Search PubMed⌕ Search

Biomedical subjects

H Westphal

Publications and source records attributed to H Westphal.

At least 73 records · Page 4Linked to original sources
PubMed1997

Expression of murine Lhx5 suggests a role in specifying the forebrain.

A LIM homeobox gene, Lim5, is known to be expressed in the forebrain of Xenopus and zebrafish (Toyama et al. [1995] Dev. Biol. 170:583-593). Results from developmental and comparative studies of its mouse ortholog, Lhx5, indicate that this gene may play important roles in forebrain development. Lhx5 expression is detected in the most anterior portion of the neural tube at the headfold stage, overlapping partially with Otx2 expression domain. After neural tube closure, Lhx5 is expressed as a transverse stripe, covering most of the diencephalic primordium. This expression recedes to restricted areas as Dlx gene expression occurs. By midgestation, both genes, Lhx5 and Dlx5, are expressed in the diencephalon and ventral telencephalon in an alternating complementary pattern. It may be that Dlx inhibits Lhx5, and this may represent a step of early regionalization of the forebrain. Lhx5 is also expressed in midbrain, hindbrain, and spinal cord, overlapping extensively with Lhx1 starting from day E10.5 of gestation. The early, persistent, and dynamic expression of Lhx5 suggests a regulatory function in forebrain formation.

Amino Acid Sequence↗
PubMed1997

Hypogonadism and obesity in mice with a targeted deletion of the Nhlh2 gene.

The family of basic helix-loop-helix (bHLH) genes comprises transcription factors involved in many aspects of growth and development. We have previously described two bHLH transcription factors, Nhlh1 and Nhlh2 (originally named NSCL1 and NSCL2). The nucleotide and predicted protein sequences of Nhlh1 and Nhlh2 are homologous within their bHLH domain where there are only three conservative amino acid differences. During murine embryogenesis, Nhlh1 and Nhlh2 share an overlapping but distinct pattern of expression in the developing nervous system. To improve our understanding of the role of these genes during neurogenesis, we have generated mice containing targeted deletions of both genes and here describe our results for Nhlh2. Loss of Nhlh2 results in a disruption of the hypothalamic-pituitary axis in mice. Male Nhlh2-/- mice are microphallic, hypogonadal and infertile with alterations in circulating gonadotropins, a defect in spermatogenesis and a loss of instinctual male sexual behaviour. Female Nhlh2-/- mice reared alone are hypogonadal, but when reared in the presence of males, their ovaries and uteri develop normally and they are fertile. Both male and female homozygotes exhibit progressive adult-onset obesity. Nhlh2 is expressed in the ventral-medial and lateral hypothalamus, Rathke's pouch and in the anterior lobe of the adult pituitary. Our results support a role for Nhlh2 in the onset of puberty and the regulation of body weight metabolism.

Animals↗
PubMed1997

Lhx2, a LIM homeobox gene, is required for eye, forebrain, and definitive erythrocyte development.

We investigated the function of Lhx2, a LIM homeobox gene expressed in developing B-cells, forebrain and neural retina, by analyzing embryos deficient in functional Lhx2 protein. Lhx2 mutant embryos are anophthalmic, have malformations of the cerebral cortex, and die in utero due to severe anemia. In Lhx2-/- embryos specification of the optic vesicle occurs; however, development of the eye arrests prior to formation of an optic cup. Deficient cellular proliferation in the forebrain results in hypoplasia of the neocortex and aplasia of the hippocampal anlagen. In addition to the central nervous system malformations, a cell non-autonomous defect of definitive erythropoiesis causes severe anemia in Lhx2-/- embryos. Thus Lhx2 is necessary for normal development of the eye, cerebral cortex, and efficient definitive erythropoiesis.

Anemia↗
PubMed1996

Interactions of the LIM-domain-binding factor Ldb1 with LIM homeodomain proteins.

The LIM homeodomain (LIM-HD) proteins, which contain two tandem LIM domains followed by a homeodomain, are critical transcriptional regulators of embryonic development. The LIM domain is a conserved cysteine-rich zinc-binding motif found in LIM-HD and LMO (rhombotin or Ttg) proteins, cytoskeletal components, LIM kinases and other proteins. LIM domains are protein-protein interaction motifs, can inhibit binding of LIM-HD proteins to DNA and can negatively regulate LIM-HD protein function. How LIM domains exert these regulatory effects is not known. We have now isolated a new LIM-domain-binding factor, Ldb1, on the basis of its ability to interact with the LIM-HD protein Lhx1 (Lim1). High-affinity binding by Ldb1 requires paired LIM domains and is restricted to the related subgroup of LIM domains found in LIM-HD and LMO proteins. The highly conserved Xenopus Ldb protein XLdb1, interacts with Xlim-1, the Xenopus orthologue of Lhx1. When injected into Xenopus embryos, XLdb1 (or Ldb1) can synergize with Xlim-1 in the formation of partial secondary axes and in activation of the genes encoding goosecoid (gsc), chordin, NCAM and XCG7, demonstrating a functional as well as a physical interaction between the two proteins.

Amino Acid Sequence↗
PubMed1996

Cyclopia and defective axial patterning in mice lacking Sonic hedgehog gene function.

Targeted gene disruption in the mouse shows that the Sonic hedgehog (Shh) gene plays a critical role in patterning of vertebrate embryonic tissues, including the brain and spinal cord, the axial skeleton and the limbs. Early defects are observed in the establishment or maintenance of midline structures, such as the notochord and the floorplate, and later defects include absence of distal limb structures, cyclopia, absence of ventral cell types within the neural tube, and absence of the spinal column and most of the ribs. Defects in all tissues extend beyond the normal sites of Shh transcription, confirming the proposed role of Shh proteins as an extracellular signal required for the tissue-organizing properties of several vertebrate patterning centres.

Animals↗
PubMed1996

Modulatory actions of dopamine on NMDA receptor-mediated responses are reduced in D1A-deficient mutant mice.

The role of D1 dopamine (DA) receptors in mediating the ability of DA to modulate responses attributable to activation of NMDA receptors was examined in mice lacking D1A dopamine receptors. Specifically, experiments were designed to test the hypothesis that the ability of DA to potentiate responses mediated by activation of NMDA receptors was attributable to activation of D1 receptors. Based on this hypothesis, we would predict that in the D1A mutant mouse, either DA would not induce enhancement of NMDA-mediated responses, or the enhancement would be severely attenuated. The results provided evidence to support the hypothesis. In mutant mice, DA and D1 receptor agonists did not potentiate responses mediated by activation of NMDA receptors. In contrast, in control mice, both DA and D1 receptor agonists markedly potentiated responses mediated by activation of NMDA receptors. The effects of DA in attenuating responses mediated by activation of non-NMDA receptors also were altered in the mutant, suggesting that this action of DA may require coupling or interactions between D1 and D2 receptors. The present studies also provided an opportunity to assess some of the basic electrophysiological and morphological properties of neostriatal neurons in mice lacking D1A DA receptors. Resting membrane potential, action potential parameters, input resistance, excitability, somatic size, dendritic extent, and estimates of spine density in mutants and controls were similar, suggesting that these basic neurophysiological and structural properties have not been changed by the loss of the D1A DA receptor.

Animals↗
PubMed1996

Molecular cloning, structure, and chromosomal localization of the mouse LIM/homeobox gene Lhx5.

Lhx5, the mouse ortholog of the Xenopus Xlim-5, is a LIM/homeobox gene expressed in the central nervous system during both embryonic development and adulthood. During development its domain of expression is mainly localized at the most anterior portion of the neural tube, and it precedes the morphological differentiation of the forebrain; for this reason we believe that Lhx5 could play an important role in forebrain patterning. Here we present the structural organization and the chromosomal localization of the Lhx5 gene. The gene is composed of five exons spanning more than 10 kb of genomic sequence. The first and second LIM domains are encoded by the first and second exon, while the codons of the homeobox are split between the third and the fourth exons. The structure of Lhx5 is similar to that of other LIM/homeodomain proteins, Lhx1/lim1 and Lhx3/lim3, but differs from that of other LIM genes, such as mec3 and LMO1/Rbtn1, in which the codons for the LIM domains are interrupted by introns. We have mapped Lhx5 to the central region of mouse chromosome 5.

Animals↗
PubMed1996

Cell-specific expression of the human gonadotropin-releasing hormone gene in transgenic animals.

We have previously demonstrated that 1131 base pairs (bp) of the human gonadotropin-releasing hormone (hGnRH) gene promoter can target simian virus 40 T antigen expression to GnRH neurons in transgenic mice. In these animals, GnRH neurons were transformed before they migrated to their final location in the rostral hypothalamus, complicating an analysis of cell-specific expression. To localize regions of the hGnRH promoter that are important for cell-specific expression, we created transgenic mice with various 5'-flanking regions of the hGnRH gene fused to the luciferase reporter gene. When 3828 or 1131 bp of the hGnRH promoter 5'-flanking DNA were used (-3828/+5LUC and -1131/+5LUC, respectively), luciferase expression in adult transgenic mice was observed in the rostral hypothalamus and olfactory tissues, regions which have been shown to be loci of GnRH-expressing neurons. Luciferase expression was not observed in other brain or peripheral tissues. Double-labeled in situ hybridization further demonstrated that luciferase expression was invariably colocalized with GnRH expression. When transgenic animals were created with a construct consisting of 484 bp of the hGnRH 5'-flanking DNA fused to the luciferase gene (-484/+5LUC), luciferase expression was not observed in the hypothalamus or in olfactory tissues. This is the first report localizing DNA sequences responsible for cell-specific expression of the GnRH gene in vivo.

Age Factors↗
PubMed1996

Defects in enteric innervation and kidney development in mice lacking GDNF.

Glial-lial-cell-line-derived neurotrophic factor (GDNF) has been isolated as neurotrophic factor for midbrain dopaminergic neurons. Because of its neurotrophic activity on a wide range of neuronal populations in vitro and in vivo, GDNF is being considered as a potential therapeutic agent for neuronal disorders. During mammalian development, it is expressed not only in the nervous system, but also very prominently in the metanephric kidney and the gastrointestinal tract, suggesting possible functions during organogenesis. We have investigated the role of GDNF during development by generating a null mutation in the murine GDNF locus, and found that mutant mice show kidney agenesis or dysgenesis and defective enteric innervation. We demonstrate that GDNF induces ureter bud formation and branching during metanephros development, and is essential for proper innervation of the gastrointestinal tract.

Animals↗
PubMed1996

Efficient in vivo manipulation of mouse genomic sequences at the zygote stage.

We describe a transgenic mouse line carrying the cre transgene under the control of the adenovirus EIIa promoter that targets expression of the Cre recombinase to the early mouse embryo. To assess the ability of this recombinase to excise loxP-flanked DNA sequences at early stages of development, we bred EIIa-cre transgenic mice to two different mouse lines carrying loxP-flanked target sequences: (i) a strain with a single gene-targeted neomycin resistance gene flanked by 1oxP sites and (ii) a transgenic line carrying multiple transgene copies with internal loxP sites. Mating either of these loxP-carrying mouse lines to EIIa-cre mice resulted in first generation progeny in which the loxP-flanked sequences had been efficiently deleted from all tissues tested, including the germ cells. Interbreeding of these first generation progeny resulted in efficient germ-line transmission of the deletion to subsequent generations. These results demonstrate a method by which loxP-flanked DNA sequences can be efficiently deleted in the early mouse embryo. Potential applications of this approach are discussed, including reduction of multicopy transgene loci to produce single-copy transgenic lines and introduction of a variety of subtle mutations into the line.

Animals↗
PubMed1996

Specification of pituitary cell lineages by the LIM homeobox gene Lhx3.

During pituitary organogenesis, the progressive differentiation of distinct pituitary-specific cell lineages from a common primordium involves a series of developmental decisions and inductive interactions. Targeted gene disruption in mice showed that Lhx3, a LIM homeobox gene expressed in the pituitary throughout development, is essential for differentiation and proliferation of pituitary cell lineages. In mice homozygous for the Lhx3 mutation, Rathke's pouch formed but failed to grow and differentiate; such mice lacked both the anterior and intermediate lobes of the pituitary. The determination of all pituitary cell lineages, except the corticotrophs, was affected, suggesting that a distinct, Lhx3-independent ontogenetic pathway exists for the initial specification of this lineage.

Animals↗
PubMed1996

A targeted mutation of the D3 dopamine receptor gene is associated with hyperactivity in mice.

While most effects of dopamine in the brain are mediated by the D1 and D2 receptor subtypes, other members of this G protein-coupled receptor family have potentially important functions. D3 receptors belong to the D2-like subclass of dopamine receptors, activation of which inhibits adenylyl cyclase. Using targeted mutagenesis in mouse embryonic stem cells, we have generated mice lacking functional D3 receptors. A premature chain-termination mutation was introduced in the D3 receptor gene after residue Arg-148 in the second intracellular loop of the predicted protein sequence. Binding of the dopamine antagonist [125I]iodosulpride to D3 receptors was absent in mice homozygous for the mutation and greatly reduced in heterozygous mice. Behavioral analysis of mutant mice showed that this mutation is associated with hyperactivity in an exploratory test. Homozygous mice lacking D3 receptors display increased locomotor activity and rearing behavior. Mice heterozygous for the D3 receptor mutation show similar, albeit less pronounced, behavioral alterations. Our findings indicate that D3 receptors play an inhibitory role in the control of certain behaviors.

