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J L Rubenstein

Publications and source records attributed to J L Rubenstein.

At least 19 recordsLinked to original sources
PubMed2001

Fate map of the avian anterior forebrain at the four-somite stage, based on the analysis of quail-chick chimeras.

To better understand the topological organization of the primordia within the anterior forebrain, we made a fate map of the rostral neural plate in the chick. Homotopic grafts at the four-somite stage were allowed to survive for up to 9 days to enable an analysis of definitive brain structures. In some cases, the topography of the grafted neuroepithelia was compared with gene expression patterns. The midpoint of the anterior neural ridge maps upon the anterior commissure in the closed neural tube, continuing concentrically into the preoptic area and optic field. Non-neural epithelium just in front of this median ridge gives rise to the adenohypophysis. Areas for the presumptive pallial commissure, septum, and prosencephalic choroidal tissue lie progressively more posteriorly along the ridge, peripheral to the telencephalic entopeduncular and striatopallidal primordia (the subpallium), and the pallium (olfactory bulb, dorsal ventricular ridge, and cortical domains). Subpallial structures lie topologically anterior to the pallial formations, and both are concentric to the septum. Within the pallium, the major cortical domains (Wulst and caudolateral, parahippocampal, and hippocampal cortices) appear posterior to the dorsal ventricular ridge. The amygdaloid region appears concentrically across both the subpallial and pallial regions. This fate map shows that the arrangement of the prospective primordia in the neural plate is basically a flattened representation of topological relationships present in the mature brain, though marked phenomena of differential growth and selective tangential migration of some cell populations complicate the histogenetic constitution of the mature telencephalon.

Animals↗
PubMed2001

Evidence that GRIP, a PDZ-domain protein which is expressed in the embryonic forebrain, co-activates transcription with DLX homeodomain proteins.

The DLX homeodomain proteins control development of the basal ganglia and branchial arches. To identify co-factors that regulate DLX function we utilized the yeast two-hybrid assay, and found a DLX interacting protein (DIP2) which binds to the N-terminal region of DLX2 via a PDZ domain. DIP2 appears to be an alternatively spliced form of GRIP1, a protein known to bind AMPA glutamate receptors via PDZ domains. Thus, we named it GRIP1b. We provide evidence that GRIP1b can function as a transcriptional co-activator of DLX2 and DLX5. Glutamate receptors inhibit this co-activation. These results suggest that some PDZ proteins may regulate transcription via their interactions with homeodomain proteins. Furthermore, these results suggest a link between glutamate receptors, PDZ proteins and the DLX transcription factors, all of which are co-expressed in the developing basal ganglia.

Alternative Splicing↗
PubMed2001

The CRE/CREB pathway is transiently expressed in thalamic circuit development and contributes to refinement of retinogeniculate axons.

The development of precise connections in the mammalian brain proceeds through refinement of initially diffuse patterns, a process that occurs largely within critical developmental windows. To elucidate the molecular pathways that orchestrate these early periods of circuit remodeling, we have examined the role of a calcium- and cAMP-regulated transcriptional pathway. We show that there is a window of CRE/CREB-mediated gene expression in the developing thalamus, which precedes neocortical expression. In the LGN, this wave of gene expression occurs prior to visual experience, but requires retinal function. Mutant mice with reduced CREB expression show loss of refinement of retinogeniculate projections. These results suggest an important role of the CRE/CREB transcriptional pathway in the coordination of experience-independent circuit remodeling during forebrain development.

Aging↗
PubMed2001

Sorting of striatal and cortical interneurons regulated by semaphorin-neuropilin interactions.

Most striatal and cortical interneurons arise from the basal telencephalon, later segregating to their respective targets. Here, we show that migrating cortical interneurons avoid entering the striatum because of a chemorepulsive signal composed at least in part of semaphorin 3A and semaphorin 3F. Migrating interneurons expressing neuropilins, receptors for semaphorins, are directed to the cortex; those lacking them go to the striatum. Loss of neuropilin function increases the number of interneurons that migrate into the striatum. These observations reveal a mechanism by which neuropilins mediate sorting of distinct neuronal populations into different brain structures, and provide evidence that, in addition to guiding axons, these receptors also control neuronal migration in the central nervous system.

Animals↗
PubMed2001

Pax-6 regulates expression of SFRP-2 and Wnt-7b in the developing CNS.

