Abstract
At the end of the first larval stage, the nematode Caenorhabditis elegans developing in harsh environmental conditions is able to choose an alternative developmental path called the dauer diapause. Dauer larvae exhibit different physiology and behaviors from non-dauer larvae. Using focused ion beam-scanning electron microscopy (FIB-SEM), we volumetrically reconstructed the anterior sensory apparatus of C. elegans dauer larvae with unprecedented precision. We provide a detailed description of some neurons, focusing on structural details that were unknown or unresolved by previously published studies. They include the following: (1) dauer-specific branches of the IL2 sensory neurons project into the periphery of anterior sensilla and motor or putative sensory neurons at the sub-lateral cords; (2) ciliated endings of URX sensory neurons are supported by both ILso and AMso socket cells near the amphid openings; (3) variability in amphid sensory dendrites among dauers; and (4) somatic RIP interneurons maintain their projection into the pharyngeal nervous system. Our results support the notion that dauer larvae structurally expand their sensory system to facilitate searching for more favorable environments.
Highlights
The non-parasitic nematode Caenorhabditis elegans has a rapid reproductive life cycle passing four larval stages (Brenner, 1974; Sulston and Horvitz, 1977)
To get a near-to-native isotropic high-resolution 3D-insight into the anterior sensory apparatus of C. elegans dauer larvae we used high-pressure freezing followed by freeze substitution, minimal resin embedding, and focused ion beam-scanning electron microscopy (FIB-SEM) acquisition as previously described (Schieber et al, 2017)
We analyzed the anterior regions of sensilla of three dauer hermaphrodites by FIB-SEM image stacks, DauerE1, DauerE2, and DauerE3
Summary
The non-parasitic nematode Caenorhabditis elegans has a rapid reproductive life cycle passing four larval stages (Brenner, 1974; Sulston and Horvitz, 1977). This underlies either self-fertilization by hermaphrodites or sexual reproduction involving males (Sulston and Horvitz, 1977). Dauer larvae can survive for months without food (Klass and Hirsh, 1976). This is possible due to specific anatomical adaptations like a sealed mouth, a switch in metabolism to lipid storage, and protection. Dauer larvae are nonfeeding, with inactive pharynx and reduced intestine (Cassada and Russell, 1975; Popham and Webster, 1979; Albert and Riddle, 1983)
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