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P Gruss

Publications and source records attributed to P Gruss.

At least 109 records · Page 6Linked to original sources
PubMed1997

Current views on eye development.

Several genes involved in the regulation of eye development in different species have been identified. Structural and functional conservation have been found between some of these genes in organisms as diverse as Drosophila and mouse. One notable example is the relationship between the mouse Pax6 gene and eyeless of Drosophila. Ectopic expression of eyeless or mouse Pax6 in Drosophila results in the formation of additional eyes. Recently, another homeobox gene, Six3, was found to promote ectopic lens formation in fish embryos. The next step will be to unravel the associated regulatory pathways of these genes and assess the degree to which they display evolutionary conservation. This will be important in order to assimilate these findings with current anatomical and embryological models. It seems reasonable to believe that in the near future the characterization of the whole framework required for vertebrate eye development will be accomplished.

Animals↗
PubMed1997

Identification of the vertebrate Iroquois homeobox gene family with overlapping expression during early development of the nervous system.

In Drosophila the decision processes between the neural and epidermal fate for equipotent ectodermal cells depend on the activity of proneural genes. Members of the Drosophila Iroquois-Complex (Iro-C) positively regulate the activity of certain proneural AS-C genes during the formation of external sensory organs. We have identified and characterized three mouse Iroquois-related genes: Irx1, -2 and -3, which have a homeodomain very similar to that of the Drosophila Iro-C genes. The sequence similarity implies that these three genes represent a separate homeobox family. All three genes are expressed with distinct spatio/temporal patterns during early mouse embryogenesis. These patterns implicate them in a number of embryonic developmental processes: the A/P and D/V patterning of specific regions of the central nervous system (CNS), and regionalization of the otic vesicle, branchial epithelium and limbs.

Amino Acid Sequence↗
PubMed1997

Retinoic acid mediates Pax6 expression during in vitro differentiation of embryonic stem cells.

Neural cells are found rarely during differentiation of embryonic stem (ES) cells in vitro. To increase the yield of neuronal and glial cells from ES cells, we designed a differentiation procedure in which embryoid bodies were grown in medium containing retinoic acid (RA) and a low level (1%) of fetal calf serum. Using this procedure we were able to obtain neurofilament or glial fibrillary acidic protein-positive cells in 90% of outgrowths of embryonic bodies. Differentiation was dependent on the RA concentration, whereas depletion of RA favored the appearance of cardiac muscle cells. Differentiation of ES cells correlated with increased activity of Pax6, a transcription factor involved in central nervous system development. Pax6 was not expressed in undifferentiated ES cells, nor after differentiation by depletion of leukemia inhibitory factor or by overgrowth. After embryoid body formation and subsequent attachment, only infrequently did a few cells express Pax6. Addition of RA resulted in the appearance of Pax6-expressing cells in a concentration-dependent manner, with a peak at 100 nM RA. The presented differentiation procedure can be used for studying the molecular biology of neurogenesis in vitro.

Animals↗
PubMed1997

Pax6-dependent regulation of adhesive patterning, R-cadherin expression and boundary formation in developing forebrain.

Mutations in the gene for the transcription factor, Pax6, induce marked developmental abnormalities in the CNS and the eye, but the cellular mechanisms that underlie the phenotype are unknown. We have examined the adhesive properties of cells from the developing forebrain in Small eye, the Pax6 mutant mouse. We have found that the segregation normally observed in aggregates of cortical and striatal cells in an in vitro assay is lost in Small eye. This correlates with an alteration of in vivo expression of the homophilic adhesion molecule, R-cadherin. Moreover, the boundary between cortical and striatal regions of the telencephalon is dramatically altered in Small eye: radial glial fascicles do not form at the border, and the normal expression of R-cadherin and tenascin-C at the border is lost. These data suggest a link between the transcription factor, Pax6, R-cadherin expression, cellular adhesion and boundary formation between developing forebrain regions.

Animals↗
PubMed1997

Fkh5-deficient mice show dysgenesis in the caudal midbrain and hypothalamic mammillary body.

The murine winged helix gene Fkh5 is specifically expressed in the developing central nervous system (CNS). Early embryonic Fkh5 expression is restricted to the mammiliary body region of the caudal hypothalamus, midbrain, hindbrain and spinal cord. Postnatally, signals persist in specific nuclei of the mammillary body and in the midbrain. We generated Fkh5 deficient mice by homologous recombination to assess its in vivo function. At birth, Fkh5-deficient mice are viable and indistinguishable from wild-type and Fkh5 heterozygous littermates. However, about one third die within the first two days and another fifth before weaning. Surviving Fkh5-deficient mice become growth retarded within the first week and remain smaller throughout their whole life span. Fkh5-deficient females on 129Sv x C57BL/6 genetic background are fertile, but do not nurture their pups. More detailed analysis of Fkh5-deficient brains reveals distinct alterations in the CNS. In the midbrain, mutant mice exhibit reduced inferior colliculi and an overgrown anterior cerebellum. Furthermore, the hypothalamic mammillary body of Fkh5-deficient brains lacks the medial mammillary nucleus. These results suggest that Fkh5 plays a major role during CNS development.