Wnt signaling regulates a wide range of developmental processes such as proliferation, cell migration, axon guidance, and cell fate determination. In this report, we studied the expression of secreted frizzled related protein-2 (SFRP-2), which codes for a putative Wnt inhibitor, in the developing nervous system. SFRP-2 is expressed in several discrete neuroepithelial domains, including the diencephalon, the insertion of the eminentia thalami into the caudal telencephalon, and the pallial-subpallial boundary (PSB). We also noted that Wnt-7b expression was similar to SFRP-2 expression. Because many of these structures are disrupted in Pax-6 mutant mice, we examined SFRP-2 and Wnt-7b expression in the forebrains of Pax-6 Sey/Sey mice. We found that Pax-6 mutants lack SFRP-2 expression in the PSB and diencephalon. Interestingly, Pax-6 mutants also lack Wnt-7b expression in the PSB, but Wnt-7b expression in the diencephalon is preserved. Furthermore, in the spinal cord of Pax-6 mutants, SFRP-2 and Wnt-7b expression was greatly reduced. Our results suggest that by virtue of its apposition to Wnt-7b expression, SFRP-2 may modulate its function, particularly at boundaries such as the PSB, and that changes in Wnt signaling contribute to the phenotype of Pax-6 mutants.

Animals↗
PubMed2001

Coordinate expression of Fgf8, Otx2, Bmp4, and Shh in the rostral prosencephalon during development of the telencephalic and optic vesicles.

Previous studies suggest that Fgf8 has a key role in regulating vertebrate development. In the rostral head of the embryonic chicken, there are increasing numbers of separate Fgf8 domains; these are present in tissues that appear to have previously expressed Otx2. As Fgf8 expression becomes established, Otx2 expression weakens, but remains in cells abutting the Fgf8 expression domain. These Fgf8 expression domains are closely associated with tissues expressing Bmp4 and Shh. Based on analogy with the embryonic limb, we suggest that Fgf8, Bmp4 and Shh function together in patterning regions of the embryonic head. Gene expression changes are particularly prominent in 14-21 somite stage embryos in the rostral forebrain, during early morphogenesis of the telencephalic and optic vesicles, when several new interfaces of Fgf8, Bmp4 and Shh are generated. To gain insights into the functions of fibroblast growth factor 8 (FGF8) in the embryonic forebrain, we studied the effects of implanting beads containing this protein in the dorsal prosencephalon of embryonic day 2 chicken embryos. Ectopic FGF8 had profound effects on morphogenesis of the telencephalic and optic vesicles. It disrupted formation of the optic stalk and caused a transformation of the pigment epithelium into neural retina. Within the telencephalon, FGF8 beads frequently induced a sulcus that had features of an ectopic rostral midline. The sulcus separated the telencephalon into rostral and caudal vesicles. Furthermore, we present evidence that FGF8 can regulate regionalization of the prosencephalon through inhibition of Otx2 and Emx2 expression. Thus, these experiments provide evidence that FGF8 can regulate both morphogenesis and patterning of the rostral prosencephalon (telencephalic and optic vesicles). FGF8 beads can induce midline properties (e.g. a sulcus) and can modulate the specification and differentiation of adjacent tissues. We suggest that some of these effects are through regulating the expression of homeobox genes (Otx2 and Emx2) that are known to participate in forebrain patterning.

Age Factors↗
PubMed2001

Tbr1 regulates differentiation of the preplate and layer 6.

During corticogenesis, early-born neurons of the preplate and layer 6 are important for guiding subsequent neuronal migrations and axonal projections. Tbr1 is a putative transcription factor that is highly expressed in glutamatergic early-born cortical neurons. In Tbr1-deficient mice, these early-born neurons had molecular and functional defects. Cajal-Retzius cells expressed decreased levels of Reelin, resulting in a reeler-like cortical migration disorder. Impaired subplate differentiation was associated with ectopic projection of thalamocortical fibers into the basal telencephalon. Layer 6 defects contributed to errors in the thalamocortical, corticothalamic, and callosal projections. These results show that Tbr1 is a common genetic determinant for the differentiation of early-born glutamatergic neocortical neurons and provide insights into the functions of these neurons as regulators of cortical development.

Animals↗
PubMed2001

Bone morphogenetic protein-2 (BMP-2) signaling to the Col2alpha1 gene in chondroblasts requires the homeobox gene Dlx-2.

