The Nuclear Pore Complex Function of Sec13 Protein Is Required for Cell Survival during Retinal Development

Xubo Niu,Jian Hong,Xiaofeng Zheng,David B Melville,Ela W Knapik,Anming Meng,Jinrong Peng

doi:10.1074/jbc.m114.547190

Abstract

Sec13 is a dual function protein, being a core component of both the COPII coat, which mediates protein trafficking from the endoplasmic reticulum to the Golgi apparatus, and the nuclear pore complex (NPC), which facilitates nucleo-cytoplasmic traffic. Here, we present a genetic model to differentiate the roles of these two functions of Sec13 in vivo. We report that sec13(sq198) mutant embryos develop small eyes that exhibit disrupted retinal lamination and that the mutant retina contains an excessive number of apoptotic cells. Surprisingly, we found that loss of COPII function by oligonucleotide-mediated gene knockdown of sec31a and sec31b or brefeldin A treatment did not disrupt retinal lamination, although it did result in digestive organ defects similar to those seen in sec13(sq198), suggesting that the digestive organ defects observed in sec13(sq198) are due to loss of COPII function, whereas the retinal lamination defects are due to loss of the NPC function. We showed that the retinal cells of sec13(sq198) failed to form proper nuclear pores, leading to a nuclear accumulation of total mRNA and abnormal activation of the p53-dependent apoptosis pathway, causing the retinal defect in sec13(sq198). Furthermore, we found that a mutant lacking Nup107, a key NPC-specific component, phenocopied the retinal lamination phenotype as observed in sec13(sq198). Our results demonstrate a requirement for the nuclear pore function of Sec13 in development of the retina and provide the first genetic evidence to differentiate the contributions of the NPC and the COPII functions of Sec13 during organogenesis.

Highlights

Sec13 is a core component in both the protein trafficking complex and the nuclear pore complex (NPC)
We found that loss of COPII function by oligonucleotide-mediated gene knockdown of sec31a and sec31b or brefeldin A treatment did not disrupt retinal lamination, it did result in digestive organ defects similar to those seen in sec13sq198, suggesting that the digestive organ defects observed in sec13sq198 are due to loss of COPII function, whereas the retinal lamination defects are due to loss of the NPC function
Retinal Lamination Is Disrupted in the sec13sq198 Mutant— Immunostaining showed that Sec13 was highly expressed in the wild-type AB line (WT) retinal cells but was only barely detectable in the sec13sq198 mutant retinal cells (Fig. 1A), suggesting that Sec13 is likely to play a role in retinogenesis

Summary

Background

Sec is a core component in both the protein trafficking complex and the nuclear pore complex (NPC). Our results demonstrate a requirement for the nuclear pore function of Sec in development of the retina and provide the first genetic evidence to differentiate the contributions of the NPC and the COPII functions of Sec during organogenesis. Studies of zebrafish genetic mutant sec13sq198 [7] and of the morpholino-mediated gene knockdown approach [8, 9] have shown that the COPII function of Sec is essential for the organogenesis of digestive organs and craniofacial cartilage. We show the following: 1) the retina lamination phenotype in sec13sq198 is not entirely due to the compromised COPII function, and 2) disruption of the NPCs in the sec13sq198 retina is the primary cause for developmental defects of the retina This conclusion is supported by the fact that a zebrafish mutant lacking Nup107 phenocopies the sec13sq198 retina lamination phenotype. Our data clearly demonstrate an important role for the NPC function of Sec in the process of retinal development

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION