Slow cycling intestinal stem cell and Paneth cell responses to Trichinella spiralis infection.

There is limited information regarding responses by slow cycling stem cells during T. spiralis-induced T-cell mediated intestinal inflammation and how such responses may relate to those of Paneth cells. Transgenic mice, in which doxycycline induces expression of histone 2B (H2B)-green fluorescent protein (GFP), were used. Following discontinuation of doxycycline ("chase" period), retention of H2B-GFP enabled the identification of slow cycling stem cells and long-lived Paneth cells. Inflammation in the small intestine (SI) was induced by oral administration of T. spiralis muscle larvae. Epithelial retention of H2B-GFP per crypt cell position (cp) was studied following immunohistochemistry and using the Score and Wincrypts program. Compared to non-infected controls, there was significant reduction in the number of H2B-GFP-retaining stem cells in T. spiralis-infected small intestines. H2B-GFP-retaining stem cells peaked at around cp 4 in control sections, but smaller peaks at higher cell positions (>10) were seen in sections of inflamed small intestines. In the latter, there was a significant increase in the total number of Paneth cells, with significant reduction in H2B-GFP-retaining Paneth cells, but a marked increase in unlabelled (H2B-GFP-negative) Paneth cells. In conclusion, following T. spiralis-infection, putative slow cycling stem cell numbers were reduced. A marked increase in newly generated Paneth cells at the crypt base led to higher cell positions of the remaining slow cycling stem cells.

ID4 levels dictate the stem cell state in mouse spermatogonia.

Spermatogenesis is a classic model of cycling cell lineages that depend on a balance between stem cell self-renewal for continuity and the formation of progenitors as the initial step in the production of differentiated cells. The mechanisms that guide the continuum of spermatogonial stem cell (SSC) to progenitor spermatogonial transition and precise identifiers of subtypes in the process are undefined. Here we used an Id4-eGfp reporter mouse to discover that EGFP intensity is predictive of the subsets, with the ID4-EGFPBright population being mostly, if not purely, SSCs, whereas the ID4-EGFPDim population is in transition to the progenitor state. These subsets are also distinguishable by transcriptome signatures. Moreover, using a conditional overexpression mouse model, we found that transition from the stem cell to the immediate progenitor state requires downregulation of Id4 coincident with a major change in the transcriptome. Collectively, our results demonstrate that the level of ID4 is predictive of stem cell or progenitor capacity in spermatogonia and dictates the interface of transition between the different functional states.

Swap70b is required for convergent and extension cell movement during zebrafish gastrulation linking Wnt11 signalling and RhoA effector function.

Swap70 functions as a guanine nucleotide exchange factor for Rac and RhoA regulating F-actin cytoskeletal rearrangements and playing a crucial role in mammalian cell activation, migration, adhesion and invasion. Here we show that the zebrafish orthologue, Swap70b, is required for convergent and extension cell movement during gastrulation. Swap70b morphants exhibited broader and shorter body axis but cell fate specification appeared normal. While ectopic Swap70b expression robustly rescued Wnt11 morphants, RhoA overexpression was sufficient to rescue Swap70b morphants, establishing Swap70b as a novel member of the non-canonical Wnt/PCP pathway downstream of Wnt11 and upstream of RhoA. This is distinct from the related Def6a protein that acts downstream of Wnt5b. Def6a/Swap70b morphants resemble Ppt/Slb double mutant embryos suggesting that Swap70b and Def6a delineate Wnt11 and Wnt5b signalling pathways.

Heterogeneity in histone 2B-green fluorescent protein-retaining putative small intestinal stem cells at cell position 4 and their absence in the colon.

