Figure 3: Developmental series of thread ultrastructure. | Nature Communications

Figure 3: Developmental series of thread ultrastructure.

From: Coiling and maturation of a high-performance fibre in hagfish slime gland thread cells

Figure 3

(a) TEM sections of slime threads from very immature to fully mature GTCs. The thread depicted in (1) consists of a bundle of about ten, 12-nm IFs. Threads increase in girth by the addition of more IFs, and eventually by the addition of MTs (2). In the next stage (3), 12-nm IFs become more tightly packed, which creates electron lucent halos (asterisk) around the MTs. Further IF compaction is accompanied by the appearance of a fluffy rind (arrowheads) on the thread surface (4), which likely corresponds to the direct addition of IF subunits or proteins to the thread rather than the bundling of mature IFs. In the final stage, IF proteins compact further, MTs are lost, the spaces they occupied are filled in, and the fluffy rind disappears. In fully mature GTCs, the thread takes up the vast majority of the cell volume and adjacent threads are packed so tightly that they conform to each other (5). Scale bars are all 200 nm. (b) Models of thread development corresponding to each of the stages depicted in (a). The second panel illustrates the 12-nm diameter filament (arrows) that wraps around the thread at this stage in development (c) Young thread from stage (2) showing the wrapping filament (arrow), which is evident as regularly spaced circular sections and corresponding lines that cross the thread at an average angle of about 86°. (d) Cross-section of a thread from stage (4) showing a MT penetrating from the side (3). (e) TEM of thread longitudinal section depicting MTs within a developing thread. Scale bars, 500 nm (c–e).

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