The Wnts are a family of glycoproteins that regulate cell proliferation, fate decisions, and differentiation. In our study, we examined the contribution of Wnts to the development of ventral midbrain (VM) dopaminergic (DA) neurons. Our results show that ␤-catenin is expressed in DA precursor cells and that ␤-catenin signaling takes place in these cells, as assessed in TOPGAL [Tcf optimal-promoter ␤-galactosidase] reporter mice. We also found that Wnt-1, -3a, and -5a expression is differentially regulated during development and that partially purified Wnts distinctively regulate VM development. Wnt-3a promoted the proliferation of precursor cells expressing the orphan nuclear receptor-related factor 1 (Nurr1) but did not increase the number of tyrosine hydroxylase-positive neurons. Instead, Wnt-1 and -5a increased the number of rat midbrain DA neurons in rat embryonic day 14.5 precursor cultures by two distinct mechanisms. Wnt-1 predominantly increased the proliferation of Nurr1؉ precursors, up-regulated cyclins D1 and D3, and down-regulated p27 and p57 mRNAs. In contrast, Wnt-5a primarily increased the proportion of Nurr1؉ precursors that acquired a neuronal DA phenotype and up-regulated the expression of Ptx3 and c-ret mRNA. Moreover, the soluble cysteine-rich domain of Frizzled-8 (a Wnt inhibitor) blocked endogenous Wnts and the effects of Wnt-1 and -5a on proliferation and the acquisition of a DA phenotype in precursor cultures. These findings indicate that Wnts are key regulators of proliferation and differentiation of DA precursors during VM neurogenesis and that different Wnts have specific and unique activity profiles.T he development of midbrain dopaminergic (DA) neurons requires a complex combination of transcriptional regulators and diffusible signals to control both the acquisition and maintenance of a neurotransmitter-specific phenotype. The orphan nuclear receptor-related factor 1 (Nurr1, also known as NR4A2) is the only factor known to be required by midbrain precursor cells for the acquisition of a midbrain DA phenotype (1-4). Null mutations in other transcriptional regulators expressed in DA neurons, such as the homeodomain proteins Lmx1b and Ptx3, result in the loss of midbrain DA neurons after their birth (5-7). With regard to soluble diffusible signals, intersections of Shh (ventrally) and FGF8 (in the isthmus) create sites for the induction of DA neurons (8). Members of the Wnt family of secreted glycoproteins are also expressed in the midbrain (9) and are known to regulate precursor proliferation (10-12), fate decisions (13-17), and neuronal differentiation (18)(19)(20) in the nervous system. Interestingly, deletion of Wnt-1 results in the loss of DA neurons (21) and of the entire midbrain-hindbrain junction (22,23). Another mutant mouse with a similar phenotype in the midbrain is the LRP6 (low-density lipoprotein receptor-related protein 6) null (24), which lacks a receptor necessary for Wnt signaling. Combined, these findings suggest an important role for Wnts during the development of mid...

Promoter-specific recruitment of histone acetyltransferase activity is often critical for transcriptional activation. We present a detailed study of the interaction between the histone acetyltransferase complexes SAGA and NuA4, and transcription activators. We demonstrate by affinity chromatography and photo-cross-linking label transfer that acidic activators directly interact with Tra1p, a shared subunit of SAGA and NuA4. Mutations within the COOH-terminus of Tra1p disrupted its interaction with activators and resulted in gene-specific transcriptional defects that correlated with lowered promoter-specific histone acetylation. These data demonstrate that the essential Tra1 protein serves as a common target for activators in both SAGA and NuA4 acetyltransferases.

In utero exposure to ⌬ 9 -tetrahydrocannabinol (⌬ 9 -THC), the active component from marijuana, induces cognitive deficits enduring into adulthood. Although changes in synaptic structure and plasticity may underlie ⌬ 9 -THC-induced cognitive impairments, the neuronal basis of ⌬ 9 -THC-related developmental deficits remains unknown. Using a Boyden chamber assay, we show that agonist stimulation of the CB 1 cannabinoid receptor (CB1R) on cholecystokinin-expressing interneurons induces chemotaxis that is additive with brain-derived neurotrophic factor (BDNF)-induced interneuron migration. We find that Src kinase-dependent TrkB receptor transactivation mediates endocannabinoid (eCB)-induced chemotaxis in the absence of BDNF. Simultaneously, eCBs suppress the BDNF-dependent morphogenesis of interneurons, and this suppression is abolished by Src kinase inhibition in vitro. Because sustained prenatal ⌬ 9 -THC stimulation of CB1Rs selectively increases the density of cholecystokinin-expressing interneurons in the hippocampus in vivo, we conclude that prenatal CB 1R activity governs proper interneuron placement and integration during corticogenesis. Moreover, eCBs use TrkB receptor-dependent signaling pathways to regulate subtype-selective interneuron migration and specification.corticogenesis ͉ drug abuse ͉ neurotrophin E ndogenous cannabinoids, such as anandamide (AEA) and 2-arachidonoylglycerol (2-AG), modulate synaptic plasticity by the retrograde control of neurotransmitter release (1). Accordingly, a compartmentalization of endocannabinoid (eCB) synthesis and action has been demonstrated in adult brain (1-3). eCBs are predominantly synthesized in dendritic compartments and signal through presynaptic G i/o protein-coupled CB 1 cannabinoid receptors (CB 1 Rs) (4-6). The adult phenotype of cannabinoid systems is achieved through a series of developmentally regulated events culminating in high CB 1 R expression on cholecystokinin (CCK)-containing GABAergic interneurons (CB 1 R ϩ cells) in the hippocampus and neocortex (3,5,6).Recent studies have demonstrated the existence of functional CB 1 Rs in developing cortical neurons (7). A coincidence of eCB synthesis and release and CB 1 R activation within axonal growth cones was postulated to provide an eCB-driven reinforcement loop that regulates axonal growth and guidance (8). Although the functional significance of CB 1 Rs during assembly of cortical neuronal circuitries is unknown, their developmental impact is illustrated by long-lasting cognitive, motor, and social disturbances in offspring exposed prenatally to cannabis (9, 10).The majority of cortical interneurons are derived from extracortical precursor pools and undergo long-distance migration before inhabiting specific cortical layers (11, 12). Interneuron specification is in part governed by epigenetic cues within the neocortex, including brain-derived neurotrophic factor (BDNF) (12-14). Considering that pyramidal cells in the juvenile neocortex harbor the capacity of eCB synthesis and release (15), we hypothesiz...