Stem cells have been identified in two locations in small intestinal crypts; those intercalated between Paneth cells and another population (which retains DNA label) are located above the Paneth cell zone, at cell position 4. Because of disadvantages associated with the use of DNA label, doxycycline-induced transient transgenic expression of histone 2B (H2B)-green fluorescent protein (GFP) was investigated. H2B-GFP-retaining putative stem cells were consistently seen, with a peak at cell position 4, over chase periods of up to 112 days. After a 28-day chase, a subpopulation of the H2B-GFP-retaining cells was cycling, but the slow cycling status of the majority was illustrated by lack of expression of pHistone H3 and Ki67. Although some H2B-GFP-retaining cells were sensitive to low-dose radiation, the majority was resistant to low- and high-dose radiation-induced cell death, and a proportion of the surviving cells proliferated during subsequent epithelial regeneration. Long-term retention of H2B-GFP in a subpopulation of small intestinal Paneth cells was also seen, implying that they are long lived. In contrast to the small intestine, H2B-GFP-retaining epithelial cells were not seen in the colon from 28-day chase onward. This implies important differences in stem cell function between these two regions of the gastrointestinal tract, which may have implications for region-specific susceptibility to diseases (such as cancer and ulcerative colitis), in which epithelial stem cells and their progeny are involved.

DEF6, a novel substrate for the Tec kinase ITK, contains a glutamine-rich aggregation-prone region and forms cytoplasmic granules that co-localize with P-bodies.

Localization of DEF6 (SLAT/IBP), a Rho-family guanine nucleotide exchange factor, to the center of the immune synapse is dependent upon ITK, a Tec-family kinase that regulates the spatiotemporal organization of components of T cell signaling pathways and Cdc42-dependent actin polymerization. Here we demonstrate that ITK both interacts with DEF6 and phosphorylates DEF6 at tyrosine residues Tyr(210) and Tyr(222). Expression of a GFP-tagged Y210E-Y222E phosphomimic resulted in the formation of DEF6 cytoplasmic granules that co-localized with decapping enzyme 1 (DCP1), a marker of P-bodies; sites of mRNA degradation. Similarly treatment of cells with puromycin or sodium arsenite, reagents that arrest translation, also resulted in the accumulation of DEF6 in cytoplasmic granules. Bioinformatics analysis identified a glutamine-rich, heptad-repeat region; a feature of aggregating proteins, within the C-terminal region of DEF6 with the potential to promote granule formation through a phosphorylation-dependent unmasking of this region. These data suggest that in addition to its role as a GEF, DEF6 may also function in regulating mRNA translation.

Def6 is required for convergent extension movements during zebrafish gastrulation downstream of Wnt5b signaling.

During gastrulation, convergent extension (CE) cell movements are regulated through the non-canonical Wnt signaling pathway. Wnt signaling results in downstream activation of Rho GTPases that in turn regulate actin cytoskeleton rearrangements essential for co-ordinated CE cell movement. Rho GTPases are bi-molecular switches that are inactive in their GDP-bound stage but can be activated to bind GTP through guanine nucleotide exchange factors (GEFs). Here we show that def6, a novel GEF, regulates CE cell movement during zebrafish gastrulation. Def6 morphants exhibit broadened and shortened body axis with normal cell fate specification, reminiscent of the zebrafish mutants silberblick and pipetail that lack Wnt11 or Wnt5b, respectively. Indeed, def6 morphants phenocopy Wnt5b mutants and ectopic overexpression of def6 essentially rescues Wnt5b morphants, indicating a novel role for def6 as a central GEF downstream of Wnt5b signaling. In addition, by knocking down both def6 and Wnt11, we show that def6 synergises with the Wnt11 signaling pathway.

ID4 regulates mammary gland development by suppressing p38MAPK activity.

The ID family of helix-loop-helix proteins regulates cell proliferation and differentiation in many different developmental pathways, but the functions of ID4 in mammary development are unknown. We report that mouse Id4 is expressed in cap cells, basal cells and in a subset of luminal epithelial cells, and that its targeted deletion impairs ductal expansion and branching morphogenesis as well as cell proliferation induced by estrogen and/or progesterone. We discover that p38MAPK is activated in Id4-null mammary cells. p38MAPK is also activated following siRNA-mediated Id4 knockdown in transformed mammary cells. This p38MAPK activation is required for the reduced proliferation and increased apoptosis in Id4-ablated mammary glands. Therefore, ID4 promotes mammary gland development by suppressing p38MAPK activity.

