Biology subjects

Handford, P.

Publications and source records attributed to Handford, P..

3 recordsLinked to original sources

bioRxiv2021

Delta C2 Domain β1-2 loop contributes to robust Notch signalling

Accurate Notch signalling is critical for organism development and homeostasis. Fine-tuning of Notch-ligand interactions have substantial impact on signalling-outputs. Recent structural studies identified a conserved N-terminal C2 domain in human Notch ligands which conferred phospholipid binding in vitro. Here we show that Drosophila ligands adopt the same C2 domain structure with analogous variations in the loop regions, including the so-called {beta}1-2 loop that has been associated with phospholipid binding. Mutations in the {beta} 1-2 loop of Delta C2 domain retain Notch binding but have impaired ability to interact with phospholipids in vitro. To investigate its role in vivo we deleted five residues within the {beta} 1-2 loop of endogenous Delta by CRISPR/Cas9 gene editing. Strikingly, this change compromised ligand function. The modified Delta enhanced phenotypes produced by Delta loss of function alleles and suppressed that of Notch alleles. As the modified protein was present on the cell surface in normal amounts, these results argue that C2 domain phospholipid-binding is necessary for robust signalling in vivo where the balance of cis and trans ligand-receptor interactions is finely tuned.

developmental biology↗

bioRxiv2019

Phylogeography of two Andean frogs: Test of vicariance versus elevational gradient models of diversification

The tropical and subtropical Andes have among the highest levels of biodiversity in the world. Understanding the forces that underlie speciation and diversification in the Andes is a major focus of research. Here we tested two hypotheses of species origins in the Andes: 1. Vicariance mediated by orogenesis or shifting habitat distribution. 2. Parapatric diversification along elevational environmental gradients. We also sought insights on the factors that impacted the phylogeography of co-distributed taxa, and the influences of divergent species ecology on population genetic structure. We used phylogeographic and coalescent analyses of nuclear and mitochondrial DNA sequence data to compare genetic diversity and evolutionary history of two frog species: Pleurodema borellii (Family: Leiuperidae, 130 individuals; 20 sites), and Hypsiboas riojanus (Family: Hyllidae, 258 individuals; 23 sites) across their shared range in northwestern Argentina. The two showed concordant phylogeographic structuring, and our analyses support the vicariance model over the elevational gradient model. However, Pleurodema borellii exhibited markedly deeper temporal divergence ([≥]4 Ma) than H. riojanus (1-2 Ma). The three main mtDNA lineages of P. borellii were nearly allopatric and diverged between 4-10 Ma. At similar spatial scales, differentiation was less in the putatively more habitat-specialized H. riojanus than in the more generalist P. borellii. Similar allopatric distributions of major lineages for both species implies common causes of historical range fragmentation and vicariance. However, different divergence times among clades presumably reflect different demographic histories, permeability of different historical barriers at different times, and/or difference in life history attributes and sensitivities to historical environmental change. Our research enriches our understanding of the phylogeography of the Andes in northwestern Argentina.

evolutionary biology↗

bioRxiv2017

Structural and functional dissection of the interplay between lipid and Notch binding by human Notch ligands

AbstractRecent data have expanded our understanding of Notch signaling by identifying a C2 domain at the N-terminus of Notch ligands which has both lipid- and receptor-binding properties. We present novel structures of human ligands Jagged2 and DLL4 and human Notch-2, together with functional assays, which suggest that ligand-mediated coupling of membrane recognition and Notch binding is likely to be critical in establishing the optimal context for Notch signaling. Comparisons between the Jagged and Delta family show a huge diversity in the structures of the loops at the apex of the C2 domain implicated in membrane recognition and Jagged1 missense mutations which affect these loops and are associated with extrahepatic biliary atresia lead to a loss of membrane recognition, but do not alter Notch binding. Taken together, these data suggest that C2 domain binding to membranes is an important element in tuning ligand-dependent Notch signaling in different physiological contexts.

biochemistry↗