Biomedical subjects

Lino Tessarollo

Publications and source records attributed to Lino Tessarollo.

At least 37 records · Page 2Linked to original sources

PubMed2004

Neurotrophins in the ear: their roles in sensory neuron survival and fiber guidance.

We review the history of neurotrophins in the ear and the current understanding of the function of neurotrophins in ear innervation, development and maintenance. Only two neurotrophins, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), and their receptors, tyrosine kinase B (TrkB) and TrkC, appear to provide trophic support for inner ear sensory neuron afferents. Mice lacking either both receptors or both ligands lose essentially all sensory innervation of targets in the vestibular and auditory systems of the ear. Analyzes of single mutants show less complete and differential effects on innervation of the different sensory organs within the ear. BDNF and TrkB are most important for survival of vestibular sensory neurons whereas NT-3 and TrkC are most important for survival of cochlear sensory neurons. The largely complementary roles of BDNF to TrkB and NT-3 to TrkC signaling do not reflect specific requirements for innervation of different classes of hair cells. Most neurons express both receptors. Instead, the losses observed in single mutants are related to the spatio-temporal expression pattern of the two neurotrophins. In an area where only one neurotrophin is expressed at a particular time in development, the other neurotrophin is not present to compensate for this absence, resulting in death of neurons innervating that region. Decisive evidence for this suggestion is provided by transgenic mice in which the BDNF coding region has been inserted into the NT-3 gene, resulting in expression of BDNF instead of NT-3. The expression of BDNF in the spatio-temporal pattern of NT-3 results in survival of almost all neurons that are normally lost in the NT-3 mutant. Thus, BDNF and NT-3 have a high level of functional equivalence for inner ear sensory neuron survival. Further analysis of the patterns of afferent fiber losses in mutations that do not develop differentiated hair cells shows that the expression of neurotrophins is remarkably strong and can support afferent innervation. Indeed, BDNF may be one of the earliest genes expressed selectively in hair cells and it appears to be regulated somewhat independently of the genes needed for hair cell differentiation.

Animals↗

PubMed2004

Telomere-associated protein TIN2 is essential for early embryonic development through a telomerase-independent pathway.

TIN2 is a negative regulator of telomere elongation that interacts with telomeric DNA repeat binding factor 1 (TRF1) and affects telomere length by a telomerase-dependent mechanism. Here we show that inactivation of the mouse TRF1-interacting protein 2 (TIN2) gene results in early embryonic lethality. We further observed that the embryonic lethality of TIN2 mutant mice was not affected by inactivation of the telomerase reverse transcriptase gene, indicating that embryonic lethality is not the result of telomerase-dependent changes in telomere length or function. Our findings suggest that TIN2 has a role independent of telomere length regulation that is essential for embryonic development and cell viability.

Animals↗

PubMed2004

Expression of telomerase RNA template, but not telomerase reverse transcriptase, is limiting for telomere length maintenance in vivo.

Telomerase consists of two essential components, the telomerase RNA template (TR) and telomerase reverse transcriptase (TERT). The haplo-insufficiency of TR was recently shown to cause one form of human dyskeratosis congenita, an inherited disease marked by abnormal telomere shortening. Consistent with this finding, we recently reported that mice heterozygous for inactivation of mouse TR exhibit a similar haplo-insufficiency and are deficient in the ability to elongate telomeres in vivo. To further assess the genetic regulation of telomerase activity, we have compared the abilities of TR-deficient and TERT-deficient mice to maintain or elongate telomeres in interspecies crosses. Homozygous TERT knockout mice had no telomerase activity and failed to maintain telomere length. In contrast, TERT(+/-) heterozygotes had no detectable defect in telomere elongation compared to wild-type controls, whereas TR(+/-) heterozygotes were deficient in telomere elongation. Levels of TERT mRNA in heterozygous mice were one-third to one-half the levels expressed in wild-type mice, similar to the reductions in telomerase RNA observed in TR heterozygotes. These findings indicate that both TR and TERT are essential for telomere maintenance and elongation but that gene copy number and transcriptional regulation of TR, but not TERT, are limiting for telomerase activity under the in vivo conditions analyzed.

Animals↗

PubMed2004

Ablation of TrkA function in the immune system causes B cell abnormalities.

