Teething during sleep: Ultrastructural analysis of pharyngeal muscle and cuticular grinder during the molt in Caenorhabditis elegans.

Alessandro P Sparacio,David M Raizen,Nicholas F Trojanowski,Matthew D Nelson,Karen Snetselaar,Myon-Hee Lee

doi:10.1371/journal.pone.0233059

Alessandro P Sparacio, David M Raizen + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0233059

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Abstract

Complex extracellular structures exist throughout phylogeny, but the dynamics of their formation and dissolution are often opaque. One example is the pharyngeal grinder of the nematode Caenorhabditis elegans, an extracellular structure that ruptures bacteria during feeding. During each larval transition stage, called lethargus, the grinder is replaced with one of a larger size. Here, we characterize at the ultrastructural level the deconstruction of the larval grinder and the construction of the adult grinder during the fourth larval stage (L4)-to-adult transition. Early in L4 lethargus, pharyngeal muscle cells trans-differentiate from contractile to secretory cells, as evidenced by the appearance of clear and dense core vesicles and disruptions in sarcomere organization. This is followed, within minutes, by the dissolution of the L4 grinder and the formation and maturation of the adult grinder. Components of the nascent adult grinder are deposited basally, and are separated from the dissolving larval grinder by a visible apical layer. The complete grinder is a lamellated extracellular matrix comprised of five layers. Following grinder formation, pharyngeal muscle cells regain ultrastructural contractile properties, and muscle contractions resume. Our findings add to our understanding of how complex extracellular structures assemble and dissemble.

Highlights

Complex extracellular structures are found in all lineages of organisms and are responsible for much of the vast diversity in structure seen throughout biology
We used pumping cessation (PC), which occurs at the beginning of lethargus, to establish a time zero (t = 0) for grinder development during L4 lethargus
In the time window between 15- and 30-minutes post-Pumping cessation (PC), we observed two distinct grinders, smaller anterior and larger posterior, while 45 to 120-minutes post-PC, the larval grinder became increasingly amorphous as it moved into the luminal space

Summary

Introduction

Complex extracellular structures are found in all lineages of organisms and are responsible for much of the vast diversity in structure seen throughout biology. At 30 minutes post-PC (Fig 8A), layer 4 is further broken down, as evidenced by depletion of the electron-dense blebs, and the distance between the apical end of pm6/pm7 and the remnants of the L4 grinder is increased.

Results

Conclusion