In silico analysis indicates a similar gene expression pattern between human brain and testis

OBJECTIVES

Previous data has reported similarity between human brain and testis gene expression patterns. Brain is the most important tissue in human speciation. Hence, it means that human testis could also play a crucial role in human speciation if these two tissues exhibit similar gene expression patterns. However, previous reports were based on only limited and scattered data. Determining the large scale anatomy of gene expression patterns of various human tissues could draw a more convincing conclusion, and better our understanding of the correlation/inter-correlation among different tissues. Furthermore, it could also provide a clue for evolutionary study.

METHODS

To obtain gene expression information for large-scale data analysis, expression data of 760 Unigenes in seventeen human tissues (liver, lung, testis, brain, ovary, uterus, colon, stomach, heart, eye, kidney, spleen, gall bladder, breast, thymus, prostate and pancreas) were retrieved by DDD (differential digital display) analysis, and this expression data was subjected to clustering analysis. These Unigenes represent a wide range of genes classified according to their characterization and function.

RESULTS

Among the 17 tissues, the highest similarity in gene expression patterns was between human brain and testis, based on DDD and clustering analysis. Genes contributing to the similarity include ribosomal protein (RP) genes as well as genes involved in transcription, translation and cell division.

CONCLUSIONS

Present results provide evidence to support the proposal that human testis and brain share the highest similarity of gene expression patterns. The implications of the similarity regarding that both brain and testis contributed to human speciation are discussed.

Whole-Organ Magnetic Resonance Imaging Score (WORMS) of the knee in osteoarthritis

OBJECTIVES

To describe a semi-quantitative scoring method for multi-feature, whole-organ evaluation of the knee in osteoarthritis (OA) based on magnetic resonance imaging (MRI) findings. To determine the inter-observer agreement of this scoring method. To examine associations among the features included in the scoring method.

METHODS

Nineteen knees of 19 patients with knee OA were imaged with MRI using conventional pulse sequences and a clinical 1.5 T MRI system. Images were independently analyzed by two musculoskeletal radiologists using a whole-organ MRI scoring method (WORMS) that incorporated 14 features: articular cartilage integrity, subarticular bone marrow abnormality, subarticular cysts, subarticular bone attrition, marginal osteophytes, medial and lateral meniscal integrity, anterior and posterior cruciate ligament integrity, medial and lateral collateral ligament integrity, synovitis/effusion, intraarticular loose bodies, and periarticular cysts/bursitis. Intraclass correlation coefficients (ICC) were determined for each feature as a measure of inter-observer agreement. Associations among the scores for different features were expressed as Spearman Rho.

RESULTS

All knees showed structural abnormalities with MRI. Cartilage loss and osteophytes were the most prevalent features (98% and 92%, respectively). One of the least common features was ligament abnormality (8%). Inter-observer agreement for WORMS scores was high (most ICC values were >0.80). The individual features showed strong inter-associations.

CONCLUSION

The WORMS method described in this report provides multi-feature, whole-organ assessment of the knee in OA using conventional MR images, and shows high inter-observer agreement among trained readers. This method may be useful in epidemiological studies and clinical trials of OA.

Characterization of Salmonella enterica serotype newport isolated from humans and food animals

