A study showing how a common molecular program in cells diverges during embryonic development to give rise to different neural cell types is published in Nature this week, providing a framework for examining the emergence of cellular diversity. A hallmark for the cerebral cortex is the extreme diversity of interneurons, including the two largest subtypes of cortical interneurons: parvalbumin- (PV) and somatostatin- (SST) positive cells. These cells are morphologically and functionally distinct but arise from common lineages within the medial ganglionic eminence. To better understand the origin of these cells, researchers from New York University compared the RNA expression and chromatin accessibility in the precursors to these cells during embryogenesis. They find that PV and SST cells initially share a molecular program that establishes a general interneuron identity before becoming diversified through the actions of cell type-specific transcription factors. The maintenance of their distinct fates is stabilized in mature cells through the crystallization of unique chromatin landscapes, the study's authors write. "Our analysis revealed that RNA expression gives an instantaneous measure of the developmental state of a cell, whereas chromatin provides both a history of the developmental progression of a cell and a predictor of its future identity."
Combining genomic data and computational analyses, a team led by researchers from Mexico's Center for Research and Advanced Studies of the National Polytechnic Institute have reconstructed the migration history of Polynesia, a series of islands scattered across the Pacific Ocean. Little is known about when and how these islands were populated and archeological estimates for settlement dates are disputed. As reported in Nature, the researchers computationally analyzed genome-wide data from 430 modern-day individuals from 21 Pacific Island populations to reconstruct a Polynesian migration sequence that begins with a serial founder expansion, characterized by directional loss of variants, that originated in Samoa and spread first through the Cook Islands. It then spread to the Society Islands in the 11th century, the western Austral Islands and Tuāmotu Archipelago in the 12th century, and lastly to the widely separated, but genetically connected, megalithic statue-building cultures of the Marquesas Islands in the north, Raivavae in the south, and Easter Island in the east. GenomeWeb has more on this, here.