The nerve growth factor (NGF) receptor TrkA is widely expressed in non-neural tissues suggesting pleiotropic functions outside the nervous system. Based on pharmacological and immuno-depletion experiments, it has been hypothesized that NGF plays an important role in the normal development and function of the immune system. However, attempts to unravel these functions by conventional gene targeting in mice have been hampered by the early postnatal lethality caused by null mutations. We have developed a novel 'reverse conditional' gene targeting strategy by which TrkA function is restored specifically in the nervous system. Mice lacking TrkA in non-neuronal tissues are viable and appear grossly normal. All major immune system cell populations are present in normal numbers and distributions. However, mutant mice have elevated serum levels of certain immunoglobulin classes and accumulate B1 cells with aging. These data, confirmed in a classical reconstitution model using embryonic fetal liver from TrkA-null mice, demonstrate that endogenous NGF modulates B cell development through TrkA in vivo. Furthermore, they demonstrate that many of the dramatic effects previously reported by pharmacological or immuno-depletion approaches do not reflect physiological developmental roles of TrkA in the immune system.

Animals↗

PubMed2003

Hypermethylation of the Ink4b locus in murine myeloid leukemia and increased susceptibility to leukemia in p15(Ink4b)-deficient mice.

The Ink4b gene (Cdkn2b) encodes p15(Ink4b), a cyclin-dependent kinase inhibitor. It has been implicated in playing a role in the development of acute myeloid leukemia (AML) in man, since it is hypermethylated with high frequency. We provide evidence that the gene is a tumor suppressor for myeloid leukemia in mice. The evidence is twofold: (1) retrovirus-induced myeloid leukemias of the myelomonocytic phenotype were found to have hypermethylation of the 5' CpG island of the Ink4b gene, and this could be correlated with reduced mRNA expression, as demonstrated by TaqMan real-time PCR. p15(Ink4b) mRNA expression in a leukemia cell line, with hypermethylation at the locus, was induced following treatment with 5-aza-2'-deoxycytidine. (2) Targeted deletion of one allele in mice by removal of exon 2 increases their susceptibility to retrovirus-induced myeloid leukemia. Mice deficient in both alleles were not more susceptible to myeloid disease than those deficient in one allele, raising the possibility that there are opposing forces related to the development of myeloid leukemia in Ink4b null mice.

Animals↗

PubMed2003

BRCA2 deficiency in mice leads to meiotic impairment and infertility.

The role of Brca2 in gametogenesis has been obscure because of embryonic lethality of the knockout mice. We generated Brca2-null mice carrying a human BAC with the BRCA2 gene. This construct rescues embryonic lethality and the mice develop normally. However, there is poor expression of the transgene in the gonads and the mice are infertile, allowing examination of the function of BRCA2 in gametogenesis. BRCA2-deficient spermatocytes fail to progress beyond the early prophase I stage of meiosis. Observations on localization of recombination-related and spermatogenic-related proteins suggest that the spermatocytes undergo early steps of recombination (DNA double strand break formation), but fail to complete recombination or initiate spermiogenic development. In contrast to the early meiotic prophase arrest of spermatocytes, some mutant oocytes can progress through meiotic prophase I, albeit with a high frequency of nuclear abnormalities, and can be fertilized and produce embryos. Nonetheless, there is marked depletion of germ cells in adult females. These studies provide evidence for key roles of the BRCA2 protein in mammalian gametogenesis and meiotic success.

Animals↗

PubMed2003

Corpus callosum deficiency in transgenic mice expressing a truncated ephrin-A receptor.

The A-class of the erythropoietin-producing hepatocellular carcinoma cell-derived (EphA) tyrosine kinase receptors and their ligands, the A-ephrins, play critical roles in the specification of topographic axon projection maps during development. In this study, the role of the EphA subfamily in callosal projections was investigated using transgenic mice expressing a kinase deletion mutant of EphA5. In approximately half of these transgenic mice, cerebral cortical neurons in various cortical regions (primary and secondary somatosensory cortices and frontal as well as visual areas) failed to project to the contralateral cortex. When commissural axons were examined with DiI labeling, few callosal fibers were found to traverse the midline in both the adult and neonatal transgenic mice. This defect in callosal development correlates with the expression of the transgene, because neurons in the superficial layers of the motor cortex, where transgene expression is low, show normal contralateral projection through the corpus callosum. In addition, multiple EphA receptors are expressed in callosal neurons and ephrin-A5 stimulates neurite outgrowth of callosal neurons in vitro. The midline glia structures important for callosal axon midline crossing appear normal in the transgenic mice, suggesting that the defects are unrelated to defective guidance structures at the midline. These observations suggest critical functions for EphA receptor in establishing callosal connections during brain development.

Agenesis of Corpus Callosum↗

PubMed2003

Cdk2 knockout mice are viable.

