The GM-CSF receptor utilizes ß-catenin and Tcf4 to specify macrophage lineage differentiation.

Granulocyte-macrophage colony stimulating factor (GM-CSF) promotes the growth, survival, differentiation and activation of normal myeloid cells and is essential for fully functional macrophage differentiation in vivo. To better understand the mechanisms by which growth factors control the balance between proliferation and self-renewal versus growth-suppression and differentiation we have used the bi-potent FDB1 myeloid cell line, which proliferates in IL-3 and differentiates to granulocytes and macrophages in response to GM-CSF. This provides a manipulable model in which to dissect the switch between growth and differentiation. We show that, in the context of signaling from an activating mutant of the GM-CSF receptor ß subunit, a single intracellular tyrosine residue (Y577) mediates the granulocyte fate decision. Loss of granulocyte differentiation in a Y577F second-site mutant is accompanied by enhanced macrophage differentiation and accumulation of ß-catenin together with activation of Tcf4 and other Wnt target genes. These include the known macrophage lineage inducer, Egr1. We show that forced expression of Tcf4 or a stabilised ß-catenin mutant is sufficient to promote macrophage differentiation in response to GM-CSF and that GM-CSF can regulate ß-catenin stability, most likely via GSK3ß. Consistent with this pathway being active in primary cells we show that inhibition of GSK3ß activity promotes the formation of macrophage colonies at the expense of granulocyte colonies in response to GM-CSF. This study therefore identifies a novel pathway through which growth factor receptor signaling can interact with transcriptional regulators to influence lineage choice during myeloid differentiation.

Identification of genes differentially expressed by prematurely fused human sutures using a novel in vivo - in vitro approach.

Craniosynostosis is the premature fusion of calvarial sutures. It results from abnormal differentiation or proliferation of cells within the osteogenic fronts of growing calvarial bones. To date, research has focused on animal models and in vitro organ and tissue culture to determine the molecular mechanisms controlling calvarial suture morphogenesis. Here, we test a new, in vivo-in vitro approach based on the hypothesis that calvarial suture cells passaged in minimal medium exhibit a stable gene expression profile similar to undifferentiated osteoblastic cells that can provide a benchmark for comparison with in vivo expression of differentiated tissue. We show that tissue-specific expression is lost after the first passage and, using cDNA microarrays, compare expression between fused suture tissue from craniosynostosis patients and in vitro de-differentiated explant cells. A large number of differentially expressed genes were identified, including novel genes WIF1, LEF1, SATB2, RARRES1, DEFA1, DMP1, PTPRZ1, and PTPRC, as well as those commonly associated with human suture morphogenesis, e.g., FGF2, MSX2, and BMP2. Two differentially expressed genes, WIF1 and FGF2, were further examined in an in vivo-in vivo comparison between unfused and prematurely fused tissue. The same pattern of differential expression was observed in each case, further validating the ability of our in vivo-in vitro approach to identify genes involved in in vivo human calvarial tissue differentiation.

Unravelling the molecular control of calvarial suture fusion in children with craniosynostosis.

BACKGROUND: Craniosynostosis, the premature fusion of calvarial sutures, is a common craniofacial abnormality. Causative mutations in more than 10 genes have been identified, involving fibroblast growth factor, transforming growth factor beta, and Eph/ephrin signalling pathways. Mutations affect each human calvarial suture (coronal, sagittal, metopic, and lambdoid) differently, suggesting different gene expression patterns exist in each human suture. To better understand the molecular control of human suture morphogenesis we used microarray analysis to identify genes differentially expressed during suture fusion in children with craniosynostosis. Expression differences were also analysed between each unfused suture type, between sutures from syndromic and non-syndromic craniosynostosis patients, and between unfused sutures from individuals with and without craniosynostosis. RESULTS: We identified genes with increased expression in unfused sutures compared to fusing/fused sutures that may be pivotal to the maintenance of suture patency or in controlling early osteoblast differentiation (i.e. RBP4, GPC3, C1QTNF3, IL11RA, PTN, POSTN). In addition, we have identified genes with increased expression in fusing/fused suture tissue that we suggest could have a role in premature suture fusion (i.e. WIF1, ANXA3, CYFIP2). Proteins of two of these genes, glypican 3 and retinol binding protein 4, were investigated by immunohistochemistry and localised to the suture mesenchyme and osteogenic fronts of developing human calvaria, respectively, suggesting novel roles for these proteins in the maintenance of suture patency or in controlling early osteoblast differentiation. We show that there is limited difference in whole genome expression between sutures isolated from patients with syndromic and non-syndromic craniosynostosis and confirmed this by quantitative RT-PCR. Furthermore, distinct expression profiles for each unfused suture type were noted, with the metopic suture being most disparate. Finally, although calvarial bones are generally thought to grow without a cartilage precursor, we show histologically and by identification of cartilage-specific gene expression that cartilage may be involved in the morphogenesis of lambdoid and posterior sagittal sutures. CONCLUSION: This study has provided further insight into the complex signalling network which controls human calvarial suture morphogenesis and craniosynostosis. Identified genes are candidates for targeted therapeutic development and to screen for craniosynostosis-causing mutations.

Genetic regulators of myelopoiesis and leukemic signaling identified by gene profiling and linear modeling.

Mechanisms controlling the balance between proliferation and self-renewal versus growth suppression and differentiation during normal and leukemic myelopoiesis are not understood. We have used the bi-potent FDB1 myeloid cell line model, which is responsive to myelopoietic cytokines and activated mutants of the granulocyte macrophage-colony stimulating factor (GM-CSF) receptor, having differential signaling and leukemogenic activity. This model is suited to large-scale gene-profiling, and we have used a factorial time-course design to generate a substantial and powerful data set. Linear modeling was used to identify gene-expression changes associated with continued proliferation, differentiation, or leukemic receptor signaling. We focused on the changing transcription factor profile, defined a set of novel genes with potential to regulate myeloid growth and differentiation, and demonstrated that the FDB1 cell line model is responsive to forced expression of oncogenes identified in this study. We also identified gene-expression changes associated specifically with the leukemic GM-CSF receptor mutant, V449E. Signaling from this receptor mutant down-regulates CCAAT/enhancer-binding protein alpha (C/EBPalpha) target genes and generates changes characteristic of a specific acute myeloid leukemia signature, defined previously by gene-expression profiling and associated with C/EBPalpha mutations.

Identifying nineteenth century genealogical links from genotypes.

We have developed a likelihood method to identify moderately distant genealogical relationships from genomewide scan data. The aim is to compare the genotypes of many pairs of people and identify those pairs most likely to be related to one another. We have tested the algorithm using the genotypes of 170 Tasmanians with multiple sclerosis recruited into a haplotype association study. It is estimated from genealogical records that approximately 65% of Tasmania's current population of 470,000 are direct descendants of the 13,000 female founders living in this island state of Australia in the mid-nineteenth century. All cases and four to five relatives of each case have been genotyped with microsatellite markers at a genomewide average density of 4 cM. Previous genealogical research has identified 51 pairwise relationships linking 56 of the 170 cases. Testing the likelihood calculation on these known relative pairs, we have good power to identify relationships up to degree eight (e.g. third cousins once removed). Applying the algorithm to all other pairs of cases, we have identified a further 61 putative relative pairs, with an estimated false discovery rate of 10%. The power to identify genealogical links should increase when the new, denser sets of SNP markers are used. Except in populations where there is a searchable electronic database containing virtually all genealogical links in the past six generations, the algorithm should be a useful aid for genealogists working on gene-mapping projects, both linkage studies and association studies.