Direction-oriented fiber guiding with a tunable tri-layer-3D scaffold for periodontal regeneration.

Multilayered scaffolds mimicking mechanical and biological host tissue architectures are the current prerequisites for successful tissue regeneration. We propose our tunable tri-layered scaffold, designed to represent the native periodontium for potential regenerative applications. The fused deposition modeling platform is used to fabricate the novel movable three-layered polylactic acid scaffold mimicking in vivo cementum, periodontal ligament, and alveolar bone layers. The scaffold is further provided with multiple angulated fibers, offering directional guidance and facilitating the anchorage dependence on cell adhesion. Additionally, surface modifications of the scaffold were made by incorporating coatings like collagen and different concentrations of gelatin methacryloyl to enrich the cell adhesion and proliferation. The surface characterization of our designed scaffolds was performed using tribological studies, atomic force microscopy, contact angle measurement, scanning electron microscopy, and micro-computed tomography. Furthermore, the material characterization of this scaffold was investigated by attenuated total reflectance-Fourier transformed infrared spectroscopy. The scaffold's mechanical characterization, such as strength and compression modulus, was demonstrated by compression testing. The L929 mouse fibroblast cells and MG63 human osteosarcoma cells have been cultured on the scaffold. The scaffold's superior biocompatibility was evaluated using fluorescence dye with fluorescence microscopy, scanning electron microscopy, in vitro wound healing assay, MTT assay, and flow cytometry. The mineralization capability of the scaffolds was also studied. In conclusion, our study demonstrated the construction of a multilayered movable scaffold, which is highly biocompatible and most suitable for various downstream applications such as periodontium and in situ tissue regeneration of complex, multilayered tissues.

Laser-Induced Intracellular Delivery: Exploiting Gold-Coated Spiky Polymeric Nanoparticles and Gold Nanorods under Near-Infrared Pulses for Single-Cell Nano-Photon-Poration.

This study explores the potential of laser-induced nano-photon-poration as a non-invasive technique for the intracellular delivery of micro/macromolecules at the single-cell level. This research proposes the utilization of gold-coated spiky polymeric nanoparticles (Au-PNPs) and gold nanorods (GNRs) to achieve efficient intracellular micro/macromolecule delivery at the single-cell level. By shifting the operating wavelength towards the near-infrared (NIR) range, the intracellular delivery efficiency and viability of Au-PNP-mediated photon-poration are compared to those using GNR-mediated intracellular delivery. Employing Au-PNPs as mediators in conjunction with nanosecond-pulsed lasers, a highly efficient intracellular delivery, while preserving high cell viability, is demonstrated. Laser pulses directed at Au-PNPs generate over a hundred hot spots per particle through plasmon resonance, facilitating the formation of photothermal vapor nanobubbles (PVNBs). These PVNBs create transient pores, enabling the gentle transfer of cargo from the extracellular to the intracellular milieu, without inducing deleterious effects in the cells. The optimization of wavelengths in the NIR region, coupled with low laser fluence (27 mJ/cm2) and nanoparticle concentrations (34 µg/mL), achieves outstanding delivery efficiencies (96%) and maintains high cell viability (up to 99%) across the various cell types, including cancer and neuronal cells. Importantly, sustained high cell viability (90-95%) is observed even 48 h post laser exposure. This innovative development holds considerable promise for diverse applications, encompassing drug delivery, gene therapy, and regenerative medicine. This study underscores the efficiency and versatility of the proposed technique, positioning it as a valuable tool for advancing intracellular delivery strategies in biomedical applications.

Holistic approach to waste mobil oil bioremediation: Valorizing waste through biosurfactant production for soil restoration.