BACKGROUND: Cyclin-dependent kinases (Cdks) and their cyclin regulatory subunits control cell growth and division. Cdk2/cyclin E complexes are thought to be required because they phosphorylate the retinoblastoma protein and drive cells through the G1/S transition into the S phase of the cell cycle. In addition, Cdk2 associates with cyclin A, which itself is essential for cell proliferation during early embryonic development. RESULTS: In order to study the functions of Cdk2 in vivo, we generated Cdk2 knockout mice. Surprisingly, these mice are viable, and therefore Cdk2 is not an essential gene in the mouse. However, Cdk2 is required for germ cell development; both male and female Cdk2(-/-) mice are sterile. Immunoprecipitates of cyclin E1 complexes from Cdk2(-/-) spleen extracts displayed no activity toward histone H1. Cyclin A2 complexes were active in primary mouse embryonic fibroblasts (MEFs), embryo extracts and in spleen extracts from young animals. In contrast, there was little cyclin A2 kinase activity in immortalized MEFs and spleen extracts from adult animals. Cdk2(-/-) MEFs proliferate but enter delayed into S phase. Ectopic expression of Cdk2 in Cdk2(-/-) MEFs rescued the delayed entry into S phase. CONCLUSIONS: Although Cdk2 is not an essential gene in the mouse, it is required for germ cell development and meiosis. Loss of Cdk2 affects the timing of S phase, suggesting that Cdk2 is involved in regulating progression through the mitotic cell cycle.

Animals↗

PubMed2003

Hepatic vascular tumors, angiectasis in multiple organs, and impaired spermatogenesis in mice with conditional inactivation of the VHL gene.

von Hippel-Lindau (VHL) disease is a multisystem inherited cancer syndrome characterized by the development of highly vascular tumors including hemangioblastomas of the retina and central nervous system, pheochromocytomas, and clear cell renal carcinoma, which result from somatic inactivation of the wild-type VHL allele in cells harboring a germ-line VHL mutation. Homozygous inactivation of the VHL gene in mice resulted in embryonic lethality. To produce a mouse model that closely mimics human VHL disease and avoids embryonic lethality, we used Cre/lox site-specific recombination technology. We generated mice carrying conditional VHL alleles and a cre transgene under the control of the human beta-actin promoter, which directs cre expression in a mosaic pattern in multiple organs. VHL(f/d)/Cre mice developed multiple, hepatic hemangiomas that led to premature death, as well as angiectasis and angiogenesis in multiple organs. Interestingly, testes of male VHL(f/d)/Cre mice were unusually small with severely reduced sperm count resulting in infertility. Loss of pVHL function in this VHL conditional knockout mouse model results in an extensive abnormal vascular phenotype in multiple mouse organs, which will provide a useful animal model for testing potential antiangiogenic therapies for VHL disease treatment. Importantly, the phenotypic defects in sperm development observed in these mice support a novel role for VHL in spermatogenesis. This VHL conditional knockout mouse model will provide an in vivo system for studying the functional requirement of the VHL gene in reproductive biology.

Actins↗

PubMed2003

Bcl11a is essential for normal lymphoid development.

Bcl11a (also called Evi9) functions as a myeloid or B cell proto-oncogene in mice and humans, respectively. Here we show that Bcl11a is essential for postnatal development and normal lymphopoiesis. Bcl11a mutant embryos lack B cells and have alterations in several types of T cells. Phenotypic and expression studies show that Bcl11a functions upstream of the transcription factors Ebf1 and Pax5 in the B cell pathway. Transplantation studies show that these defects in Bcl11a mutant mice are intrinsic to fetal liver precursor cells. Mice transplanted with Bcl11a-deficient cells died from T cell leukemia derived from the host. Thus, Bcl11a may also function as a non-autonomous T cell tumor suppressor gene.

Animals↗

PubMed2003

Selective removal of the selenocysteine tRNA [Ser]Sec gene (Trsp) in mouse mammary epithelium.

