The Hair Fibre: Proteins, Structure and Development by Jeffrey E. Plowman Duane P. Harland & Santanu Deb-Choudhury

Author:Jeffrey E. Plowman, Duane P. Harland & Santanu Deb-Choudhury
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

How these initial bundles form is discussed in more detail in Chap. 11. These initial bundles are probably formed of heterodimers of K31 and K85 (K35’s role is less clear) and they probably begin forming before the appearance of the first matrix-forming KAPs . We use the word “probably” because the precise relationship between the onset of expression, cytoplasmic protein concentration and the onset of ultrastructure is not well understood (Chap. 7). What we do know is that the first KAPs begin to express in the mid-upper bulb, above the level of the dermal papilla and this occurs after the first expression of keratin and probably about the same time as the first keratin structures (proto-macrofibrils) appear or shortly after this point.

What role KAPs play in the initial stages of proto-macrofibril assembly (either associated with desmosomes or free within the cytoplasm) is unclear. Some studies suggest keratin-KAP interactions are essential for seeding of proto-macrofibrils from desmosomes [88] or for free floating proto-macrofibrils [89]. However, observations of proto-macrofibrils from below the region of KAP expression and also those in which KAPs appear to be infiltrating matrix free macrofibrils (Fig. 10.8) suggests a more complex relationship [90, 91].

Fig. 10.8(a) Transmission electron micrographs of cortex cell from Zone C of wool follicle showing infiltration of growing macrofibrils by matrix material (KAPs ). Label I and II indicate macrofibrils in adjacent cells in which matrix material appears to have different levels of electron density from heavy metal staining. Gaps within the macrofibril appear to be devoid of cytoplasmic components (e.g., ribosomes). (b) Example of a cross-section of an early forming keratin bundle from proximal Zone B, showing filaments with spaces. ((a) reprinted from J. Ultrastruct. Res., 1971, Chapman and Gemmell [90], with permission from Elsevier; (b) reprinted from J. Text. Eng. McKinnon, Harland [87], permission from The Textile Machinery Society of Japan)

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