The combustion of mobil oil leads to the emission of toxic compounds in the environment. In this study, the aromatic and aliphatic hydrocarbon fractions present in a waste mobil oil collected from automobile market were comprehensively identified and their toxicity was evaluated using wheat grain. Lysinibacillus sphaericus strain IITR51 isolated and characterized previously could degrade 30-80% of both aliphatic and aromatic hydrocarbons in liquid culture. Interestingly, the strain IITR51 produced 627 mg/L of rhamnolipid biosurfactant by utilizing 3% (v/v) of waste mobil oil in the presence of 1.5% glycerol as additional carbon source. In a soil microcosm study by employing strain IITR51, 50-86% of 3-6 ring aromatic hydrocarbons and 63-98% of aliphatic hydrocarbons (C8 to C22) were degraded. Addition of 60 µg/mL rhamnolipid biosurfactant enhanced the degradation of both aliphatic and aromatic hydrocarbons from 76.88% to 61.21%-94.11% and 78.27% respectively. The degradation of mobil oil components improved the soil physico-chemical properties and increased soil fertility to 64% as evident by the phytotoxicity assessments. The findings indicate that strain IITR51 with degradation capability coupled with biosurfactant production could be a candidate for restoring hydrocarbon contaminated soils.

Functionally gradient three-dimensional graphene foam-based polymeric scaffolds for multilayered tissue regeneration.

Physiological bioengineering of multilayered tissues requires an optimized geometric organization with comparable biomechanics. Currently, polymer-reinforced three-dimensional (3D) graphene foams (GFs) are gaining interest in tissue engineering due to their unique morphology, biocompatibility, and similarity to extracellular matrixes. However, the homogeneous reinforcement of single polymers throughout a GF matrix does not provide tissue-level organization. Therefore, a triple-layered structure is developed in a GF matrix to closely mimic native tissue structures of the periodontium of the teeth. The scaffold aims to overcome the issue of layer separation, which generally occurs in multilayered structures due to the poor integration of various layers. The 3D GF matrix was reinforced with a polycaprolactone (PCL), polyvinyl alcohol (PVA), and PCL-hydroxyapatite (HA) mixture, added sequentially, via spin coating, vacuum, and hot air drying. Later, PVA was dissolved to create a middle layer, mimicking the periodontal fibers, while the layers present on either side resembled cementum and alveolar bone, respectively. Scanning electron microscopy and micro-computed tomography revealed the structure of the scaffold with internal differential porosities. The nanoindentation and tensile testing demonstrated the closeness of mechanical properties to that of native tissues. The biocompatibility was assessed by the MTT assay with MG63 cells (human osteosarcoma cells) exhibiting high adhesion and proliferation rate inside the 3D architecture. Summing up, this scaffold has the potential for enhancing the regeneration of various multilayered tissues.

Sustainable strategies for combating hydrocarbon pollution: Special emphasis on mobil oil bioremediation.

The global rise in industrialization and vehicularization has led to the increasing trend in the use of different crude oil types. Among these mobil oil has major application in automobiles and different machines. The combustion of mobil oil renders a non-usable form that ultimately enters the environment thereby causing problems to environmental health. The aliphatic and aromatic hydrocarbon fraction of mobil oil has serious human and environmental health hazards. These components upon interaction with soil affect its fertility and microbial diversity. The recent advancement in the omics approach viz. metagenomics, metatranscriptomics and metaproteomics has led to increased efficiency for the use of microbial based remediation strategy. Additionally, the use of biosurfactants further aids in increasing the bioavailability and thus biodegradation of crude oil constituents. The combination of more than one approach could serve as an effective tool for efficient reduction of oil contamination from diverse ecosystems. To the best of our knowledge only a few publications on mobil oil have been published in the last decade. This systematic review could be extremely useful in designing a micro-bioremediation strategy for aquatic and terrestrial ecosystems contaminated with mobil oil or petroleum hydrocarbons that is both efficient and feasible. The state-of-art information and future research directions have been discussed to address the issue efficiently.

Pulsed laser assisted high-throughput intracellular delivery in hanging drop based three dimensional cancer spheroids.

