CO-OCCURRENCE MATRIX IN LONGITUDINAL DIFFERENTIATION OF MRI IMAGES OF PATIENTS WITH AD, MCI, AND HEALTHY INDIVIDUALS

Background: Texture analysis based on the gray level co-occurrence matrix (GLCM) has been applied to brain magnetic resonance images (MRI) to detect subtle differences among healthy and lesioned tissue occurring in several neurological conditions, but it has rarely been used in longitudinal AD studies. Objectives: To perform a longitudinal study by applying GLCM to brain MRI of AD and MCI patients and of healthy controls (HC), to verify the suitability of this technique to help detect the evolution of these conditions. Methods: Participants were 14 AD, 21 MCI and 17 HC, who had 2 T1-MRI obtained ~12 months apart. MRI were segmented using the AAL atlas. 3D GLCMs were computed for five voxel distances, for 16 regions per subject. A total of 55 texture parameters were extracted per region per subject. Statistical differences were evaluated using a t test. Results: Significant differences were found only for the MCI group, for the left precentral gyrus and left supplementary motor area, for which the correlation parameter decreased over time at different distances. Conclusions: This result could be due to a subtle motor loss in the MCI group before the onset of AD symptoms, or even, patients in the MCI group could progress to neurodegenerative diseases other than AD. The next step is to compare the obtained texture parameters between groups using analysis of covariance.

Cytogenetics of coffee

The genus Coffea L. has around 100 native species distributed in tropical and subtropical areas in Africa, and the most important economic species are C. arabica and C. canephora. C. arabica is exceptional in the genus since it is the only species so far analyzed which is self-compatible, and a natural polyploid with 2n=4x=44 chromosomes; it is considered to be a segmental allopolyploid because it presents a disomic inheritance and a regular meiotic behavior. All other species in the genus are self-incompatible diploids with 2n=2x=22. Cytogenetic studies in Coffea, undertaken since 1912, have followed various phases: initial studies were limited only to establishing chromosome counts. Subsequent studies characterized the karyotypes of various species using conventional cytological techniques. As the somatic metaphase chromosomes of coffee are very small (1 - 3 µm) and morphologically symmetrical, these studies resulted in uniform karyotypes that show almost no differences among species. Since genetic improvement of coffee trees has progressed mainly by means of interspecific hybridizations involving wild species, analyses of microsporogenesis in species and hybrids were needed to establish their genetic affinity and relationships. The first successful attempts to differentiate coffee chromosomes longitudinally were made by mapping pachytene chromomeric patterns and by C and NOR banding techniques. From 1998 onwards, the use of banding techniques with the fluorochromes DAPI and CMA3, and also the cytomolecular technique FISH using rDNA probes, has increased the longitudinal differentiation of coffee chromosomes. The use of the GISH technique with total genomic DNA has revealed the parental species that originated C. arabica species.

In situ nick translation of meiotic chromosomes to demonstrate homologous heterochromatin heterogeneity

The in situ nick translation procedure performed on fixed meiotic chromosomes partially cleaved with restriction endonucleases shows a different staining of homologous heterochromatic regions, which could be explained through a differential restriction endonuclease cleavage. Mutations occurring before massive tandem duplication and involving those DNA motifs that produce these heterochromatic blocks, together with the absence of DNA recombination that characterizes these particular regions, could explain the observed results. This method for chromosome labelling is most useful to demonstrate a certain level of heterochromatin heterogeneity that is present in the genome of living species but remained cryptic to other techniques that are also able to induce longitudinal differentiation of the chromosomes.Key words: cytogenetics, nick translation, meiosis, heterochromatin.