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Biomedical subjects

P Gruss

Publications and source records attributed to P Gruss.

At least 37 records · Page 2Linked to original sources
PubMed2001

Pax3 acts cell autonomously in the neural tube and somites by controlling cell surface properties.

Pax3 is a member of the paired-box-containing transcription factors. It is expressed in the developing somites, dorsal spinal cord, mesencephalon and neural crest derivatives. Several loss-of-function mutations are correlated with the Splotch phenotype in mice and Waardenburg syndrome in humans. Malformations include a lack of muscle in the limb, a failure of neural tube closure and dysgenesis of numerous neural crest derivatives. In this study we have used embryonic stem (ES) cells to generate a lacZ knock-in into the Pax3 locus. The Pax3 knock-in Splotch allele (Sp(2G)) was used to generate Pax3-deficient ES cells in order to investigate whether, in chimeric embryos, Pax3 is acting cell autonomously in the somites and the neural tube. We found that while Pax3 function is essential for the neuroepithelium and somites, a wild-type environment rescues mutant neural crest cells. In the two affected embryonic tissues, mutant and wild-type cells undergo segregation and do not intermingle. The contribution of mutant cells to the neural tube and the somites displayed temporal differences. All chimeric embryos showed a remarkable contribution of blue cells to the neural tube at all stages analyzed, indicating that the Pax3-deficient cells are not excluded from the neural epithelium while development proceeds. In contrast, this is not true for the paraxial mesoderm. The somite contribution of Pax3(-/-) ES cells becomes less frequent in older embryos as compared to controls with Pax3(+/-) ES cells. We propose that although Pax3 function is related to cell surface properties, its role may differ in various tissues. In fact, apoptosis was found in Pax3-deficient cells of the lateral dermomyotome but not in the neural tube.

Animals↗
PubMed2001

Control of retinal ganglion cell axon growth: a new role for Sonic hedgehog.

Retinal ganglion cell (RGC) axons grow towards the diencephalic ventral midline during embryogenesis guided by cues whose nature is largely unknown. We provide in vitro and in vivo evidence for a novel role of Sonic hedgehog (SHH) as a negative regulator of growth cone movement. SHH suppresses both the number and the length of neurites emerging from the chick retina but not from neural tube or dorsal root ganglia explants, without interfering with their rate of proliferation and differentiation. Similarly, retroviral-mediated ectopic expression of Shh along the chick visual pathway greatly interferes the growth of RGC axons. Upon SHH addition to grown neurites, the intracellular level of cAMP decreases, suggesting that the dampening of growth cone extension mediated by SHH may involve interaction with its receptor Patched which is expressed by RGC. Based on these findings, we propose that Shh expression at the chiasm border defines a constrained pathway within the ventral midline which serves to guide the progression of RGC axons.

Animals↗
PubMed2001

Isolation and characterization of a downstream target of Pax6 in the mammalian retinal primordium.

The transcription factor Pax6 is required for eye morphogenesis in humans, mice and insects, and can induce ectopic eye formation in vertebrate and invertebrate organisms. Although the role of Pax6 has intensively been studied, only a limited number of genes have been identified that depend on Pax6 activity for their expression in the mammalian visual system. Using a large-scale in situ hybridization screen approach, we have identified a novel gene expressed in the mouse optic vesicle. This gene, Necab, encodes a putative cytoplasmic Ca(2+)-binding protein and coincides with Pax6 expression pattern in the neural ectoderm of the optic vesicle and in the forebrain pretectum. Remarkably, Necab expression is absent in both structures in Pax6 mutant embryos. By contrast, the optic vesicle-expressed homeobox genes Rx, Six3, Otx2 and Lhx2 do not exhibit an altered expression pattern. Using gain-of-function experiments, we show that Pax6 can induce ectopic expression of Necab, suggesting that Necab is a direct or indirect transcriptional target of Pax6. In addition, we have found that Necab misexpression can induce ectopic expression of the homeobox gene Chx10, a transcription factor implicated in retina development. Taken together, our results provide evidence that Necab is genetically downstream of Pax6 and that it is a part of a signal transduction pathway in retina development.

