Tissue-specific requirements for specific domains in the FERM protein Moe/Epb4.1l5 during early zebrafish development

• Main Authors: Jensen Abbie M, Christensen Arne K
• Format: Article
• Language: English
• Published: BMC 2008-01-01
• Series: BMC Developmental Biology
• Online Access: http://www.biomedcentral.com/1471-213X/8/3
• ISSN: 1471-213X

<p>Abstract</p> <p>Background</p> <p>The FERM domain containing protein Mosaic Eyes (Moe) interacts with Crumbs proteins, which are important regulators of apical identity and size. In zebrafish, loss-of-function mutations in <it>moe </it>result in defects in brain ventricle formation, retinal pigmented epithelium and neural retinal development, pericardial edema, and tail curvature. In humans and mice, there are two major alternately spliced isoforms of the Moe orthologue, Erythrocyte Protein Band 4.1-Like 5 (Epb4.1l5), which we have named Epb4.1l5^longand Epb4.1l5^short, that differ after the FERM domain. Interestingly, Moe and both Epb4.1l5 isoforms have a putative C' terminal Type-I PDZ-Binding Domain (PBD). We previously showed that the N' terminal FERM domain in Moe directly mediates interactions with Crumbs proteins and Nagie oko (Nok) in zebrafish, but the function of the C'terminal half of Moe/Epb4.1l5 has not yet been examined.</p> <p>Results</p> <p>To define functionally important domains in zebrafish Moe and murine Epb4.1l5, we tested whether injection of mRNAs encoding these proteins could rescue defects in zebrafish <it>moe</it>^-embryos. Injection of either <it>moe </it>or <it>epb4.1l5</it>^{<it>long </it>}mRNA, but not <it>epb4.1l5</it>^{<it>short </it>}mRNA, could rescue <it>moe</it>^-embryonic defects. We also tested whether mRNA encoding C' terminal truncations of Epb4.1l5^longor chimeric constructs with reciprocal swaps of the isoform-specific PBDs could rescue <it>moe</it>^-defects. We found that injection of the Epb4.1l5^shortchimera (Epb4.1l5^{short+long_PBD}), containing the PBD from Epb4.1l5^long, could rescue retinal and RPE defects in <it>moe</it>^-mutants, but not brain ventricle formation. Injection of the Epb4.1l5^longchimera (Epb4.1l5^{long+short_PBD}), containing the PBD from Epb4.1l5^short, rescued retinal defects, and to a large extent rescued RPE integrity. The only construct that caused a dominant phenotype in wild-type embryos, was Epb4.1l5^{long+short_PBD}, which caused brain ventricle defects and edema that were similar to those observed in <it>moe</it>^-mutants. Lastly, the morphology of rod photoreceptors in <it>moe</it>^-mutants where embryonic defects were rescued by <it>moe </it>or <it>epb4.1l5</it>^{<it>long </it>}mRNA injection is abnormal and their outer segments are larger than normal.</p> <p>Conclusion</p> <p>Taken together, the data reveal tissue specificity for the function of the PBD in Epb4.1l5^long, and suggest that additional C' terminal sequences are important for zebrafish retinal development. Additionally, our data provide further evidence that Moe is a negative regulator of rod outer segment size.</p>