Regulation of anterior-posterior axis patterning and convergent extension by aquaporin-3b during xenopus gastrulation.

Abstract

Convergent extension (CE) is a key morphogenetic process during gastrulation that drives anterior-posterior axis elongation through coordinated cell behaviors and signaling pathways, including noncanonical Wnt signaling. Our studies have revealed that the aquaglyceroporin aqp3b (aqp3L) gene plays a role in Xenopus gastrulation. Using morpholino oligonucleotides to inhibit aqp3b translation, we observed CE defects in Keller explants, which were rescued by Dvl, PKC and RhoA, but not Rac1 or Cdc42, implicating Aqp3b in noncanonical Wnt signaling. Rac1 and Cdc42 have been shown to promote cell migration in dorsal mesoderm cells. Their failure to rescue the absence of aqp3b suggested that Aqp3b may not promote active cell migration. Inhibition of aqp3b also impaired PKC localization to the cell membrane in animal caps. Other studies have shown that PKC can activate Cdc42 downstream of Dvl-independent Wnt/Ca2+ signaling, which promotes CE. Since PKC, but not Cdc42 rescued aqp3b morphants, Aqp3b may instead act upstream of Dsh-dependent PKC activation. Dorsal mesodermal cells in Xenopus embryos during gastrulation exhibit two distinct cell behavior patterns: convergent extension and cell migration in activin-treated animal caps. Aqp3b promotes tissue elongation: a hallmark for CE, while inhibition reduces elongation. A consequence of aqp3b misexpression revealed the downregulation of anterior markers (goosecoid, otx2, noggin) and upregulation of posterior markers (Xbra, hoxB9). Anterior genes promote cell migration rather than CE. Thus, these data are consistent with the rescue experiments and suggest that Aqp3b may inhibit active migration of posterior dorsal mesoderm cells. Finally, aqp3b induced FGF2 and eFGF expression in activin-treated animal caps. Studies have shown activation of Xbra and other posterior genes by FGF signaling. Thus, Aqp3b may modulate the FGF/Xbra signaling in promoting convergent extension. These findings suggest that Aqp3b may promote CE by antagonizing cell migration.