The multiple hats of Vasa: its functions in the germline and in cell cycle progression

Abstract

Vasa, an ATP-dependent RNA helicase, is broadly conserved among various organisms from cnidarians to mammals. It has a rich history of utility as a germline marker, and is believed to function as a positive translational regulator in the determination and maintenance of germline cells. Studies in non-model organisms, however, revealed that Vasa is also present in somatic cells of many tissues. In many cases these cells are multipotent, are non-germline associated, and give rise to a variety of different tissue types. Recent work now also demonstrates that Vasa functions in the regulation of the cell cycle. Here, we discuss this newly described function of Vasa in mitotic and meiotic cell cycles, and we address the conundrum created within these observations, that is, that most cells are mitotically independent of Vasa, yet when Vasa is present in a cell, it appears to be essential for cell cycle progression.

Fig. 1

Adapted diagram from Fig.4G of Pek and Kai (2011). Hypothetical model of how Vas, Aubergine, (Aub) and Spindle-E (Spn-E) function during mitosis to facilitate robust Barr chromosomal localization. Vasa may promote local recruitment of Barr near pericentromeric regions. Alternatively, Vas could also promote long-range association of Barr with chromosomes.

Fig. 2

Adapted diagram from Yajima and Wessel (2011). A summary diagram of the dynamic localization of Vasa (red) during cell cycle progression.

Fig. 3

Hypothetical function of Vasa on spindles. Vasa is recruited on spindles during M-phase to locally regulate the mitotic cyclins and other mRNAs for rapid cell cycling in sea urchin embryonic cells.

Fig. 4

Adapted diagram from Yajima and Wessel (2011b). Vasa distribution during the unequal division during the 8- to 16-cell transition. At prophase, Vasa localizes to microtubules that are located at the vegetal pole just prior to an asymmetric division. At anaphase, Vasa on the vegetal-side is maintained, whereas on the opposite pole it disappears. Two bottom panels are magnified views of the white squared field. Scale bar, 5 μm.

Fig. 5

Places to go, things to do. Summary of Vasa expressing cells and known diversity of Vasa functions.