Salmonella enterica serotype Newport isolates resistant to at least nine antimicrobials (including extended-spectrum cephalosporins), known as serotype Newport MDR-AmpC isolates, have been rapidly emerging as pathogens in both animals and humans throughout the United States. Resistance to extended-spectrum cephalosporins is associated with clinical failures, including death, in patients with systemic infections. In this study, 87 Salmonella serotype Newport strains were characterized by pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing and examined for the presence of class 1 integrons and bla(CMY) genes. Thirty-five PFGE patterns were observed with XbaI, and three of these patterns were indistinguishable among isolates from humans and animals. Fifty-three (60%) Salmonella serotype Newport isolates were identified as serotype Newport MDR-AmpC, including 16 (53%) of 30 human isolates, 27 (93%) of 29 cattle isolates, 7 (70%) of 10 swine isolates, and 3 (30%) of 10 chicken isolates. However, 28 (32%) Salmonella serotype Newport isolates were susceptible to all 16 antimicrobials tested. The bla(CMY) gene was present in all serotype Newport MDR-AmpC isolates. Furthermore, the plasmid-mediated bla(CMY) gene was transferable via conjugation to an Escherichia coli strain. The transconjugant showed the MDR-AmpC resistance profile. Thirty-five (40%) of the isolates possessed class 1 integrons. Sequence analyses of the integrons showed that they contained aadA, which confers resistance to streptomycin, or aadA and dhfr, which confer resistance to trimethoprim-sulfamethoxazole. One integron from a swine isolate contained the sat-1 gene, which encodes resistance to streptothricin, an antimicrobial agent that has never been approved for use in the United States. In conclusion, Salmonella serotype Newport MDR-AmpC was commonly identified among Salmonella serotype Newport isolates recovered from humans and food animals. These findings support the possibility of transmission of this organism to humans through the food chain.

Preferential production of latent transforming growth factor ?-2 by primary prostatic epithelial cells and its activation by prostate-specific antigen

Three mammalian isoforms of transforming growth factor-beta (TGFbeta) are known, TGFbeta1, 2, and 3, that have non-overlapping functions during development. However, their specific roles in cancers such as prostate cancer are less clear. Here we show that primary cultures of prostatic epithelial cells preferentially produce and activate the latent TGFbeta2 isoform. Paired cultures of normal and malignant prostate cells from prostate cancer patients produced predominantly the TGFbeta2 isoform, with 30- to 70-fold less TGFbeta1. By mono-Q ion exchange chromatography, three major peaks of latent TGFbeta2 activity were observed corresponding to the known small latent TGFbeta2 complex, the known large latent TGFbeta2 complex and a novel eluting peak of latent TGFbeta2. Although prostate cells are known to activate latent TGFbeta, the mechanism for activation is currently unclear. We investigated whether prostate specific antigen (PSA), a serine protease used as a clinical marker for prostate cancer, could play a role in the activation of latent TGFbeta. Unlike plasmin, a known activator of both latent TGFbeta1 and 2, PSA specifically activated the recombinant small latent form of TGFbeta2, but not TGFbeta1. Prostate epithelial cells, therefore, preferentially produce the TGFbeta2 isoform and PSA, a protease produced by the prostate, specifically targets the activation of this TGFbeta isoform. PSA-mediated activation of latent TGFbeta2 may be an important mechanism for autocrine TGFbeta regulation in the prostate and may potentially contribute to the formation of osteoblastic lesions in bone metastatic prostate cancer.

Inhibition of phosphatidylinositol 3-kinase dephosphorylates BAD and promotes apoptosis in myeloid leukemias

The phosphatidylinositol 3-kinase (PI3K)/AKT protein kinase pathway is involved in cell growth, proliferation, and apoptosis. The functional activation of PI3K/AKT provides survival signals and blockade of this pathway may facilitate cell death. Downstream targets of PI3K-AKT include the proapoptotic protein BAD, caspase-9, NF-kappaB, and Forkhead. We have previously reported that BAD is constitutively phosphorylated in primary acute myeloid leukemia (AML) cells, a post-transcriptional modification, which inactivates its proapoptotic function. In this study, we tested the hypothesis that the inhibition of PI3K by LY294002 results in the dephosphorylation of AKT and BAD, and thus promote leukemia cell apoptosis. We investigated the effects of LY294002 in megakaryocytic leukemia-derived MO7E cells, primary AML and normal bone marrow progenitor cells. In MO7E cells, LY294002 reduced AKT kinase activity, induced dephosphorylation of AKT and BAD, and increased apoptosis. Concomitant inhibition of mitogen-activated protein kinase signaling or combination with all-trans retinoic acid further enhanced apoptosis of leukemic cells. In primary AML samples, clonogenic cell growth was significantly reduced. Normal hematopoietic progenitors were less affected, suggesting preferential targeting of leukemia cells. In conclusion, the data suggest that the inhibition of the PI3K/AKT signaling pathway restores apoptosis in AML and may be explored as a novel target for molecular therapeutics in AML.

