Strain-dependent expression of VH gene families

The tremendous diversity of the antibody specificity repertoire stems from the ability of each developing B cell to select one out of many possible variable, diversity, and joining gene segments by specific rearrangement of the DNA. The mechanism by which V region gene segments is selected is not known. Moreover, evidence for both random and nonrandom expression of VH genes in mature B cells has been presented previously. In this report, the technique of in situ hybridization is used to accurately measure at the single cell level VH gene family expression in LPS-induced cells from several strains. In this way, at least one-third of the B cells are stimulated and a large sampling of activated splenocytes from each strain analyzed. The use of in situ hybridization eliminates any potential biases resulting from transformation protocols. In addition, because all populations of cells are analyzed by both in situ hybridization and immunocytochemical staining with anti-IgM, the proportion of cells detected by in situ hybridization could be compared with the proportion of B cells, blasts, and plasma cells in the population. It was concluded from these comparisons that the cells being detected by in situ hybridization under the conditions described are plasmablasts and plasma cells. Therefore, an accurate measure of the functional and expressed VH gene repertoire could be made. The results clearly demonstrate strain-dependent variation in VH gene family expression, particularly VH 7183 and VH J558 with up to three-fold differences observed. Thus, either there is considerable strain variation in the number of functional VH gene family segments or the expression of VH genes is not entirely random.     

The organization and expression of histone gene families

The reiteration frequency of the genes that encode the structural proteins of the mammalian ribosome was studied with a set of cloned cDNA probes containing several different mouse r-protein mRNA sequences. Results from a reassociation kinetics analysis, Southern blotting experiments and gene cloning studies collectively indicate that each individual r-protein species is represented by multiple genes in mammals. Among the examples studied, the multiplicity of mouse r-protein genes varied from about 7 to 20, a striking contrast to the low copy numbers observed in less evolutionarily advanced eucaryotes. The multiplicity of individual r-protein genes in humans and rodents is similar.     

Transposon-induced inversions activate gene expression in the maize pericarp

Chromosomal inversions can have considerable biological and agronomic impacts including disrupted gene function, change in gene expression, and inhibited recombination. Here, we describe the molecular structure and functional impact of six inversions caused by Alternative Transpositions between p1 and p2 genes responsible for floral pigmentation in maize. In maize line p1-wwB54, the p1 gene is null and the p2 gene is expressed in anther and silk but not in pericarp, making the kernels white. By screening for kernels with red pericarp, we identified inversions in this region caused by transposition of Ac and fractured Ac (fAc) transposable elements. We hypothesize that these inversions place the p2 gene promoter near a p1 gene enhancer, thereby activating p2 expression in kernel pericarp. To our knowledge, this is the first report of multiple recurrent inversions that change the position of a gene promoter relative to an enhancer to induce ectopic expression in a eukaryote.     

Intron-mediated enhancement of heterologous gene expression in maize

Chimeric genes containing the coding sequence for bacterial chloramphenicol acetyl transferase (CAT) have been introduced by electroporation into maize protoplasts (Black Mexican Sweet) and transient expression monitored by enzyme assays. Levels of CAT expression were enhanced 12-fold and 20-fold respectively by the inclusion of maize alcohol dehydrogenase-1 introns 2 and 6 in the chimeric construct. This enhancement was seen when the intron was placed within the 5 translated region but not when it was located upstream of the promoter or within the 3 untranslated region. Deletion of exon sequences adjacent to intron 2 abolished its ability to mediate enhancement of CAT gene expression. Northern analysis of protoplasts electroporated with intron constructs revealed elevated levels of CAT mRNA. However, this elevation was insufficient to account for the increased enzyme activity. One explanation of these results is that splicing affects both the quantity of mRNA.     

Heat-inducible expression of FLP gene in maize cells

The soybean heat-shock gene promoter ( Gmhsp 17.5-E ) has been used to direct expression of gusA and FLP genes in maize cells. At inducible temperatures, in transient expression assays, gusA gene expression controlled by the heat-shock promoter is about 10-fold higher than the expression directed by the CaMV 35S promoter. The Gmhsp 17.5-E promoter preserves its regulatory functions in heterologous maize cells after random integration into genomic DNA.
Heat-shock inducible expression of the FLP gene was investigated by co-transformation of the FLP expression vector (pHsFLP) and a recombination test vector (pUFNeo-FmG) into maize protoplasts. Co-transformed protoplasts were incubated at 42°C for 2 h. This treatment induced recombination of 20–25% of the available FRT sites in transient assays. As a result of heat-shock treatment of stably co-transformed maize cells, activation of gusA gene expression and an associated decrease or elimination of NPT-II activity in transgenic maize lines was observed. Molecular evidence was obtained of the expected DNA excision process catalyzed by the FLP protein in maize transgenic cells. Thus, the experiments presented in this paper indicate that the FLP protein can recognize and subsequently recombine the FRT target sites that had integrated into plant genomic DNA, and that regulated expression of the FLP gene is possible in maize cells using the soybean heat-shock promoter.     

The encyclopedia of maize kernel gene expression

正The maize kernel contains two filial products of the double fertilization, wherein one of the two sperm cells(1C, the DNA content of a haploid genome) from a pollen grain fertilizes the egg(1 C) to form the zygote and the other sperm fuses with the central cell(2C) to produce the primary endosperm. The zygote(2C) undergoes a series of asymmetric and symmetric divisions and axial patterning, eventually differ-