On 2014 Jan 22, Markus Meissner commented:

Regulation of actin cytoskeleton networks is fundamental for cell migration. These networks can power the protrusion of the cell plasma membrane, termed lamellipodia, for movement. Actin-related proteins 2 and 3 (Arp2/3) form a complex which can nucleate or form branching of actin filaments. There has been a number of nucleating promoting factors identified for the Arp2/3 complex in different cellular locations. However, there is less evidence of inhibitory factors for the Arp2/3 complex. To date the only inhibitory factors for Arp2/3 identified are in endocytic pits and endosomes and until recently it was an unknown whether a protein could inhibit Arp2/3 at the lamellipodia.<br> This study is the first to present evidence of an inhibitory protein for the Arp2/3 complex in lamellipodia protrusion which counteracts the WAVE complex in actin polymerisation. The authors demonstrate with convincing experiments that a novel protein, termed Arpin, can inhibit the Arp2/3 complex in vitro. Using a range of different model systems they validate that Arpin controls cell migration and ‘steering’ and hence appears to be evolutionary conserved.. In both, mammalian cells and amoeba, the Arpin knockout causes the cells to cover an extensive territory owing to the inability of the cells to slow down and change trajectories. Moreover, when Arpin is injected into fish keratocytes, they observed a marked alteration in cell movements.<br> Overall, the paper is very interesting and convincingly shows that Arpin is a conserved inhibitor of Arp2/3. Despite the amount of data, demonstrating a highly complex interaction of Arp2/3, Wave and Arp, the authors present a rather simplified model that will certainly increase in complexity over time.

Review by Jamie Whitelaw on behalf of the Glagow Toxoplasma journal club (Allison Jackson, Clare Harding, Elena Jimenez-Ruis, Eleanor Wong, Nicole Andenmatten, Saskia Egarter, Fernanda LaTorre Barragan, Robyn Kent, Johannes Stortz, Gurman Pall, Lilach Sheiner, Gary Ward and Markus Meissner).

On 2014 Jan 22, Markus Meissner commented:

Regulation of actin cytoskeleton networks is fundamental for cell migration. These networks can power the protrusion of the cell plasma membrane, termed lamellipodia, for movement. Actin-related proteins 2 and 3 (Arp2/3) form a complex which can nucleate or form branching of actin filaments. There has been a number of nucleating promoting factors identified for the Arp2/3 complex in different cellular locations. However, there is less evidence of inhibitory factors for the Arp2/3 complex. To date the only inhibitory factors for Arp2/3 identified are in endocytic pits and endosomes and until recently it was an unknown whether a protein could inhibit Arp2/3 at the lamellipodia.<br> This study is the first to present evidence of an inhibitory protein for the Arp2/3 complex in lamellipodia protrusion which counteracts the WAVE complex in actin polymerisation. The authors demonstrate with convincing experiments that a novel protein, termed Arpin, can inhibit the Arp2/3 complex in vitro. Using a range of different model systems they validate that Arpin controls cell migration and ‘steering’ and hence appears to be evolutionary conserved.. In both, mammalian cells and amoeba, the Arpin knockout causes the cells to cover an extensive territory owing to the inability of the cells to slow down and change trajectories. Moreover, when Arpin is injected into fish keratocytes, they observed a marked alteration in cell movements.<br> Overall, the paper is very interesting and convincingly shows that Arpin is a conserved inhibitor of Arp2/3. Despite the amount of data, demonstrating a highly complex interaction of Arp2/3, Wave and Arp, the authors present a rather simplified model that will certainly increase in complexity over time.

Review by Jamie Whitelaw on behalf of the Glagow Toxoplasma journal club (Allison Jackson, Clare Harding, Elena Jimenez-Ruis, Eleanor Wong, Nicole Andenmatten, Saskia Egarter, Fernanda LaTorre Barragan, Robyn Kent, Johannes Stortz, Gurman Pall, Lilach Sheiner, Gary Ward and Markus Meissner).