Differentiation-retarding factor

DIA (differentiation inhibitory activity)/DRF (differentiation retarding factor)... 

Another aspect of LIF was revealed by studies on the activity that prevents differentiation of totipotent ES cells derived from normal blastocysts (Williams et al., 1988 Smith et al., 1988 Gough et al., 1989 Smith et al., 1992). It is known that to maintain the totipotency of ES cells, they must be grown on a feeder layer of fibroblasts. The activity secreted by the feeder layer fibroblasts, termed DIA (differentiation inhibitory activity) or DRF (differentiation retarding factor), has been purified, and its characteristics suggest that DIA/DRF may be identical to LIF. Indeed, not only does LIF exhibit the same activities as DIA and DRF in vitro, but also ES cells cultured with LIF can retain their totipotency. When the ES cells treated with LIF are injected into mouse blastocysts and then introduced into pseudo-pregnant females, they contribute extensively to the development of all of the somatic tissues (Williams et al., 1988 Gough et al., 1989). 

If precipitation-dissolution reactions dominate (this is sorption by Sposito s definition), there are simply no differentiable isotherms (defined as a functional relationship between S and C) relating solid and aqueous concentrations (Bryant et al., 1987). The above-mentioned retardation factor formulations (equation (10.3)) are not applicable. A more complete form of the ADR equation may be (Fetter, 1993, p.l 15),... 

Because the radius, r, is expressed as a reduced distance (relative to unit radius inclusion) in Figs. 2-4, the physical path length is given by R dh, where R is a scale factor representing the actual radius of the inclusion. Thus, the differential retardation, dP, caused by an element of swollen rubber at point J is given by dP = v (np - n )R dh... 

Petersen [12] points out that this criterion is invalid for more complex chemical reactions whose rate is retarded by products. In such cases, the observed kinetic rate expression should be substituted into the material balance equation for the particular geometry of particle concerned. An asymptotic solution to the material balance equation then gives the correct form of the effectiveness factor. The results indicate that the inequality (23) is applicable only at high partial pressures of product. For low partial pressures of product (often the condition in an experimental differential tubular reactor), the criterion will depend on the magnitude of the constants in the kinetic rate equation. 

Electron microscopic observations have shown that the cells of isolated gastrula ectoderm after some days in culture develop in their periphery a zone which contains vacuoles and in some cells the basal bodies of cilia. These are the same structures as found in epidermis. They are not found in the ectoderm, which was induced by the vegetalising factor. Obviously gastrula ectoderm is already determined to special pathways during differentiation, but its developmental fate can still be changed. In ectoderm treated with actinomycin D the vacuolar zone is retarded in its development (Grunz, 1973). A more general problem is raised by these experiments. Obviously, the induction of the ectoderm leads not only to an acquisition of new properties but also to a loss of properties which would have been expressed in the uninduced ectoderm. 

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