Nuclear hormone receptor CHR3 is a critical regulator of all four larval molts of the nematodeCaenorhabditis elegans

Abstract

CHR3 (nhr-23, NF1F4), the homologue of Drosophila DHR3 and mammalian ROR͞RZR͞RevErbA nuclear hormone receptors, is important for proper epidermal development and molting in the nematode Caenorhabditis elegans. Disruption of CHR3 (nhr-23) function leads to developmental changes, including incomplete molting and a short, fat (dumpy) phenotype. Here, we studied the role of CHR3 during larval development by using expression assays and RNA-mediated interference. We show that the levels of expression of CHR3 (nhr-23) cycle during larval development and reduction of CHR3 function during each intermolt period result in defects at all subsequent molts. Assaying candidate gene expression in populations of animals treated with CHR3 (nhr-23) RNAmediated interference has identified dpy-7 as a potential gene acting downstream of CHR3. These results define CHR3 as a critical regulator of all C. elegans molts and begin to define the molecular pathway for its function.molting ͉ development N uclear hormone receptors (NHRs) form a large superfamily of transcription factors that are important for the regulation of cell metabolism, development, and reproduction (1-3). The typical receptor consists of six domains. The most conserved domain is the DNA-binding domain (DBD) and is characteristic for the NHR superfamily. It is formed by two zinc finger motifs that are conserved through evolution (4-6). A second, less conserved domain is the ligand-binding domain, located in the C terminus of the molecule and involved in binding of small hydrophobic molecules, hormones of the steroid class, thyroid hormone, retinoic acid stereoisomers, farnesoids, prostaglandins, and terpenoids (2). The generally accepted classification of NHRs is based on homology in both the DBD and the ligandbinding domain and the specific ligands (if known), which activate the receptors. The majority of NHRs have no known ligands and usually are referred to as orphan receptors.The NHRs are present in a majority of Metazoan species higher than diploblasts. NHRs apparently evolved from a single gene present in a Metazoan ancestor before the divergence of diploblastic species (4-6). There are about 70 NHRs in vertebrates, 22 in Drosophila We previously have cloned the C. elegans orphan NHR CHR3 (19), which is a homologue of Drosophila DHR3 (20), Manduca sexta MHR3 (21), and mammalian ROR͞RZR͞Rev ErbA (22, 23). For clarity, we refer to it in this paper by using both its common and gene names, CHR3 (nhr-23). The gene is classified as NR1F4 in a unified nomenclature system for the NHR superfamily (24). We previously showed that CHR3 (nhr-23) is expressed in the epidermis of C. elegans throughout development and that it was required for proper molting (16).Molting is a complex of developmental processes characteristic for a clad Ecdysozoa, which includes arthropods, tardigrades, onychophorans, nematodes, nematomorphs, kinorhynchs, and priapulids (25). At each molt, there is production of the new outer-body cover, the exoskeleton, and the old part is shed. Molting represents...

The Caenorhabditis elegans Cathepsin Z-like Cysteine Protease, Ce-CPZ-1, Has a Multifunctional Role during the Worms' Development

“…Interestingly, inhibition of nhr-23, nhr-25, and lrp-1 gene expression also resulted in some morphological abnormalities. All these genes, including cpz-1, are highly expressed in the major hypodermal cells in all larval stages of nematodes, which supports their involvement in epidermal differentiation during or after molting (45,46,48).…”

“…The arrested L1-L2 worms were unable to shed their cuticle properly during molting as whole cuticles or parts of cuticle remained attached to the rectum (38,39). Soaking or feeding of all four larval stages of worms in nhr-23 dsRNA also resulted in molting defects, however, in the later developmental stages of the worms suggesting that nhr-23 may also regulate molting at each of the C. elegans larval developmental stages (47,48). So far, it is not clear whether both proteins have a direct function or their role is through downstream gene(s) that are not activated because of the nhr-23 or nhr-25 RNAi inactivation.…”

The Caenorhabditis elegans IMPAS gene, imp-2, is essential for development and is functionally distinct from related presenilins

“…Thus, DAF-9 is unlikely to be the direct target regulated by Ce-imp-2. NHR-23 and NHR-25 are nuclear receptors, and NHR-25 is a homolog of mammalian FTZ-F1 receptor or FTZ-F1-like protein involved in regulation of cholesterol homeostasis (41)(42)(43). LET-512 is a member of the lipid kinase family that regulates localization and expression of Ce-LRP-1 in C. elegans (44).…”

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).…”