Amino Acid Sequence↗
PubMed1996

D1 dopamine receptor-deficient mouse: cocaine-induced regulation of immediate-early gene and substance P expression in the striatum.

Psychomotor stimulants such as cocaine alter gene expression in neurons of the striatum. Whereas many of these effects are mediated by D1 dopamine receptors, the involvement of other dopamine receptor subtypes or neurotransmitters is likely. To distinguish between these possibilities, regulation by cocaine of immediate-early genes and genes encoding neuropeptides was analysed in mice that lack functional D1 receptors. Gene expression was examined with in situ hybridization histochemistry. In these animals, cocaine failed to induce the immediate-early genes c-fos and zif 268. In contrast, substance P expression was abnormally increased by this drug. These results demonstrate that some of the effects of cocaine on gene regulation are mediated via D1 receptor-dependent mechanisms, as evidenced by the absence of immediate-early gene induction in D1-deficient mice, whereas others also involve additional, non-D1 receptor mechanisms, as shown for substance P expression.

Animals↗
PubMed1996

Glucose-6-phosphatase dependent substrate transport in the glycogen storage disease type-1a mouse.

Glycogen storage disease type 1a (GSD-1a) is caused by a deficiency in microsomal glucose-6-phosphatase (G6Pase), the key enzyme in glucose homeostasis. A G6Pase knockout mouse which mimics the pathophysiology of human GSD-1a patients was created to understand the pathogenesis of this disorder, to delineate the mechanisms of G6Pase catalysis, and to develop future therapeutic approaches. By examining G6Pase in the liver and kidney, the primary gluconeogenic tissues, we demonstrate that glucose-6-P transport and hydrolysis are performed by separate proteins which are tightly coupled. We propose a modified translocase catalytic unit model for G6Pase catalysis.

Animals↗
PubMed1996

Mice homozygous for an insertional mutation in the Zp3 gene lack a zona pellucida and are infertile.

Mammalian oocytes synthesize and secrete a zona pellucida that surrounds the growing oocytes, ovulated eggs and preimplantation embryos. The extracellular zona matrix is composed of three glycoproteins (ZP1, ZP2, ZP3) that are involved in folliculogenesis, species-specific fertilization, and passage of the early embryo down the oviduct. We have established a mouse line in which Zp3 has been inactivated by homologous recombination with an insertional mutation. Neither Zp3 transcripts nor ZP3 protein was detected in female mice homozygous for the mutation (Zp3-/-), whereas both ZP1 and ZP2 were present in mutant oocytes. Homozygous mutant Zp3-/- mice had follicles with germinal-vesicle-intact oocytes but that lacked a zona pellucida matrix and had a disorganized corona radiata. Although mutant oocytes underwent germinal vesicle breakdown (GVBD) prior to ovulation, the cumulus-oocyte complex was markedly disrupted and the oocytes were often separate from the cumulus cells. After hormone-induced ovulation, cumulus masses were present in the oviducts of homozygous mutant mice, but zona-free eggs were observed in only half of the females and, in these, less than 10% of the normal number [correction of mumber] of eggs were detected. No zona-free 2-cell embryos were recovered from homozygous mutant Zp3-/- female mice after mating with males proven to be fertile, and none became visibly pregnant or produced offspring. These results demonstrate that a genetic defect in a zona pellucida gene causes infertility and, given the conserved nature of the zona pellucida, a similar phenotype is expected in other mammals.

Animals↗
PubMed1995

An apoptotic defect in lens differentiation caused by human p53 is rescued by a mutant allele.

If deprived of wild-type p53 function, the body loses a guardian that protects against cancer. Restoration of p53 function has, therefore, been proposed as a means of counteracting oncogenesis. This concept of therapy requires prior knowledge with regard to proper balance of p53 function in a given target tissue. We have addressed this problem by targeting expression of the wild-type human p53 gene to the lens, a tissue entirely composed of epithelial cells that differentiate into elongated fiber cells. Transgenic mice expressing wild-type human p53 develop microphthalmia as a result of a defect in fiber formation that sets in shortly after birth. We see apoptotic cells that fail to undergo proper differentiation. In an effort to directly link the observed lens phenotype to the activity of the wild-type human p53 transgene, we also generated mice expressing a mutant human p53 allele that lacks wild-type function. A normal lens phenotype is restored in double transgenic animals that carry both wild-type and mutant human p53 alleles. Our study highlights the difficulties that can arise if p53 levels are improperly balanced in a differentiating tissue.

Aging↗