Multicluster Pcdh diversity is required for mouse olfactory neural circuit assembly

<jats:title>Pattern formation in the brain</jats:title> <jats:p> Neurons in the developing brain cooperate to build circuits. Mountoufaris <jats:italic>et al.</jats:italic> found that ∼50 variable protocadherin genes support a combinatorial identity code that allows millions of olfactory neuron axons to sort into ∼2000 glomeruli. Sharing olfactory receptors drives axons to one glomerulus, and protocadherin diversity allows the multiple axons to touch each other as they converge. On the other hand, Chen <jats:italic>et al.</jats:italic> found that a single C-type protocadherin underlies the tiled distribution of serotonergic neurons throughout the central nervous system. These neurons, which share protocadherin identity, enervate broad swaths evenly without touching neighboring neurons. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6336" page="411" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aai8801">411</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6336" page="406" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aal3231">406</jats:related-article> </jats:p>