To elucidate the hidden dynamics of extracellular-signal-regulated kinase (ERK) signalling networks, we developed a simulation model of ERK signalling networks by constraining in silico dynamics based on in vivo dynamics in PC12 cells. We predicted and validated that transient ERK activation depends on rapid increases of epidermal growth factor and nerve growth factor (NGF) but not on their final concentrations, whereas sustained ERK activation depends on the final concentration of NGF but not on the temporal rate of increase. These ERK dynamics depend on Ras and Rap1 dynamics, the inactivation processes of which are growth-factor-dependent and -independent, respectively. Therefore, the Ras and Rap1 systems capture the temporal rate and concentration of growth factors, and encode these distinct physical properties into transient and sustained ERK activation, respectively.

Taspase1 was identified as the threonine endopeptidase that cleaves mixed-lineage leukemia (MLL) for proper

Repair of cartilage injury with hyaline cartilage continues to be a challenging clinical problem. Because of the limited number of chondrocytes in vivo, coupled with in vitro de-differentiation of chondrocytes into fibrochondrocytes, which secrete type I collagen and have an altered matrix architecture and mechanical function, there is a need for a novel cell source that produces hyaline cartilage. The generation of induced pluripotent stem (iPS) cells has provided a tool for reprogramming dermal fibroblasts to an undifferentiated state by ectopic expression of reprogramming factors. Here, we show that retroviral expression of two reprogramming factors (c-Myc and Klf4) and one chondrogenic factor (SOX9) induces polygonal chondrogenic cells directly from adult dermal fibroblast cultures. Induced cells expressed marker genes for chondrocytes but not fibroblasts, i.e., the promoters of type I collagen genes were extensively methylated. Although some induced cell lines formed tumors when subcutaneously injected into nude mice, other induced cell lines generated stable homogenous hyaline cartilage-like tissue. Further, the doxycycline-inducible induction system demonstrated that induced cells are able to respond to chondrogenic medium by expressing endogenous Sox9 and maintain chondrogenic potential after substantial reduction of transgene expression. Thus, this approach could lead to the preparation of hyaline cartilage directly from skin, without generating iPS cells.

No abstract

We have examined the roles of BMP4, Shh, and retinoic acid in establishing the proximal-distal and dorsal-ventral axes in the developing Xenopus eye. Misexpression of BMP4 caused the absence of an optic stalk and the expansion of dorsal and distal markers, tbx2/3/5, and pax6, at the expense of ventral and proximal markers vax2 and pax2. When Shh or Noggin, an antagonist of BMPs, was misexpressed, the reverse expression patterns of these marker genes were observed. These results suggest that BMP4 is involved in the specification of not only dorsal in the optic cup but also distal in the optic vesicle. Because Shh did not suppress bmp4 expression, unlike Noggin, Shh and BMP4 may antagonistically regulate common downstream genes in developing eye. We also found the difference between the effects of Shh and retinoic acid, another possible ventralizing factor, suggesting that Shh could promote ventralization independently of retinoic acid. These findings provide important clues to the coordinate and antagonistic actions of BMP4, Shh, and retinoic acid in axes specifications of Xenopus eyes.