Multiple Roles for Egalitarian in Polarization of the Drosophila Egg Chamber

Abstract

The Drosophila egg chamber provides a useful model for examining mechanisms by which cell fates are specified and maintained in the context of a complex tissue. The egg chamber is also an excellent model for understanding the mechanism by which cytoskeletal filaments are organized and the critical interplay between cytoskeletal organization, polarity establishment, and cell fate specification. Previous work has shown that Egalitarian (Egl) is required for specification and maintenance of oocyte fate. Mutants in egl either completely fail to specify an oocyte, or if specified, the oocyte eventually reverts back to nurse cell fate. Due to this very early role for Egl in egg chamber maturation, it is unclear whether later stages of egg chamber development also require Egl function. In this report, we have depleted Egl at specific stages of egg chamber development. We demonstrate that in early-stage egg chambers, Egl has an additional role in organization of oocyte microtubules. In the absence of Egl function, oocyte microtubules completely fail to reorganize. As such, the localization of microtubule motors and their cargo is disrupted. In addition, Egl also appears to function in regulating the translation of critical polarity determining messenger RNAs (mRNAs). Finally, we demonstrate that in midstage egg chambers, Egl does not appear to be required for microtubule organization, but rather for the correct spatial localization of oskar, bicoid, and gurken mRNAs.

A new isoform of Drosophila non-muscle Tropomyosin 1 interacts with Kinesin-1 and functions in oskar mRNA localization

“…In order to deplete Khc, we expressed a short hairpin RNA (shRNA) against khc using a germline driver (Sanghavi et al, 2016). As expected, expression of this shRNA resulted in substantial depletion of Khc (Fig.…”

“…The shRNAs were expressed using a previously characterized germline driver (Sanghavi et al, 2016). Ovarian lysates were prepared from these flies and examined by blotting using our antiTm1 antibody.…”

“…no AKIN01-A, Cytoskeleton, Inc.; 1:150, western blotting, 1:1500); chicken anti-Oskar (Sanghavi et al, 2016;1:50); FITC-conjugated mouse anti-α-tubulin (cat. no F2168-.2ML, Sigma; 1:100); mouse anti-β-galactosidase (cat.…”

“…Ovaries were processed for immunofluorescence as previously described (Sanghavi et al, 2016). In situ hybridization was used to detect bcd, grk, nos and CycB mRNA and was performed using a published procedure (Sanghavi et al, 2013).…”

“…Their localization is thought to depend primarily on Dynein (MacDougall et al, 2003;Schnorrer et al, 2000). Although the exact link between these mRNAs and Dynein has not been identified, the available evidence suggests that this role is performed by Egl (Dienstbier et al, 2009;Sanghavi et al, 2016).…”