Animals↗
PubMed1996

Temporal control of the Cre recombinase in transgenic mice by a tetracycline responsive promoter.

Gene-targeted mice derived from embryonic stem cells are a useful tool to study gene function during development. However, if the mutation is embryonic lethal and the gene is deleted from the onset of development, later functions in adult animals cannot be studied. Recently, the bacterial Cre-loxP site-specific recombination system has successfully been used in transgenic animals to produce tissue-specific and temporal deletions [Gu et al. (1993) Cell, 73, 1155"""""" Gu et al. (1994) Science, 265,103--106; Kuhn et al. (1995) Science, 269, 1427-1429]. We have evaluated the tetracycline responsive binary system [Gossen and Bujard (1992) Proc. Natl. Acad. Sci. USA, 89, 5547-5551] for its ability to transiently express the Cre recombinase in transgenic mice. In this system, a transactivator fusion protein composed of the tetracycline repressor (tetR) and the acidic domain of the herpes simplex viral protein 16 (VP16) can regulate the expression of the Cre gene from a promoter containing tet-operator (tetO) sequences. In the absence of tetracycline, the Cre gene is expressed and will induce site-specific recombination between two loxP sites. In the presence of tetracycline, the Cre gene will not be expressed and recombination will not occur.

Animals↗
PubMed1996

Ectopic lens induction in fish in response to the murine homeobox gene Six3.

Recent findings show an unexpected conservation of genes involved in vertebrate and insect eye development. The Drosophila homeobox gene sine oculis is crucial for eye development. Its murine homologue, Six3 is expressed in the anterior neural plate, a region which is involved in lens induction in Xenopus. To examine whether Six3 participates in the process of eye formation, mouse Six3 was ectopically expressed in fish embryos. The results show that Six3 is sufficient to promote ectopic lens formation in the area of the otic vesicle and that retinal tissue is not a prerequisite for ectopic lens differentiation. Our findings suggest a conserved function for Six3 in metazoan eye development.

Animals↗
PubMed1996

Pax genes and their roles in cell differentiation and development.

Members of the Pax gene family are expressed in various tissues during ontogenesis. Evidence for their crucial role in morphogenesis, organogenesis, cell differentiation and oncogenesis is provided by rodent mutants and human diseases. Additionally, recent experimental in vivo and in vitro approaches have led to the identification of molecules that interact with Pax proteins.

Animals↗
PubMed1996

Pax2 contributes to inner ear patterning and optic nerve trajectory.

During gestation, the paired box-containing gene Pax2 is expressed in the mid-hindbrain area, developing eye and inner ear. We generated Pax2 null mutant mice, which show the requirement of Pax2 for the establishment of axonal pathways along the optic stalks and ventral diencephalon. In mutant brains, the optic tracts remain totally ipsilateral due to agenesis of the optic chiasma. Furthermore, Pax2 mutants show extension of the pigmented retina into the optic stalks and failure of the optic fissure to close resulting in coloboma. In the inner ear, Pax2 mutants show agenesis of the cochlea and the spiral ganglion, i.e., the parts of the organ responsible for auditory function and in whose primordium Pax2 is expressed. Our results identify Pax2 as a major regulator of patterning during organogenesis of the eye and inner ear and indicate its function in morphogenetic events required for closure of the optic fissure and neural tube.

Animals↗
PubMed1996

Forebrain patterning defects in Small eye mutant mice.

Pax6 is a member of the Pax gene family of transcriptional regulators that exhibits a restricted spatiotemporal expression in the developing central nervous system, eye and nose. Mutations in Pax6 are responsible for inherited malformations in man, rat and mouse. To evaluate the role of Pax6 in forebrain development, we studied in detail mouse Small eye/Pax6 mutant brains. This analysis revealed severe defects in forebrain regions where Pax6 is specifically expressed. The establishment of some expression boundaries along the dorsoventral axis of the secondary prosencephalon is distorted and the specification of several ventral structures and nuclei is abolished. Specifically, the development of the hypothalamo-telencephalic transition zone and the ventral thalamus is distorted. Our detailed analysis included a comparison of the expression of Pax6, Dlx1 and several other genes during embryonic mouse brain development in wild-type and in the mutant Small eye (Sey) brain. The results from the analysis of normal brain development show that the restricted expression of Pax6 and Dlx1 at E12.5 dpc respect domains within the forebrain, consistent with the implications of the prosomeric model for the organisation of the forebrain (L. Puelles and J. L. R. Rubenstein (1993) Trends Neurosci. 16, 472-479). Furthermore, we found an early restriction of Pax6 and Dlx1 expression into presumptive histogenetic fields that correlate with the formation of distinct forebrain structures and nuclei. Our results are discussed in light of changes in adhesive properties in the Sey brain that might control segregation, assembly and cell migration of progenitors of specific forebrain regions.

