Introduction to special issue

Mind-boggling brain development

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Science  12 Oct 2018:
Vol. 362, Issue 6411, pp. 170-171
DOI: 10.1126/science.aav5687

Coronal section of the neocortex in a juvenile mouse. Double immunostaining shows microglia (green) and inhibitory interneurons (red), whereas nuclear counterstaining is in blue.

IMAGE: PAOLA SQUARZONI

The human brain contains billions of well-connected neurons. Neural neighborhoods perform different tasks: Some coordinate movement, whereas others hum along planning dinner. The mature brain is a complex assembly of networks, structures, and tracts. Like cities and their neighborhoods, however, the brain does not arise fully formed. Rather, operational patterns and developmental constraints guide the proliferating neurons that build the typical adult human brain. Just as cities are governed by both hard and soft infrastructure—e.g., highways channel traffic and laws define what sort of building can occur and where—the placement and function of neurons in the brain respond to multiple cues during development. In this special issue, we look behind the scenes of this elaborate process that places each neuron where it belongs or—sadly, in the cases of neurodevelopmental disorders—does not.

Generation of these neurons, along with the equally numerous accessory cells, requires enthusiastic progenitor cells. Early in development, straightforward proliferative programs morph to produce diverse cell types. With shifting cascades of transcription factors, each newborn neuron is shaped by its unique time and place.

Glia, originally viewed as bystanders in neurodevelopment, are now known to be quite the opposite. Radial glia are builders of both neural neighborhoods and highways along which neurons move. The immune system, once thought to be excluded from the brain, is also crucial to brain formation: Microglial cells regulate circuit formation and convey physiological information. Evolution constrains development according to successful precedents. Think about that with your marvelously formed brain.

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