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. 2023 Mar 10;12:e81405. doi: 10.7554/eLife.81405

Figure 3. Geometry of hagfish epidermal threads.

(A) Three levels of epidermal thread structure. (Left-middle) At the micro-scale, the thread traces a right-handed helix, the centerline of which is arranged in a switchback pattern on the inner surface of the cell membrane. Yellow arrow denotes the direction of increase; white arrows denote direction of helical rotation. (Right) At the nano-scale, a thread consists of a dense bundle of intermediate filament proteins, shown here in transmission electron microscopy (TEM) (see also Figure 3—figure supplement 1). (B) The peaks and valleys of the projected thread sections were used as landmarks for morphometric analysis. Blue dots, peaks; white dots, valleys; white dashed line, centerline. ϕ, thread diameter; θ, helical pitch angle; D, helical diameter. (C) Variations in thread geometry with respect to a morpho-space defined by thread diameter ϕ, helical pitch angle θ, and helical diameter D. With increasing pitch angle θ, thread diameter ϕ increases (p<0.05; linear regression model) and helical diameter D decreases (p<0.001), illustrated with idealized threads.

Figure 3—source data 1. Geometry of epidermal threads sampled using laser confocal microscopy.

Figure 3.

Figure 3—figure supplement 1. Morphology of epidermal threads.

Figure 3—figure supplement 1.

(A) Scanning electron microscopy (SEM) images showing details of a single epidermal thread cell (ETC) thread on the epidermal surface abraded with sandpaper, showing subfilament structure. (B) Transmission electron microscopy (TEM) of an ETC in cross-section, showing sub-micron structures of threads as parallelly aligned filament bundles, which is consistent with the thread structure observed in the Atlantic hagfish (Myxine glutinosa) (Blackstad, 1963).