Non-random distribution of high density chromatin detected at opposite ends of T-banded human metaphase chromosomes

Previous research using microdensitometric scanning and computer graphic image analysis showed that T-banded segments of human metaphase chromosomes usually exhibit an asymmetrical distribution of high density (HD) chromatin between sister chromatids. Here, we employed the same methods to analyze HD chromatin distribution at opposite ends of T-banded human lymphocyte chromosomes. This study revealed that in most chromosomes with an asymmetrical distribution of HD chromatin at both ends, the highest densities of each arm were located in opposite chromatids. The frequency of this configuration was 0.792 per chromosome, indicating that the highest chromatin densities of the terminal segments of T-banded human chromosomes were non-randomly distributed at opposite chromosome arms. The possible relationship of this observation to the mode of replication of the terminal chromosome region is briefly discussed.

A proposal of a standardised nomenclature for terminal minute sister chromatid exchanges

We described spontaneous minute sister chromatid exchanges (SCE) in telomeric regions of human and Chinese hamster ovary (CHO) chromosomes more than 10 years ago. These structures, which we called t-SCE, were detected by means of highly precise quantitative microphotometrical scanning and computer graphic image analysis. Recently, several authors using the CO-FISH method also found small SCEs in telomeric regions and called them T-SCE. The use of different terms for designating the same phenomenon should be avoided. We propose ter SCE as a uniform nomenclature for minute telomeric SCEs.

Retardo mental, malformaciones congénitas y aberraciones cromosómicas subteloméricas crípticas / Mental retardation, congenital malformations and subtelomeric chromosome aberrations

Los recientes progresos tecnológicos ocurridos en citogenética molecular han permitido la detección de numerosas minúsculas aberraciones en la región cromosómica contigua al telómero o segmento subtelomérico, que han sido relacionadas con diversos cuadros de retardo mental, malformaciones congénitas y otros síndromes de interés médico. Investigaciones previas, llevadas a cabo mediante exploración microfotométrica y análisis gráfico computacional del subtelómero, revelaron diferentes patrones de distribución de las densidades de la cromatina y la existencia de intercambios sumamente pequeños entre cromátidas hermanas en dicho segmento cromosómico. La detección de aberrraciones crípticas sindromáticas, el elevado número de intercambios cromosómicos y las observaciones microscópicas sobre la estructura subtelomérica sugieren que reflejan la gran actividad genómica y la complejidad estructural prevalente en la región. En la presente revisión se describen brevemente varios síndromes cromosómicos subteloméricos, así como la estructura molecular y citológica de la región subtelomérica y las principales funciones del segmento cromosómico terminal a fin de brindar un panorama general sobre esta área de investigaciones en rápido crecimiento de considerable significación biomédica.