Targeted intracellular delivery of biomolecules and therapeutic cargo enables the controlled manipulation of cellular processes. Laser-based optoporation has emerged as a versatile, non-invasive technique that employs light-based transient physical disruption of the cell membrane and achieves high transfection efficiency with low cell damage. Testing of the delivery efficiency of optoporation-based techniques has been conducted on single cells in monolayers, but its applicability in three-dimensional (3D) cell clusters/spheroids has not been explored. Cancer cells grown as 3D tumor spheroids are widely used in anti-cancer drug screening and can be potentially employed for testing delivery efficiency. Towards this goal, we demonstrated the optoporation-based high-throughput intracellular delivery of a model fluorescent cargo (propidium iodide, PI) within 3D SiHa human cervical cancer spheroids. To enable this technique, nano-spiked core-shell gold-coated polystyrene nanoparticles (ns-AuNPs) with a high surface-to-volume ratio were fabricated. ns-AuNPs exhibited high electric field enhancement and highly localized heating at an excitation wavelength of 680 nm. ns-AuNPs were co-incubated with cancer cells within hanging droplets to enable the rapid aggregation and assembly of spheroids. Nanosecond pulsed-laser excitation at the optimized values of laser fluence (45 mJ cm-2), pulse frequency (10 Hz), laser exposure time (30 s), and ns-AuNP concentration (5 × 1010 particles per ml) resulted in the successful delivery of PI dye into cancer cells. This technique ensured high delivery efficiency (89.6 ± 2.8%) while maintaining high cellular viability (97.4 ± 0.4%), thereby validating the applicability of this technique for intracellular delivery. The optoporation-based strategy can enable high-throughput single cell manipulation, is scalable towards larger 3D tissue constructs, and may provide translational benefits for the delivery of anti-cancer therapeutics to tumors.

Mechanical, corrosion and biocompatibility behaviour of Mg-3Zn-HA biodegradable composites for orthopaedic fixture accessories.

Development of biodegradable implants has grown into one of the important areas in medical science. Degradability becomes more important for orthopaedic accessories used to support fractured and damaged bones, in order to avoid second surgery for their removal after healing. Clinically available biodegradable orthopaedic materials are mainly made of polymers or ceramics. These orthopaedic accessories have an unsatisfactory mechanical strength, when used in load-bearing parts. Magnesium and its alloys can be suitable candidate for this purpose, due to their outstanding strength to weight ratio, biodegradability, non-toxicity and mechanical properties, similar to natural bone. The major drawback of magnesium is its low corrosion resistance, which also influences its mechanical and physical characteristics in service condition. An effort has been taken in this research to improve the corrosion resistance, bioactivity and mechanical strength of biodegradable magnesium alloys by synthesizing Mg-3wt% Zn matrix composite, reinforced with thermally treated hydroxyapatite(HA) [Ca10(PO4)6(OH)2], a bioactive and osteogenic ceramic. Addition of 5wt% HA is found effective in reducing the corrosion rate by 42% and improvement in the compressive yield strength of biodegradable magnesium alloy by 23%. In-vitro evaluation, up to 56 days, reveal improved resistance to degradation with HA reinforcement to Mg. Osteoblast cells show better growth and proliferation on HA reinforced surfaces of the composite. Mg-HA composite structure shows impressive potential to be used in orthopaedic fracture fixing accessories.

Risk factors associated with the onset and progression of Alzheimer's disease: A systematic review of the evidence.

A systematic review was conducted to identify risk factors associated with the onset and progression of Alzheimer's disease (AD). Moderate and high quality systematic reviews were eligible for inclusion. Primary studies reporting on non-genetic risk factors associated with neuropathologically or clinically confirmed AD were considered. Eighty one systematic reviews reporting on AD onset and 12 reporting on progression satisfied the eligibility criteria. Four hundred and thirty-two relevant primary studies reporting on onset were identified; however, only those published between 2010 and 2012 (n=65) were included in the qualitative synthesis. Several factors including statins, light-to-moderate alcohol consumption, compliance with a Mediterranean diet, higher educational attainment, physically and cognitively stimulating activities, and APOE ε2 appeared to be associated with a decreased risk of AD onset. The evidence was suggestive of an increased risk of AD associated with head injury in males, age, diabetes mellitus, conjugated equine estrogen use with medroxyprogesterone acetate, current smoking, and lower social engagement. With respect to genetic factors, APOE ε4 remained the strongest predictor of AD. Physical and cognitive activities were associated with a beneficial effect on cognitive function and other indicators of dementia progression while higher educational attainment was associated with faster cognitive decline. Although suggestive of an association, the current evidence for a majority of the identified putative factors for AD onset and progression was weak, at best due to conflicting findings across studies or inadequate evidence. Further research is required to confirm the etiological or protective role of a number of risk factors.

