@article{bloom_ledon-rettig_infante_everly_hanken_nascone-yoder_2013, title={Developmental origins of a novel gut morphology in frogs}, volume={15}, ISSN={["1525-142X"]}, DOI={10.1111/ede.12035}, abstractNote={SUMMARYPhenotypic variation is a prerequisite for evolution by natural selection, yet the processes that give rise to the novel morphologies upon which selection acts are poorly understood. We employed a chemical genetic screen to identify developmental changes capable of generating ecologically relevant morphological variation as observed among extant species. Specifically, we assayed for exogenously applied small molecules capable of transforming the ancestral larval foregut of the herbivorous Xenopus laevis to resemble the derived larval foregut of the carnivorous Lepidobatrachus laevis. Appropriately, the small molecules that demonstrate this capacity modulate conserved morphogenetic pathways involved in gut development, including downregulation of retinoic acid (RA) signaling. Identical manipulation of RA signaling in a species that is more closely related to Lepidobatrachus, Ceratophrys cranwelli, yielded even more similar transformations, corroborating the relevance of RA signaling variation in interspecific morphological change. Finally, we were able to recover the ancestral gut phenotype in Lepidobatrachus by performing a reverse chemical manipulation to upregulate RA signaling, providing strong evidence that modifications to this specific pathway promoted the emergence of a lineage‐specific phenotypic novelty. Interestingly, our screen also revealed pathways that have not yet been implicated in early gut morphogenesis, such as thyroid hormone signaling. In general, the chemical genetic screen may be a valuable tool for identifying developmental mechanisms that underlie ecologically and evolutionarily relevant phenotypic variation.}, number={3}, journal={EVOLUTION & DEVELOPMENT}, author={Bloom, Stephanie and Ledon-Rettig, Cris and Infante, Carlos and Everly, Anne and Hanken, James and Nascone-Yoder, Nanette}, year={2013}, month={May}, pages={213–223} }
 @article{reed_womble_dush_tull_bloom_morckel_devlin_nascone-yoder_2009, title={Morphogenesis of the Primitive Gut Tube Is Generated by Rho/ROCK/Myosin II-Mediated Endoderm Rearrangements}, volume={238}, ISSN={["1097-0177"]}, DOI={10.1002/dvdy.22157}, abstractNote={AbstractDuring digestive organogenesis, the primitive gut tube (PGT) undergoes dramatic elongation and forms a lumen lined by a single‐layer of epithelium. In Xenopus, endoderm cells in the core of the PGT rearrange during gut elongation, but the morphogenetic mechanisms controlling their reorganization are undetermined. Here, we define the dynamic changes in endoderm cell shape, polarity, and tissue architecture that underlie Xenopus gut morphogenesis. Gut endoderm cells intercalate radially, between their anterior and posterior neighbors, transforming the nearly solid endoderm core into a single layer of epithelium while concomitantly eliciting “radially convergent” extension within the gut walls. Inhibition of Rho/ROCK/Myosin II activity prevents endoderm rearrangements and consequently perturbs both gut elongation and digestive epithelial morphogenesis. Our results suggest that the cellular and molecular events driving tissue elongation in the PGT are mechanistically analogous to those that function during gastrulation, but occur within a novel cylindrical geometry to generate an epithelial‐lined tube. Developmental Dynamics 238:3111–3125, 2009. © 2009 Wiley‐Liss, Inc.}, number={12}, journal={DEVELOPMENTAL DYNAMICS}, author={Reed, Rachel A. and Womble, Mandy A. and Dush, Michel K. and Tull, Rhesa R. and Bloom, Stephanie K. and Morckel, Allison R. and Devlin, Edward W. and Nascone-Yoder, Nanette M.}, year={2009}, month={Dec}, pages={3111–3125} }