Superchromosomal organization and its cytogenetic consequences in the Eukaryota

Centromeric association of a microchromosome. A new category of non-random arrangement of metaphase chromosomes

A supernumerary microchromosome measuring 0.5-1 microns found in over half of the metaphases of a CREST scleroderma patient and his daughter has been characterized by various cytogenetic techniques. The microchromosome consisted of constitutive heterochromatin and contained nuclear antigens reacting with specific anti-kinetochore antibodies. The most remarkable property of the microchromosome was its non-random position: it was closely associated with the centromere of any of the normal chromosomes in the majority of the metaphases. Furthermore, an inordinately high rate of Y chromosome aneuploidy was found in the CREST scleroderma patient. The origin and structure of the microchromosome, its possible connection with the CREST variant of scleroderma, and the phenomenon of centromeric association are discussed.

["Artificial" chromosomes]

The structural elements required for chromosome replication, segregation, and stability are replication origins, centromeres, and telomeres. DNA sequences capable of organizing these three elements have been isolated from yeast chromosomal DNA by means of recombinant DNA techniques and yeast cell transformation. It is now possible to combine these sequences into "artificial" chromosomes for yeast cells to obtain more insight into chromosome structure and function. Evidence is presented that the construction of artificial chromosomes functional in higher eukaryotes will be possible in the near future.

An interphase model for mitotic chromosome organization in eukaryota

A model for the spatial relationship of the arrangement of the chromosomes in the nucleus in eukaryota is presented. Evidence is derived from light and electron microscopic studies, application of autoradiographic and banding techniques; on the organization, structure and behaviour of chromosomes during interphase and other stages of cell cycle. This model visualizes the entire chromosomal DNA as a single uninemic multirepliconic continuum where the chromosomes with their centromeres and telomeres have a predetermined arrangement among themselves as well as in relation to the nucleolus and nuclear membrane. This orderly arrangement is presumably maintained through interchromosomal connections. The impact of this model on the interpretation of various cytogenetic phenomena is discussed.