Purified Wnt proteins influence cell proliferation and differentiation in the limb bud

Derk Ten Berge

Isolated Wnt proteins are active on a variety of cells, and can act as mitogens, which we have been studying in vertebrate limbs. During day 11 of embryogenesis, the mouse limb bud is a relatively simple organ that consists of proliferating mesenchymal cells surrounded by ectoderm. Later, cells condense in the interior of the buds and form cartilage while exterior cells maintain an undifferentiated proliferative state. We have used implanted beads as a local source of purified Wnt protein and show that Wnt proteins are powerful inducers of proliferation of primitive mesenchymal cells.

WntD pathway-mediated regulation of NF-kB activity during development and the innate immune response

Mark A. McElwain, Dennis C. Ko, Michael D. Gordon

Signaling pathways such as those regulating Nuclear Factor-kappaB (NF-kB)-like transcription factors control many aspects of embryonic development and adult homeostasis. Often, the same pathway is used repeatedly to accomplish different tasks, raising the question of how these pathways are regulated in different biological contexts.  While much is known about the major pathways transduced through NF-kB family members, much is still to be learned about how other signaling mechanisms control NF-kB activity. Recently, we demonstrated that Drosophila WntD regulates embryonic dorsal/ventral axis specification and the adult innate immune response by signaling through the Drosophila NF-kb homolog Dorsal. Identifying the WntD receptor and other downstream components is essential for understanding how the signal is transduced, and how axis specification and the immune response are regulated. We have found several candidate pathway components identified in a suppressor screen for modifiers of a WntD overexpression phenotype

Activation of Wnt Signaling During Adult Lung Injury and Repair
Cati Logan

In the lung, several mutant phenotypes have revealed that the Wnt pathway is required for lung development, but its function in adult tissues is not well understood. Here, we have examined the activation of Wnt signaling in adult lungs using two different Wnt reporter mice, TOP-Gal and BAT-Gal. Both reporter lines reveal Wnt signaling in Clara cells, suggesting that Wnts may play a role in Clara cell formation or maintenance. To test this hypothesis, we stimulated Clara cell formation using a Naphthalene-mediated injury model and followed Wnt reporter activation during lung repair in TOP-Gal mice. Naphthalene administration selectively ablates Clara cells and is followed by Clara cell regeneration. New Clara cells arise from an injury-resistant progenitor population called Variant Clara cells, which that reside at specific locations within the lung and proliferate in response to Clara cell loss. TOP-Gal is expressed in Clara Cells within Neuroepithelial Bodies, which harbor Variant Clara cells. BrdU labeling experiments have shown that TOP-Gal positive Clara cells are proliferative, suggesting that the TOP-Gal reporter may mark progenitors for the bronchiolar epithelium and that Wnt signaling is activated during Clara cell regeneration.
The reporter genes are also expressed in cilliated cells, which remain present following Clara cell ablation, and flatten to cover the denuded basement membrane once Clara cells are lost. This finding suggests that Wnt signaling may additionally regulate ciliated cells during lung injury. Current experiments are aimed at assessing the role of Wnt signaling during lung repair by perturbing this pathway in lungs using both in vivo and in vitro approaches.