Characterization of Xenopus laevis Guanine Deaminase reveals new insights for its expression and function in the embryonic kidney.

The mammalian guanine deaminase (GDA), called cypin, is important for proper neural development, by regulating dendritic arborization through modulation of microtubule (MT) dynamics. Additionally, cypin can promote MT assembly in vitro. However, it has never been tested whether cypin (or other GDA orthologs) binds to MTs or modulates MT dynamics. Here, we address these questions and characterize Xenopus laevis GDA (Gda) for the first time during embryonic development. We find that exogenously-expressed human cypin and Gda both display a cytosolic distribution in primary embryonic cells. Furthermore, while expression of human cypin can promote MT polymerization, Xenopus Gda has no effect. Additionally, we find that the tubulin-binding CRMP homology domain is only partially conserved between cypin and Gda. This likely explains the divergence in function, as we discovered that the cypin region containing the CRMP homology and PDZ-binding domain is necessary for regulating MT dynamics. Finally, we observed that gda is strongly expressed in the kidneys during late embryonic development, although it does not appear to be critical for kidney development. Together, these results suggest that GDA has diverged in function between mammals and amphibians, and that mammalian GDA plays an indirect role in regulating MT dynamics. This article is protected by copyright. All rights reserved.