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Biomedical subjects

Alan Bernstein

Publications and source records attributed to Alan Bernstein.

34 records · Page 2Linked to original sources
PubMed2003

Presenilin-1 and presenilin-2 exhibit distinct yet overlapping gamma-secretase activities.

Presenilin-1 (PS1) and presenilin 2 (PS2) are proposed to be transmembrane aspartyl proteases that cleave amyloid precursor protein and Notch. PS1- and PS2-mediated activities were individually characterized using blastocyst-derived (BD) cells and membranes from PS1+/--PS2-/- and PS1-/-PS2+/+ mice, respectively. The relative amounts of PS1 and PS2 in the various BD cells were determined from the intensities of the anti-PS1 and anti-PS2 immunoblot signals by comparison with standard curves using radiolabeled PS1 and PS2 standards produced by in vitro transcription and translation. Cellular membranes from wild type, PS1-/-PS2+/+, and PS1+/--PS2-/- but not PS1-/-PS2-/- BD cells generated the Abeta40 and Abeta42 products from the C100FLAG substrate. PS1-associated gamma-secretase displays considerably higher specific activity than PS2-associated gamma-secretase. Moreover, the PS1+/-PS2-/- BD cells and corresponding membranes exhibited much higher gamma-secretase activity as compared with other BD cells and membranes. The PS1-mediated gamma-secretase activity correlated better with the amount of PS1 that is modifiable by a photoactivated active site-directed gamma-secretase inhibitor rather than total PS1; hence, only a small portion (<14%) of the PS1 in wild-type membranes appears to be engaged in an active gamma-secretase complex. This finding suggests that PS1 may serve other biological functions in addition to that associated with its gamma-secretase activity. Furthermore, the PS1 gamma-secretase complex and the PS2 gamma-secretase complex activities can be discriminated on the basis of their susceptibility to inhibition by a potent gamma-secretase inhibitor. The distinct yet overlapping enzymatic properties of the PS1 gamma-secretase complex and the PS2 gamma-secretase complex imply that these two putative aspartyl class proteases may contribute to different biological processes.

Affinity Labels↗
PubMed2003

A unique pattern of Tie1 expression in the developing murine lung.

The molecular mechanisms responsible for organ-specific differences in vascular development are not well established. Animals lacking the receptor tyrosine kinase Tie1 die of hemorrhage and pulmonary edema. Furthermore, cells lacking Tie1 are excluded from blood vessels of the mature lung. These findings suggest the importance of Tie1 in the pulmonary vasculature. We quantified the organ-specific expression of Tie1 during embryonic and postnatal murine development using both quantitative real-time polymerase chain reaction (PCR) and chemiluminescence employing a tie1.lacZ reporter. In the lung, Tie1 expression increases markedly immediately prior to birth and rises further in the newborn animal, a pattern not found in other organs. Furthermore, expression of Tie1 in the lung is also unique by its persistent increase in the adult animal. This unique pattern of Tie1 gene expression in the embryonic and mature lung supports a distinct role for Tie1 in the development and function of the pulmonary vasculature.

Animals↗
PubMed2003

Requirement of PDZ-containing proteins for cell cycle regulation and differentiation in the mouse lens epithelium.

The roles of PDZ domain-containing proteins such as Dlg and Scrib have been well described for Drosophila; however, their requirement for mammalian development is poorly understood. Here we show that Dlg, Scrib, MAGI1, MAGI3, and MPDZ are expressed in the mouse ocular lens. We demonstrate that the increase in proliferation and defects in cellular adhesion and differentiation observed in epithelia of lenses that express E6, a viral oncoprotein that can bind to several PDZ proteins, including the human homologs of Dlg and Scrib, is dependent on E6's ability to bind these proteins via their PDZ domains. Analyses of lenses from mice carrying an insertional mutation in Dlg (dlg(gt)) show increased proliferation and proliferation in spatially inappropriate regions of the lens, a phenotype similar to that of lenses expressing E6. The results from this study indicate that multiple PDZ domain-containing proteins, including Dlg and Scrib, may be required for maintaining the normal pattern of growth and differentiation in the lens. Furthermore, the phenotypic similarities among the Drosophila dlg mutant, the lenses of dlg(gt) mice, and the lenses of E6 transgenic mice suggest that Dlg may have a conserved function in regulating epithelial cell growth and differentiation across species.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Hematopoietic stem cell and progenitor defects in Sca-1/Ly-6A-null mice.

