Loss of SEC-23 inCaenorhabditis elegansCauses Defects in Oogenesis, Morphogenesis, and Extracellular Matrix Secretion

Abstract

SEC-23 is a component of coat protein complex II (COPII)-coated vesicles involved in the endoplasmic reticulum-to-Golgi transport pathway of eukaryotes. During postembryonic life, Caenorhabditis elegans is surrounded by a collagenous exoskeleton termed the cuticle. From a screen for mutants defective in cuticle secretion, we identified and characterized a sec-23 mutant of C. elegans. By sequence homology, C. elegans has only the single sec-23 gene described herein. In addition to the cuticle secretion defect, mutants fail to complete embryonic morphogenesis. However, they progress through the earlier stages of embryogenesis, including gastrulation, and achieve substantial morphogenesis before death. We demonstrated a maternal component of SEC-23 function sufficient for progression through the earlier stages of embryogenesis and explaining the limited phenotype of the zygotic mutant. By RNA-mediated interference, we investigated the effects of perturbing COPII function during various postembryonic stages. During larval stages, major defects in cuticle synthesis and molting were observed. In the adult hermaphrodite, reduction of SEC-23 function by RNAmediated interference caused a rapid onset of sterility, with defects in oogenesis including early maturation of the germline nuclei, probably a result of the observed loss of the GLP-1 receptor from the membrane surfaces adjacent to the developing germline nuclei. INTRODUCTIONThe cuticle of the nematode Caenorhabditis elegans is a collagenous extracellular matrix (ECM) synthesized by a specialized underlying ectodermal cell layer, termed the hypodermis, that surrounds the body of the animal. During its life cycle, C. elegans synthesizes this ECM on five occasions, once in the embryo before hatching and then at the end of each larval stage before molting. During each synthesis, the components of the cuticle are secreted apically from the hypodermal cells and then polymerize on the outside of the apical surface. The cuticle consists predominantly of small collagens encoded by a multigene family. The nematode cuticle collagens share a common overall structure, the procollagen chains being ϳ30 kDa and having short, interrupted blocks of Gly-X-Y collagen sequence and clusters of conserved cysteine residues (Kramer, 1997;Johnstone, 2000). They are most similar to the nonfibrillar FACIT collagens of vertebrates (Shaw and Olsen, 1991).For the fibrillar collagens of vertebrates, trimerization of monomers occurs within the endoplasmic reticulum (ER). Hydroxylation of a proportion of the proline residues within the repeat domains is required to stabilize the collagen structures (Kivirikko and Pihlajaniemi, 1998). This reaction is catalyzed by prolyl 4-hydroxylase, an ER enzyme that also acts as a molecular chaperone by retaining unfolded collagen chains in the ER, releasing them for transport to the Golgi apparatus for further processing only when they have folded correctly (Walmsley et al., 1999). Although less is known about the assembly and secretion of the nematode cuticula...

Extracellular leucine-rich repeat proteins are required to organize the apical extracellular matrix and maintain epithelial junction integrity inC. elegans

“…Mutants for the tetraspanin tsp-15, which show various cuticle abnormalities, also show seam epidermal protrusions and junction connectivity defects (Moribe et al, 2004). Finally, sec-23 mutations that impair cuticle secretion (and presumably secretion of eLRRon proteins as well) cause embryonic rupturing at the two-to threefold stage as described here for sym-1; let-4(RNAi) embryos (Roberts et al, 2003). It is possible that redundancy among the >170 cuticle collagens in C. elegans masks more widespread requirements for the cuticular ECM in maintaining junction integrity.…”

Conserved Ankyrin Repeat Proteins and Their NIMA Kinase Partners Regulate Extracellular Matrix Remodeling and Intracellular Trafficking in Caenorhabditis elegans

“…In addition, studies on mammalian megalin suggest that C. elegans LRP-1 could promote molting in part by regulating the uptake of proteases and protease inhibitors (May et al 2007;Marzolo and Farfan 2011;Etique et al 2013). In addition to LRP-1, several other genes required for molting also affect intracellular trafficking and sterol-LRP-1 uptake including dab-1/Disabled, hgrs-1/VPS27, and sec-23/ SEC23 (Kamikura and Cooper 2003;Roberts et al 2003;Roudier et al 2005;Holmes et al 2007;Yochem et al 2015).…”

SEC23B is required for the maintenance of murine professional secretory tissues

“…However, knockdown of either Sec23 isoform in zebrafish induced a phenotype similar to crusher, suggesting that zebrafish SEC23B may also be involved in cartilage maturation (23). A Caenorhabditis elegans Sec23 mutant also exhibits defective secretion of the DPY-7 collagen gene (38). The absence of skeletal abnormalities in SEC23B-deficient neonates and lack of evidence for retention of collagen I in the ER of Sec23b gt/gt MEFs suggest that mammalian SEC23B may not contribute to collagen secretion and bone development, or that its role is largely compensated by SEC23A.…”