Red spruce forest regeneration dynamics across a gradient from Acadian forest to old field in Greenwich,Prince Edward Island National Park,Canada

Red spruce forests have declined considerably throughout their range in the past decades. As agricultural fields are abandoned and land becomes available for reforestation, the possibility arises for red spruce forests to expand onto them. This study addresses the potential for red spruce forests to expand onto adjacent old fields in Greenwich, Prince Edward Island National Park, Canada. We examined red spruce distribution and abundance, plant species diversity and changes in community composition along a gradient from the interior of red spruce forests out towards the centre of adjacent old fields. Examining the patterns of red spruce distribution and abundance revealed that, where cultivation and logging have been abandoned recently in the fields and forests, regeneration is limited to the forest stands, but in the sites with older fields and forests, regeneration extends into and is more vigorous in the fields. Although species diversity varied from forest to field only for the tree and shrub layers, important changes occurred in the ground species composition. There is no evidence yet that the herbaceous species present in the forest stands will colonise the old fields. The results suggest that both environmental differences among sites and length of time since the fields were abandoned explain red spruce regeneration patterns. In order to more accurately assess the potential for red spruce regeneration in old fields, long-term monitoring of the production, dispersal and viability of red spruce seeds from adjacent forests and of the constraints to seedling establishment and survival in old fields will be needed.     

Mechanism of cleavage of apurinic sites by 9-aminoellipticine

We have studied the kinetics of breakage of apurinic (AP) sites by the intercalating agent 9-aminoellipticine using fluorimetric methods with single (ss)- and double (ds)-stranded apurinic DNA. In order to understand the chemical process, high performance liquid chromatography was used to follow the reaction kinetics with the apurinic oligonucleotide model T(AP)T. The unstable intermediate, which is responsible for the beta-elimination step, is a Schiff base resulting from the interaction of the amino group of the aromatic amine with the aldehyde function of the deoxyribose moiety (AP site). Fluorescence occurs simultaneously with the breakage of both ss and ds DNA and of the oligonucleotide and arises from the formation of a conjugated double bond on the Schiff base through the beta-elimination reaction. In optimal conditions, the second order rate constant for the fluorescence build up is 15 x 10(3) min-1 M-1 for ds DNA and 0.105 x 10(3) min-1 M-1 for T(AP)T. The ability of 9-aminoellipticine to induce fluorescence and breakage of ss DNA and T(AP)T shows that intercalation is not essential for this reaction to occur. Nevertheless, the greater rate constant with DNA suggests that stacking is an important parameter for the reaction of the aromatic amine with the AP site.     

Efficient and easy synthesis of octathymidylate covalently linked to intercalating 9-aminoellipticine

Reductive amination of 3'-apurinic octathymidylate with 9-aminoellipticine provides octathymidylate covalently linked to intercalating ellipticine through a 3,4-dihydroxypentamethylene linker. Studies of its binding properties to poly(rA) reveals the formation of two different complexes depending of the temperature (Tm 13 degrees C and 38 degrees C) with dT/rA stoichiometry respectively equal to 2/1 and 1/1. When compared to parent octathymidylate, stability of the latter duplex is enhanced by the interaction energy provided by the dye moiety.     

Synthesis and Biophysical Properties of Oligothymidylates Containing Alkoxyphosphoramidate Internucleoside Linkages

Abstract

The synthesis and the biophysical properties of oligothymidylate analogs containing N-methoxy- and N-benzyloxyphosphoramidate combined with phosphodiester internucleoside linkages are reported.     

Novel strategies towards construction of non-ionic and achiral backbones in antisense oligonucleotides.

A convenient synthesis of a thymidine (T) nucleoside dimer (T-3'-CH2-O-NCH3-CH2-4'-T) 12 has been accomplished via a nucleoside coupling reaction. An alternative synthesis of 3'-deoxy-3'-C-hydroxymethyl-thymidine is described. The new dimer and methodology is useful for the development of backbone-modified antisense oligonucleosides.     

Step-by-step control by MALDI-TOF MS of an oligonucleotide synthesis on standard CPG solid-support

MALDI-TOF mass spectrometry was used to monitor DNA solid-phase synthesis on long-chain alkylamine controlled-pore glass (LCAA-CPG) with a standard succinyl linker between the solid support and the growing oligonucleotide.     

Molecular and cytogenetic characterisation of a small interstitial de novo 20p13-->p12.3 deletion in a patient with severe growth deficit

We report on a small de novo interstitial deletion of the short arm of chromosome 20, 46,XY,del(20)(p12.3p13), in a young boy with hypotonia, moderate development delay, mild facial dysmorphism and severe growth failure. This patient did not show major features of Alagille-Watson Syndrome (AWS) which are common in more proximal 20p deletions. Standard and high resolution chromosome banding analysis revealed an apparent terminal deletion. Nevertheless, using chromosomal fluorescent in situ hybridization (FISH) and molecular analysis with polymorphic markers, we demonstrated that the abnormal chromosome resulted from a de novo interstitial deletion of paternal origin spanning from D20S842 to D20S900 and covering approximately 6 Mb. These findings indicate that a karyotype can lead to insufficient characterization of an apparently terminal deletion, and that one or a few genes in 20p13-->p12.3 bands are important for normal growth.