Mice homozygous for an allele encoding the selenocysteine (Sec) tRNA [Ser]Sec gene (Trsp) flanked by loxP sites were generated. Cre recombinase-dependent removal of Trsp in these mice was lethal to embryos. To investigate the role of Trsp in mouse mammary epithelium, we deleted this gene by using transgenic mice carrying the Cre recombinase gene under control of the mouse mammary tumor virus (MMTV) long terminal repeat or the whey acidic protein promoter. While both promoters target Cre gene expression to mammary epithelium, MMTV-Cre is also expressed in spleen and skin. Sec tRNA [Ser]Sec amounts were reduced by more than 70% in mammary tissue with either transgene, while in skin and spleen, levels were reduced only with MMTV-Cre. The selenoprotein population was selectively affected with MMTV-Cre in breast and skin but not in the control tissue, kidney. Moreover, within affected tissues, expression of specific selenoproteins was regulated differently and often in a contrasting manner, with levels of Sep15 and the glutathione peroxidases GPx1 and GPx4 being substantially reduced. Expression of the tumor suppressor genes BRCA1 and p53 was also altered in a contrasting manner in MMTV-Cre mice, suggesting greater susceptibility to cancer and/or increased cell apoptosis. Thus, the conditional Trsp knockout mouse allows tissue-specific manipulation of Sec tRNA and selenoprotein expression, suggesting that this approach will provide a useful tool for studying the role of selenoproteins in health.

Alleles↗

PubMed2002

Heterozygous knock-out mice for brain-derived neurotrophic factor show a pathway-specific impairment of long-term potentiation but normal critical period for monocular deprivation.

Genetic deletion of a single allele of the BDNF gene affects hippocampal LTP and causes several behavioral phenotypes, including deficits in spatial learning. In the developing visual cortex, overexpression of BDNF accelerates the time course of the critical period for monocular deprivation (MD), and exogenous administration of BDNF alters the outcome of MD. We asked whether reduced levels of BDNF could affect visual cortex plasticity by studying long-term potentiation (LTP) induction and the effects of MD in heterozygous BDNF knock-out mice. We found that theta burst stimulation that induced LTP in the layer IV-III pathway of wild-type (wt) mice caused only a transient potentiation in BDNF+/- mice, and that this potentiation vanished in 25 min. In contrast, LTP elicited by stimulation of the white matter (WM), a form of LTP that can be induced only during the critical period, occurred normally in wt and BDNF+/- mice. The effects of MD during the critical period were similar in wt and BDNF+/- mice, indicating that layer IV-evoked, layer III LTP is not required for ocular dominance plasticity. We then asked whether reduction of cortical BDNF levels could prolong the critical period for MD and for the WM-evoked, layer III LTP induction. We found that in adult BDNF+/- mice, WM-evoked, layer III LTP was not inducible, and that the critical period for MD terminated normally. We conclude that deletion of one copy of the BDNF gene selectively impairs LTP of the layer IV-III pathway but does not alter ocular dominance plasticity.

Animals↗

PubMed2002

Synaptic defects in ataxia mice result from a mutation in Usp14, encoding a ubiquitin-specific protease.

Mice that are homozygous with respect to a mutation (ax(J)) in the ataxia (ax) gene develop severe tremors by 2-3 weeks of age followed by hindlimb paralysis and death by 6-10 weeks of age. Here we show that ax encodes ubiquitin-specific protease 14 (Usp14). Ubiquitin proteases are a large family of cysteine proteases that specifically cleave ubiquitin conjugates. Although Usp14 can cleave a ubiquitin-tagged protein in vitro, it is unable to process polyubiquitin, which is believed to be associated with the protein aggregates seen in Parkinson disease, spinocerebellar ataxia type 1 (SCA1; ref. 4) and gracile axonal dystrophy (GAD). The physiological substrate of Usp14 may therefore contain a mono-ubiquitin side chain, the removal of which would regulate processes such as protein localization and protein activity. Expression of Usp14 is significantly altered in ax(J)/ax(J) mice as a result of the insertion of an intracisternal-A particle (IAP) into intron 5 of Usp14. In contrast to other neurodegenerative disorders such as Parkinson disease and SCA1 in humans and GAD in mice, neither ubiquitin-positive protein aggregates nor neuronal cell loss is detectable in the central nervous system (CNS) of ax(J) mice. Instead, ax(J) mice have defects in synaptic transmission in both the central and peripheral nervous systems. These results suggest that ubiquitin proteases are important in regulating synaptic activity in mammals.

Alleles↗

PubMed2002

Mistargeting hippocampal axons by expression of a truncated Eph receptor.

Topographic mapping of axon terminals is a general principle of neural architecture that underlies the interconnections among many neural structures. The Eph family tyrosine kinase receptors and their ligands, the ephrins, have been implicated in the formation of topographic projection maps. We show that multiple Eph receptors and ligands are expressed in the hippocampus and its major subcortical projection target, the lateral septum, and that expression of a truncated Eph receptor in the mouse brain results in a pronounced alteration of the hippocamposeptal topographic map. Our observations provide strong support for a critical role of Eph family guidance factors in regulating ontogeny of hippocampal projections.

Animals↗

PubMed2002

Brain-derived neurotrophic factor is essential for opiate-induced plasticity of noradrenergic neurons.