Antimicrobial susceptibility and genetic relatedness of Salmonella serovars isolated from animal-derived dog treats in the USA

OBJECTIVES

The objectives of this study were to determine the potential risk of dog treats in transmitting Salmonella to humans in the USA, and to characterize genetic relatedness and antimicrobial resistance among the isolates.

METHODS

A total of 158 dog treats derived from pig ears and other animal parts were randomly collected nationwide and assayed for the presence of Salmonella. The Salmonella isolates were characterized using serotyping, pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing.

RESULTS

Forty-one percent (65/158) of samples were positive for Salmonella. Eighty-four Salmonella isolates, comprising 24 serotypes, were recovered from the 65 positive samples. Fourteen samples were contaminated with more than one Salmonella serotype. PFGE analysis of 78 Salmonella isolates yielded 64 patterns. S. Infantis with PFGE patterns indistinguishable from those of strains identified in Canadian outbreaks in 1999 were recovered in several dog treat products. The majority of Salmonella isolates were susceptible to the antimicrobials tested; however, resistance was observed to tetracycline (26%), streptomycin (23%), sulfamethoxazole (19%), chloramphenicol (8%) and ampicillin (8%). Twenty-eight (36%) Salmonella isolates were resistant to at least one antimicrobial and 10 (13%) isolates displayed resistance to four or more antimicrobials. Two isolates were identified as S. Typhimurium DT104 with the characteristic penta-resistance phenotype (ampicillin, chloramphenicol, streptomycin, sulfamethoxazole and tetracycline). One S. Brandenburg isolate was resistant to eight antimicrobials. Seven Salmonella isolates also contained class I integrons encoding resistance genes to aminoglycosides, beta-lactam and streptothricin antimicrobials.

CONCLUSIONS

The study indicates that animal-derived dog treats in the USA could be a potential source of animal and human infections with Salmonella, including multidrug-resistant Salmonella strains.

Using a pericentromeric interspersed repeat to recapitulate the phylogeny and expansion of human centromeric segmental duplications

Despite considerable advances in sequencing of the human genome over the past few years, the organization and evolution of human pericentromeric regions have been difficult to resolve. This is due, in part, to the presence of large, complex blocks of duplicated genomic sequence at the boundary between centromeric satellite and unique euchromatic DNA. Here, we report the identification and characterization of an approximately 49-kb repeat sequence that exists in more than 40 copies within the human genome. This repeat is specific to highly duplicated pericentromeric regions with multiple copies distributed in an interspersed fashion among a subset of human chromosomes. Using this interspersed repeat (termed PIR4) as a marker of pericentromeric DNA, we recovered and sequence-tagged 3 Mb of pericentromeric DNA from a variety of human chromosomes as well as nonhuman primate genomes. A global evolutionary reconstruction of the dispersal of PIR4 sequence and analysis of flanking sequence supports a model in which pericentromeric duplications initiated before the separation of the great ape species (>12 MYA). Further, analyses of this duplication and associated flanking duplications narrow the major burst of pericentromeric duplication activity to a time just before the divergence of the African great ape and human species (5 to 7 MYA). These recent duplication exchange events substantially restructured the pericentromeric regions of hominoid chromosomes and created an architecture where large blocks of sequence are shared among nonhomologous chromosomes. This report provides the first global view of the series of historical events that have reshaped human pericentromeric regions over recent evolutionary time.

