeal arches, which is also observed in the pharyngeal expression during mouse embryonic development. The third expression in the swim bladder starts from 28 hpf and persists till adulthood which makes pbx1 the earliest marker for swim bladder. In comparison to other organs, very little is known about swim bladder development, thus