Germline Transgenic Methods for Tracking Cells and Testing Gene Function During Regeneration in the Axolotl

The salamander is the only tetrapod that regenerates complex body structures throughout life. Deciphering the underlying molecular processes of regeneration is fundamental for regenerative medicine and developmental biology, but the model organism had limited tools for molecular analysis. We describe a comprehensive set of germline transgenic strains in the laboratory-bred salamander Ambystoma mexicanum(axolotl) that open up the cellular and molecular genetic dissection of regeneration. We demonstrate tissue-dependent control of gene expression in nerve, Schwann cells, oligodendrocytes, muscle, epidermis, and cartilage. Furthermore, we demonstrate the use of tamoxifen-induced Cre/loxP-mediated recombination to indelibly mark different cell types. Finally, we inducibly overexpress the cell-cycle inhibitor p16INK4a, which negatively regulates spinal cord regeneration. These tissue-specific germline axolotl lines and tightly inducible Cre drivers and LoxP reporter lines render this classical regeneration model molecularly accessible

Expanding the Morphogenetic Repertoire: Perspectives from the Drosophila Egg

Tissue and organ architectures are incredibly diverse, yet our knowledge of the morphogenetic behaviors that generate them is relatively limited. Recent studies have revealed unexpected mechanisms that drive axis elongation in the Drosophila egg, including an unconventional planar polarity signaling pathway, a distinctive type of morphogenetic movement termed “global tissue rotation,” a molecular corset-like role of extracellular matrix, and oscillating basal cellular contractions. We review here what is known about Drosophila egg elongation, compare it to other instances of morphogenesis, and highlight several issues of general developmental relevance

Current Biology, Vol. 13, 2125--2137, December 16, 2003, 2003 Elsevier Science Ltd. All rights reserved. DOI 10.1016/j.cub.2003.11.054 Shroom Induces Apical Constriction

this report we used the undifferentiated cells of sociated with enrichment of apically localized actin very early Xenopus embryos as a source of heterologous filaments and required the small GTPase Rap1 but not and naive epithelial cells in which to study Shroom func- Rho. Endogenous Xenopus shroom was found to be extion (Figure 1A). We show that expression of Shroom is pressed in cells engaged in apical constriction. Consistent with a role for Shroom in organizing apical constriction, sufficient to cause apical constriction in these cells, a disrupting Shroom function resulted in a specific failure novel property for a vertebrate protein. Interestingly, of hingepoint formation, defective neuroepithelial sheet- Shroom does not appear to affect nonpolarized cells bending, and failure of neural tube closure. in these early blastulae. We show that during normal Conclusions: These data demonstrate that Shroom is development, Xenopus shroom is expressed primarily an essential regulator of apical constriction during neu- in cells undergoing apical constriction. We inhibited enrulation. The finding that a single protein can initiate this dogenous Shroom activity with a dominant-negative process in epithelial cells establishes that bending of construct and with an antisense oligonucleotide. Conepithelial sheets may be patterned during development sistent with a role in generating apical constrictions, by the regulation of expression of single genes. Shroom was required specifically for the formation of hingepoints and for bending of the neuroepithelial sheet. Together, the data presented here establish that bend

Germline Transgenic Methods for Tracking Cells and Testing Gene Function during Regeneration in the Axolotl

The salamander is the only tetrapod that regenerates complex body structures throughout life. Deciphering the underlying molecular processes of regeneration is fundamental for regenerative medicine and developmental biology, but the model organism had limited tools for molecular analysis. We describe a comprehensive set of germline transgenic strains in the laboratory-bred salamander Ambystoma mexicanum (axolotl) that open up the cellular and molecular genetic dissection of regeneration.We demonstrate tissue-dependent control of gene expression in nerve, Schwann cells, oligodendrocytes, muscle, epidermis, and cartilage. Furthermore, we demonstrate the use of tamoxifen-induced Cre/loxP-mediated recombination to indelibly mark different cell types. Finally, we inducibly overexpress the cellcycle inhibitor p16INK4a, which negatively regulates spinal cord regeneration. These tissue-specific germline axolotl lines and tightly inducible Cre drivers and LoxP reporter lines render this classical regeneration model molecularly accessible

Ciliogenesis defects in embryos lacking inturned or fuzzy function are associated with failure of planar cell polarity and Hedgehog signaling

The vertebrate planar cell polarity (PCP) pathway has previously been found to control polarized cell behaviors rather than cell fate. We report here that disruption of Xenopus laevis orthologs of the Drosophila melanogaster PCP effectors inturned (in) or fuzzy (fy) affected not only PCP-dependent convergent extension but also elicited embryonic phenotypes consistent with defective Hedgehog signaling. These defects in Hedgehog signaling resulted from a broad requirement for Inturned and Fuzzy in ciliogenesis. We show that these proteins govern apical actin assembly and thus control the orientation, but not assembly, of ciliary microtubules. Finally, accumulation of Dishevelled and Inturned near the basal apparatus of cilia suggests that these proteins function in a common pathway with core PCP components to regulate ciliogenesis. Together, these data highlight the interrelationships between cell polarity, cellular morphogenesis, signal transduction and cell fate specification.close19419