Genetic Diversity Present Within the Near-Complete mtDNA Genome of 17 Breeds of Indigenous Chinese Pigs

The genetic diversity present within the near-complete mitochondrial genome (15,982 bp) was determined from 17 indigenous Chinese pig breeds and 3 European breeds. Animals were selected from 17 Chinese breeds that reflect the large phenotypic diversity of Chinese pigs and represent each of the six breed types, which are grouped based on morphological characteristics. Analysis of nucleotide diversity confirmed a high level of divergence between animals of European versus Asian origin; however, much more limited variation was observed between the 17 indigenous Chinese breeds. Each had a unique haplotype, but the lowest pairwise sequence divergence was only 0.01 +/- 0.01%, observed between the Tongcheng and Yushan Black. Comparison of control region sequence diversity revealed the 17 Chinese breeds contain a lower average pairwise distance (0.61 +/- 0.19%) than a group of European commercial breeds (0.91 +/- 0.21%). The dendrogram constructed from the near-complete mtDNA sequences showed the Chinese sequences loosely clustering into two groups. Although some correspondence with geographic origin was present, notable differences between the dendrogram and the traditional pig breed grouping system were observed.

Putative protein markers in the sera of men with prostatic neoplasms

OBJECTIVE

To describe the preliminary identification of serum proteins that may be diagnostic markers in prostate cancer.

PATIENTS AND METHODS

The study included 11 men referred for treatment of localized prostate cancer, 12 with benign prostatic hyperplasia (BPH) and 12 disease-free controls. For serum protein analysis, the protein-chip array surface-enhanced laser desorption/ionization (SELDI) technique was used (Ciphergen Biosystems, Fremont, CA). SELDI combines protein-chip technology with time-of-flight mass spectrometry, and offers the advantages of speed, simplicity and sensitivity.

RESULTS

Three protein peaks were identified in the serum of men with prostate cancer and BPH, but not in controls, with relative molecular masses of 15.2, 15.9 and 17.5 kDa. These three proteins were significantly associated with BPH and prostate cancer when compared with controls (P = 0.001, 0.004, and 0.011, respectively, Kruskal-Wallis test). Interestingly, the 17.5 kDa protein was more abundant in five men with stage T1 prostate cancer than in eight with stage T2 (P = 0.016, two tailed Mann-Whitney U-test corrected for ties).

CONCLUSIONS

These proteins, particularly the 15.9 kDa one, may be used for the diagnosis or monitoring of prostate cancer and differentiation from BPH, and have the potential for antibody-based chip SELDI-TOF technology. Identified proteins may be targets for immunotherapy.

[Changes in computed tomogram in cerebral parenchymal cysticercosis treated with albendazole]

AIM

To observe the changes in cerebral computed tomogram (CT) in cerebral parenchymal cysticercosis after albendazole treatment.

METHODS

Cerebral CT scanning was conducted in 57 patients with cerebral cysticercosis in our hospital before, during and after albendazole treatment.

RESULTS

Cerebral CT might be normal before onchospheres became cysticercariae in the brain. Small cystic lesions could turn into other CT signs of cerebral cysticercosis after albendazole treatment.

CONCLUSION

Normal cerebral CT cannot rule out the disease. Small cystic lesions are the earliest pathological and active signs of the disease. Nodular focus occurs after the death of Cysticercus and calcification is the final outcome of the disease.

TGF-beta1 suppresses apoptosis via differential regulation of MAP kinases and ceramide production

Serum deprivation induces apoptosis in NIH3T3 cells, which is associated with increased intracellular ceramide generation and with the activation of p38 mitogen-activated protein (MAP) kinase. Treatment of cells with transforming growth factor-beta1 (TGF-beta1) activated the extracellular signal regulated kinases 1 and 2 (ERK1/ERK2), inhibited the serum deprivation-induced p38 activation and the increase in intracellular ceramide formation, leading to the stimulation of cell proliferation and the suppression of apoptosis. Inhibition of p38 MAP kinase by SB203580 significantly reduced the serum-deprivation-induced apoptosis. Overexpression of p38 increased the cell apoptosis and reduced the antiapoptotic effect of TGF-beta1. Inhibition of ERK1/ERK2 by PD98059 completely inhibited the TGF-beta1-stimulated proliferation and partially inhibited the antiapoptotic effects of TGF-beta1. Neither SB203580 nor PD98059 has obvious effect on TGF-beta1-mediated inhibition of the increased ceramide generation. Serum-deprivation-induced apoptosis in NIH3T3 cells can also be blocked by broad-spectrum caspase inhibitor. TGF-beta1 treatment has an inhibitory effect on caspase activities. Our results indicate that ceramide, p38, and ERK1/ERK2 play critical but differential roles in cell proliferation and stress-induced apoptosis. TGF-beta1 suppresses the serum-deprivation-induced apoptosis via its distinct effects on complex signaling events involving the activation of ERK1/ERK2 and the inhibition of p38 activation and increased ceramide generation.

