Discovery of New Proteins Involved in Spatial Reorganization of Chromosomes

- Aiming at Understanding of the Mechanism for Genetic Information Producing Diversity of Life -

November 3, 2009

National Institute of Information and Communications Technology (NICT: the President Dr. Hideo Miyahara) is promoting a project to practically utilize a biological principle based on an idea that the mechanism by which genetic information is transmitted to offspring will provide a new insight into information and communication technology. The chromosome is a storage of genetic information that undergoes replication, recombination and inheritage, and forms a specialized configuration of bundled chromosomes to accomplish these chromosomal functions during meiosis. In the present study, factors mediating spatial reorganization were discovered and the mechanism by which the arrangement of chromosomes is changed to the specialized one in the nucleus was revealed. These findings lead to understanding of the function for genetic recombination generating diversification of life. The results will be published in Journal of Cell Biology, an international academic journal, to be published on Nov.2 2009.

Background

Meiosis is a biological process that occurs in the germ cell line to produce a sperm and an egg via recombination and reproduction of genetic information. During the process, the chromosomal arrangement is transiently changed to a special one to safely accomplish the recombination of genetic information without fail and transfer the information to daughter cells (cells produced by meiosis). Such chromosomal arrangement is commonly observed in all living organisms from unicellular organisms like yeasts to humans. It has been thought that the change is very important to effectively accomplish gene recombination and produce the diversity of life. Understanding of the mechanism by which chromosomal arrangement is changed to a special one as the field to generate the diversity of life was our long-cherished desire.

Results

In meiotic prophase, telomeres (the end structure of chromosomes) cluster at a certain point of the nuclear membrane, resulting in formation of the chromosomal bouquet bundled at telomeres (bouquet arrangement). In the present study, NICT newly discovered two proteins: One is a protein (named as Bqt 4) considered as a factor to anchor telomeres to the nuclear membrane and to produce the bouquet formation. The other was a protein (named as Bqt 3) to protect Bqt 4 from its enzymatic degradation. By the present discovery of these new proteins in addition to Bqt 1 and Bqt 2 discovered by our previous studies, it became possible to clarify the mechanism of bouquet formation within the nucleus. Moreover, understanding of the significance of the chromosomal bouquet arrangement in cell nucleus during meiosis would be advanced.

These results will be published in Journal of Cell Biology, an international academic journal, to be published on Nov.2 2009. This study was carried out in collaboration with Osaka University.

Prospects

This successful actual measurement of polarization characteristics through the space-to-ground atmosphere will enable the link budget analysis for QKD, and become a key to realize world-wide satellite QKD. It will also make it possible to develop the feasible design of a test satellite aiming for realization of space laser communications.

Reference

Terminology and Interpretations

Genetic Information
Information about morphological/physiological qualities and functions of living organisms to transfer from parent to offspring

Double-stranded DNA (deoxyribonucleic acid) is an intranuclear fibrous compound including three components of base, phosphate and deoxyribose. Genetic information of organism is represented in DNA molecule.

A region in DNA playing a role as a genetic code to produce a protein essential for living activities is termed as a gene.

The DNA molecule is 2 nm in diameter and its length stored in a human nucleus is as long as ca. 2 meter in total (When compared to a fiber of 2 mm in diameter, DNA becomes a long thin fibrous molecule of 2,000 km in length).

It is indispensable for sustaining of life to precisely replicate DNA and transfer it without producing any damage from parent cells to daughter cells.

* DNA winds itself around a protein called as histone to produce a fibrous structure called as chromatin, which is further folded more densely.

Chromosome
Chromosome is an intranuclear substance loading genetic information. Chromosome is a rod-like substance formed during cell division by assembling of chromatin into a high density. Each nucleus of human has 46 chromosomes including 2 sex chromosomes, either of which has 23 chromosomes derived from each parent. A pair of chromosomes derived from each parent is called as homologous chromosome.

Meiosis
Meiosis is one type of cell division to produce germ cells. A human germ cell containing half of the 46 chromosomes is produced through meiosis (and the number of chromosomes recovers the original one by fertilization). During meiosis, some part of homologous chromosomes is exchanged through pairing of homologous chromosomes. Recombination of genetic information as well as combination of chromosomes plays a very important role to produce the diversity of life.

Telomere
Telomere is a specialized structure at the both ends of a linear chromosome. The structure is considered to protect a chromosome and keep its genetic stability. It has been reported that a chromosome lacking the telomere might trigger apoptosis and carcinogenesis. Intranuclear location of telomeres is very important for pairing of homologous chromosomes during meiosis.

The Novel Prize in Physiology or Medicine 2009 was awarded to the works of the telomere.

Bouquet ArrangementTelomere
Bouquet arrangement is an chromosomal arrangement where telomeres assemble at a certain point of nuclear membrane. The bouquet arrangement is considered to be essential for effective recombination of genetic information. The name of “bouquet” was given to the arrangement of chromosomal bundle formed through clustering telomeres at a point.

① Telomere ② Chromosome ③ Nuclear Membrane

Bqt3 and Bqt4
Bqt 3 is a protein to protect Bqt 4 from enzymatic degradation and Bqt4 is a protein that anchors telomeres at a point of nuclear membrane.