Despite its wide use as a marker for hematopoietic stem cells (HSCs), the function of stem cell antigen-1 (Sca-1) (also known as lymphocyte activation protein-6A [Ly-6A]) in hematopoiesis remains poorly defined. We have previously established that Sca-1(-/-) T cells develop normally, although they are hyperresponsive to antigen. Here, we report detailed analysis of hematopoiesis in Sca-1-deficient animals. The differentiation potential of Sca-1-null bone marrow was determined from examination of the most mature precursors (culture colony-forming units [CFU-Cs]) to less committed progenitors (spleen CFUs [CFU-Ss]) to long-term repopulating HSCs. Sca-1-null mice are mildly thrombocytopenic with a concomitant decrease in megakaryocytes and their precursors. Bone marrow cells derived from Sca-1(-/-) mice also have decreased multipotential granulocyte, erythroid, macrophage, and megakaryocyte CFU (GEMM-CFU) and CFU-S progenitor activity. Competitive repopulation assays demonstrated that Sca-1(-/-) HSCs are at a competitive disadvantage compared with wild-type HSCs. To further analyze the potential of Sca-1(-/-) HSCs, serial transplantations were performed. While secondary repopulations using wild-type bone marrow completely repopulated Sca-1(-/-) mice, Sca-1(-/-) bone marrow failed to rescue one third of lethally irradiated wild-type mice receiving secondary bone marrow transplants from irradiation-induced anemia and contributed poorly to the surviving transplant recipients. These data strongly suggest that Sca-1 is required for regulating HSC self-renewal and the development of committed progenitor cells, megakaryocytes, and platelets. Thus, our studies conclusively demonstrate that Sca-1, in addition to being a marker of HSCs, regulates the developmental program of HSCs and specific progenitor populations.

Animals↗
PubMed2002

Cytokine signaling and hematopoietic homeostasis are disrupted in Lnk-deficient mice.

The adaptor protein Lnk, and the closely related proteins APS and SH2B, form a subfamily of SH2 domain-containing proteins implicated in growth factor, cytokine, and immunoreceptor signaling. To elucidate the physiological function of Lnk, we derived Lnk-deficient mice. Lnk(-/-) mice are viable, but display marked changes in the hematopoietic compartment, including splenomegaly and abnormal lymphoid and myeloid homeostasis. The in vitro proliferative capacity and absolute numbers of hematopoietic progenitors from Lnk(-/-) mice are greatly increased, in part due to hypersensitivity to several cytokines. Moreover, an increased synergy between stem cell factor and either interleukin (IL)-3 or IL-7 was observed in Lnk(-/-) cells. Furthermore, Lnk inactivation causes abnormal modulation of IL-3 and stem cell factor-mediated signaling pathways. Consistent with these results, we also show that Lnk is highly expressed in multipotent cells and committed precursors in the erythroid, megakaryocyte, and myeloid lineages. These data implicate Lnk as playing an important role in hematopoiesis and in the regulation of growth factor and cytokine receptor-mediated signaling.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Zinc finger protein, Hzf, is required for megakaryocyte development and hemostasis.

Using an expression gene trapping strategy, we recently identified a novel gene, hematopoietic zinc finger (Hzf), which encodes a protein containing three C(2)H(2)-type zinc fingers that is predominantly expressed in megakaryocytes. Here, we have examined the in vivo function of Hzf by gene targeting and demonstrated that Hzf is essential for megakaryopoiesis and hemostasis in vivo. Hzf-deficient mice exhibited a pronounced tendency to rebleed and had reduced alpha-granule substances in both megakaryocytes and platelets. These mice also had large, faintly stained platelets, whereas the numbers of both megakaryocytes and platelets were normal. These results indicate that Hzf plays important roles in regulating the synthesis of alpha-granule substances and/or their packing into alpha-granules during the process of megakaryopoiesis.

Animals↗
PubMed2002

Notch pathway molecules are essential for the maintenance, but not the generation, of mammalian neural stem cells.

Neural stem cells, which exhibit self-renewal and multipotentiality, are generated in early embryonic brains and maintained throughout the lifespan. The mechanisms of their generation and maintenance are largely unknown. Here, we show that neural stem cells are generated independent of RBP-Jkappa, a key molecule in Notch signaling, by using RBP-Jkappa(-/-) embryonic stem cells in an embryonic stem cell-derived neurosphere assay. However, Notch pathway molecules are essential for the maintenance of neural stem cells; they are depleted in the early embryonic brains of RBP-Jkappa(-/-) or Notch1(-/-) mice. Neural stem cells also are depleted in embryonic brains deficient for the presenilin1 (PS1) gene, a key regulator in Notch signaling, and are reduced in PS1(+/-) adult brains. Both neuronal and glial differentiation in vitro were enhanced by attenuation of Notch signaling and suppressed by expressing an active form of Notch1. These data are consistent with a role for Notch signaling in the maintenance of the neural stem cell, and inconsistent with a role in a neuronal/glial fate switch.

Animals↗
PubMed2002

Notch receptor cleavage depends on but is not directly executed by presenilins.

Notch receptors undergo three distinct proteolytic cleavages during maturation and activation. The third cleavage occurs within the plasma membrane and results in the release and translocation of the intracellular domain into the nucleus to execute Notch signaling. This so-called gamma-secretase cleavage is under the control of presenilins, but it is not known whether presenilins themselves carry out the cleavage or whether they act by means of yet-unidentified gamma-secretase(s). In this article, we show that Notch intracellular cleavage in intact cells completely depends on presenilins. In contrast, partial purification of the Notch cleavage activity reveals an activity, which is present only in protein extracts from presenilin-containing cells, and which does not comigrate with presenilin. This finding provides evidence for the existence of a specific Notch-processing activity, which is physically distinct from presenilins. We conclude from these experiments that presenilins are critically required for Notch intracellular cleavage but are not themselves directly mediating the cleavage.

