The pre-cellular Drosophila embryo contains 10 well characterized sequence-specific transcriptional repressors, which represent a broad spectrum of DNAbinding proteins. Previous studies have shown that two of the repressors, Hairy and Dorsal, recruit a common co-repressor protein, Groucho. Here we present evidence that three different repressors, Knirps, Krü ppel and Snail, recruit a different co-repressor, dCtBP. Mutant embryos containing diminished levels of maternal dCtBP products exhibit both segmentation and dorsoventral patterning defects, which can be attributed to loss of Krü ppel, Knirps and Snail activity. In contrast, the Dorsal and Hairy repressors retain at least some activity in dCtBP mutant embryos. dCtBP interacts with Krü ppel, Knirps and Snail through a related sequence motif, PXDLSXK/H. This motif is essential for the repression activity of these proteins in transgenic embryos. We propose that dCtBP represents a major form of transcriptional repression in development, and that the Groucho and dCtBP co-repressors mediate separate pathways of repression.

Signals transduced by precursor-BCRs (pre-BCRs) composed of Ig μ heavy chains (HCs) and the surrogate L chain components λ5 and VpreB are critical for B cell development. A conserved unique region (UR) of λ5 was shown to activate pre-BCR complexes in transformed cells and to engage putative ligands, but its contribution to pre-B cell development is not known. It is also not clear why the λ-like sequences in λ5 are used to select HCs that will associate mainly with κ L chains. In this study, we show that, in transformed and primary mouse B cell progenitors, receptors containing full-length HCs and lacking the λ5UR were expressed at higher surface levels, but exhibited reduced activity compared with normal pre-BCRs in supporting developmental changes that accompany the progenitor to pre-B cell transition in primary cell culture systems and in the bone marrow in vivo. In contrast, deletion of the λ5UR did not change net signaling output by the Dμ-pre-BCR, a developmentally defective receptor that exhibited impaired activity in the primary cell culture system. Moreover, the λ-like sequences in λ5 were more accommodating than κ in supporting surface expression and signaling by the different HCs. These results show that the λ5UR is important, although not essential, for surrogate L chain-dependent receptor signaling in primary cells, and furthermore may help allow discrimination of signaling competency between normal and Dμ-pre-BCRs. That the λ-like portion of λ5 in the absence of the UR was nondiscriminatory suggests that the λ5UR focuses pre-BCR-dependent selection on the HC V region.

Artykuł przedstawia bezpośrednie inwestycje zagraniczne w krajach Europy Środkowo-Wschodniej na podstawie World Investment Report 2000 opracowanego przez UNCTAD (United Nations Conference on Trade and Development). Omawia atrakcyjność inwestycyjną poszczególnych grup krajów oraz czynniki kształtujące BIZ.