To understand the role of Dlx genes in the process of chondrogenesis, we studied the expression of Dlx-2 and Dlx-5 mRNAs in a mouse clonal chondroblast cell line, TMC23. We also examined the involvement of Dlx2 in the bone morphogenetic protein-2 (BMP-2) signaling to the type II collagen gene, Col2alpha1, in this cell line. In this report, we show that the TMC23 cells express Dlx-2 and Dlx-5 mRNAs, and the levels can be upregulated by recombinant BMP-2 at an early stage of chondroblast differentiation. Addition of rBMP-2 dramatically increased type II collagen expression at both the mRNA and the protein level. Also, rBMP-2 increased transcription of Col2alpha1, as shown by stimulation of a chondrocyte-specific Col2alpha1 enhancer. The mechanism involves Dlx-2, as the stimulatory effect of rBMP-2 on the Col2alpha enhancer was blocked by an antisense oligonucleotide against Dlx-2 mRNA. The rBMP-2 signaling to the Col2alpha1 enhancer was also blocked by a dominant-negative Smad1 expression vector. These data demonstrate that Dlx-2 is a downstream target of the BMP-2 signaling pathway in chondroblasts. Therefore, we propose a model in which rBMP-2 stimulates Dlx-2 expression, which then serves as a necessary transcription factor for Col2alpha1 gene expression through a chondrocyte-specific enhancer fragment.

Bone Morphogenetic Protein 2↗
PubMed2001

Local retinoid signaling coordinates forebrain and facial morphogenesis by maintaining FGF8 and SHH.

Correlations between facial anomalies and brain defects are well characterized throughout the clinical literature, yet a developmental basis for this association has not been identified. We demonstrate that the frontonasal process, which gives rise to the mid- and upper face, and the forebrain are linked early in their morphogenesis by a local retinoid signaling event that maintains the expression of key regulatory molecules. First, we show that aldehyde dehydrogenase 6, which synthesizes the ligand, retinoic acid, is localized to the ventral epithelium of the presumptive frontonasal process of chick embryos. At least two retinoid receptors are expressed in adjacent populations of mesenchyme. Second, using synthetic pan-specific retinoid antagonists, we transiently inhibit the ability of retinoid receptors to bind retinoic acid in the rostral head and we generate embryos with a hypoplastic forebrain, fused eyes, and no frontonasal process-derived structures such as the upper beak. These defects are not due to eliminating mesenchymal progenitors, as neural crest cells still migrate into the frontonasal process, despite disruptions to retinoid signaling. Rather, these malformations result from loss of fibroblast growth factor 8 and sonic hedgehog expression, which leads to increased programmed cell death and decreased proliferation in the forebrain and frontonasal process. Most significantly, we can rescue the morphological defects by re-introducing retinoic acid, or fibroblast growth factor and sonic hedgehog proteins into antagonist-treated embryos. We propose that the local source of retinoic acid in the rostral head initiates a regulatory cascade that coordinates forebrain and frontonasal process morphogenesis.

Animals↗
PubMed2001

Requirement for Pbx1 in skeletal patterning and programming chondrocyte proliferation and differentiation.

Pbx1 and a subset of homeodomain proteins collaboratively bind DNA as higher-order molecular complexes with unknown consequences for mammalian development. Pbx1 contributions were investigated through characterization of Pbx1-deficient mice. Pbx1 mutants died at embryonic day 15/16 with severe hypoplasia or aplasia of multiple organs and widespread patterning defects of the axial and appendicular skeleton. An obligatory role for Pbx1 in limb axis patterning was apparent from malformations of proximal skeletal elements, but distal structures were unaffected. In addition to multiple rib and vertebral malformations, neural crest cell-derived skeletal structures of the second branchial arch were morphologically transformed into elements reminiscent of first arch-derived cartilages. Although the skeletal malformations did not phenocopy single or compound Hox gene defects, they were restricted to domains specified by Hox proteins bearing Pbx dimerization motifs and unaccompanied by alterations in Hox gene expression. In affected domains of limbs and ribs, chondrocyte proliferation was markedly diminished and there was a notable increase of hypertrophic chondrocytes, accompanied by premature ossification of bone. The pattern of expression of genes known to regulate chondrocyte differentiation was not perturbed in Pbx1-deficient cartilage at early days of embryonic skeletogenesis, however precocious expression of Col1a1, a marker of bone formation, was found. These studies demonstrate a role for Pbx1 in multiple developmental programs and reveal a novel function in co-ordinating the extent and/or timing of proliferation with terminal differentiation. This impacts on the rate of endochondral ossification and bone formation and suggests a mechanistic basis for most of the observed skeletal malformations.

