The Regulation of Developmental Diapause is Coordinated with Molting and Olfaction

Abstract

1Developmental and behavioral plasticity allow animals to prioritize alternative 2 genetic programs during fluctuating environments. Behavioral remodeling may be 3 acute in animals that interact with host organisms, since reproductive adults and 4 the developmentally arrested larvae often have different ethological needs for 5 chemical stimuli. To understand the genes that coordinate development and 6 behavior, we used the nematode model Pristionchus pacificus to characterize 7 mutants that inappropriately enter developmental diapause to become dauer 8 larvae (Daf-c). We found several key olfactory differences between P. pacificus 9 and C. elegans Daf-c dauers. In addition, the two P. pacificus Daf-c alleles disrupt 10 steroid synthesis required for proper regulation of the conserved canonical steroid 11 hormone receptor DAF-12, whose dauer-constitutive and cuticle exsheathment 12 phenotypes can be rescued by the feeding of ∆7-dafachronic acid. One allele, 13 csu60, has a deletion in the sole HydroxySteroid Dehydrogenase (HSD) in P. 14 pacificus. Both hsd-2(csu60) adults and dauers show enhanced attraction to a 15 beetle pheromone, possibly due to the heterochronic activation of dauer-specific 16 neuronal development in the adults. Surprisingly, this enhanced odor attraction 17 acts independently of daf-12, revealing unexpected targets of steroid hormones 18 regulating ecdysis and olfaction in P. pacificus. analysis in diverse species of nematodes as a result of comparative studies in non-52Caenorhabditis species [8][9][10]. 53The commitment to dauer entry requires external as well as internal factors. 54Multiple parallel-acting signaling factors in the dauer regulation pathway have been 55 characterized in C. elegans, such as the recognition of pheromones by G-protein-56 coupled receptors in the chemosensory amphid neurons and signal transduction 57 to the DAF-11/guanylyl cyclase pathway [11]. Favorable conditions also lead to 58 signaling in the DAF-7/TGF-ß and DAF-2/insulin-like pathways [11][12][13][14]. This 59 signaling facilitates the production of ∆4-and ∆7-dafachronic acid from the 60 cholesterol precursor, which act as ligands that bind to the highly conserved 61 nuclear hormone receptor DAF-12 and prevent DAF-12 from repressing genes 62 necessary for development to reproductive adulthood [11,[15][16][17]. Less favorable 63 conditions produce pheromones that reduce signaling in these pathways, 64 subsequently shifting DAF-12 from its inactive ligand-bound form to its active, 65ligand-free form that specifies dauer development. Despite being a non-feeding 66 and stress-resistant stage, the DL are actively motile and receptive to external 67 chemosensory and mechanical cues. For both parasitic and free-living nematodes, 68 DL share the ability to survive harsh conditions but remain receptive to 69 semiochemicals from their environment. 70The commitment to dauer also prompts the rewiring of the sensory nervous 71 system in C. elegans [6,18,19], but the molecular basis of this process remains 72 poorly unde...

The Wild Worm Codon Adapter: a web tool for automated codon adaptation of transgenes for expression in non-Caenorhabditis nematodes

“…Nippostrongylus brasiliensis, the human-parasitic filarial nematode Brugia malayi, the predatory nematode Pristionchus pacificus, and the free-living nematodes Auanema rhodensis and Auanema freiburgensis (Grant et al 2006;Lok et al 2017;Adams et al 2019;Castelletto et al 2020;Han et al 2020). Intragonadal microinjection, in which exogenous DNA is injected into either the syncytial gonad of free-living adult females (Strongyloididae species, P. pacificus), the distal gonad of free-living adult females (Auanema species), or the uterus of parasitic adult females (B. malayi), has been used to generate progeny expressing a range of transgenes (Schlager et al 2009;Lok et al 2017;Hong et al 2019;Adams et al 2019;Castelletto et al 2020;Carstensen et al 2020;Han et al 2020). Intragonadal microinjection has also been used to achieve CRISPR/Cas9-mediated mutagenesis in S. stercoralis, S. ratti, P. pacificus, and Auanema species (Witte et al 2015;Lok et al 2017;Gang et al 2017;Bryant et al 2018;Adams et al 2019;Han et al 2020).…”