Abnormal nuclear pore formation triggers apoptosis in the intestinal epithelium of elys-deficient zebrafish

<p><strong>Background & Aims:</strong> Zebrafish mutants generated by ethylnitrosourea-mutagenesis provide a powerful tool for dissecting the genetic regulation of developmental processes, including organogenesis. One zebrafish mutant, “<i>flotte lotte</i>” (<i>flo</i>), displays striking defects in intestinal, liver, pancreas, and eye formation at 78 hours postfertilization (hpf). In this study, we sought to identify the underlying mutated gene in <i>flo</i> and link the genetic lesion to its phenotype.</p> <p><strong>Methods:</strong> Positional cloning was employed to map the <i>flo</i> mutation. Subcellular characterization of <i>flo</i> embryos was achieved using histology, immunocytochemistry, bromodeoxyuridine incorporation analysis, and confocal and electron microscopy.</p> <p><strong>Results:</strong> The molecular lesion in <i>flo</i> is a nonsense mutation in the <i>elys</i> (<u>e</u>mbryonic <u>l</u>arge molecule derived from <u>y</u>olk <u>s</u>ac) gene, which encodes a severely truncated protein lacking the Elys C-terminal AT-hook DNA binding domain. Recently, the human ELYS protein has been shown to play a critical, and hitherto unsuspected, role in nuclear pore assembly. Although <i>elys</i> messenger RNA (mRNA) is expressed broadly during early zebrafish development, widespread early defects in <i>flo</i> are circumvented by the persistence of maternally expressed <i>elys</i> mRNA until 24 hpf. From 72 hpf, <i>elys</i> mRNA expression is restricted to proliferating tissues, including the intestinal epithelium, pancreas, liver, and eye. Cells in these tissues display disrupted nuclear pore formation; ultimately, intestinal epithelial cells undergo apoptosis.</p> <p><strong>Conclusions:</strong> Our results demonstrate that Elys regulates digestive organ formation.</p>