However, teasing ABT-737 cost apart the contribution of shared ancestry and developmental microenvironments is a challenging task. Compounding the difficulty in reconciling the results from these two studies is the fact that Ohtsuki et al. (2012) and Li et al. (2012) also differ in the developmental time point at which they assessed the orientation preferences of their clonally derived neurons. Li et al. (2012) found great similarity in animals

that were imaged shortly after eye opening (postnatal days 12–17 [P12–P17]), whereas Ohtsuki et al. (2012) observed more diversity in preference in older animals (P49–P62). Among sister cells derived from a single radial glia, gap junction coupling declines from P1–P2 and is nearly absent by P6 (Yu et al., 2012), with preferential chemical synaptic connectivity appearing by P10–P17 (Yu et al., 2009). It may be that this preferential clonal connectivity, along with the response similarity it helps convey, dominates early cortical networks but is eroded with visual experience and the accompanying strengthening of connections from unrelated neurons through mechanisms of Hebbian synaptic plasticity. Alternatively, the similarity in connectivity and

response properties among closely related sister neurons may be maintained throughout development, and this accounts for AT13387 concentration the degree of similarity in orientation preference that is seen in the Ohtsuki et al. (2012) study. Additional experiments that explore

the properties of early and late clonally derived populations at different postnatal ages would clarify the extent to which visual experience old impacts the patterns of connections and response properties that are specified by cell lineage. The current study by Ohtsuki et al. (2012), along with that of Li et al. (2012), establishes a clear link between cortical cell lineage and shared response properties. At the same time, they emphasize how much we have yet to understand about how lineage combines with other mechanisms to specify the connectivity and response properties of cortical circuits. “
“The complex and precise connectivity of the brain is central to neural circuit function. In sensory systems, both the structure of the stimulus and the nature of the computations performed by the brain create architectural constraints. As a result, a small number of morphological themes appear repeatedly in different brain regions. Remarkably, across the animal kingdom, many sensory systems utilize one or more of only three basic architectural elements, namely glomeruli, columns, and layers. Understanding the molecular mechanisms by which each of these core features assembles during development therefore represents a focus of considerable current research (Luo and Flanagan, 2007). In this issue of Neuron, Timofeev et al. (2012) describe a new molecular mechanism that instructs layer formation in the Drosophila brain.