Characterization Of E2F5 And Apolipoprotein E In Zebrafish

During the process of screening genes that preferentially expressed in zebrafish germ cells, we isolated an E2F family member:E2F5b, which shows a 97.9% homology to an uncharacterized E2F5a. The E2F transcription factors are thought to play an essential role in cell cycle progression. Reverse transcription polymerase chain reaction and Whole mount In situ hybridization analysis have demonstrated that both of E2F5a and E2F5b mRNAs are predominantly expressed in stages I and II oocytes. In early development, two E2F5 transcripts are expressed wildly and then restricted to brain area. Interestingly, later E2F5b mRNA is detected in the len while E2F5a mRNA is absent. Our data suggests that E2F5s may be essential for eye development and zebrafish oogenesis.Apolipoprotein E4 (APOE4) is the major genetic risk factor for later-onset Alzheimer’s disease (AD). There are two isoforms of apoE in zebrafish, apoEa and apoEb. The apoEb was characterized in fin fold regeneration before. First, we detected the expression patterns of apoEa during the development of zebrafish. The apoEa is expressed in the central neuron system (CNS) including the spinal neuron cord from 24 hour post fertilization to 5 day post fertilization (dpf). Two nonoverlapping morpholino oligos were used to block the translation of the apoEa. A 5 mispaired morpholino oligo was used as a control. During 2 dpf to 6 dpf, knockdown of apoEa in zebrafish leads to the defects inⅦneuron migration, motor axonal pathfinding and axonal outgrowth. Histological examinations (Transmission electron microscopy) demonstrated the microtubules and neurofilaments of the axons were disorganized and there were less myelinated axons. We proposed that the apoEa is essential for axonal structure, outgrowth and maintenance in zebrafish.