Analysis of Development Edited by Prof Benjamin H Willier, Prof Paul A Weiss and Prof Viktor Hamburger Pp xii + 735 (Philadelphia and London: W B Saunders Company, 1955) 105s

Mechanisms of Development

The pancreas contains both exocrine and endocrine cells, but the molecular mechanisms controlling the differentiation of these cell types are largely unknown. Despite their endodermal origin, pancreatic endocrine cells share several molecular characteristics with neurons, and, like neurons in the central nervous system, differentiating endocrine cells in the pancreas appear in a scattered fashion within a field of progenitor cells. This indicates that they may be generated by lateral specification through Notch signalling. Here, to test this idea, we analysed pancreas development in mice genetically altered at several steps in the Notch signalling pathway. Mice deficient for Delta-like gene 1 (Dll1) or the intracellular mediator RBP-JK showed accelerated differentiation of pancreatic endocrine cells. A similar phenotype was observed in mice over-expressing neurogenin 3(ngn 3) or the intracellular form of Notch3 (ref. 13) (a repressor of Notch signalling). These data provide evidence that ngn3 acts as pro-endocrine gene and that Notch signalling is critical for the decision between theendocrine and progenitor/exocrine fates in the developing pancreas.

Notch signalling controls pancreatic cell differentiation

Each year spina bifida and anencephaly, the two most common forms of neural-tube defects, occur in 1 in 1000 pregnancies in the United States1 and an estimated 300,000 or more newborns worldwide.2 Although these severe conditions have been recognized since antiquity, never before has progress been so fast and substantive, particularly in the area of prevention. The results of randomized trials indicate that at least half the cases of neural-tube defects could be prevented if women consumed sufficient amounts of the B vitamin folic acid before conception and during early pregnancy.3,4 Elsewhere in this issue of the Journal, Berry . . .

Neural-Tube Defects

Radial Glial Identity Is Promoted by Notch1 Signaling in the Murine Forebrain

Neural stem cells, which exhibit self-renewal and multipotentiality, are generated in early embryonic brains and maintained throughout the lifespan. The mechanisms of their generation and maintenance are largely unknown. Here, we show that neural stem cells are generated independent of RBP-Jκ, a key molecule in Notch signaling, by using RBP-Jκ−/− embryonic stem cells in an embryonic stem cell-derived neurosphere assay. However, Notch pathway molecules are essential for the maintenance of neural stem cells; they are depleted in the early embryonic brains of RBP-Jκ−/− or Notch1−/− mice. Neural stem cells also are depleted in embryonic brains deficient for the presenilin1 (PS1) gene, a key regulator in Notch signaling, and are reduced in PS1+/− adult brains. Both neuronal and glial differentiation in vitro were enhanced by attenuation of Notch signaling and suppressed by expressing an active form of Notch1. These data are consistent with a role for Notch signaling in the maintenance of the neural stem cell, and inconsistent with a role in a neuronal/glial fate switch.

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Notch pathway molecules are essential for the maintenance, but not the generation, of mammalian neural stem cells.

Expression of the Notch 3 intracellular domain in mouse central nervous system progenitor cells is lethal and leads to disturbed neural tube development

Tim Mitsiadis

Papers

Expression of the Notch 3 intracellular domain in mouse central nervous system progenitor cells is lethal and leads to disturbed neural tube development

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