LYL-1 deficiency induces a stress erythropoiesis.

OBJECTIVE: LYL-1 is a transcription factor containing a basic helix-loop-helix motif closely related to SCL/TAL-1, a regulator of erythroid differentiation. Because LYL-1 is expressed in erythroid cell populations, we addressed its role in erythropoiesis using knockin mice. MATERIALS AND METHODS: Erythropoiesis of LYL-1(-/-) mice was studied by progenitor assays, flow cytometry, reconstitution assays, and functional tests. Expression of LYL-1, SCL, and GATA-1 was assessed at messenger RNA level by quantitative reverse transcription polymerase chain reaction. RESULTS: LYL-1(-/-) mice displayed decreased erythropoiesis with a partial arrest in differentiation, and enhanced apoptosis associated with decreased Bcl-x(L) expression in the bone marrow (BM). In addition, LYL-1(-/-) BM cells were severely impaired in their abilities to reconstitute the erythroid lineage in competitive assays, suggesting a cell autonomous abnormality of erythropoiesis. In parallel, erythroid progenitor and precursor cells were significantly increased in the spleen of LYL-1(-/-) mice. Expression of LYL-1 was differentially regulated during maturation of erythroblasts and strikingly different between spleen- and BM-derived erythroblasts. Expression of LYL-1 decreased during erythroid differentiation in the spleen whereas it increased in the BM to reach the same level in mature erythroblasts as in the soleen. Loss of Lyl-1 expression was accompanied with an increase of SCL/TAL-1 and GATA-1 transcripts in spleen but not in BM-derived erythroblasts. Furthermore, phenylhydrazine-induced stress erythropoiesis was elevated in LYL-1(-/-) mice and mutant BM and spleen erythroid progenitors were hypersensitive to erythropoietin. CONCLUSIONS: Taken together, these results suggest that LYL-1 plays a definite role in erythropoiesis, albeit with different effects in BM specifically regulating basal erythropoiesis, and spleen, controlling stress-induced erythropoiesis.

Silencing of the inhibitor of DNA binding protein 4 (ID4) contributes to the pathogenesis of mouse and human CLL.

Inhibitor of DNA binding protein 4 (ID4) is a member of the dominant-negative basic helix-loop-helix transcription factor family that lacks DNA binding activity and has tumor suppressor function. ID4 promoter methylation has been reported in acute myeloid leukemia and chronic lymphocytic leukemia (CLL), although the expression, function, and clinical relevance of this gene have not been characterized in either disease. We demonstrate that the promoter of ID4 is consistently methylated to various degrees in CLL cells, and increased promoter methylation in a univariable analysis correlates with shortened patient survival. However, ID4 mRNA and protein expression is uniformly silenced in CLL cells irrespective of the degree of promoter methylation. The crossing of ID4(+/-) mice with Eµ-TCL1 mice triggers a more aggressive murine CLL as measured by lymphocyte count and inferior survival. Hemizygous loss of ID4 in nontransformed TCL1-positive B cells enhances cell proliferation triggered by CpG oligonucleotides and decreases sensitivity to dexamethasone-mediated apoptosis. Collectively, this study confirms the importance of the silencing of ID4 in murine and human CLL pathogenesis.

Subnuclear targeting of the RNA-binding motif protein RBM6 to splicing speckles and nascent transcripts.

