Left-right asymmetry of maturation rates in human embryonic neural development. Homo sapiens

Left-right asymmetry is a fundamental organizing feature of the human brain, and neuro-psychiatric disorders such as schizophrenia sometimes involve alterations of brain asymmetry. As early as 8 weeks post conception, the majority of human foetuses move their right arms more than their left arms, but because nerve fibre tracts are still descending from the forebrain at this stage, spinal-muscular asymmetries are likely to play an important developmental role. Here we have used gene expression profiling in 18 human embryos to show that the left side of the human spinal cord, between four and eight weeks post conception, matures slightly faster than the right side, even though both sides transition from transcriptional profiles associated with cell division and proliferation at earlier stages, to later neuronal differentiation and function. The hindbrain showed a left-right mirrored pattern compared to the spinal cord. Overall design: RNA was extracted from left and right spinal cord and left and right hindbrain from 18 human embryos ranging in age from Carnegie stage 13 to Carnegie stage 23. For library preparation, Illumina TruSeq RNA-kits (Illumina, San Diego, CA, USA) were used according to the manufacturer’s instructions. The library was sequenced using Illumina HiSeq(TM) 2000 at BGI, yielding paired reads of 90bp. The clean reads were aligned to the reference sequence GRCh37 (hg19) with SOAPaligner/SOAP2 v2.21 and Tophat (v2.08).