Animals↗
PubMed1996

Dentate gyrus formation requires Emx2.

Emx 1 and 2 are the murine homologues of the Drosophila empty spiracles gene and based on their expression pattern may be involved in the regional specification of the mammalian forebrain. During early embryogenesis, Emx2 is expressed in the presumptive cerebral cortex and olfactory bulbs and later, in the hippocampus proper and dentate gyrus. The latter are involved in memory processes. To understand the role of Emx2 in vivo, we have mutated the gene in mice. Homozygous embryos die postnatally because of severe urogenital alterations. These mice present cerebral hemispheres with a reduced size and exhibit specific morphological alterations in allocortical structures of the medial wall of the brain. The dentate gyrus is missing and the hippocampus proper is reduced. The medial limbic cortex is also severely shortened. The development of the dentate gyrus is affected at the onset of its formation with defects in the neuroepithelium from which it originates. These findings demonstrate that Emx2 is required for the development of several forebrain structures.

Animals↗
PubMed1996

Two Pax-binding sites are required for early embryonic brain expression of an Engrailed-2 transgene.

The temporally and spatially restricted expression of the mouse Engrailed (En) genes is essential for development of the midbrain and cerebellum. The regulation of En-2 expression was studied using in vitro protein-DNA binding assays and in vivo expression analysis in transgenic mice to gain insight into the genetic events that lead to regionalization of the developing brain. A minimum En-2 1.0 kb enhancer fragment was defined and found to contain multiple positive and negative regulatory elements that function in concert to establish the early embryonic mid-hindbrain expression. Furthermore, the mid-hindbrain regulatory sequences were shown to be structurally and functionally conserved in humans. The mouse paired-box-containing genes Pax-2, Pax-5 and Pax-8 show overlapping expression with the En genes in the developing brain. Significantly, two DNA-binding sites for Pax-2, Pax-5 and Pax-8 proteins were identified in the 1.0 kb En-2 regulatory sequences, and mutation of the binding sites disrupted initiation and maintenance of expression in transgenic mice. These results present strong molecular evidence that the Pax genes are direct upstream regulators of En-2 in the genetic cascade controlling mid-hindbrain development. These mouse studies, taken together with others in Drosophila and zebrafish on the role of Pax genes in controlling expression of En family members, indicate that a Pax-En genetic pathway has been conserved during evolution.

Animals↗
PubMed1996

Dysgenesis of cephalic neural crest derivatives in Pax7-/- mutant mice.

Pax7 is a member of the paired box containing gene family. Its expression pattern suggests a function in cephalic neural crest derivatives, skeletal muscle and central nervous system development. To understand the role of Pax7 during mouse embryogenesis, we used the homologous recombination technique in embryonic stem cells and generated Pax7-/- mice. Homozygous animals are born but die shortly afer weaning. They exhibit malformations in facial structures involving the maxilla and nose. Our analysis suggests that the observed phenotype is due to a cephalic neural crest defect. No obvious phenotype could be detected in the central nervous system and skeletal muscle. Functional redundancy between Pax7 and Pax3 is discussed.

Animals↗
PubMed1996

Inhibition of floor plate differentiation by Pax3: evidence from ectopic expression in transgenic mice.

The Pax genes containing a complete paired-type homeobox are expressed in restricted dorsoventral domains of the undifferentiated neuroepithelium. Their expression respond to signals that pattern the neural tube and which emanate from the notochord, floor plate and overlying ectoderm. In order to determine whether the dorsally restricted Pax3 gene can influence the fate of cells within the neural tube, we produced transgenic mice overexpressing Pax3 in the entire neural tube under the Hoxb-4 promoter/region A enhancer. In two distinct transgenic mouse lines, we observed embryos with abnormal limb, eye, brain and neural tube development. Expression of Pax3 was not sufficient to dorsalize cells from the ventral intermediate zone, which still expressed ventral markers. However, in these embryos, expression of Pax3 at the ventral midline was associated with the absence of floor plate differentiation. Under these conditions, motor neurons still differentiated in the ventral spinal cord, although in fewer numbers.

Animals↗
PubMed1996

Pax and vertebrate development.

Pax genes encode transcription factors sharing a highly conserved sequence, the paired box. Their temporally and spatially restricted expression patterns during development indicate that Pax genes are involved in important steps of nervous system formation. Mutations in Pax genes have been correlated with three mouse mutants (undulated, splotch, small eye) and two human diseases (Waardenburg syndrome, aniridia). Recent data demonstrated that deregulation of Pax genes contributes to tumor formation.

Animals↗