Research
Wnt signaling, Tissue Patterning and Growth During Development
During development, cells are allocated to different developmental lineages through a process called patterning. We are interested in two developmental patterning events that are dependent upon Wnt signaling: anterior-posterior regionalization of the brain and mesoderm patterning during axis formation.
Early Brain Patterning
The vertebrate brain is a staggeringly complex organ that arises from very simple beginnings: the neural plate. During early development, signaling pathways create subdivisions along the anteroposterior axis that become elaborated and further refined over time. A crucial regulator of brain patterning is the Midbrain Hindbrain Boundary (MHB), which itself forms in response to earlier patterning signals that act during the period of development known as gastrulation. Wnt signaling is required for MHB formation, and several Wnt ligands play roles in the process. Work in the Lekven laboratory is directed at understanding 1) regulatory inputs into patterned gene expression in the MHB and 2) downstream mechanisms for how the Wnt pathway promotes midbrain specification and growth.
Wnt signaling is deployed at multiple stages in the process of early brain regionalization. One focus of our lab is to unravel how different Wnt signals are integrated into the elaboration of brain subdivisions such as the midbrain-hindbrain boundary organizer, a conserved feature of vertebrates (Buckles). In the figure at right, the arrows point to the MHB of two zebrafish embryos: a normal one (top), and one lacking three crucial Wnt signals, Wnt1, Wnt10b, and Wnt3a (bottom). Notice how the conspicuous MHB constriction is absent in the mutant embryo. With these and other mutants, new genetic tools, and imaging technology, we will understand what, exactly, these Wnt signals do and how they are regulated.
We are applying new technologies and new imaging methods to enable novel insights into developmental processes. For instance, ultrashort-pulse two-photon microscopy can be applied to visualize multiple fluorophores simultaneously in living embryos (Gibbs et al.). The picture to the right demonstrates our application of ultrashort pulse two-photon microscopy to the analysis of EGFP reporter expression in Tg(wnt1:egfp) transgenic zebrafish embryos. We are using approaches like this, with additional lineage reporters, to understand the genetic regulation of midbrain-hindbrain boundary structure and its critical gene regulatory network. (Gibbs et al. 2017).
Wnt signaling coordinates brain and body patterning
Normal development depends on the coordination of patterning and growth: patterning to establish pools of progenitors of alternate cell types that make up an organ, and differential rates of proliferation of different cell types to make the organ in its proper proportions. The developmental contexts we are studying use Wnt signaling to drive both processes, but it is unclear whether these are similar or different outputs of the pathway. Wnt/beta-catenin signaling drives differential gene expression, thus we are focusing on transcriptional networks that include Wnts and are downstream of Wnts to understand their developmental mechanisms. Aberrant Wnt signaling causes many human cancers, therefore our findings may stimulate novel insights into how erratic Wnt signaling contributes to human disease.
We use molecular genetic methods to identify regulatory influences on Wnt gene expression and function. For instance, we have discovered that wnt8a is controlled post-transcriptionally by a microRNA based mechanism to control neural and mesodermal patterning. (Wylie et al.).
If these research questions and approaches are intriguing to you, contact us to inquire about the possibility of graduate or postdoctoral studies.