Determinants of neurological disease: Synthesis of systematic reviews.

Systematic reviews were conducted to identify risk factors associated with the onset and progression of 14 neurological conditions, prioritized as a component of the National Population Health Study of Neurological Conditions. These systematic reviews provided a basis for evaluating the weight of evidence of evidence for risk factors for the onset and progression of the 14 individual neurological conditions considered. A number of risk factors associated with an increased risk of onset for more than one condition, including exposure to pesticides (associated with an increased risk of AD, amyotrophic lateral sclerosis, brain tumours, and PD; smoking (AD, MS); and infection (MS, Tourette syndrome). Coffee and tea intake was associated with a decreased risk of onset of both dystonia and PD. Further understanding of the etiology of priority neurological conditions will be helpful in focusing future research initiatives and in the development of interventions to reduce the burden associated with neurological conditions in Canada and internationally.

As the Nasal Spine Goes, So Goes the Septum.

INTRODUCTION: "As the septum goes, so goes the nose". A well-known phrase by Maurice Cottle forms the pillar of septoplasty. Since the inception of septal surgeries, numerous methods of septoplasty have been described. But, if not performed meticulously, may lead to deformity. For a successful surgery, understanding the anatomy and addressing the anterior nasal spine and maintaining the tip integrity is vital. AIM: To study the outcomes of "ROUND ABOUT technique" to correct deviated nasal septum which focuses on the importance of anterior spine and hence maintain the tip integrity. MATERIALS AND METHODS: This was a prospective, single-centre outcome study of 35 patients with symptomatic nasal obstruction. Here, we describe a method of elevating the mucoperichondrial and mucoperiosteal flaps bilaterally, without transecting the quadrilateral cartilage of the septum. The Sino Nasal Outcome Test-22 (SNOT-22) Questionnaire was administered pre-operatively and after 3 months following surgery. The post-operative follow-up period ranged from 3 to 6 months (mean= 4.5 months) to evaluate the functional and aesthetic outcomes of the performed procedure. RESULTS: A total of 35 patients underwent surgery by this technique who presented with deviated nasal septum and variable degrees of nasal obstruction. To assess the statistical outcome, Paired t-test was applied. Mean SNOT-22 scores decreased significantly from 40.02 pre-operatively to 18.65 three months after surgery. The results sustained after 6 months (p-value <0.0001), 85% of these patients had improved breathing post-operatively and none of the patients complained any aesthetic criticisms. The patients were content and the requirement of medications post-operatively were minimal. CONCLUSION: The ROUND ABOUT technique is a very effective and safe method in correcting the septal deviations especially the ones with caudal or dorsal deflections. It also helps in maintaining the tip integrity and addressing the anterior nasal spine. It avoids the complications of conventional septoplasty.

Cardiovascular changes in atherosclerotic ApoE-deficient mice exposed to Co60 (γ) radiation.

BACKGROUND: There is evidence for a role of ionizing radiation in cardiovascular diseases. The goal of this work was to identify changes in oxidative and nitrative stress pathways and the status of the endothelinergic system during progression of atherosclerosis in ApoE-deficient mice after single and repeated exposure to ionizing radiation. METHODS AND RESULTS: B6.129P2-ApoE tmlUnc mice on a low-fat diet were acutely exposed (whole body) to Co60 (γ) (single dose 0, 0.5, and 2 Gy) at a dose rate of 36.32 cGy/min, or repeatedly (cumulative dose 0 and 2 Gy) at a dose-rate of 0.1 cGy/min for 5 d/wk, over a period of 4 weeks. Biological endpoints were investigated after 3-6 months of recovery post-radiation. The nitrative stress marker 3-nitrotyrosine and the vasoregulator peptides endothelin-1 and endothelin-3 in plasma were increased (p<0.05) in a dose-dependent manner 3-6 months after acute or chronic exposure to radiation. The oxidative stress marker 8-isoprostane was not affected by radiation, while plasma 8-hydroxydeoxyguanosine and L-3,4-dihydroxyphenylalanine decreased (p<0.05) after treatment. At 2Gy radiation dose, serum cholesterol was increased (p = 0.008) relative to controls. Percent lesion area increased (p = 0.005) with age of animal, but not with radiation treatment. CONCLUSIONS: Our observations are consistent with persistent nitrative stress and activation of the endothelinergic system in ApoE-/- mice after low-level ionizing radiation exposures. These mechanisms are known factors in the progression of atherosclerosis and other cardiovascular diseases.