RNA-binding motif (RBM) proteins comprise a large family of RNA-binding proteins whose functions are poorly understood. Since some RBM proteins are candidate alternative splicing factors we examined whether one such member of the family, RBM6, exhibited a pattern of nuclear distribution and targeting consistent with this role. Using antibodies raised against mouse RBM6 to immunostain mammalian cell lines we found that the endogenous protein was both distributed diffusely in the nucleus and concentrated in a small number of nuclear foci that corresponded to splicing speckles/interchromatin granule clusters (IGCs). Tagged RBM6 was also targeted to IGCs, although it accumulated in large bodies confined to the IGC periphery. The basis of this distribution pattern was suggested by the targeting of tagged RBM6 in the giant nuclei (or germinal vesicles (GVs)) of Xenopus oocytes. In spread preparations of GV contents RBM6 was localized both to lampbrush chromosomes and to the surface of many oocyte IGCs, where it was confined to up to 50 discrete patches. Each patch of RBM6 labelling corresponded to a bead-like structure of 0.5-1 microm diameter that assembled de novo on the IGC surface. Assembly of these novel structures depended on the repetitive N-terminal region of RBM6, which acts as a multimerization domain. Without this domain, RBM6 was no longer excluded from the IGC interior but accumulated homogeneously within it. Assembly of IGC-surface structures in mammalian cell lines also depended on the oligomerization domain of RBM6. Oligomerization of RBM6 also had morphological effects on its other major target in GVs, namely the arrays of nascent transcripts visible in lampbrush chromosome transcription units. The presence of oligomerized RBM6 on many lampbrush loops caused them to appear as dense structures with a spiral morphology that appeared quite unlike normal, extended loops. This distribution pattern suggests a new role for RBM6 in the co-transcriptional packaging or processing of most nascent transcripts.

Id4, a new candidate gene for senile osteoporosis, acts as a molecular switch promoting osteoblast differentiation.

Excessive accumulation of bone marrow adipocytes observed in senile osteoporosis or age-related osteopenia is caused by the unbalanced differentiation of MSCs into bone marrow adipocytes or osteoblasts. Several transcription factors are known to regulate the balance between adipocyte and osteoblast differentiation. However, the molecular mechanisms that regulate the balance between adipocyte and osteoblast differentiation in the bone marrow have yet to be elucidated. To identify candidate genes associated with senile osteoporosis, we performed genome-wide expression analyses of differentiating osteoblasts and adipocytes. Among transcription factors that were enriched in the early phase of differentiation, Id4 was identified as a key molecule affecting the differentiation of both cell types. Experiments using bone marrow-derived stromal cell line ST2 and Id4-deficient mice showed that lack of Id4 drastically reduces osteoblast differentiation and drives differentiation toward adipocytes. On the other hand knockdown of Id4 in adipogenic-induced ST2 cells increased the expression of Ppargamma2, a master regulator of adipocyte differentiation. Similar results were observed in bone marrow cells of femur and tibia of Id4-deficient mice. However the effect of Id4 on Ppargamma2 and adipocyte differentiation is unlikely to be of direct nature. The mechanism of Id4 promoting osteoblast differentiation is associated with the Id4-mediated release of Hes1 from Hes1-Hey2 complexes. Hes1 increases the stability and transcriptional activity of Runx2, a key molecule of osteoblast differentiation, which results in an enhanced osteoblast-specific gene expression. The new role of Id4 in promoting osteoblast differentiation renders it a target for preventing the onset of senile osteoporosis.

LYL1 activity is required for the maturation of newly formed blood vessels in adulthood.

The 2 related basic helix loop helix genes, LYL1 and TAL-1 are active in hematopoietic and endothelial lineages. While Tal-1 is essential for both hematopoietic and vascular development, the role of Lyl1 appears to be distinct as deficient mice are viable and display modest hematopoietic defects. Here, we reveal a role for Lyl1 as a major regulator of adult neovascularization. Tumors implanted into Lyl1-deficient mice showed higher proliferation and angiogenesis, as evidenced by enlarged lumens, reduced pericyte coverage and increased permeability, compared with wild type littermates. Of note, Lyl1-deficient tumor vessels exhibited an up-regulation of Tal-1, the VE-Cadherin target gene, as well as Angiopoietin-2, 3 major actors in angiogenesis. Hematopoietic reconstitution experiments demonstrated that this sustained tumor angiogenesis was of endothelial origin. Moreover, the angiogenic phenotype observed in the absence of Lyl1 function was not tumor-restricted as microvessels forming in Matrigel or originating from aortic explants were also more numerous and larger than their wild-type counterparts. Finally, LYL1 depletion in human endothelial cells revealed that LYL1 controls the expression of molecules involved in the stabilization of vascular structures. Together, our data show a role for LYL1 in the postnatal maturation of newly formed blood vessels.

