An Essential Role in Molting and Morphogenesis of Caenorhabditis elegans for ACN-1, a Novel Member of the Angiotensin-converting Enzyme Family That Lacks a Metallopeptidase Active Site

Abstract

Genome sequence analyses predict many proteins that are structurally related to proteases but lack catalytic residues, thus making functional assignment difficult. We show that one of these proteins (ACN-1), a unique multi-domain angiotensin-converting enzyme (ACE)-like protein from Caenorhabditis elegans, is essential for larval development and adult morphogenesis. Green fluorescent protein-tagged ACN-1 is expressed in hypodermal cells, the developing vulva, and the ray papillae of the male tail. The hypodermal expression of acn-1 appears to be controlled by nhr-23 and nhr-25, two nuclear hormone receptors known to regulate molting in C. elegans. acn-1(RNAi) causes arrest of larval development because of a molting defect, a protruding vulva in adult hermaphrodites, severely disrupted alae, and an incomplete seam syncytium. Adult males also have multiple tail defects. The failure of the larval seam cells to undergo normal cell fusion is the likely reason for the severe disruption of the adult alae. We propose that alteration of the ancestral ACE during evolution, by loss of the metallopeptidase active site and the addition of new protein modules, has provided opportunities for novel molecular interactions important for post-embryonic development in nematodes.The large number of protease genes in animal genomes reflects the widespread importance of proteolysis to animal physiology and development. The rich functional diversity of proteases can be attributed to the variety of catalytic mechanisms and protein structures, some of which are of a modular design, offering different levels of structural and functional complexity (1). The MEROPS data base (merops.sanger.ac.uk; release 6.3) (2) catalogs 551, 553, 563, 366, and 367 proteases for human, mouse, Drosophila melanogaster, Anopheles gambiae, and Caenorhabditis elegans, respectively. The majority of these enzymes have not been studied at the physiological and biochemical level, but it has been possible to classify most of them into families based on statistically significant similarities in primary protein structure (2).Surprisingly, a significant proportion (12-25%) of the total number of the predicted protease-like genes in the human, mouse, D. melanogaster, A. gambiae, and C. elegans genomes code for proteins that lack one or more catalytic residues and are therefore classified as "non-peptidase" family members. Some of these genes may be nonfunctional pseudogenes, but many have probably lost the catalytic activity of an ancestral protein while acquiring new functions. These non-peptidase proteins are structurally related to proteases distributed across all classes, but homologues of metallopeptidases are particularly well represented. One such protein is UNC-71, a C. elegans member of the ADAMs family, which lacks a zinc binding site and yet has acquired important roles in development (3). Our attention has recently been drawn to the fact that several invertebrate members of the angiotensin-converting enzyme (ACE) 1 (EC 3.4.15.1, peptidyl dipeptidase A) famil...

TheCaenorhabditis elegans rsd-2andrsd-6Genes Are Required for Chromosome Functions During Exposure to Unfavorable Environments

“…RNAi defects in rsd-2 mutants were also observed when unc-112, F38E11.5, bli-3, apm-1, or acn-1 genes were targeted. However, these feeding strains elicited an unanticipated sterility in wildtype animals (Rogalski et al 2000;Shim et al 2000;Edens et al 2001;Brooks et al 2003;McKay et al 2003;Frand et al 2005). These unexpectedly early RNAi phenocopies in wild type may reflect off-target silencing of related genes or secondary defects in germline development caused by the loss of the targeted gene.…”

Regulation of Sphingosine-1-phosphate Lyase Gene Expression by Members of the GATA Family of Transcription Factors

“…In the absence of ELT-2 expression, animals arrest at the L1 larval stage and die within several days due to starvation. In order to rule out the possibility that inhibition of SPL reporter expression observed in the ELT-2 RNAi-treated worms might result from a general effect of L1 larval arrest, control experiments were simultaneously performed in SPL reporter worms using RNAi against acn-1, which results in L1 arrest due to a hypodermal defect (50). As shown in pattern observed in the 350-nucleotide reporter worms shown in Fig.…”

Thehedgehog-related genequa-1 is required for molting inCaenorhabditis elegans

“…So far, the regulatory mechanisms of C. elegans molting are not yet understood, although about a dozen genes have been identified that lead to molting defects when mutated. These genes can be classified into five categories based on their possible functions: (1) proteases that are used to degrade the old cuticle, including a cathepsin Z-like cysteine protease (Cecpz-1) (Hashmi et al, 2004), and two metalloproteases, nas-36 and nas-37 (Davis et al, 2004;Suzuki et al, 2004); (2) transcriptional regulators, including nhr-23 (Kostrouchova et al, 1998(Kostrouchova et al, , 2001, nhr-25 (Asahina et al, 2000;Gissendanner and Sluder, 2000), and let-19 (Wang et al, 2004); (3) enzymes involved in cholesterol metabolism such as let-767 (Kuervers et al, 2003) or cholesterol transporters such as lrp-1 (Yochem et al, 1999); (4) molecules involved in secretion and extracellular transport such as sec-23 (Roberts et al, 2003) and CeVps-27 (Roudier et al, 2005); (5) others, such as the angiotensin converting enzyme-like non-peptidase acn-1 (Brooks et al, 2003).…”