NEW YORK (GenomeWeb News) – In studies published online today in Nature, independent research teams used transcriptional profiling, imaging, and other approaches to track gene expression patterns and cellular connections in developing and adult mammalian brains.
For the first of the studies, the Allen Institute for Brain Science's Ed Lein and colleagues described findings from an array-based study of gene expression in four prenatal human brains from mid-gestational stages that included additional imaging and brain architecture analyses.
The effort was aimed at unraveling the brain features and transcriptional events marking the early stages of human brain development, Lein and colleagues noted. Such information is expected to inform future studies of the developmental shifts that contribute to neurodevelopmental and psychiatric conditions.
The team tallied up transcriptome patterns in different parts of each brain — which represented brain development at between 15 and 16 weeks after conception and at 21 weeks after conception — using custom Agilent microarrays.
With that data, the researchers developed de novo reference maps of transcription across some 300 anatomical brain regions. In the process, they picked up on the presence of transcriptional signatures corresponding to various brain regions and to different stages of brain development.
The team also uncovered sets of genes that tend to be expressed in unison in various parts of the burgeoning brain, using a co-expression network analysis.
Such transcriptomic patterns were complemented by ultra-high resolution structural magnetic resonance imaging and in situ hybridization, which made it possible to see anatomical differences between the developing human brain and that of non-human primates and other animals studied in the past.
Together, the study's authors noted, the resulting data "provide a rich, freely accessible resource for understanding human brain development."
"The atlas of the mid-gestational human brain described here, part of the BrainSpan Atlas of the Developing Human Brain, builds on digital molecular brain atlasing efforts in mouse and in adult human by providing transcriptome resources on prenatal specimens typically inaccessible for research."
For their part, another team — from the Allen Brain Institute and the National Institute of Mental Health — put together a so-called mesoscale connectome of the adult mouse brain by using high-throughput serial two-photon tomography to image the axon projections of mouse brain cells cued to express a fluorescent protein.
The resulting map of brain cell interactions, dubbed the Allen Mouse Brain Connectivity Atlas, highlights connections across the complete mouse brain and between specific sets of cells.
"Our Connectivity Atlas represents a first systematic step towards the full understanding of the complex connectivity in the mammalian brain," the Allen Institute's Hongkui Zeng, corresponding author on the mouse brain connectome study, and colleagues wrote. They noted that further tweaks to the technical and analytical methods used will continue to improve the resolution with which such connections can be observed.
"Our approach can also be applied to animal models of human brain diseases," they concluded, "and the connectivity data generated here can be instructive to human connectome studies, which will help to further our understanding of human brain connectivity and its involvement in brain disorders."