Stem cell therapy: a novel & futuristic treatment modality for disaster injuries.

Stem cell therapy hold the potential to meet the demand for transplant cells/tissues needed for treating damages resulting from both natural and man-made disasters. Pluripotency makes embryonic stem cells and induced pluripotent stem cells ideal for use, but their teratogenic character is a major hindrance. Therapeutic benefits of bone marrow transplantation are well known but characterizing the potentialities of haematopoietic and mesenchymal cells is essential. Haematopoietic stem cells (HSCs) have been used for treating both haematopoietic and non-haematopoietic disorders. Ease of isolation, in vitro expansion, and hypoimmunogenecity have brought mesenchymal stem cells (MSCs) into limelight. Though differentiation of MSCs into tissue-specific cells has been reported, differentiation-independent mechanisms seem to play a more significant role in tissue repair which need to be addressed further. The safety and feasibility of MSCs have been demonstrated in clinical trials, and their use in combination with HSC for radiation injury treatment seems to have extended benefit. Therefore, using stem cells for treatment of disaster injuries along with the conventional medical practice would likely accelerate the repair process and improve the quality of life of the victim.

Genetic and ultrastructural studies in dilated cardiomyopathy patients: a large deletion in the lamin A/C gene is associated with cardiomyocyte nuclear envelope disruption.

Major nuclear envelope abnormalities, such as disruption and/or presence of intranuclear organelles, have rarely been described in cardiomyocytes from dilated cardiomyopathy (DCM) patients. In this study, we screened a series of 25 unrelated DCM patient samples for (a) cardiomyocyte nuclear abnormalities and (b) mutations in LMNA and TMPO as they are two DCM-causing genes that encode proteins involved in maintaining nuclear envelope architecture. Among the 25 heart samples investigated, we identified major cardiomyocyte nuclear abnormalities in 8 patients. Direct sequencing allowed the detection of three heterozygous LMNA mutations (p.D192G, p.Q353K and p.R541S) in three patients. By multiplex ligation-dependant probe amplification (MLPA)/quantitative real-time PCR, we found a heterozygous deletion encompassing exons 3-12 of the LMNA gene in one patient. Immunostaining demonstrated that this deletion led to a decrease in lamin A/C expression in cardiomyocytes from this patient. This LMNA deletion as well as the p.D192G mutation was found in patients displaying major cardiomyocyte nuclear envelope abnormalities, while the p.Q353K and p.R541S mutations were found in patients without specific nuclear envelope abnormalities. None of the DCM patients included in the study carried a mutation in the TMPO gene. Taken together, we found no evidence of a genotype-phenotype relationship between the onset and the severity of DCM, the presence of nuclear abnormalities and the presence or absence of LMNA mutations. We demonstrated that a large deletion in LMNA associated with reduced levels of the protein in the nuclear envelope suggesting a haploinsufficiency mechanism can lead to cardiomyocyte nuclear envelope disruption and thus underlie the pathogenesis of DCM.

Antibodies against recombinant shiga toxin subunit B neutralize shiga toxin toxicity in HeLa cells.

Shigella dysenteriae type 1 and Escherichia coli O157:H7 produce Shiga toxin 1 (Stx) and Shiga toxin1 (Stx1), respectively and these two toxins are almost identical. E. coli O157:H7 is the major cause of diarrhea-associated hemolytic uremic syndrome. Stx and Stx1 are AB5 type of toxin with a molecular weight of 70 kDa, comprising an enzymaticaly-active A subunit (32 kDa) and five receptor-binding B subunits (7.7 kDa). In this study DNA fragment (289 bp, Gene Bank Accn No. EF685161) coding for B chain of Stx was amplified from S. dysenteriae type1 and cloned. Shiga toxin-binding subunit was expressed and purified in native conditions by affinity and gel permeation chromatography with the yield of 5.1 mg/L in shake flask culture. For the purpose of immunization, the polypeptide was polymerized with glutaraldehyde. Hyper immune serum produced in mice reacted with the purified polypeptide and intact Shiga toxin. The anti-StxB antiserum effectively neutralized the cytotoxicity of Shiga toxin towards HeLa cells.