Amino Acid Sequence↗
PubMed2000

The murine gene, Traube, is essential for the growth of preimplantation embryos.

Little is known about the genetic control of preimplantation development. We have isolated, characterized, and mutated a previously undescribed mouse gene, Traube (Trb), essential for preimplantation development. Similar protein coding sequences are found in rats, humans, and yeast. The TRB protein contained two amino-terminal acidic domains, a leucine zipper, and three putative nuclear localization signals. The Trb gene was expressed at low levels ubiquitously early in development and became restricted to the liver and the central nervous system from E11.5 onward. Myc-tagged TRB protein was localized to the nucleus, and in a large proportion of the cells to the nucleoli. The Trb mutant embryos halted in development at the compacted morula stage at E2.5. At E3.5 they started to decompact and a day later they disintegrated and died. The observed defect was cell autonomous, as mutant cells failed to participate in the formation of chimeric embryos. The Trb mutant embryos showed a 50% reduction of the total cell number. The mutant embryos exhibited a paucity of ribosomes, polyribosomes, and rough endoplasmic reticulum. This paucity of ribosomes together with the localization of TRB to the nucleoli, the site of ribosome synthesis, suggests that TRB is involved in the synthesis of ribosomes.

Alleles↗
PubMed2000

Pax6 activity in the lens primordium is required for lens formation and for correct placement of a single retina in the eye.

The Pax6 transcription factor plays a key role in ocular development of vertebrates and invertebrates. Homozygosity of the Pax6 null mutation in human and mice results in arrest of optic vesicle development and failure to initiate lens formation. This phenotype obscures the understanding of autonomous function of Pax6 in these tissue components and during later developmental stages. We employed the Cre/loxP approach to inactivate Pax6 specifically in the eye surface ectoderm concomitantly with lens induction. Although lens induction occurred in the mutant, as indicated by Sox2 up-regulation in the surface ectoderm, further development of the lens was arrested. Hence, Pax6 activity was found to be essential in the specified ectoderm for lens placode formation. Furthermore, this mutant model allowed us for the first time to address in vivo the development of a completely normal retina in the absence of early lens structures. Remarkably, several independent, fully differentiated neuroretinas developed in a single optic vesicle in the absence of a lens, demonstrating that the developing lens is not necessary to instruct the differentiation of the neuroretina but is, rather, required for the correct placement of a single retina in the eye.

Animals↗
PubMed2000

Pax6 modulates the dorsoventral patterning of the mammalian telencephalon.

The Pax6 gene encodes a transcription factor with a restricted expression in the ventricular zone of the pallium and subpallium. We tested whether the function of Pax6 is necessary for the correct patterning and morphogenesis of the vertebrate telencephalon. Homozygous embryos of the Pax6/Small eye mutant lack functional PAX6 protein because of a point mutation of the gene. In the mutant Small eye embryos we detected a ventralization of the molecular patterning of the telencephalon at two borders, the pallium/subpallium and the lateral/medial ganglionic eminence. The results indicate that Pax6 controls the lateral limit of the expression of Nkx2.1, Shh, and Lhx6 in the prechordal neural tube, the telencephalon. This finding is in agreement with previous studies and supports a model for a common genetic mechanism for modulation of the dorsoventral patterning of the prechordal and epichordal CNS. The pattern defects caused by the loss of Pax6 function result in multiple morphological abnormalities in the Small eye brain: dysgenesis of the piriform, insular, and lateral cortices, the claustrum-endopiriform nucleus, and a failure in the differentiation of a subpopulation of the cortical precursors. Together the results demonstrate that Pax6 has an essential role for the modulation of the dorsoventral patterning of the embryonic telencephalon, influencing thereby the forebrain morphogenesis.

