This complete assembly may contain evidence of difference between a monkey and a human; Certain immune, brain and heart disorders; And other biomedical questions
The complete assembly of human chromosome 8 was reported this week in Temperate nature. While on the outside this chromosome appears typical, being neither short nor long nor distinct, its content and arrangement of DNA is important in the development of primates and humans, in many immune and developmental disorders, and in the structure and function of the chromosome sequence in general.
This linear assembly is the first of its kind for an autosomal human – a chromosome not involved in sex determination. The complete sequence of chromosome 8 is 146,259,671 base. The completed assembly fills a gap of more than 3 million bases missing from the current reference genome.
The Temperate nature The paper is entitled “Structure, function, and evolution of chromosome 8. Complete.”
One of the many interesting characteristics of Chromosome 8 is a rapidly evolving region, where the rate of mutation appears to be accelerating dramatically in humans and human-like species, unlike the rest of the human genome.
While chromosome 8 offers some insights into evolution and human biology, the researchers suggest that complete assembly of all human chromosomes will be necessary to obtain a more complete picture.
An international team of scientists collaborated on assembling and analyzing chromosome 8. The lead author of the paper is Glennis Logsdon, a postdoctoral fellow in genomics at the University of Washington School of Medicine in Seattle.
The lead author is Evan Eichler, professor of genomics at the University of Washington School of Medicine and a researcher at the Howard Hughes Medical Institute. His group has been noted for developing better methods for DNA sequencing and for analyzing mutation trends that may be important in researching primate evolution and neurological disorders.
In addition to assembling human chromosome 8, the project researchers have also created high-quality draft clusters for the binding site at the center of the chromosome, and the midsection, in chimpanzees, orangutans and macaques. The data allowed the scientists to begin plotting the evolutionary history of the 8 centromere.
Almost like examining depths of a geological site, the researchers observed, on a molecular scale, a multi-layered symmetry in how this central structure evolved from the ancestors of great apes. More old parts were pushed to the ends, similar to making room for new materials in the middle of the factory’s production line.
Other research institutions involved in the chromosome 8 assembly project include the Therapy Development Branch at the National Cancer Institute, and the Genome Information Division of the National Human Genome Research Institute, University of Bari, Italy; Center for Algorithmic Biology at Saint Petersburg State University, Russia; University of California, San Diego, Washington University in St. Louis, University of Pittsburgh, and University of California, Santa Cruz. Data were also generated using long reading sequences from Oxford Nanopore and Pacific Biosciences to solve gaps in telomere to telomere, or final chromosome assembly.
Previous research by a number of scientists pointed to regions of chromosome 8 as important in both the normal formation of the brain, as well as for some developmental differences, such as small head or skull size and facial differences. Mutations on this chromosome have also been implicated in some heart defects, certain types of cancer, premature aging syndromes, immune responses, and immune disorders such as psoriasis and Crohn’s disease.
However, it was not possible to attempt the complete sequencing of this and most other human chromosomes until recently because the technology and methods of delving into large regions of replication and identical redundancy were not available. Accurately assembling the puzzle from short DNA readings, for example, would have been extremely difficult.
The achievement of chromosome 8 assembly benefited from advances in long reading techniques, as well as from the availability of DNA material from watery moles. These are rare and abnormal tumors of the placenta.
The complete sequence of chromosome 8 now provides information that may improve, for example, an understanding of what predisposes certain parts of the chromosome’s DNA to small deletions suspected in certain forms of developmental delay, brain and heart abnormalities, and autoimmune problems.
The researchers were also able to get more information about a portion of chromosome 8 that has some of the greatest copy number variation among people. The repeat unit can vary from 53 to 326 copies.
With chromosome 8 assembly completed, researchers are looking forward to the global scientific community completing other human chromosome sets, and to new challenges in applying what has been learned to other studies of human genome sequencing.
The researchers in this study declare that there are no competing financial interests.