Cloning of human myeloid-associated differentiation marker (MYADM) gene whose expression was up-regulated in NB4 cells induced by all-trans retinoic acid

A full-length cDNA of 3192 bp isolated from human bone marrow cDNA library was predicted an ORF encoding 298 amino acids. The deduced protein, containing seven putative transmembrane segments and sharing 75.8% amino acid identity with mouse Myadm protein, was named as human MYADM. The results of Northern blot analysis showed that MYADM was ubiquitously expressed in 15 of 16 adult tissues tested, except thymus. To determine whether the novel human gene was involved in hematopoietic differentiation process as mouse Myadm did, we examined the mRNA expressive abundance of this gene between normal bone marrow cells and peripheral blood leukocytes, and detected the expression change in NB4 cells induced by all-trans retinoic acid at different induce time by the semi-quantitative RT-PCR. The results showed that the expression of the novel gene was not only significantly higher in peripheral blood leukocytes than in bone marrow cells, but also significantly up-regulated when the NB4 cells(derived from a patient with acute promyelocytic leukemia) were induced by all-trans retinoic acid (ATRA) for 48hr. It is suggested that human MYADM was also associated with the differentiation of hematopoietic cells or acute promyelocytic leukemia cells. In addition, MYADM was mapped to human chromosome 19q 13.33-q 13.4 by Radiation Hybrid mapping, and it consists of 3 exons and 2 introns and spans a 7.1-Kb genomic region.

Superinfection of Laodelphax striatellus with Wolbachia from Drosophila simulans

Wolbachia are maternally inherited, intracellular alpha-proteobacteria that infect a wide range of arthropods. They manipulate the reproduction of hosts to facilitate their spread into host populations, through ways such as cytoplasmic incompatibility (CI), parthenogenesis, feminization and male killing. The influence of Wolbachia infection on host populations has attracted considerable interest in their possible role in speciation and as a potential agent of biological control. In this study, we used both microinjection and nested PCR to show that the Wolbachia naturally infecting Drosophila simulans can be transferred into a naturally Wolbachia-infected strain of the small brown planthopper Laodelphax striatellus, with up to 30% superinfection frequency in the F(12) generation. The superinfected males of L. striatellus showed unidirectional CI when mated with the original single-infected females, while superinfected females of L. striatellus were compatible with superinfected or single-infected males. These results are, to our knowledge, the first to establish a superinfected horizontal transfer route for Wolbachia between phylogenetically distant insects. The segregation of Wolbachia from superinfected L. striatellus was observed during the spreading process, which suggests that Wolbachia could adapt to a phylogenetically distant host with increased infection frequency in the new host population; however, it would take a long time to establish a high-frequency superinfection line. This study implies a novel way to generate insect lines capable of driving desired genes into Wolbachia-infected populations to start population replacement.