Adult hematopoietic stem and progenitor cells require either Lyl1 or Scl for survival.

Scl and Lyl1 encode two related basic-helix-loop-helix transcription factors implicated in T cell acute lymphoblastic leukemia. Previous studies showed that Scl is essential for embryonic and adult erythropoiesis, while Lyl1 is important for B cell development. Single-knockout mice have not revealed an essential function for Scl or Lyl1 in adult hematopoietic stem cells (HSCs). To determine if maintenance of HSCs in single-knockout mice is due to functional redundancy, we generated Lyl1;Scl-conditional double-knockout mice. Here, we report a striking genetic interaction between the two genes, with a clear dose dependence for the presence of Scl or Lyl1 alleles for HSC function. Bone marrow repopulation assays and analyses demonstrated rapid loss of hematopoietic progenitors due to apoptosis. The function of HSCs could be rescued by a single allele of Lyl1 but not Scl. These results show that expression of at least one of these factors is essential for maintenance of adult HSC function.

The paralogous hematopoietic regulators Lyl1 and Scl are coregulated by Ets and GATA factors, but Lyl1 cannot rescue the early Scl-/- phenotype.

Transcription factors are key regulators of hematopoietic stem cells (HSCs), yet the molecular mechanisms that control their expression are largely unknown. Previously, we demonstrated that expression of Scl/Tal1, a transcription factor required for the specification of HSCs, is controlled by Ets and GATA factors. Here we characterize the molecular mechanisms controlling expression of Lyl1, a paralog of Scl also required for HSC function. Two closely spaced promoters directed expression to hematopoietic progenitor, megakaryocytic, and endothelial cells in transgenic mice. Conserved binding sites required for promoter activity were bound in vivo by GATA-2 and the Ets factors Fli1, Elf1, Erg, and PU.1. However, despite coregulation of Scl and Lyl1 by the same Ets and GATA factors, Scl expression was initiated prior to Lyl1 in embryonic stem (ES) cell differentiation assays. Moreover, ectopic expression of Scl but not Lyl1 rescued hematopoietic differentiation in Scl-/- ES cells, thus providing a molecular explanation for the vastly different phenotypes of Scl-/- and Lyl1-/- mouse embryos. Furthermore, coregulation of Scl and Lyl1 later during development may explain the mild phenotype of Scl-/- adult HSCs.

lyl-1 and tal-1/scl, two genes encoding closely related bHLH transcription factors, display highly overlapping expression patterns during cardiovascular and hematopoietic ontogeny.

The TAL-1/SCL and LYL-1 genes encode two closely related basic helix-loop-helix transcription factors involved in child T-acute lymphoblastic leukemia through chromosomal rearrangements and transcriptional deregulation. During ontogeny, Tal-1/SCL is required for hematopoietic cell generation, both in the yolk sac, where erythro-myeloid cells are first produced, then in the intra-embryonic compartment, where hematopoietic stem cells independently arise. We describe here the expression pattern of lyl-1 in mouse embryos from 7 to 14 days post coitus using in situ hybridization, as well as beta-Galactosidase (beta-Gal) expression in lyl-1-lacZ knock-in embryos, which express a C-terminally truncated Lyl-1 protein fused to the beta-Galactosidase (Lyl-1Delta/beta-Gal). In addition, we compare lyl-1 expression pattern with that of tal-1/scl. Similar to Tal-1/SCL, Lyl-1 mRNA expression occurs in the developing cardiovascular and hematopoietic systems. However, contrary to tal-1/scl, lyl-1 is not expressed in the developing nervous system. In lyl-1-lacZ knock-in heterozygous and homozygous embryos, beta-Gal expression completely correlates with Lyl-1 mRNA expression in the intra-embryonic compartment and is present: (1) in the developing hematopoietic system, precisely where hematopoietic stem cells emerge, and thereafter in the fetal liver; (2) in the developing vascular system; and (3) in the endocardium. In contrast, whereas Lyl-1 mRNA is expressed in yolk sac-derived endothelial and hematopoietic cells, Lyl-1Delta/beta-Gal is either absent or poorly expressed in these cell types, thus differing from Tal-1/SCL, which is highly expressed there at both mRNA and protein levels.

