This Week in The Journal
Astrocytes Transplanted to Developing Brain Mimic Native Cells
Sabrina Chierzi, J. Benjamin Kacerovsky, Albert H. K. Fok, Sylvie Lahaie, Arielle Shibi Rosen, et al.
(see pages 1509–1529)
Astrocytes support and communicate with neurons and other cells to participate in sensory, metabolic, and energetic processes. The cells, which have complex morphological and physiological characteristics, spread out across cortices in a nonoverlapping tiled manner. Though researchers have learned much about astrocytes in recent years, they still know little about how the cells mature and become specialized to carry out their myriad tasks across the brain. This week, Chierzi et al. explore astrocyte transplantation in mice. The authors first isolated and cultured genetically labeled (Tomato+) astrocytes from cerebral cortex of postnatal day 4 (P4) to P8 mice. The astrocytes were then transplanted into the cortex of P3–P7 mice, a period of active proliferation and development of astrocytes. At 7 d post-transplantation (DPT), the astrocytes were found mostly in cortical Layer 1 but also at deeper levels. At 35–47 DPT and 110–130 DPT, the cells displayed their typical complex arborizations and specialized endfeet wrapped around blood vessels. The vast majority of Tomato+ cells expressed a marker of astrocytes (Sox9) but not of other glial types. Remarkably, the number of transplanted astrocytes held steady a year later at 368 DPT. Transplanted and native astrocytes populated the cortex in the usual nonoverlapping tiled pattern. Under cellular stress such as disease or injury, astrocytes adopt a reactive phenotype, which often includes expression of glial fibrillary acidic protein (GFAP). Transplanted astrocytes did not have elevated levels of GFAP, indicating that they were not constitutively reactive. Transplanted astrocytes expressed excitatory amino acid (glutamate) transporters, aquaporin channels, and gap junction proteins at similar levels to native cells, and were associated with a comparable number of excitatory and inhibitory synapses. Astrocytes transplanted to the brains of more mature mice (P34–P43) survived, but they did not mature and integrate in the same way that they did in the developing cortex, and they displayed a more reactive phenotype. Cortical astrocytes transplanted into the developing (P5–P8) cerebellar cortex survived and integrated but retained a more cortical structural and molecular phenotype. Conversely, cerebellar astrocytes transplanted to the cerebellar cortex took on a more typical cerebellar phenotype. The findings demonstrate that astrocyte transplantation provides a unique way to study this vital cell type in healthy and diseased brain settings.
Tractography-based reconstructions of language-associated pathways: left superior longitudinal fasciculus (SLF) and left arcuate fasciculus (AF).
Early Parent–Child Speech Interactions Enhance Brain Development
Elizabeth Huber, Neva M. Corrigan, Vasily L. Yarnykh, Naja Ferjan Ramírez, and Patricia K. Kuhl
(see pages 1590–1599)
Can chatting with your baby improve their brain development? Researchers have long suspected so, but studies investigating that question are rare in children younger than 3 years. Recent studies have shown, however, that socially interactive language exchanges are more important to long-term language development than one-sided inputs. This week, Huber et al. examine the relationship between parent–child language interactions recorded between ages 6–24 months and white matter tract myelination at age 2 years measured with brain imaging. They focused on the left arcuate fasciculus (AF) and superior longitudinal fasciculus (SLF), dorsal brain pathways associated with language development and ability. They counted the frequency of parent–infant conversational turns (CTs), a measure of back-and-forth exchanges that require sustained engagement of attention. From diffusion magnetic resonance imaging scans, the authors used macromolecular proton fraction (MPF) mapping as a measure of myelination. More incidents of CTs and greater growth in CTs over time predicted higher MPF in the left AF and SLF at 26 months, indicating that more parent–child speech interactions spurred myelination in language brain tracts. The interactive nature of the exchanges was key to the increased myelin development; total adult speech exposure, child-directed speech input and children’s speech-related utterances did not predict myelin density. Further longitudinal analysis showed that increased CTs and growth in CTs at 6 and 14 months were especially important to myelination of the AF. The findings have implications for brain development beyond childhood; the left AF and SLF tracts are associated with expressive and receptive language skills and with adult language performance. Beyond a variety of language-related competencies, the arcuate has also been linked to general cognitive processes related to attention and working memory. The findings show that parent–child speech interactions contribute to white matter development within the first 2 years of life, much earlier than previously shown—as early as 6 months of age. Increasing these interactions during infancy could therefore set kids up for success by optimizing language-associated brain development.
