The McNeill lab is interested in how tissue growth and tissue organization are coordinately regulated during normal development and regeneration, and how loss of this control leads to human disease.

We investigate how these processes are regulated using both Drosophila and mouse genetics for in vivo analysis, as well as tissue culture and organoid approaches. The lab has a long tradition of investigating how Fat cadherins function in Hippo pathway-regulated growth control, planar cell polarity (PCP) tissue organization and metabolism. Fat cadherins are enormous cell adhesion molecules that bind via cadherin-cadherin interactions to another large cadherin called Dachsous (Ds). The Hippo pathway is a highly conserved signaling pathway that regulates proliferation and apoptosis via control of the activity of the transcriptional co-activators Yorkie/YAP. We use Drosophila as a genetically tractable organism to investigate the basic and conserved mechanisms of Fat function and the control of Hippo pathway activity. Our very recent work has uncovered a novel and exciting role for Fat cadherins in regeneration.

By studying Fat cadherins and the Hippo pathway in both fly and mouse models, we capitalize on each system’s strengths. We integrate biochemical studies with our genetic analysis to extend our knowledge and test our hypotheses. For example we used classical biochemical analysis to demonstrate that Fat is processed from a 560kDa precursor to a mature cell-surface receptor composed of a 110kDa transmembrane domain and a 450kDa extracellular domain composed of 34 cadherin repeats, EGF and LaminG domains that mediates binding to Ds. We showed binding of Fat to Ds promotes Fat phosphorylation and signaling to the Hippo pathway. Now we are using proteomic screening to identify Fat cadherin pathway effectors, using BioID to identify interaction partners in a near physiological context. We also showed that Ft cadherins undergo sequential cleavages release a cytosolic fragment that is imported into mitochondria (Fat-mito), where it binds Ndufv2, a component of CI. To identify the protease involved, we will now conduct a high throughput siRNA screen to identify genes essential for the mitochondrial localization of Fat/Fat4.

Our work on Fat and the Hippo pathway in mouse models has revealed a critical and unsuspected role for the Hippo growth control pathway in morphogenesis. Using whole animal conditional and organ-culture approaches, we found that loss of NF2 or LATS or overexpression of YAP leads to growth and elongation of the collecting ducts in the absence of branching morphogenesis. To understand better how branching is affected, we will conduct high-resolution time-lapse imaging of the induction of branching morphogenesis. We will also assay tissue tension at junctions in the bud, and the trunk of developing.

In addition to our studies on Fat and the Hippo pathway, a new area of exciting research in the lab focuses on a novel nuclear protein that we call Speg ( for Sperm- and egg -less) that we isolated in genetic screens in Drosophila. Remarkably that we have found Speg is essential for chromatin structure and fertility in flies, mice and fish. This project is taking us into exploring how changes in the nuclear envelope impact gene expression and cell fate.