X

Quality Statement

Pacific Biosciences is committed to providing high-quality products that meet customer expectations and comply with regulations. We will achieve these goals by adhering to and maintaining an effective quality-management system designed to ensure product quality, performance, and safety.

X

Image Use Agreement

By downloading, copying, or making any use of the images located on this website (“Site”) you acknowledge that you have read and understand, and agree to, the terms of this Image Usage Agreement, as well as the terms provided on the Legal Notices webpage, which together govern your use of the images as provided below. If you do not agree to such terms, do not download, copy or use the images in any way, unless you have written permission signed by an authorized Pacific Biosciences representative.

Subject to the terms of this Agreement and the terms provided on the Legal Notices webpage (to the extent they do not conflict with the terms of this Agreement), you may use the images on the Site solely for (a) editorial use by press and/or industry analysts, (b) in connection with a normal, peer-reviewed, scientific publication, book or presentation, or the like. You may not alter or modify any image, in whole or in part, for any reason. You may not use any image in a manner that misrepresents the associated Pacific Biosciences product, service or technology or any associated characteristics, data, or properties thereof. You also may not use any image in a manner that denotes some representation or warranty (express, implied or statutory) from Pacific Biosciences of the product, service or technology. The rights granted by this Agreement are personal to you and are not transferable by you to another party.

You, and not Pacific Biosciences, are responsible for your use of the images. You acknowledge and agree that any misuse of the images or breach of this Agreement will cause Pacific Biosciences irreparable harm. Pacific Biosciences is either an owner or licensee of the image, and not an agent for the owner. You agree to give Pacific Biosciences a credit line as follows: "Courtesy of Pacific Biosciences of California, Inc., Menlo Park, CA, USA" and also include any other credits or acknowledgments noted by Pacific Biosciences. You must include any copyright notice originally included with the images on all copies.

IMAGES ARE PROVIDED BY Pacific Biosciences ON AN "AS-IS" BASIS. Pacific Biosciences DISCLAIMS ALL REPRESENTATIONS AND WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, NON-INFRINGEMENT, OWNERSHIP, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL Pacific Biosciences BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, PUNITIVE, OR CONSEQUENTIAL DAMAGES OF ANY KIND WHATSOEVER WITH RESPECT TO THE IMAGES.

You agree that Pacific Biosciences may terminate your access to and use of the images located on the PacificBiosciences.com website at any time and without prior notice, if it considers you to have violated any of the terms of this Image Use Agreement. You agree to indemnify, defend and hold harmless Pacific Biosciences, its officers, directors, employees, agents, licensors, suppliers and any third party information providers to the Site from and against all losses, expenses, damages and costs, including reasonable attorneys' fees, resulting from any violation by you of the terms of this Image Use Agreement or Pacific Biosciences' termination of your access to or use of the Site. Termination will not affect Pacific Biosciences' rights or your obligations which accrued before the termination.

I have read and understand, and agree to, the Image Usage Agreement.

I disagree and would like to return to the Pacific Biosciences home page.

Pacific Biosciences
Contact:

SMRT Sequencing Helps Crack the Code of Elusive Centromeres

Wednesday, August 7, 2019

Crucial assembly sites and mitosis mediators, centromeres are central to every cell, but missing from even the most complete genome assemblies. 

Until now.

In a PLOS Biology paper, Amanda Larracuente and colleagues at the University of Rochester and Barbara G. Mellone of the University of Connecticut, described how they sequenced the repetitive regions of the fruit fly genome, including its centromeres, using SMRT Sequencing. 

Embedded in blocks of highly repetitive satellite DNA, centromeres have eluded efforts at assembly.

Only recently, long-read single molecule sequencing technologies have made it possible to obtain assemblies of highly repetitive parts of multicellular genomes such as the human Y chromosome centromere and maize centromere 10. This is the first time researchers have sequenced all the centromeres in any multicellular organism.

“Our study shows that combining long-read sequencing with ChIP-seq and chromatin fiber FISH is a powerful approach to discover centromeric DNA sequences and their organization,” the authors wrote. “Our overall strategy therefore provides a blueprint for determining the composition and organization of centromeric DNA in other species.”

Drosophila salivary gland polytene chromosomes. Photo by Elissa Lei (NIH)

Drosophila melanogaster proved the ideal model to investigate centromere genomic organization, as it has a relatively small genome (roughly 180 Mb), organized in just three autosomes (chromosome 2, 3, and 4) and two sex chromosomes (X and Y). The estimated centromere sizes in Drosophila cultured cells range between 200 and 500 kb and map to regions within large blocks of tandem repeats.

It has been believed that satellites are likely the major structural elements of Drosophila, human and mouse centromeres. By tracking the histone H3 variant centromere protein A (CENP-A), the team was able to identify the fruit fly centromeres and found that they primarily occupy islands of complex DNA enriched in retroelements flanked by large blocks of simple satellites. They estimate that approximately 70% of the functional centromeric DNA of D. melanogaster is composed of complex DNA islands, which are rich in non-LTR retroelements and buried within large blocks of tandem repeats. 

“They likely went undetected in previous studies of centromere organization because three of the five islands are either missing or incomplete in the published reference D. melanogaster genome … having an improved reference genome assembly is crucial for identifying centromeric DNA sequences,” the authors state. 

The retroelements they found were not merely present near centromeres, but were components of the active centromere cores.

“Why retroelements are such ubiquitous components of centromeres and whether they play an active role in centromere function remain open questions,” the authors wrote.

Additional avenues worth exploring include identifying associated tandem repeats, as well as mapping the span of the CENP-A domain and its binding sites. 

“Knowing the identity of D. melanogaster centromeric DNA will enable the functional interrogation of these elements in this powerhouse model organism,” the authors wrote. 

 

Subscribe for blog updates:

Archives