Age Factors↗
PubMed2001

Gsh2 and Pax6 play complementary roles in dorsoventral patterning of the mammalian telencephalon.

The telencephalon has two major subdivisions, the pallium and subpallium. The pallium, which primarily consists of glutamatergic cortical structures, expresses dorsal molecular markers, whereas the subpallium, which primarily consists of the GABAergic basal ganglia, expresses ventral molecular markers. Here, we present evidence that the progenitor and postmitotic cells flanking the pallial/subpallial boundary (PSB) in the embryonic mouse can be subdivided into multiple regions that express unique combinations of transcription factors. The domains that immediately flank the PSB are the ventral pallium (VP) and the dorsal lateral ganglionic eminence (dLGE). The early expression of the Pax6 and Gsh2 homeobox transcription factors overlaps in the region of the dLGE. Analyses of mice that lack functional alleles of either Gsh2 or Pax6 demonstrate that these genes have complementary roles in patterning the primordia flanking the PSB. In the Gsh2 mutants, the dLGE is respecified into a VP-like structure, whereas in the Pax6 mutants the VP is respecified into a dLGE-like structure. The role of Pax6 in dorsalizing the telencephalon is similar to its role in the spinal cord, supporting the hypothesis that some dorsoventral patterning mechanisms are used at all axial levels of the central nervous system.

Animals↗
PubMed2001

Distinct cortical migrations from the medial and lateral ganglionic eminences.

Recent evidence suggests that projection neurons and interneurons of the cerebral cortex are generally derived from distinct proliferative zones. Cortical projection neurons originate from the cortical ventricular zone (VZ), and then migrate radially into the cortical mantle, whereas most cortical interneurons originate from the basal telencephalon and migrate tangentially into the developing cortex. Previous studies using methods that label both proliferative and postmitotic cells have found that cortical interneurons migrate from two major subdivisions of the developing basal telencephalon: the medial and lateral ganglionic eminences (MGE and LGE). Since these studies labeled cells by methods that do not distinguish between the proliferating cells and those that may have originated elsewhere, we have studied the contribution of the MGE and LGE to cortical interneurons using fate mapping and genetic methods. Transplantation of BrdU-labeled MGE or LGE neuroepithelium into the basal telencephalon of unlabeled telencephalic slices enabled us to follow the fate of neurons derived from each of these primordia. We have determined that early in neurogenesis GABA-expressing cells from the MGE tangentially migrate into the cerebral cortex, primarily via the intermediate zone, whereas cells from the LGE do not. Later in neurogenesis, LGE-derived cells also migrate into the cortex, although this migration occurs primarily through the subventricular zone. Some of these LGE-derived cells invade the cortical plate and express GABA, while others remain within the cortical proliferative zone and appear to become mitotically active late in gestation. In addition, by comparing the phenotypes of mouse mutants with differential effects on MGE and LGE migration, we provide evidence that the MGE and LGE may give rise to different subtypes of cortical interneurons.

Animals↗
PubMed2000

Ventral neural patterning by Nkx homeobox genes: Nkx6.1 controls somatic motor neuron and ventral interneuron fates.

There is growing evidence that sonic hedgehog (Shh) signaling regulates ventral neuronal fate in the vertebrate central nervous system through Nkx-class homeodomain proteins. We have examined the patterns of neurogenesis in mice carrying a targeted mutation in Nkx6.1. These mutants show a dorsal-to-ventral switch in the identity of progenitors and in the fate of postmitotic neurons. At many axial levels there is a complete block in the generation of V2 interneurons and motor neurons and a compensatory ventral expansion in the domain of generation of V1 neurons, demonstrating the essential functions of Nkx6.1 in regional patterning and neuronal fate determination.

Animals↗
PubMed2000

Pallial and subpallial derivatives in the embryonic chick and mouse telencephalon, traced by the expression of the genes Dlx-2, Emx-1, Nkx-2.1, Pax-6, and Tbr-1.