Acetylcysteine↗
PubMed2002

Synaptic glutamate receptor clustering in mice lacking the SH3 and GK domains of SAP97.

Postsynaptic targeting of the Drosophila tumour suppressor discs-large (Dlg) critically depends on its SH3 and GK domains. Here, we asked whether these domains are also involved in subcellular targeting of the mammalian Dlg homolog SAP97 and its interacting partners in CNS cortical neurons by analysing a recently described mouse mutant lacking the SH3 and GK domains of SAP97. Both wildtype and truncated SAP97 were predominantly expressed in perinuclear regions, in a pattern suggesting association with the endoplasmic reticulum. Weaker immunoreactivity was found in neurites colocalizing with both dendritic and axonal markers. As SAP97 has been implicated in the early intracellular processing of the glutamate receptor GluR1, we studied biochemical maturation and subcellular localization of GluR1 in the mutants. Both the glycosylation pattern and synaptic clustering of GluR1 were indistinguishable from wildtype mice. Synaptic clustering of the guanylate kinase domain interacting protein GKAP was also intact. Our data demonstrate that truncation of the SH3 and GK domains of SAP97 in mice does neither change its subcellular distribution nor does it disrupt synaptic structure or protein clustering, as opposed to severe missorting of the respective mutant Dlg protein in Drosophila.

Adaptor Proteins, Signal Transducing↗
PubMed2002

AHSCs: more important than ever in the century of health research.

We are in the midst ofa profound revolution in health research, a revolution being driven by our emerging understanding of the molecular basis of life and human disease. This revolution is creating a century of health research, characterized by the convergence of virtually all disciplines, from mathematics to the social sciences and humanities. This convergence of disciplines is introducing radical changes and opportunities in the discovery and R&D process of health research. Academic health sciences centres (AHSCs) are strategically placed to contribute to, and benefit from, this revolution. To that end AHSCs require exceptional visionary leadership, a commitment to clinical and research excellence, a full appreciation of the complete tripartite mission of AHSCs, and the development of an outward-looking stance that includes the development of public policy. The federal governments clear and sustained commitment to health research, as demonstrated recently by the 15% increase to the Canadian Institutes of Health Research budget, provides an important opportunity for AHSCs to demonstrate their crucial role in both the development of an innovative and cost-effective healthcare system and to Canada's broader social and economic agenda.

Academic Medical Centers↗
PubMed2002

Identification of radiation-responsive genes in vitro using a gene trap strategy predicts for modulation of expression by radiation in vivo.

A large number of genes are known to be responsive to ionizing radiation, and there is strong evidence for the existence of inducible radiation resistance in mammalian cells. We have developed a gene trap insertional mutagenesis strategy to identify novel genes involved in responses to radiation. Using this approach, we have isolated four gene-trap integrations in embryonic stem cells. In three cases (9A, 3E and 9H) the trapped genes are radiation-inducible, and in one (7D) the gene is down-regulated. Sequence analysis of fusion transcripts from three of the integrations indicate one novel gene (3E), the mouse homologue (9A) of a known but uncharacterized human gene that encodes a protein with significant homology to several GTPase-activating proteins and a murine locus, Mym (9H). The embryonic stem cell clone with the 9A insertion was introduced into the mouse germline, and the in vivo expression pattern of 9A was studied in detail. A unique, spatially restricted pattern of expression in embryos and adult animals was observed. There is tissue-specific in vivo induction of the 9A gene in adult mice by radiation. This study demonstrates the potential of the gene trap approach for the identification and functional analysis of novel radiation-regulated genes. Similar strategies may facilitate the discovery and characterization of genes involved in other cellular stress responses.

Amino Acid Sequence↗
PubMed2001

Identification and characterization of presenilin-independent Notch signaling.

Presenilin (PS) proteins control the proteolytic cleavage that precedes nuclear access of the Notch intracellular domain. Here we observe that a partial activation of the HES1 promoter can be detected in PS1/PS2 (PS1/2) double null cells using Notch1 Delta E constructs or following Delta 1 stimulation, despite an apparent abolition of the production and nuclear accumulation of the Notch intracellular domain. PS1/2-independent Notch activation is sensitive to Numblike, a physiological inhibitor of Notch. PS1/2-independent Notch signaling is also inhibited by an active gamma-secretase inhibitor in the low micromolar range and is not inhibited by an inactive analogue, similar to PS-dependent Notch signaling. However, experiments using a Notch1-Gal4-VP16 fusion protein indicate that the PS1/2-independent activity does not release Gal4-VP16 and is therefore unlikely to proceed via an intramembranous cleavage. These data reveal that a novel PS1/2-independent mechanism plays a partial role in Notch signal transduction.

Amyloid Precursor Protein Secretases↗