Multiple roles of Id4 in developmental myelination: predicted outcomes and unexpected findings.

Myelination in the central nervous system is a complex process requiring the integration of oligodendrocyte progenitor differentiation and the coordinate expression of myelin genes. This study addresses the role of the helix-loop-helix protein Id4 in these two events. Overexpression of Id4 in oligodendrocyte progenitors prevents differentiation and consequently decreases the endogenous expression of all myelin genes. Conversely, progenitors lacking Id4 display precocious differentiation both in vitro and in vivo, and this phenotype is partially compensated by increased apoptosis. Besides this role, Id4 also has the ability to decrease the activity of specific myelin promoters, since Id4 overexpression decreases the activity of luciferase reporter genes driven by the ceramide galactosyltransferase (CGT) or myelin basic protein (MBP) promoter, but not by a myelin proteolipid protein (PLP) promoter. Consistent with these results, the expression levels of MBP and CGT are greater in neonatal Id4 null mice when compared with wild-type siblings and correlate with the early detection of MBP immunoreactive myelinated fibers. In contrast, the levels of other myelin proteins, such as PLP and myelin associated glycoprotein (MAG) are decreased in the Id4 null mice. MAG expression is localized to the soma rather than the fibers of immunoreactive cells in the neonatal brain and compensated at later developmental stages. These data support the role of Id4 as oligodendrocyte differentiation inhibitor with the ability to differentially regulate the expression and subcellular distribution of myelin gene products.

The SCL relative LYL-1 is required for fetal and adult hematopoietic stem cell function and B-cell differentiation.

Hematopoietic stem cells (HSCs) arise, self-renew, or give rise to all hematopoietic lineages through the effects of transcription factors activated by signaling cascades. Lyl-1 encodes a transcription factor containing a basic helix-hoop-helix (bHLH) motif closely related to scl/tal, which controls numerous decisions in embryonic and adult hematopoiesis. We report here that Lyl-1 null mice are viable and display normal blood cell counts, except for a reduced number of B cells resulting from a partial block after the pro-B stage. Nevertheless, the deletion of Lyl-1 results in a diminution in the frequency of immature progenitors (Lin(-), CD34(-), sca-1(+), c-kit(+) [LSK], and LSK-side population [LSK-SP]) and in S(12) colony-forming unit (CFU-S(12)) and long-term culture-initiating cell (LTC-IC) content in embryonic day 14 fetal liver (E14 FL) and adult bone marrow (BM). More important, Lyl-1(-/-) E14 FL cells and BM are severely impaired in their competitive reconstituting abilities, especially with respect to B and T lineage reconstitution. Thus, ablation of Lyl-1 quantitatively and functionally affects HSCs, a cell population that transcribes Lyl-1 more actively than their differentiated progenies. Our results demonstrate for the first time that Lyl-1 functions are important for HSC properties and B-cell differentiation and that they are largely distinct from scl functions.

Comprehensive metabolic profiling of mono- and polyglutamated folates and their precursors in plant and animal tissue using liquid chromatography/negative ion electrospray ionisation tandem mass spectrometry.

