Abstract
In warm-blooded vertebrate embryos (mammals and birds), the axial tissues of the body form from a growth zone at the tail end, Hensen's node, which generates neural, mesodermal, and endodermal structures along the midline. While most cells only pass through this region, the node has been suggested to contain a small population of resident stem cells. However, it is unknown whether the rest of the node constitutes an instructive niche that specifies this self-renewal behavior. Here, we use heterotopic transplantation of groups and single cells and show that cells not destined to enter the node can become resident and self-renew. Long-term resident cells are restricted to the posterior part of the node and single-cell RNA-sequencing reveals that the majority of these resident cells preferentially express G2/M phase cell-cycle-related genes. These results provide strong evidence that the node functions as a niche to maintain self-renewal of axial progenitors.
Highlights
In warm-blooded vertebrate embryos, the axial tissues of the body form from a growth zone at the tail end, Hensen’s node, which generates neural, mesodermal, and endodermal structures along the midline
Rather than defining a distinct cell population arising very early in development, the node represents a dynamic region at the tip of the primitive streak, which appears as a morphological “node” from HH4 [1] in chick
The initial cells that make up this region are derived from two distinct cell populations, which meet at the tip of the elongating primitive streak (HH3 to 3+ in chick) [2,3,4]
Summary
In warm-blooded vertebrate embryos (mammals and birds), the axial tissues of the body form from a growth zone at the tail end, Hensen’s node, which generates neural, mesodermal, and endodermal structures along the midline. Long-term resident cells are restricted to the posterior part of the node and single-cell RNA-sequencing reveals that the majority of these resident cells preferentially express G2/M phase cellcycle–related genes These results provide strong evidence that the node functions as a niche to maintain self-renewal of axial progenitors. At a cell-population level, grafts of groups of cells transplanted repeatedly between older and younger tailbud regions can contribute to midline structures over two or more hosts, while again some cells remain in the tailbud [14, 19] These findings have led to the idea that some cells in the node (most likely a very small subset) may have the ability to self-renew, perhaps indefinitely, displaying stem cell behavior. Long-term resident cells are preferentially located in the posterior part of the node, and display enriched expression of G2/M cell cycle markers
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