All-trans retinoic acid (RA) is well known as a biologically active form of vitamin A and a teratogen. The identification of nuclear receptors for this ligand suggests strongly that it is an endogenous signal molecule, and measurements of RA and teratogenic manipulations suggest further that RA is a morphogen specifying the anteroposterior axis during limb development. Besides the limb, RA and other retinoids affect development of other organs, including the central nervous system (CNS). None of these other effects has been investigated in detail. Our purpose here was to begin analysing the effects of RA on CNS development in Xenopus laevis. We find that RA acts on the developing CNS, transforming anterior neural tissue to a posterior neural specification. These and other findings raise the possibility that RA mediates an inductive interaction regulating anteroposterior differentiation within the CNS. Following recent reports implicating transforming growth factor-beta 2-like and fibroblast growth factor-like factors in mesoderm induction, this indicates that a different type of signal molecule (working through a nuclear receptor, not a plasma membrane receptor) might mediate inductive cell interactions during early embryonic development.

No abstract

environmental effects as a cause of father-son phenotypic similarity by rearing young in groups (Table 1).A slightly smaller mean body size of wild satellites has been interpreted as suggesting that poorly growing chicks disproportionately develop into satellites'. Small body size differences between morphs developed among our captives, despite ad libi-

A ratio-fluorescence assay was developed for on-line localization and quantification of lipid oxidation in living cells. The assay explores the oxidative sensitivity of C11-BOD-IPY 581a591 . Upon oxidation, the fluorescence of this fluorophore shifts from red to green. The probe incorporates readily into cellular membranes and is about twice as sensitive to oxidation as arachidonic acid. Using confocal microscopy, the cumene hydroperoxide-induced oxidation of C11-BODIPY 581a591 was visualized at the sub-cellular level in rat-1 fibroblasts. Preloading of the cells with tocopherol retarded this oxidation. The data demonstrate that C11-BODIPY 581a591 is a valuable tool to quantify lipid oxidation and anti-oxidant efficacy in single cells.z 1999 Federation of European Biochemical Societies.

No abstract