Research

Our research is focused on understanding how tissues and organs take shape during embryonic development. Current projects in the lab are addressing fundamental questions about mechanisms underlying organ formation:


1. What mechanisms establish left-right asymmetry in developing organs?

Several internal organs develop left-right asymmetries. For example, the initially symmetric heart tube undergoes rightward looping to establish the relative positions of chambers, septa and vascular connections. Perturbation of left-right asymmetries often results in congenital heart malformations that can include atrioventricular septal defects, double outlet right ventricle and transposition of the great arteries. Our goal is to identify genes and mechanisms that advance our understanding of how organ asymmetry is established and provide candidate genes for human congenital disease.

Since left-right asymmetry is a conserved feature of the vertebrate body plan, we are using the zebrafish embryo as model vertebrate to investigate the earliest steps of symmetry breaking. Prior to asymmetric development of organs, the first asymmetry in the embryo is at the molecular level. A conserved Nodal (TGF-beta) signaling cascade is asymmetrically initiated on the left side of vertebrate embryos.  In the zebrafish embryo, the left-sided Nodal homolog is called southpaw (spaw) (Fig. 1). This early asymmetric patterning of the embryo provides left-right information that is used to guide subsequent asymmetric development of organs.

research Fig 1

Evidence from several vertebrates (human, mouse, rabbit, frog and zebrafish) indicates motile cilia generate asymmetric fluid flows that direct left-sided Nodal signaling. In zebrafish, these ‘left-right cilia’ are found in a transient embryonic organ called Kupffer’s vesicle (Fig. 2). Several ongoing projects are aimed at understanding how ciliated cells in Kupffer’s vesicle (KV) are organized into a functional unit capable of generating coordinated fluid flows and left-right signals. 

research Fig 2

2. What biophysical interactions drive organ formation? 

Organ development depends cell behaviors that are governed by mechanical forces and tensions. Biochemical signaling pathways have been identified that regulate cell behaviors, but how these pathways interact with mechanical forces in the embryo remains poorly understood. As a part of the Syracuse Soft and Living Matter consortium, we are collaborating with Dr. M. Lisa Manning’s group in the Department of Physics at Syracuse University to combine high-resolution in vivo imaging and mathematical modeling to study how interactions between molecular signals and mechanical forces control organ formation. We are using simulations of cell behaviors in Kupffer’s vesicle (KV) to make predictions about forces between cells that are necessary for proper epithelial morphogenesis and organ development (Fig. 3).

We are coupling our mathematical models with real-time imaging to study how tissue-tissue interactions influence cell behaviors. We have developed a mosaic labeling technique that allows morphometric analysis of single KV cells in a living embryo (Fig. 4). The goal of this research is to understand how external forces generated by neighboring tissues impact cell shapes in developing organs.  

research Fig 4 v1

Several tools have been developed to track and manipulate the cells that give rise to the Kupffer’s vesicle (KV) organ. A group of ~25 mesenchymal precursor cells—called dorsal forerunner cells (DFCs)—migrate together during gastrulation stages and then differentiate into KV cells around a central fluid-filled lumen. A couple of hours later, the KV organ breaks down, and individual cells migrate away to incorporate into neighboring tissues. Thus, the zebrafish KV can be used to investigate multiple cellular behaviors—collective migration, mesenchymal-to-epithelial transition, cell polarization, lumen formation and expansion, cell shape changes, epithelial-to-mesenchymal transition, and individual cell migration—that drive tissue and organ morphogenesis.


3. What mechanisms control the form and function of cilia in development?

In addition to directing left-right asymmetry, cilia play other critical roles during embryonic development and throughout adult life. Defects in cilia during development can cause congenital malformations in nearly every system in the body. However, the mechanisms that control formation and function of embryonic cilia remain poorly understood. Our goal is to identify molecular targets that can be used to develop pharmacological approaches to prevent or treat cilia-associated defects.

Recent work has implicated the vacuolar-type H+-ATPase (V-ATPase) proton (H+) pump in cilia formation and function. We are using hair cells in neuromasts of the lateral line in zebrafish embryos to probe how V-ATPase regulates cilia. Neuromasts contain a cluster of ~7 hair cells, and each hair cell has a single long microtubule-based kinocilium projecting from the surface of the embryo (Fig. 5). These cilia are is ideal for antibody staining and live imaging. We are developing new tools to measure V-ATPase activity in living hair cells during development and understand how V-ATPase impacts cilia form and function. 

research Fig 5