Animals↗
PubMed2000

Pax7 is required for the specification of myogenic satellite cells.

The paired box transcription factor Pax7 was isolated by representational difference analysis as a gene specifically expressed in cultured satellite cell-derived myoblasts. In situ hybridization revealed that Pax7 was also expressed in satellite cells residing in adult muscle. Cell culture and electron microscopic analysis revealed a complete absence of satellite cells in Pax7(-/-) skeletal muscle. Surprisingly, fluorescence-activated cell sorting analysis indicated that the proportion of muscle-derived stem cells was unaffected. Importantly, stem cells from Pax7(-/-) muscle displayed almost a 10-fold increase in their ability to form hematopoietic colonies. These results demonstrate that satellite cells and muscle-derived stem cells represent distinct cell populations. Together these studies suggest that induction of Pax7 in muscle-derived stem cells induces satellite cell specification by restricting alternate developmental programs.

Age Factors↗
PubMed2000

Reduced Pax2 gene dosage increases apoptosis and slows the progression of renal cystic disease.

The murine cpk mouse develops a rapid-onset polycystic kidney disease (PKD) with many similarities to human PKD. During kidney development, the transcription factor Pax2 is required for the specification and differentiation of the renal epithelium. In humans, Pax2 is also expressed in juvenile cystic kidneys where it correlates with cell proliferation. In this report, Pax2 expression is demonstrated in the cystic epithelium of the mouse cpk kidneys. To assess the role of Pax2 during the development of polycystic kidney disease, the progression of renal cysts was examined in cpk mutants carrying one or two alleles of Pax2. Reduced Pax2 gene dosage resulted in a significant inhibition of renal cyst growth while maintaining more normal renal structures. The inhibition of cyst growth was not due to reduced proliferation of the cystic epithelium, rather to increased cell death in the Pax2 heterozygotes. Increased apoptosis with reduced Pax2 gene dosage was also observed in normal developing kidneys. Thus, increased cell death is an integral part of the Pax2 heterozygous phenotype and may be the underlying cause of Pax gene haploinsufficiency. That the cystic epithelium requires Pax2 for continued expansion underscores the embryonic nature of the renal cystic cells and may provide new insights toward growth suppression strategies.

Animals↗
PubMed2000

Pax genes and the differentiation of hormone-producing endocrine cells in the pancreas.

Despite the pivotal role of the pancreas in hormonally-regulated pathways in the body, e.g. glucose homeostasis, the genetic mechanisms defining it have for many years remained largely enigmatic. After years out of the spotlight, pancreas development has once again come to centre stage. To a large extent, this is due to recent advances made through the detailed analysis of transgenic mice which have been engineered to carry mutations in specific developmental control genes. This review specifically focuses on the specification of the endocrine pancreas lineage and in particular on the role of the developmental control genes Pax4 and Pax6 in the generation of specific endocrine cell types. The comparison of various phenotypes of different mouse mutants affecting endocrine development supports a model in which Pax4 and Pax6 are required for the differentiation of certain endocrine cell lineages and implies a potential for acting at different levels of endocrine development.

Animals↗
PubMed2000

Cloning and expression of xSix3, the Xenopus homologue of murine Six3.

The vertebrate Six family of transcription factor genes are homologues of the fruitfly gene sine oculis (so). Human, murine, avian and fish (medaka, zebrafish) homologues have recently been cloned. We report the cloning and developmental pattern of expression of xSix3, the Xenopus laevis homologue of Six3. In addition, we have compared all the known sequences of vertebrate Six3 genes. xSix3 is very homologous to Six3 in other vertebrates in terms of amino acid sequence. The reported developmental pattern of expression of Six3 in chick and mouse includes not only the developing eyes and the ventral diencephalic tissue between them, but also a large, sagittally-oriented telencephalic region. The distribution of xSix3, however, is virtually restricted to the eyes and ventral diencephalon, showing only a very small territory of expression in the telencephalon.

