Centromeres are functional chromosomal loci involved in an overall process that delivers sister chromatids equally into daughter cells during mitosis and meiosis. A complex of centromeric DNA and proteins is formed at the primary constriction point, and is referred to as the kinetochore. Since this function is essential for all eukaryotes, the process and centromeric proteins involved are conserved among eukaryotes. On the other hand, the DNA components and structures of centromeres are highly variable among eukaryotes. In the last decade, a plethora of investigations concerning plant centromeric components including centromeric DNA and proteins have been conducted which have shed light on these enigmatic chromosomal regions and associated functions. In this review, an overview of plant centromeric components including centromeric proteins (CENP-C, centromere specific histone H3 variants, and MIS12) and centromeric DNA and structures of plant centromeres (Arabidopsis, rice, and Luzula) are presented.

View full abstract

Formation of metaphase chromosome is well organized process to ensure faithful and proper segregation of genomic information into two daughter cells. However, the chromosome higher structure remains unclear partly because of the lack in the information on protein constituent of chromosomes, namely the proteome of chromosomes. Then, we performed the proteome analyses of human metaphase chromosome. In addition to the proteome of highly purified chromosomes which is composed of 107 chromosome proteins, biochemical behaviors of each protein were clarified. Furthermore, comparative proteome analyses among chromosomes from different isolation methods and different types of cell lines enabled us to establish chromosome four-layer model and to classify chromosome proteins into four different groups, chromosome structural proteins (CSPs), chromosome peripheral proteins (CPPs), chromosome coating proteins (CCPs), and chromosome fibrous proteins (CFPs). CSPs amount to 89.3 % of chromosome proteins. CSPs are proteins which are localized to chromosomes in vivo and found after thorough purification such as histones, HMGs, topoIIa, and condensins. CSPs are therefore most likely essential for a chromosome structure. Centromeric, telomeric, chromosome passenger proteins are also classified into CSPs group. CPPs group is composed of proteins which amount to 3.1 % of chromosome proteins and are localized to chromosome periphery. A part of CPPs, like nucleolin and ASURA, were confirmed by us to contribute accurate chromosome segregation during mitosis. CCPs are proteins attached to chromosomes during isolation process, thus are not intrinsic chromosome proteins. CFPs are cytoskeleton proteins, such as β-actin and vimentin, having nature to form fibers. CFPs are surrounding mitotic chromosomes in vivo and are tightly bound to isolated chromosomes unevenly. Consequently, a data set of protein constituent of chromosomes now offer lead for further studies on chromosome structure. Chromosome proteomes and the individual proteins known so far are reviewed in relation to the chromosome structure.

View full abstract

Farfugium japonicum, Asteraceae, Japanese name: Tsuwabuki, is a traditional garden plant of Japan. At present more than 100 horticultural cultivars are known, and most of them have been selected from wild populations. In order to obtain cytological information on F. japonicum as horticultural resource, chromosome numbers, meiotic chromosome behaviors and pollen stainabilities were examined on wild plants from 70 collection sites selected from the whole range of distributional areas in Japan. Except for one aneuploid (2n=61) plant which has a common leaf morphology, all 177 individuals of var. japonicum were counted to be 2n=60. Meiotic division is normal and 30 bivalents were observed at metaphase I. The frequency of stainable pollen grains was high (93.9±8.8%, N=60). Other three taxa of this species, var. giganteum, var. luchuense and var. formosanum, were also observed to be 2n=60. From the cytogenetical viewpoint, F. japonicum is considered to be a stable diploid, although its chromosome number is relatively high.

View full abstract

The present communication describes a case of spontaneous triploidy in Aldrichina grahami (Calliphoridae: Diptera). The diploid complement consists of 2n=12, with five pairs of meta/submetacentric autosomes and a pair of telocentric sex chromosomes (XX in females and XY in males), while the triploid individuals revealed eighteen chromosomes with fifteen autosomes and an XXY sex chromosomes in their complement.

View full abstract