Background: The forebrain consists of multiple structures necessary to achieve elaborate functions. Proper patterning is, therefore, a prerequisite for the generation of optimal functional areas. Only a few factors have been shown to control the genetic networks that establish early forebrain patterning.

The specification of neuronal cell types in the developing neural tube is orchestrated by signaling centers. However, how patterned territories of the central nervous system (CNS) are organized into structures with appropriate size and shape is still unclear. We report that in the absence of the mouse transcription factor mBtd/Sp8, a posterior shift of the isthmic organizer (IsO) occurs, suggesting a crucial role for Sp8 in this process. In addition, large patches of cells ectopically expressing Fgf8, Otx2 and/or Wnt1 in the rostral hindbrain are detected in Sp8 mutant embryos. In this context, midbrain dopaminergic neurons are found posterior to the IsO. Furthermore, we provide evidence that cell proliferation in the mid-and hindbrain is tightly controlled by Sp8 activity. Our observations are consistent with a role for Sp8 in restricting Fgf8 expression at the IsO.

BackgroundThe homeobox containing transcription factor Uncx4.1 is, amongst others, expressed in the mouse midbrain. The early expression of this transcription factor in the mouse, as well as in the chick midbrain, points to a conserved function of Uncx4.1, but so far a functional analysis in this brain territory is missing. The goal of the current study was to analyze in which midbrain neuronal subgroups Uncx4.1 is expressed and to examine whether this factor plays a role in the early development of these neuronal subgroups.ResultsWe have shown that Uncx4.1 is expressed in GABAergic, glutamatergic and dopaminergic neurons in the mouse midbrain. In midbrain dopaminergic (mDA) neurons Uncx4.1 expression is particularly high around E11.5 and strongly diminished already at E17.5. The analysis of knockout mice revealed that the loss of Uncx4.1 is accompanied with a 25% decrease in the population of mDA neurons, as marked by tyrosine hydroxylase (TH), dopamine transporter (DAT), Pitx3 and Ngn2. In contrast, the number of glutamatergic Pax6-positive cells was augmented, while the GABAergic neuron population appears not affected in Uncx4.1-deficient embryos.ConclusionWe conclude that Uncx4.1 is implicated in the development of mDA neurons where it displays a unique temporal expression profile in the early postmitotic stage. Our data indicate that the mechanism underlying the role of Uncx4.1 in mDA development is likely related to differentiation processes in postmitotic stages, and where Ngn2 is engaged. Moreover, Uncx4.1 might play an important role during glutamatergic neuronal differentiation in the mouse midbrain.

Embryonic stem cells (ES) are pluripotent and may therefore serve as a source for the generation of specific cell types required for future therapies based on cell replacement. The isolation of defined cell populations from a certain lineage or tissue is a prerequisite for the analysis of the potential of such ES-derived cells in animal transplantation studies. Here, using the Cre/loxP system, we report the generation of murine ES cells conditionally expressing the hrGFP gene at the cell surface. Such ES cells can be differentiated in vitro into neurons displaying GFP activity in neurites. Transgenic mice derived from these ES cells permit the targeting of GFP-expression to specific tissues and provide material from the three germ layers suitable for molecular and biochemical analysis. Stem Cells 2005;23:10-15

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