A study on the section sensitivity profile in multi-row-detector spiral CT

The section sensitivity profile (SSP) was well understood in the case of single-row-detector spiral CT. With the introduction of multi-row-detector spiral CT and the transition into cone-beam spiral CT, a revisit to the SSP issue becomes necessary. In this paper, the SSP of multi-row-detector spiral CT is formulated for the half-scan interpolation method at any transverse position. Based on the SSP formula, numerical simulation is performed to quantify the characteristics of the SSP with the number of detector rows up to 40. It is shown that the SSP varies as a function of the pitch and the number of detector rows. Given an appropriate selection of the pitch and the number of detector rows, the SSP does not change very much over the field of view in terms of the mean, the slice thickness, and the skewness of the SSP. Although in general applications the SSP at the gantry iso-center can be used as the representative of the SSP family, for more accurate analyses the spatial variation of the SSP must be taken into account.

Characterization of antimicrobial resistance among Escherichia coli O111 isolates of animal and human origin

Fifty isolates of Escherichia coli serogroup O111 recovered from humans and various animal species over a 24-year period (1976-1999) were examined for typical virulence-associated factors and susceptibilities to antimicrobials of human and veterinary significance. Nine H (flagellar) types were identified including nonmotile (n = 24), 32 (n = 12), negative (n = 5), and 56 (n = 3). Thirty-five (70%) isolates possessed at least one Shiga-toxin-producing E. coli (STEC)-associated virulence determinants (eae, stxl, stx2, hlyA) via PCR analysis. Of these 35 isolates, 20 possessed eae, stxl, and hlyA genes, whereas three isolates possessed eae, stxl, stx2, and hylA genes. Multiple antibiotic resistance was observed in 70% of the 50 E. coli O111 isolates. The majority of isolates displayed resistance to streptomycin, sulfamethoxazole, tetracycline, and kanamycin. Bacterial resistance to ampicillin, gentamicin, chloramphenicol, trimethoprim and apramycin was also observed. Integrons were identified in 23 (46%) of the E. coli isolates assayed, with a 1-kb amplicon being most frequently observed. DNA sequencing of these integrons revealed the presence of the aadA gene, encoding resistance to streptomycin. Two integrons of 1.5 and 2 kb contained the aadA2 and either dfrI or dfrXII genes, encoding resistance to streptomycin and trimethoprim, respectively. Integrons were also identified from isolates dating back to 1982. Isolates were further genetically characterized via ribotyping, which identified 15 distinct ribogroups, with 62% of isolates clustering into four major ribogroups. Certain riboprint patterns from different animal species, including humans, were observed in isolates spanning the 24-year collection period, suggesting the dissemination of specialized pathogenic O111 clones.

[Relationship of age, sex, body weight, smoking, blood lipids and fibrinolytic activities in healthy subjects]

Relationship of plasma activities of tissue-type plasminogen activator (tPA) and plasminogen activator inhibitor-1(PAI-1) with age, sex, body weight, smoking, blood lipids were studied in 131 healthy subjects. The results demonstrated that plasma PAI-1 activity increased with age and body weight. PAI-1/t-PA ratio was higher in smoking than in non-smoking subjects. With multivariate analyses, plasma PAI-1 activity was positively correlated with age, body weight index(BMI) in males, and positively correlated with low-density-lipoprotein-cholesterol(LDL) in females, and negatively correlated with plasma tPA activity. Plasma triglyceride, high-density-lipoprotein-cholesterol did not show a correlation to PAI-1 or tPA activity. It is indicated that age, BMI, blood lipids may contribute to moderate fibrinolytic activities and that smoking may affect fibrinolytic function.

Prevalence of streptogramin resistance genes among Enterococcus isolates recovered from retail meats in the Greater Washington DC area

The prevalence of streptogramin resistance genes in enterococci recovered from retail poultry in the Greater Washington DC area was examined. Forty-three chicken and 32 turkey retail samples were analysed. Thirty-one non-Enterococcus faecalis enterococcal strains were isolated that displayed MICs of quinupristin-dalfopristin and virginiamycin of > or = 4 mg/L. These included Enterococcus faecium (turkey n = 4, chicken n = 23), Enterococcus gallinarum (turkey n = 2, chicken n = 1) and Enterococcus hirae (chicken n = 1). The presence of streptogramin resistance genes was examined by PCR in all non-E. faecalis isolates. The vat(E) gene was detected in 10/23 chicken E. faecium and from 2/4 turkey E. faecium. No other streptogramin resistance genes were detected by PCR. In addition, erm(B) was detected in all the E. faecium and E. gallinarum found in turkeys and in 7/23 E. faecium found in chickens. The vat(E) gene was transferable by conjugation from only two of the 12 E. faecium isolates (one from chicken and one from turkey). This study suggests that there is a high prevalence of low-level streptogramin resistance among enterococci found in retail poultry and that other, yet to be identified, mechanisms operate in these isolates that confer streptogramin resistance in enterococci.

