Bulk Actin Dynamics Drive Phase Segregation in Zebrafish Oocytes

Abstract

Highlights d Bulk actin polymerization waves move through the oocyte from animal to vegetal d An animal-to-vegetal actin gradient triggers animal-directed actin flows d Actin flows drag the ooplasm toward the animal pole via differential friction d Actin comets formed on yolk granules push them toward the vegetal pole

Integration of luminal pressure and signalling in tissue self-organization

“…Although lumina are widespread in many tissues, their roles have so far been studied in limited contexts. The roles of the lumen (Chan et al, 2019;Dumortier et al, 2019;Ryan et al, 2019), interstitial fluid (Petridou et al, 2019) and yolk (Shamipour et al, 2019) in early development require further exploration. For example, in early marine embryos with a hydroskeleton shell around a fluid-filled body cavity (such as sea anemone), fluid pressure is known to be required for body movement (Kier, 2012); however, the interplay between pressure and signalling in embryo morphogenesis and patterning is less well understood.…”

Cytoskeleton Force Exertion in Bulk Cytoplasm

“…deep in the cytoplasm is often obscured by the very bright cortex (Field and Lenart, 2011). The development of actin live probes including life-act and Utrophin has allowed important new discoveries on the specific function of bulk actin (Li et al, 2008;Almonacid et al, 2015;Shamipour et al, 2019).…”

“…Those served to draw a large part of our current understanding of actin assembly and force generation, needed for other processes like lamellipodium based migration (Theriot et al, 1994;Laurent et al, 1999;Pantaloni et al, 2001). In addition, comet tails also form around other pathogens including viruses (Welch and Way, 2013), as well as at the surface of endosomes, lysosomes or yolk granules (Taunton et al, 2000;Shamipour et al, 2019), suggesting that they could promote the intracellular motion of many types of cargos in the cytoplasm.…”

“…During microbe escape, actin tails also appear to connect to the cortex of evaginating membranes, raising the possibility that the tail could push on more elastic or viscoelastic elements to support forward progression of the bacterium against load (Sechi et al, 1997). Because some actin tails appear smaller than their cargos, it is likely that visco-elastic interactions of the tail with other elements may be required in some instances (Shamipour et al, 2019).…”

“…Thus, this mechanism may have similarities with MT aster centering from bulk dynein forces. Whether this mechanism directly contributes to center organelles like the nucleus in cells remains to be tested, but similar bulk actin flows, have been shown to exist in fish embryos and influence the organization of their cytoplasm (Shamipour et al, 2019).…”