We have isolated both a genomic and near full length cDNA clone for a D-class cyclin gene from the perennial weed leafy spurge. Sequence analysis indicates that this gene has the highest similarity to CYCLIN D3-2 of Arabidopsis. This gene is preferentially expressed in growing shoot apices and is up-regulated in adventitious buds on resumption of growth following loss of correlative inhibition (apical dominance). CYCLIN D3-2 is also induced in nongrowing adventitious buds of plants treated with gibberellic acid or after removal of leaves—treatments known to up-regulate expression of G1 to S phase transition–specific genes such as HISTONE H3 in adventitious buds. CYCLIN D3-2 was not induced on removal of the apical and axillary buds. Expression of CYCLIN D3-2 is down-regulated in adventitious crown buds during initiation of ecodormancy in early winter. Sequence comparisons of CYCLIN D3-2 with its putative orthologue from Arabidopsis identified several conserved motifs in the promoter region and a conserved region capable of forming a stable hairpin loop in the 5′ untranslated region. Conservation of these noncoding sequences across species strongly suggests they have a regulatory function.

Bud dormancy is the primary mechanism by which the many perennial weeds escape herbicidal and mechanical control. We developed a 2,654-element Euphorbiaceae cDNA microarray using 1,886 sequenced cDNAs from the model perennial weed leafy spurge, 384 cDNAs from cassava, and 384 control genes from other plant, animal, and bacterial species. This array was used to follow changes in gene expression in root buds of leafy spurge following loss of paradormancy. The differential expression of several genes previously identified as being induced following loss of paradormancy was confirmed by microarray analysis. In addition, genes encoding an asparagine synthase, a phosphate-inducible protein, and a curculin-like (mannose-binding) lectin family protein were found to be rapidly up-regulated upon loss of paradormancy. Several genes involved in flavonoid biosynthesis were found to be rapidly down-regulated upon loss of paradormancy. The potential impact of flavonoid biosynthesis on auxin transport in response to bud growth is discussed.

Oligosaccharides are present in human milk in large amounts and in a high variety. We have previously shown that these oligosaccharides are strong inhibitors of proliferation and inducers of differentiation in intestinal cell lines. To elucidate the molecular mechanism, we investigated the influence on cell cycle events via flow cytometry and expression levels by using quantitative real-time RT–PCR. Human intestinal cells, i.e. HT-29, HIEC and Caco-2 cells, were exposed to neutral or acidic human milk oligosaccharides. Both fractions induced a concentration-dependent G2/M arrest. Cell cycle analysis for HT-29 revealed 37 % of cells in G1 and 35 % in G2/M (neutral oligosaccharides) and incubation with acidic oligosaccharides led to 42 % cells in G1 and 40 % in G2/M. In control experiments without oligosaccharides we found 71 % of cells to be in G1 and 17 % in G2/M. This G2/M arrest was associated with changes in mRNA expression of cyclin A and B. A G2/M arrest with concomitant alterations of cell cycle gene expression could also be shown for HIEC and Caco-2 cells. Analysing the expression of cyclin-dependent kinase inhibitors p21cip1 and p27kip1 and the tumour suppressor p53 we observed that the expression of p21cip1 was p53-independent and necessary for arresting cells in the G2/M phase, while p27kip1 was associated with differentiation effects. Both neutral and acidic human milk oligosaccharides were able to induce epidermal growth factor receptor, extracellular signal-regulated kinase 1/2 and p38 phosphorylation. These results suggest that oligosaccharides from human milk inhibited intestinal cell proliferation and altered cell cycle dynamics by affecting corresponding regulator genes and mitogen-activated protein kinase signalling.

Cell cycle regulatory proteins have been characterized in somatic cells and exhibit phase-specific expression patterns. Changes in expression of these regulatory proteins have not been clearly characterized in early preimplantation mouse embryos. This study utilized indirect immunofluorescence to determine the expression pattern of G1/S phase cyclins D and E; S, G2/M phase cyclins A and B1, and cdk 2 during the first three cell cycles of mouse embryo development. Cyclin D demonstrated low expression throughout the first cell cycle but had a somatic-like pattern of expression in cycles 2 and 3 with peak expression at G1 declining through S phase to a low during G2. Cyclin E was present at peak levels in G1 declining through S to a low in G2 during both the first and third cell cycles, but remained at moderate levels during the entire second cell cycle. Cyclin A was maintained at moderate levels throughout the first two cell cycles but showed a somatic-like pattern with a low level in G1 increasing during S phase with peak levels during G2 of the third cell cycle. Cyclin B consistently demonstrated a pattern opposite to a somatic G2/M cyclin, with peak levels in G1 declining through S phase to a low in G2 during each of the three cell cycles examined. Cdk 2 was present at consistent levels during G1 and S phases of all three cell cycles declining slightly in G2.