A role for Noggin in the development of oligodendrocyte precursor cells.

Oligodendrocyte precursor cells (OPCs) can be differentiated in culture into either oligodendrocytes or type-2 astrocytes (2As), depending on the culture conditions. Whereas oligodendrocyte development can occur in the absence of inducing signals, 2A development apparently cannot. Fetal calf serum (FCS) and bone morphogenetic proteins (BMPs) are powerful inducers of 2A development in culture, but there is no compelling evidence that OPCs develop into astrocytes in vivo.

Axonal self-destruction and neurodegeneration.

Neurons seem to have at least two self-destruct programs. Like other cell types, they have an intracellular death program for undergoing apoptosis when they are injured, infected, or not needed. In addition, they apparently have a second, molecularly distinct self-destruct program in their axon.

Posttranscriptional regulation of p18 and p27 Cdk inhibitor proteins and the timing of oligodendrocyte differentiation.

A cell-intrinsic timer helps control when rodent oligodendrocyte precursor cells (OPCs) exit the cell cycle and terminally differentiate when cultured in platelet-derived growth factor (PDGF) and thyroid hormone (TH). There is evidence that the cyclin-dependent kinase inhibitor (CKI) p27/Kip1 (p27) is a component of this TH-regulated timer, as it increases as OPCs proliferate and is required for the timer to operate accurately. Here, we provide evidence that another CKI, p18/INK (p18), may also be a component of the timer: it increases as OPCs proliferate, and its overexpression in OPCs accelerates the timer, causing the cells to differentiate prematurely.

A Novel Type of Glial Cell Associated with Nodes of Ranvier in Rat Optic Nerve.

Using Golgi impregnation and intracellular injection of horseradish peroxidase, we show that the adult rat optic nerve contains two distinct types of astrocyte-like glial cells: one has mainly radially oriented processes that terminate on blood vessels or on the pial surface; the other has mainly longitudinally oriented processes that associate with, and often terminate at, nodes of Ranvier, but do not end on blood vessels or the pial surface. The sequence of appearance of the two types of glial cells in the developing nerve, taken together with previous immunocytochemical findings, suggests that these cells may correspond to the two types of astrocytes previously described in cultures of perinatal optic nerve cells-those with mainly radially oriented processes corresponding to type-1 astrocytes and those with mainly longitudinally oriented processes corresponding to type-2 astrocytes. To our knowledge, this is the first description of a class of central nervous system (CNS) glial cell whose processes are primarily associated with nodes of Ranvier.