This work reports the use of reversed-phase ion-pair chromatography coupled to electrospray ionisation mass spectrometry for the simultaneous profiling of folate-based metabolites including natural folates, their polyglutamatyl derivatives and their biosynthetic precursors in plant and animal tissue. A simple sample preparation method, using 0.1% citric acid and ascorbic acid in ice-cold methanol, was used to extract and stabilise the folates, and three internal standards were used. Chromatography was on a C18 column using slow gradient elution with a mobile phase consisting of methanol/water with 5 mM dimethylhexylamine. Mass spectrometric detection was performed by multiple reaction monitoring in seven separate time windows in negative ion mode over the 25 min run time. Full, quantitative analysis was obtained for 16 folates and a 'semi-quantitative' analysis was possible for all other folates with up to eight conjugated glutamate residues by reference to structurally related calibration standards. The precision, accuracy and recovery of the method were generally within the accepted guidelines for a quantitative bioanalytical method and the method was linear over the range 0.2 to 10 ng of individual folate per sample. The method was applied to profile mono- and polyglutamated tetrahydrofolates (including subcellular analysis) in a range of plant species, including Arabidopsis, spinach, Brassica and wheat; the technique was also successfully applied to the profiling of folates in mouse tissue.

Id4 is required for the correct timing of neural differentiation.

Complex intrinsic and extrinsic mechanisms determine neural cell fate during development of the nervous system. Using Id4 deficient mice, we show that Id4 is required for normal development of the central nervous system (CNS), timing neural differentiation in the developing forebrain. In the absence of Id4, the ventricular zone of the neocortex, future hippocampus as well as lateral and medial ganglionic eminences exhibited a 20-30% reduction in mitotic neural precursor cells (NPCs). Although the number of apoptotic cells was significantly increased, the neocortex of Id4(-/-) embryos was consistently thicker due to premature neuronal differentiation, which resulted in an increase in early-born neurons in the adult Id4(-/-) cortex. Late-born cortical neurons and astrocytes in the cortex, septum, hippocampus and caudate putamen of Id4(-/-) adult brains were decreased, however, likely due to the depletion of the NPC pool. Consequently, adult Id4(-/-) brains were smaller and exhibited enlarged ventricles. In vitro analysis of neurosphere cultures revealed that proliferation of Id4-deficient NPCs was impaired and that BMP2-mediated astrocyte differentiation was accelerated in the absence of Id4. Together, these in vivo and in vitro data suggest a crucial role for Id4 in regulating NPC proliferation and differentiation.

Efficient delivery of Cre-recombinase to neurons in vivo and stable transduction of neurons using adeno-associated and lentiviral vectors.

BACKGROUND: Inactivating genes in vivo is an important technique for establishing their function in the adult nervous system. Unfortunately, conventional knockout mice may suffer from several limitations including embryonic or perinatal lethality and the compensatory regulation of other genes. One approach to producing conditional activation or inactivation of genes involves the use of Cre recombinase to remove loxP-flanked segments of DNA. We have studied the effects of delivering Cre to the hippocampus and neocortex of adult mice by injecting replication-deficient adeno-associated virus (AAV) and lentiviral (LV) vectors into discrete regions of the forebrain. RESULTS: Recombinant AAV-Cre, AAV-GFP (green fluorescent protein) and LV-Cre-EGFP (enhanced GFP) were made with the transgene controlled by the cytomegalovirus promoter. Infecting 293T cells in vitro with AAV-Cre and LV-Cre-EGFP resulted in transduction of most cells as shown by GFP fluorescence and Cre immunoreactivity. Injections of submicrolitre quantities of LV-Cre-EGFP and mixtures of AAV-Cre with AAV-GFP into the neocortex and hippocampus of adult Rosa26 reporter mice resulted in strong Cre and GFP expression in the dentate gyrus and moderate to strong labelling in specific regions of the hippocampus and in the neocortex, mainly in neurons. The pattern of expression of Cre and GFP obtained with AAV and LV vectors was very similar. X-gal staining showed that Cre-mediated recombination had occurred in neurons in the same regions of the brain, starting at 3 days post-injection. No obvious toxic effects of Cre expression were detected even after four weeks post-injection. CONCLUSION: AAV and LV vectors are capable of delivering Cre to neurons in discrete regions of the adult mouse brain and producing recombination.