Amino Acid Sequence↗
PubMed2000

The lack of Emx2 causes impairment of Reelin signaling and defects of neuronal migration in the developing cerebral cortex.

Neocorticogenesis in mice homozygous for an Emx2 null allele is the topic of this article. The development of both main components of neocortex, primordial plexiform layer derivatives and cortical plate, was analyzed, paying special attention to radial migration of neurons forming the cortical plate. The products of the Reelin gene, normally playing a key role in orchestrating radial migration of these neurons, display normal distribution at the beginning of the cortical neuronogenesis but are absent in the neocortical marginal zone of the mutant mice at the time when the cortical plate is laid down. As a consequence, the development of radial glia is impaired, and neurons making up the cortical plate display abnormal migration patterns. In addition, restricted defects along the rostrocaudal and the mediolateral axes are present in the subplate, suggesting an Emx2-specific role in priming the proper development of this layer.

Animals↗
PubMed2000

Identification of a novel mouse Iroquois homeobox gene, Irx5, and chromosomal localisation of all members of the mouse Iroquois gene family.

The Drosophila genes of the Iroquois-Complex encode homeodomain containing transcription factors that positively regulate the activity of certain proneural Achaete/Scute-C (AS-C) genes during the formation of external sensory organs (J. L. Gomez-Skarmeta and J. Modolell, EMBO J 17:181-190, 1996). Previously, we have identified three highly-related genes of the mouse Iroquois gene family that exert specific expression patterns in the central nervous system (A. Bosse et al., Mech Dev 69:169-181, 1997). In the present paper, we report the identification of a novel member of the Iroquois gene family, Irx5, that shows a restricted spatio/temporal expression during early mouse embryogenesis, distinct from the expression of Irx1-3. An extensive sequence analysis of 20 Iroquois-like genes from seven organisms reveals a high conservation of the homeodomain. Phylogenetic tree reconstruction showed a clustering of the members of the Iroquois gene family into groups of orthologous genes. Together, with the data obtained from the chromosomal mapping analysis, the results indicate that these genes have appeared in vertebrates during evolution as a result of gene duplication.

Animals↗
PubMed2000

Perinatal lethality of microtubule-associated protein 1B-deficient mice expressing alternative isoforms of the protein at low levels.

Microtubule-associated protein 1B (MAP1B) has been implicated in axogenesis in cultured cells. To gain insight into the functions that MAP1B plays in vivo, we analyzed a strain of Map1B mutant mice generated by a gene trapping approach. Homozygous mice die on the first day after birth, probably due to a severe abnormal development of the nervous system. They present alterations in the structure of several brain regions. The normal Map1B gene yields different protein isoforms from alternatively spliced transcripts. The smaller isoforms were present in wild type, hetero-, and homozygous mice, but their expression was higher in the mutants than in the wild-type. Moreover, trace amounts of MAP1B protein were also observed in Map1B homozygous mutants, indicating an alternative splicing around the gene trap insertion. Thus, the Map1B gene trapped mutation reported in this work did not generated a null mutant, but a mouse with a drastic deficiency in MAP1B expression. Analyses of these mice indicate the presence of several neural defects and suggest the participation of MAP1B in neuronal migration.

Alternative Splicing↗
PubMed2000

Transcription factor expression during pancreatic islet regeneration.

Recent studies by a number of laboratories have identified transcription factors that are involved in pancreatic development. Indeed, marked abnormalities in pancreatic development result from deficiencies in these molecules, which include, among others, PDX-1, islet-1 (Isl-1), and Pax-6. These studies have prompted us to evaluate the expression of Isl-1 and Pax-6 in the pancreas of the interferon-gamma (IFNgamma) transgenic mouse, which exhibits new islet growth and expansion of ducts throughout the life of the animal. We have previously demonstrated that PDX-1 is strikingly expressed in the ducts of the IFNgamma transgenic mouse. This latter observation compelled us to examine expression of hepatocyte nuclear factor-3beta (HNF3beta), which mediates PDX-1 gene transcription, in the IFNgamma transgenic pancreas as well. As a result of these studies, we now demonstrate marked expression of these transcription factors in the pancreatic ducts of IFNgamma transgenic mice. These data suggest a role for these transcription factors during pancreatic regeneration in the IFNgamma transgenic mouse.

