mibnn2002, found from an allele screen, showed early segmentation defect and severe cell death phenotypes, which are different from previously known mib mutants. Despite distinct morphological phenotypes, the typical mib molecular phenotypes: her4 down-regulation, neurogenic phenotype and cold sensitive dlc expression pattern, still remained. The linkage analysis also indicated that mibnn2002 is a new mib allele. Failure of specification in anterior 7-10 somites is likely due to lack of foxc1a expression in mibnn2002 homozygotes. Somites and somite markers gradually appeared after 7-10 somite stage, suggesting that foxc1a is only essential for the formation of anterior 7-10 somites. Apoptosis began around 16-somite stage with p53 up-regulation. To find the possible links of mib, foxc1a and apoptosis, transcriptome analysis was employed. About 140 genes, including wnt3a, foxc1a and mib, were not detected in the homozygotes. Overexpression of foxc1a mRNA in mibnn2002 homozygotes partially rescued the anterior somite specification. In the process of characterizing mibnn2002 mutation, we integrated the scaffolds containing mib locus into chromosome 2 (or linkage group 2, LG2) based on synteny comparison and transcriptome results. Genomic PCR analysis further supported the conclusion and showed that mibnn2002 has a chromosomal deletion with the size of about 9.6 Mbp.

Zebrafish cops6 encodes a putative deubiquitylating enzyme (DUB) that belongs to the JAMM family. It consists of 297 amino acids and includes the Mov34/MPN/PAD-1 (PF01398) domain. Ubiquitylation is involved in many cellular processes and deconjugation of ubiquitinmodified substrates is important to maintain a sufficient amount of free ubiquitin in the cell. Here, we report our findings regarding the general function of the cops6 gene, as a continuation of our previous studies involving DUB knockdown screening. We have found that cops6 plays different roles in early embryonic development in the zebrafish, including dorsoventral patterning, convergent extension movement and brain formation. In addition, our findings indicate that cops6 plays an anti-apoptotic role during segmentation. Overall, the present study that consolidates our previous work on zebrafish DUB genes, corroborates the hypothesis of multi-functional roles for DUB genes during development.

No abstract

Treacher Collins syndrome (TCS) is a rare congenital birth disorder (1 in 50,000 live births) characterized by severe craniofacial defects. Recently, the authors' group unfolded the pathogenesis of polr1c Type 3 TCS by using the zebrafish model. Facial development depends on the neural crest cells, in which polr1c plays a role in regulating their expression. In this study, the authors aimed to identify the functional time window of polr1c in TCS by the use of photo-morpholino to restore the polr1c expression at different time points. Results suggested that the restoration of polr1c at 8 hours after fertilization could rescue the TCS facial malformation phenotype by correcting the neural crest cell expression, reducing the cell death, and normalizing the p53 mRNA expression level in the rescued morphants. However, such recovery could not be reproduced if the polr1c is restored after 30 hours after fertilization.

No abstract