Mesenchymal stem cell-based therapy: a new paradigm in regenerative medicine.

Mesenchymal stem cells (MSCs), adherent fibroblastoid cells, present in bone marrow and many other tissues can be easily isolated and expanded in vitro. They are capable of differentiating into different cell types such as osteoblasts, chondrocytes, adipocytes, cardiomyocytes, hepatocytes, endothelial cells and neuronal cells. Such immense plasticity coupled with their ability to modulate the activity of immune cells makes them attractive for stem cell-based therapy aimed at treating previously incurable disorders. Preclinical studies have reported successful use of MSCs for delivering therapeutic proteins and repairing defects in a variety of disease models. These studies highlighted the in vivo potential of MSCs and their ability to home to injury sites and modify the microenvironment by secreting paracrine factors to augment tissue repair. Their therapeutic applicability has been widened by genetic modification to enhance differentiation and tissue targeting, and use in tissue engineering. Clinical trials for diseases such as osteogenesis imperfecta, graft-versus-host disease and myocardial infarction have shown some promise, demonstrating the safe use of both allogeneic and autologous cells. However, lack of knowledge of MSC behaviour and responses in vitro and in vivo force the need for basic and animal studies before heading to the clinic. Contrasting reports on immunomodulatory functions and tumorigenicity along with issues such as mode of cell delivery, lack of specific marker, low survival and engraftment require urgent attention to harness the potential of MSC-based therapy in the near future.

PU.1 and partners: regulation of haematopoietic stem cell fate in normal and malignant haematopoiesis.

During normal haematopoiesis, cell development and differentiation programs are accomplished by switching 'on' and 'off' specific set of genes. Specificity of gene expression is primarily achieved by combinatorial control, i.e. through physical and functional interactions among several transcription factors that form sequence-specific multiprotein complexes on regulatory regions (gene promoters and enhancers). Such combinatorial gene switches permit flexibility of regulation and allow numerous developmental decisions to be taken with a limited number of regulators. The haematopoietic-specific Ets family transcription factor PU.1 regulates many lymphoid- and myeloid-specific gene promoters and enhancers by interacting with multiple proteins during haematopoietic development. Such protein-protein interactions regulate DNA binding, subcellular localization, target gene selection and transcriptional activity of PU.1 itself in response to diverse signals including cytokines, growth factors, antigen and cellular stresses. Specific domains of PU.1 interact with many protein motifs such as bHLH, bZipper, zinc fingers and paired domain for regulating its activity. This review focuses on important protein-protein interactions of PU.1 that play a crucial role in regulation of normal as well as malignant haematopoiesis. Precise delineation of PU.1 protein-partner interacting interface may provide an improved insight of the molecular mechanisms underlying haematopoietic stem cell fate regulation. Its interactions with some proteins could be targeted to modulate the aberrant signalling pathways for reversing the malignant phenotype and to control the generation of specific haematopoietic progeny for treatment of haematopoietic disorders.

Mesenchymal stem cells: molecular targets for tissue engineering.

Mesenchymal stem cells (MSCs) represent an adherent, fibroblast-like population present not only in the bone marrow, but in a number of tissues, including blood, adipose tissue, muscle, and dermis. Their extensive proliferation and transdifferentiation potential makes them best suited for tissue engineering applications. Identification of growth factors and signaling pathways involved in self-renewal and differentiation is important for designing strategies to overcome replicative senescence and attain directed differentiation. Wnt, bone morphogenetic protein (BMP), and Notch pathways have been implicated to play key roles in self-renewal and differentiation of hematopoietic, intestinal, and epidermal stem cells. They are also involved in regulating MSC differentiation. However, MSC self-renewal has not received much attention, with Nucleostemin being the only recently identified proliferation molecule. Although immortalization using viral oncogenes and telomerase has been achieved, transformation in long-term cultures is a potential risk. Understanding of the mechanisms governing osteogenic differentiation of MSCs is expanding with the recent identification of two major transcription factors, Osterix and Runx2. Enhanced expansion as well as osteogenic differentiation of MSCs can be attained using a combinatorial approach involving co-expression of proliferation and differentiation genes. However, a thorough understanding of the molecular mechanism is necessary for enhancing the self-renewal ability and osteogenic potential in vitro.