Chronic opiate exposure induces numerous neurochemical adaptations in the noradrenergic system, including upregulation of the cAMP-signaling pathway and increased expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. These adaptations are thought to compensate for opiate-mediated neuronal inhibition but also contribute to physical dependence, including withdrawal after abrupt cessation of drug exposure. Little is known about molecules that regulate the noradrenergic response to opiates. Here we report that noradrenergic locus ceruleus (LC) neurons of mice with a conditional deletion of BDNF in postnatal brain respond to chronic morphine treatment with a paradoxical downregulation of cAMP-mediated excitation and lack of dynamic regulation of TH expression. This was accompanied by a threefold reduction in opiate withdrawal symptoms despite normal antinociceptive tolerance in the BDNF-deficient mice. Although expression of TrkB, the receptor for BDNF, was high in the LC, endogenous BDNF expression was absent there and in the large majority of other noradrenergic neurons. Therefore, a BDNF-signaling pathway originating from non-noradrenergic sources is essential for opiate-induced molecular adaptations of the noradrenergic system.

Animals↗

PubMed2002

Genomic instability in mice lacking histone H2AX.

Higher order chromatin structure presents a barrier to the recognition and repair of DNA damage. Double-strand breaks (DSBs) induce histone H2AX phosphorylation, which is associated with the recruitment of repair factors to damaged DNA. To help clarify the physiological role of H2AX, we targeted H2AX in mice. Although H2AX is not essential for irradiation-induced cell-cycle checkpoints, H2AX-/- mice were radiation sensitive, growth retarded, and immune deficient, and mutant males were infertile. These pleiotropic phenotypes were associated with chromosomal instability, repair defects, and impaired recruitment of Nbs1, 53bp1, and Brca1, but not Rad51, to irradiation-induced foci. Thus, H2AX is critical for facilitating the assembly of specific DNA-repair complexes on damaged DNA.

Amino Acid Sequence↗

PubMed2002

Mitf and Tfe3, two members of the Mitf-Tfe family of bHLH-Zip transcription factors, have important but functionally redundant roles in osteoclast development.

The Mitf-Tfe family of basic helix-loop-helix-leucine zipper (bHLH-Zip) transcription factors encodes four family members: Mitf, Tfe3, Tfeb, and Tfec. In vitro, each protein in the family can bind DNA as a homo- or heterodimer with other family members. Mutational studies in mice have shown that Mitf is essential for melanocyte and eye development, whereas Tfeb is required for placental vascularization. Here, we uncover a role for Tfe3 in osteoclast development, a role that is functionally redundant with Mitf. Although osteoclasts seem normal in Mitf or Tfe3 null mice, the combined loss of the two genes results in severe osteopetrosis. We also show that Tfec mutant mice are phenotypically normal, and that the Tfec mutation does not alter the phenotype of Mitf, Tfeb, or Tfe3 mutant mice. Surprisingly, our studies failed to identify any phenotypic overlap between the different Mitf-Tfe mutations. These results suggest that heterodimeric interactions are not essential for Mitf-Tfe function in contrast to other bHLH-Zip families like Myc/Max/Mad, where heterodimeric interactions seem to be essential.

Alleles↗

PubMed2002

Cdc25b phosphatase is required for resumption of meiosis during oocyte maturation.

In a wide variety of animal species, oocyte maturation is arrested temporarily at prophase of meiosis I (ref. 1). Resumption of meiosis requires activation of cyclin-dependent kinase-1 (CDK1, p34cdc2), one component of maturation-promoting factor (MPF). The dual specificity phosphatases Cdc25a, Cdc25b and Cdc25c are activators of cyclin-dependent kinases; consequently, they are postulated to regulate cell-cycle progression in meiosis and mitosis as well as the DNA-damage response. We generated Cdc25b-deficient (Cdc25b-/-) mice and found that they are viable. As compared with wildtype cells, fibroblasts from Cdc25b-/- mice grew vigorously in culture and arrested normally in response to DNA damage. Female Cdc25b-/- mice were sterile, and Cdc25b-/- oocytes remained arrested at prophase with low MPF activity. Microinjection of wildtype Cdc25b mRNA into Cdc25b-/- oocytes caused activation of MPF and resumption of meiosis. Thus, Cdc25b-/- female mice are sterile because of permanent meiotic arrest resulting from the inability to activate MPF. Cdc25b is therefore essential for meiotic resumption in female mice. Mice lacking Cdc25b provide the first genetic model for studying the mechanisms regulating prophase arrest in vertebrates.

Animals↗