Cell migration is important for development and its aberrant regulation contributes to many diseases. The Scar/WAVE complex is essential for Arp2/3 mediated lamellipodia formation during mesenchymal cell migration and several coinciding signals activate it. However, so far, no direct negative regulators are known. We have identified Nance-Horan Syndrome-like 1 protein (NHSL1) as a novel, direct binding partner of the Scar/WAVE complex, which co-localise at protruding lamellipodia. This interaction is mediated by the Abi SH3 domain and two binding sites in NHSL1. Furthermore, active Rac binds to NHSL1 at two regions that mediate leading edge targeting of NHSL1 suggesting that Rac recruits NHSL1. Surprisingly, NHSL1 inhibits cell migration through its interaction with the Scar/WAVE complex. Mechanistically, NHSL1 may reduce cell migration efficiency by impeding Arp2/3 activity, as measured in cells using a novel Arp2/3 FRET-FLIM biosensor, resulting in reduced F-actin content of lamellipodia, and consequently impairing the stability of lamellipodia protrusions.Scar/WAVE complex 6 . Lpd functions to promote cell migration via the Scar/WAVE complex 6,7 , which is consistent with a positive role for the Scar/WAVE complex in enhancing migration [8][9][10][11] . Several signals including active Rac, tyrosine phosphorylation and binding to phosphoinositides are known to activate the Scar/WAVE complex 2 .However, so far, it is not known how the Scar/WAVE complex is directly inhibited at the leading edge.Here, we identify NHSL1 (Nance-Horan Syndrome-like 1) protein as a negative regulator of cell migration and we found that this is mediated by its interaction with the Scar/WAVE complex. NHSL1 belongs to the poorly investigated Nance-Horan Syndrome protein family along with Nance-Horan Syndrome (NHS) and NHSL2 proteins. Mutations in the NHS gene cause Nance-Horan syndrome, which is characterised by dental abnormalities, developmental delay, and congenital cataracts [12][13][14] . We show that NHSL1 directly binds to the Scar/WAVE complex and co-localises with it at the very edge of protruding lamellipodia. We found that active Rac binds to NHSL1 at two regions that mediate leading edge targeting of NHSL1 suggesting that Rac recruits NHSL1. The negative regulatory function of NHSL1 in cell migration may be due to its role in lamellipodia since we found that it reduces lamellipodia stability. NHSL1 acts to reduce Arp2/3 activity, which is consistent with our finding that NHSL1 reduces F-actin content of lamellipodia via its interaction with the Scar/WAVE complex. Taken together, our data suggest that NHSL1 negatively regulates the Scar/WAVE complex, and hence reduces Arp2/3 activity, to control lamellipodia stability and consequently cell migration efficiency. Results NHSL1 localises to the very edge of lamellipodiaThe Nance-Horan Syndrome (NHS) protein family consists of the Nance-Horan Syndrome (NHS) protein, Nance-Horan Syndrome-like 1 (NHSL1) protein and Nance-Horan Syndrome-like 2 (NHSL2) protein [12][13][14][15][16] . E...

Cell migration is important for development and its aberrant regulation contributes to many diseases. The Scar/WAVE complex is essential for Arp2/3 mediated lamellipodia formation during mesenchymal cell migration and several coinciding signals activate it. However, so far, no direct negative regulators are known. Here we identify Nance-Horan Syndrome-like 1 protein (NHSL1) as a direct binding partner of the Scar/WAVE complex, which co-localise at protruding lamellipodia. This interaction is mediated by the Abi SH3 domain and two binding sites in NHSL1. Furthermore, active Rac binds to NHSL1 at two regions that mediate leading edge targeting of NHSL1. Surprisingly, NHSL1 inhibits cell migration through its interaction with the Scar/WAVE complex. Mechanistically, NHSL1 may reduce cell migration efficiency by impeding Arp2/3 activity, as measured in cells using a Arp2/3 FRET-FLIM biosensor, resulting in reduced F-actin density of lamellipodia, and consequently impairing the stability of lamellipodia protrusions.

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This study reports the development of a valid assessment tool for suturing in robotic surgery. Given that checklists are simple to use, there is significant scope for this checklist to be used in surgical training.