Pallial and subpallial morphological subdivisions of the developing chicken telencephalon were examined by means of gene markers, compared with their expression pattern in the mouse. Nested expression domains of the genes Dlx-2 and Nkx-2.1, plus Pax-6-expressing migrated cells, are characteristic for the mouse subpallium. The genes Pax-6, Tbr-1, and Emx-1 are expressed in the pallium. The pallio-subpallial boundary lies at the interface between the Tbr-1 and Dlx-2 expression domains. Differences in the expression topography of Tbr-1 and Emx-1 suggest the existence of a novel "ventral pallium" subdivision, which is an Emx-1-negative pallial territory intercalated between the striatum and the lateral pallium. Its derivatives in the mouse belong to the claustroamygdaloid complex. Chicken genes homologous to these mouse genes are expressed in topologically comparable patterns during development. The avian subpallium, called "paleostriatum," shows nested Dlx-2 and Nkx-2.1 domains and migrated Pax-6-positive neurons; the avian pallium expresses Pax-6, Tbr-1, and Emx-1 and also contains a distinct Emx-1-negative ventral pallium, formed by the massive domain confusingly called "neostriatum." These expression patterns extend into the septum and the archistriatum, as they do into the mouse septum and amygdala, suggesting that the concepts of pallium and subpallium can be extended to these areas. The similarity of such molecular profiles in the mouse and chicken pallium and subpallium points to common sets of causal determinants. These may underlie similar histogenetic specification processes and field homologies, including some comparable connectivity patterns.

Age Factors↗
PubMed2000

Origin and molecular specification of striatal interneurons.

The striatum, the largest component of the basal ganglia, contains projection neurons and interneurons. Whereas there is considerable agreement that the lateral ganglionic eminence (LGE) is the origin of striatal projection neurons, less is known about the origin of striatal interneurons. Using focal injections of retrovirus into the ventral telencephalon in vitro, we demonstrate that most striatal interneurons tangentially migrate from the medial ganglionic eminence (MGE) or the adjacent preoptic/anterior entopeduncular areas (POa/AEP) and express the NKX2.1 homeodomain protein. Although the majority of striatal interneurons (cholinergic, calretinin(+), and parvalbumin(+)) maintain the expression of NKX2.1 into adulthood, most of the interneurons expressing somatostatin (SOM), neuropeptide Y (NPY), and neural nitric oxide synthase (NOS) appear to downregulate the expression of NKX2.1 as they exit the neuroepithelium. Analysis of striatal development in mice lacking Nkx2.1 suggests that this gene is required for the specification of nearly all striatal interneurons. Similar analysis of mice lacking the Mash1 basic helix-loop-helix (bHLH) or both the Dlx1 and Dlx2 homeodomain transcription factors demonstrates that these genes are required for the differentiation of striatal interneurons. Mash1 mutants primarily have a reduction in early-born striatal interneurons, whereas Dlx1/2 mutants primarily have reduced numbers of late-born striatal interneurons. We also present evidence implicating the Lhx6 and Lhx7 LIM-homeobox genes in the development of distinct interneuron subtypes. Finally, we hypothesize that, within the MGE, radially migrating cells generally become projection neurons, whereas tangentially migrating cells mainly form interneurons of the striatum and cerebral cortex.

Animals↗
PubMed2000

A highly conserved enhancer in the Dlx5/Dlx6 intergenic region is the site of cross-regulatory interactions between Dlx genes in the embryonic forebrain.

Four Dlx homeobox genes, Dlx1, Dlx2, Dlx5, and Dlx6 are expressed in the same primordia of the mouse forebrain with temporally overlapping patterns. The four genes are organized as two tail-to-tail pairs, Dlx1/Dlx2 and Dlx5/Dlx6, a genomic arrangement conserved in distantly related vertebrates like zebrafish. The Dlx5/Dlx6 intergenic region contains two sequences of a few hundred base pairs, remarkably well conserved between mouse and zebrafish. Reporter transgenes containing these two sequences are expressed in the forebrain of transgenic mice and zebrafish with patterns highly similar to endogenous Dlx5 and Dlx6 expression. The activity of the transgene is drastically reduced in mouse mutants lacking both Dlx1 and Dlx2, consistent with the decrease in endogenous Dlx5 and Dlx6 expression. These results suggest that cross-regulation by Dlx proteins, mediated by the intergenic sequences, is essential for Dlx5 and Dlx6 expression in the forebrain. This hypothesis is supported by cotransfection and DNA-protein binding experiments. We propose that the Dlx genes are part of a highly conserved developmental pathway that regulates forebrain development.

Animals↗