PU.1: An ETS family transcription factor that regulates leukemogenesis besides normal hematopoiesis.

The hematopoietic transcription factor PU.1, which is required for lymphomyeloid differentiation of stem cells, was originally identified as an oncogene. In erythroid progenitors, the integration of spleen focus-forming virus (SFFV) into the PU.1 locus causes its overexpression, which blocks their terminal differentiation into erythrocytes and ultimately leads to the development of erythroleukemia. However, in myeloid lineages, PU.1 promotes granulocytic and monocytic differentiation, and graded reduction in its expression blocks their differentiation or maturation and thereby causes myelogenous leukemia. Thus, in addition to normal hematopoietic regulation, PU.1 plays a significant role in leukemogenesis. In the following review, we have consolidated our understanding of the role of transcription factor PU.1 in the development of erythroid as well myeloid leukemia.

Hematopoietic stem cell antigen CD34: role in adhesion or homing.

CD34 is highly glycosylated surface antigen of enormous clinical utility in the identification, enumeration, and purification of engraftable lymphohematopoietic progenitors for transplantation. However, recently its importance in the specific marking of most immature hematopoietic stem/progenitor cells have been questioned by addressing long-term reconstitution capability of CD34(-) hematopoietic cellular fractions. These controversies have stimulated a demand for elucidation of the structure, function, and molecular interactions of CD34 to define exactly its biological significance in clinical regimens. There is accumulating data showing the participation of CD34 in adhesion or perhaps homing of lymphohematopoietic progenitors. On the other hand, CD34 has been demonstrated to down-regulate cytokine-induced differentiation and proliferation of CD34(+) cells. Studies in CD34 knockout mice revealed normal hematopoiesis but a profound delay in hematopoietic reconstitution after sublethal irradiation of the mice. In short, CD34 expression is likely to represent a specific state of hematopoietic development that may have altered adhering properties with expanding and differentiating capabilities in both in vitro and in vivo conditions. This article focuses on the adhesive properties of CD34 and its potential role in homing, which are likely to mimic lymphocyte homing to the inflammatory sites.

Stem cell c-KIT and HOXB4 genes: critical roles and mechanisms in self-renewal, proliferation, and differentiation.

Hematopoietic stem cells (HSCs) possess a distinct ability to perpetuate through self-renewal and to generate progeny that differentiate into mature cells of myeloid and lymphoid lineages. A better understanding of the molecular mechanisms by which HSCs replicate and differentiate from the perspective of developing new approaches for HSC transplantation is necessary for further advances. The interaction of the receptor tyrosine kinase--c-KIT--with its ligand stem cell factor plays a key role in HSC survival, mitogenesis, proliferation, differentiation, adhesion, homing, migration, and functional activation. Evidence that activating site-directed point mutations in the c-KIT gene contributes to its ligand-independent constitutive activation, which induces enhanced proliferation of HSCs, is accumulating. Similarly, and equally important, self-renewal is a process by which HSCs generate daughter cells via division. Self-renewal is necessary for retaining the HSC pool. Therefore, elucidating the molecular machinery that governs self-renewal is of key importance. The transcription factor, HOXB4 is a key molecule that has been reported to induce the in vitro expansion of HSCs via self-renewal. However, critical downstream effector molecules of HOXB4 remain to be determined. This concisely reviewed information on c-KIT and HOXB4 helps us to update our understanding of their function and mechanism of action in self-renewal, proliferation, and differentiation of HSCs, particularly modulation by c-KIT mutant interactions, and HOXB4 overexpression showing certain therapeutic implications.