Identification of vat(E) in Enterococcus faecalis isolates from retail poultry and its transferability to Enterococcus faecium

Sixteen isolates of Enterococcus faecalis were recovered from retail poultry samples (seven chickens and nine turkeys) purchased from grocery stores in the greater Washington, D.C., area. PCR for known streptogramin resistance genes identified vat(E) in five E. faecalis isolates (three isolates from chickens and two isolates from turkeys). The vat(E) gene was transmissible on a ca. 70-kb plasmid, along with resistance to erythromycin, tetracycline, and streptomycin, by conjugation to E. faecalis and Enterococcus faecium recipient strains. DNA sequencing showed little variation between E. faecalis vat(E) genes from the chicken samples; however, one E. faecalis vat(E) gene from a turkey sample possessed 5 nucleotide changes that resulted in four amino acid substitutions. None of these substitutions in the vat(E) allele have previously been described. This is the first report of vat(E) in E. faecalis and its transferability to E. faecium, which indicates that E. faecalis can act as a reservoir for the dissemination of vat(E)-mediated streptogramin resistance to E. faecium.

MLO-Y4 osteocyte-like cells support osteoclast formation and activation

Osteocytes are terminally differentiated cells of the osteoblast lineage that have become embedded in mineralized matrix and may send signals that regulate bone modeling and remodeling. The hypothesis to be tested in this study is that osteocytes can stimulate and support osteoclast formation and activation. To test this hypothesis, an osteocyte-like cell line called MLO-Y4 and primary murine osteocytes were used in coculture with spleen or marrow cells. MLO-Y4 cells support osteoclast formation in the absence of 1,25-dihydroxyvitamin D3 [1,25(OD)2D3] or any other exogenous osteotropic factor. These cells alone stimulate osteoclast formation to the same extent or greater than adding 1,25(OH)2D3. Coaddition of 1,25(OH)2D3 with MLO-Y4 cells synergistically increased osteoclast formation. Optimal osteoclast formation and pit formation on dentine was observed with 200-1,000 MLO-Y4 cells per 0.75-cm2 well. No osteoclast formation was observed with 2T3, OCT-1, or MC3T3-E1 osteoblast cells (1,000 cells/well). Conditioned media from the MLO-Y4 cells had no effect on osteoclast formation, indicating that cell contact is necessary. Serial digestions of 2-week-old mouse calvaria yielded populations of cells that support osteoclast formation when cocultured with 1,25(OH)2D3 and marrow, but the population that remained in the bone particles supported the greatest number of osteoclasts with or without 1,25(OH)2D3. To examine the mechanism whereby these cells support osteoclast formation, the MLO-Y4 cells were compared with a series of osteoblast and stromal cells for expression of macrophage colony-stimulating factor (M-CSF), RANKL, and osteoprotegerin (OPG). MLO-Y4 cells express and secrete large amounts of M-CSF. MLO-Y4 cells express RANKL on their surface and their dendritic processes. The ratio of RANKL to OPG mRNA is greatest in the MLO-Y4 cells compared with the other cell types. RANK-Fc and OPG-Fc blocked the formation of osteoclasts by MLO-Y4 cells. These studies suggest that both RANKL and OPG may play a role in osteocyte signaling, OPG and M-CSF as soluble factors and RANKL as a surface molecule that is functional in osteocytes or along their exposed dendritic processes.