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My textbook( COMPREHENSIVE TEXTBOOK OF PHYSIOLOGY VOL-1 by GK PAL) says:

Microfilaments project into microvilli present on the epithelial surface such as on the intestinal mucosa, and extend up to the tip of microvilli. They help in microvilli movement.

How far is the second sentence correct? When I searched on Wikipedia( in a page about microvilli) I found following:

As mentioned, microvilli are formed as cell extensions from the plasma membrane surface.Actin filaments, present in the cytosol, are most abundant near the cell surface. These filaments are thought to determine the shape and movement of the plasma membrane.

So does these two imply that there is some sort of movement (due to actin) in microvilli?

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Just the presence of actin filaments does not mean a cellular structure that contains it would be dynamic. Moreover there are different types of actin filaments (filopodia, lamellipodia etc) and they have different dynamics.

Microvilli closely resemble filopodia; both these structures also share some regulatory and structural proteins (other than actin). However, there are some differences which makes filopodia highly dynamic in comparison to microvilli (Sebé-Pedrós et al., 2013; Sauvanet et al., 2016).

Microvilli, though not as dynamic as filopodia, are not static structures. They can grow and retract and there are regulatory mechanisms that govern these processes (Sauvanet et al., 2016).

REGULATION AND DYNAMICS OF MICROVILLI AND MICROVILLAR COMPONENTS

Microvilli on cultured cells are dynamic structures with three phases in their life cycle: (a) the generation of microvilli growing at 5 nm/s, (b) a steady state of ∼5 min, and (c) a retraction phase with a rate of 1.2 nm/s (Gorelik et al. 2003). This leads to an average life cycle of 12.1 ± 5.6 min. The turnover of microvillar proteins has been recognized for a long time (Stidwill et al. 1984). The F-actin core in the microvilli of Caco-2 cells at steady state treadmills, with a rate of monomer addition at the barbed end of approximately 1.5–3.0 s−1 (Loomis et al. 2003, Tyska & Mooseker 2002), corresponding to approximately 0.2 μm/min. The protocadherin intermicrovillar link stabilizes microvilli of intestinal epithelial cells, resulting in a prolonged steady state (Crawley et al. 2014). The actin filaments in the core of stereocilia treadmill more slowly, at 0.002–0.04 subunits s−1 (Rzadzinska et al. 2004) or hardly at all (Zhang et al. 2012).

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  • $\begingroup$ so does the movement implies growth and retraction? $\endgroup$ – JM97 Dec 19 '16 at 14:16
  • $\begingroup$ @JM97 yes. It is pretty much evident from the quoted text. For more details you can check out the article. $\endgroup$ – WYSIWYG Dec 19 '16 at 14:26

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