Role of c-Myb in chondrogenesis.

The Myb locus encodes the c-Myb transcription factor involved in controlling a broad variety of cellular processes. Recently, it has been shown that c-Myb may play a specific role in hard tissue formation; however, all of these results were gathered from an analysis of intramembranous ossification. To investigate a possible role of c-Myb in endochondral ossification, we carried out our study on the long bones of mouse limbs during embryonic development. Firstly, the c-myb expression pattern was analyzed by in situ hybridization during endochondral ossification of long bones. c-myb positive areas were found in proliferating as well as hypertrophic zones of the growth plate. At early embryonic stages, localized expression was also observed in the perichondrium and interdigital areas. The c-Myb protein was found in proliferating chondrocytes and in the perichondrium of the forelimb bones (E14.5-E17.5). Furthermore, protein was detected in pre-hypertrophic as well as hypertrophic chondrocytes. Gain-of-function and loss-of-function approaches were used to test the effect of altered c-myb expression on chondrogenesis in micromass cultures established from forelimb buds of mouse embryos. A loss-of-function approach using c-myb specific siRNA decreased nodule formation, as well as downregulated the level of Sox9 expression, a major marker of chondrogenesis. Transient c-myb overexpression markedly increased the formation of cartilage nodules and the production of extracellular matrix as detected by intense staining with Alcian blue. Moreover, the expression of early chondrogenic genes such as Sox9, Col2a1 and activity of a Col2-LUC reporter were increased in the cells overexpressing c-myb while late chondrogenic markers such as Col10a1 and Mmp13 were not significantly changed or were downregulated. Taken together, the results of this study demonstrate that the c-Myb transcription factor is involved in the regulation and promotion of endochondral bone formation.

Towards dissecting molecular routes of intercellular communication in the tumour microenvironment: phenotypic plasticity of stem cell-associated markers in co-culture (carcinoma cell/fibroblast) systems.

Increasing evidence attributes tumour fates to a small population of cells (cancer stem cells) capable of surviving therapeutic interventions. Investigation of their characteristics, especially in cross-talk with other cell types of the tumour microenvironment, can pave the way to innovative therapeutic concepts. The central issue of this study was to evaluate the impact of stroma on tumour cells with stem cell-like features in a squamous cell carcinoma model (FaDu). Six different types of experimental conditions were tested using distinct compositions of the culture system, and both morphologic and molecular features of the tumour cells were analysed. In detail, FaDu cells alone were used as a control, compared to tumour cells from co-culture, with squamous cell cancer-derived stromal fibroblasts or normal skin human fibroblasts, both in the direct and indirect (insert) systems, adding analysis of side population cells of FaDu culture. Measurements were taken on days 2, 7 and 9 of culture and immediately after preparation in the case of the side population. A panel of antibodies against keratins 8, 10, 19, stem cell markers CD29, CD44, CD133, as well as biotinylated adhesion/growth-regulatory galectin 1 served as a toolbox for phenotypic characterization. Co-culture with fibroblasts prepared from tumour stroma and with dermal fibroblasts affected marker presentation, maintaining an undifferentiated stage phenotypically related to stem cells. Side-population cells showed close relationship to cancer stem cells in these characteristics. In conclusion, normal and tumour stromal fibroblasts are capable of shifting the marker expression profile of FaDu cells to a stem cell-like phenotypic pattern in co-culture.

Impairment of Sox9 expression in limb buds of rats homozygous for hypodactyly mutation.

Rat hypodactyly (hd) is an autosomal recessive mutation manifesting in homozygotes as reduction or loss of digits II and III. We mapped the hd allele to a short segment of chromosome 10, containing 16 genes. None of these genes has been shown to influence limb development yet. In situ hybridization showed no changes in several important patterning genes (Shh, Fgf8, Bmp2, 4, 7). However, we found that expression of cartilage condensation marker Sox9, and Bmp receptor Bmpr1b (acting as an upstream activator of Sox9 expression) is absent from the subepithelial mesenchyme of the digit condensations II and III. The failure of the chondrogenic condensations to extend towards the subepithelial mesenchyme may reduce the size of digit primordia and underlie the subsequent loss of phalanges and reduction of metacarpals/metatarsals in hd rats.

Transcription factor c-Myb is involved in the regulation of the epithelial-mesenchymal transition in the avian neural crest.

Multipotential neural crest cells (NCCs) originate by an epithelial-mesenchymal transition (EMT) during vertebrate embryogenesis. We show for the first time that the key hematopoietic factor c-Myb is synthesized in early chick embryos including the neural tissue and participates in the regulation of the trunk NCCs. A reduction of endogenous c-Myb protein both in tissue explants in vitro and in embryos in ovo, prevented the formation of migratory NCCs. A moderate over-expression of c-myb in naive intermediate neural plates triggered the EMT and NCC migration probably through cooperation with BMP4 signaling because (i) BMP4 activated c-myb expression, (ii) elevated c-Myb caused accumulation of transcripts of the BMP4 target genes msx1 and slug, and (iii) the reduction of c-Myb prevented the BMP4-induced formation of NCCs. The data show that in chicken embryos, the c-myb gene is expressed prior to the onset of hematopoiesis and participates in the formation and migration of the trunk neural crest.