Allelic exclusion of the immunoglobulin heavy chain locus is independent of its nuclear localization in mature B cells

In developing B cells, the immunoglobulin heavy chain (IgH) locus is thought to move from repressive to permissive chromatin compartments to facilitate its scheduled rearrangement. In mature B cells, maintenance of allelic exclusion has been proposed to involve recruitment of the non-productive IgH allele to pericentromeric heterochromatin. Here, we used an allele-specific chromosome conformation capture combined with sequencing (4C-seq) approach to unambigously follow the individual IgH alleles in mature B lymphocytes. Despite their physical and functional difference, productive and non-productive IgH alleles in B cells and unrearranged IgH alleles in T cells share many chromosomal contacts and largely reside in active chromatin. In brain, however, the locus resides in a different repressive environment. We conclude that IgH adopts a lymphoid-specific nuclear location that is, however, unrelated to maintenance of allelic exclusion. We additionally find that in mature B cells—but not in T cells—the distal V_H regions of both IgH alleles position themselves away from active chromatin. This, we speculate, may help to restrict enhancer activity to the productively rearranged V_H promoter element.     

Short-term exposure to cadmium modifies phosphorylation of gill proteins in the sea mussel.

1. Sea mussels were exposed to cadmium for short periods of time. The excised gills were incubated with radioactive orthophosphate. The gill proteins were separated by 1- and 2-dimensional gel electrophoresis and the phosphorylation state of the proteins was determined by image analysis of autoradiographs. 2. 1-Dimensional gel electrophoresis revealed that exposure of the animals to cadmium stimulated phosphorylation of the gill proteins in a cadmium concentration-dependent manner. 3. 2-Dimensional gel electrophoresis showed that cadmium differentially affected the phosphorylation of various proteins. Major alterations were observed in the basic, high mol. wt proteins and in the acidic, low mol. wt polypeptides.     

Synthesis of stress proteins under normal and heat shock conditions in gill tissue of sea mussels (Mytilus edulis) after chronic exposure to cadmium.

1. Sea mussels were exposed to 16.5 micrograms Cd/1 under semi-field conditions for almost one year. The isolated gills were incubated with 35S-methionine or -cysteine. 2. Chronic exposure to cadmium neither altered the rate of amino acid incorporation nor induced expression of heat shock proteins in the gills. 3. Heat shock imposed after chronic exposure to cadmium resulted in an increased synthesis of heat shock proteins, especially those of high molecular weight. 4. Synthesis of cadmium-binding, low molecular weight proteins was observed at any point of the exposure time. Their cadmium-binding capacity and rate of synthesis, after the initial increase, remained unchanged throughout the exposure.