Animals↗
PubMed2000

Expression of PTTG and prc1 genes during telencephalic neurogenesis.

We present the first time/space analysis using in situ hybridization for PTTG and prc1 genes during development of the mouse telencephalon. During the stages E11.5-E13.5 PTTG and prc1 are expressed in most tissues of the embryo. Within the telencephalon, PTTG and prc1 are found exclusively inside of the ventricular zone (VZ). The intensity of the expression of both genes in the ventricular zone reaches its peak by E15.5. Expression starts to decrease by E18.5, it is still visible at least up to P2 and not detectable in the adult brains. Expression of the prc1 gene, but not that of the PTTG, is also found in the mitoticaly active cells outside of the VZ within the telencephalon. Most of the cells expressing the PTTG gene were found in the lower part of the ventricular zone suggesting that the level of PTTG mRNA is regulated during different phases of the mitotic cycle.

Animals↗
PubMed2000

Expanded retina territory by midbrain transformation upon overexpression of Six6 (Optx2) in Xenopus embryos.

During vertebrate eye development, the expression of the homeobox gene Six6 is restricted to the neural retina and is initiated later than Rx and Pax6 in the presumptive retina field. We show here that overexpression of mouse Six6 in Xenopus embryos can induce transformation of competent tissue of the anterior neural plate into retinal tissue. In Six6 injected embryos, the molecular identity of the presumptive midbrain and rostral hindbrain regions was lost, as shown by the absence of XEn-2 and Xpax2 expression, being replaced by the ectopic expression of the retinal markers Xpax6 and Xrx. When allowed to grow further, Six6 injected embryos developed ectopic eye-like structures in the rostral brain and showed a transformation of the midbrain into retina. Similar results were obtained upon overexpression of Six3 or Xsix3, revealing a possible redundance of Six3 and Six6 activities. Taken together, results obtained suggest that during normal retina development, the relatively late expressed Six6 gene becomes part of a network of retinal homeobox genes that are linked together by positive feedback loops. Furthermore, our results demonstrate that the primitive neural ectoderm of the future midbrain and rostral hindbrain is competent to form retinal tissue.

Animals↗
PubMed2000

The novel PCR-based technique of genotyping applied to identification of scrambler mutation in mice.

For a wide range of research purposes it is necessary to perform genotyping, i.e. to test which alleles, each corresponding to a particular locus, are present in the individual genome. Here we suggest a protocol of genotyping for mice with scrambler (scm) mutation. This mutation results in the aberrant splicing of the corresponding mRNA and affects the expression of mdab1 protein. Traditional approaches using genomic Southern hybridization or PCR with specific primers are not suitable for the genotyping of scm because of the lack of comprehensive information on the organization of the gene and on the presence of repetitive sequences in the known region. Here we propose a quick and highly reproducible method for genotyping scm mutant mice. The protocol consists of the following steps: isolation of genomic DNA, digestion with the restriction endonuclease, anchoring of resulting fragments with the adapter, and PCR amplification using adapter-specific primers. The final product of PCR amplification has a characteristic length which is different for the wt (wild type) and scm alleles. Thus, the characteristic pattern of bands obtained for each individual mouse specimen serves as criteria for the presence of wild type and/or scm allele. We believe that this approach could have wider application. The protocol can be easily modified and used as a convenient tool for identification of other genomic defects including those artificially introduced into genome by knockout or gene-trap techniques.

Animals↗