Hybrid de novo genome assembly and centromere characterization of the gray mouse lemur (Microcebus murinus).


The de novo assembly of repeat-rich mammalian genomes using only high-throughput short read sequencing data typically results in highly fragmented genome assemblies that limit downstream applications. Here, we present an iterative approach to hybrid de novo genome assembly that incorporates datasets stemming from multiple genomic technologies and methods. We used this approach to improve the gray mouse lemur (Microcebus murinus) genome from early draft status to a near chromosome-scale assembly.We used a combination of advanced genomic technologies to iteratively resolve conflicts and super-scaffold the M. murinus genome.We improved the M. murinus genome assembly to a scaffold N50 of 93.32 Mb. Whole genome alignments between our primary super-scaffolds and 23 human chromosomes revealed patterns that are congruent with historical comparative cytogenetic data, thus demonstrating the accuracy of our de novo scaffolding approach and allowing assignment of scaffolds to M. murinus chromosomes. Moreover, we utilized our independent datasets to discover and characterize sequences associated with centromeres across the mouse lemur genome. Quality assessment of the final assembly found 96% of mouse lemur canonical transcripts nearly complete, comparable to other published high-quality reference genome assemblies.We describe a new assembly of the gray mouse lemur (Microcebus murinus) genome with chromosome-scale scaffolds produced using a hybrid bioinformatic and sequencing approach. The approach is cost effective and produces superior results based on metrics of contiguity and completeness. Our results show that emerging genomic technologies can be used in combination to characterize centromeres of non-model species and to produce accurate de novo chromosome-scale genome assemblies of complex mammalian genomes.





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Publication Info

Larsen, Peter A, R Alan Harris, Yue Liu, Shwetha C Murali, C Ryan Campbell, Adam D Brown, Beth A Sullivan, Jennifer Shelton, et al. (2017). Hybrid de novo genome assembly and centromere characterization of the gray mouse lemur (Microcebus murinus). BMC biology, 15(1). p. 110. 10.1186/s12915-017-0439-6 Retrieved from https://hdl.handle.net/10161/21537.

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Beth Ann Sullivan

James B. Duke Distinguished Professor

Research in the Sullivan Lab is focused on chromosome organization, with a specific emphasis on the genomics and epigenetics of the chromosomal locus called the centromere. The centromere is a specialized chromosomal site involved in chromosome architecture and movement, and when defective, is linked to cancer, birth defects, and infertility. The lab has described a unique type of chromatin (CEN chromatin) that forms exclusively at the centromere by replacement of core histone H3 by the centromeric histone variant CENP-A. Their studies also explore the composition of CEN chromatin and its relationship to the underlying highly repetitive alpha satellite DNA at the centromere. The Sullivan lab also discovered that genomic variation within alpha satellite DNA affects where the centromere is built and how well it functions. The Sullivan lab was part of the Telomere-to-Telomere T2T Consortium that used ultra long read sequencing and optical mapping to completely assemble each human chromosome, including through millions of basepairs of alpha satellite DNA at each centromere. Dr. Sullivan's group also builds human artificial chromosomes (HACs), using them as tools to test components required for a viable, transmissible chromosome and to study centromeric transcription and chromosome stability. The lab also studies formation and fate of chromosome abnormalities associated with birth defects, reproductive abnormalities, and cancer. Specifically, they study chromosomal abnormalities with two centromeres, called dicentric chromosomes. Originally described by Nobelist Barbara McClintock in the 1930s, dicentrics in most organisms are considered inherently unstable chromosomes because they trigger genome instability. However, dicentric chromosomes in humans are very stable and are often transmitted through multiple generations of a family. Using several approaches to experimentally reproduce dicentric chromosomes in human cells, the lab explores mechanisms of dicentric formation and their long-term fate.


Anne Daphne Yoder

Braxton Craven Distinguished Professor of Evolutionary Biology

My work integrates field inventory activities with molecular phylogenetic techniques and geospatial analysis to investigate Madagascar, an area of the world that is biologically complex, poorly understood, and urgently threatened. Madagascar has been designated as one of the most critical geographic priorities for conservation action, retaining less than 10% of the natural habitats that existed before human colonization. It is critical that information be obtained as quickly as possible to document the biota that occurs in the remaining and highly threatened forested areas of western Madagascar, to gain an understanding of the evolutionary processes and associated distributional patterns that have shaped this diversity, and to use this information to help set conservation priorities. Phylogenetic and biogeographic analysis of Malagasy vertebrates, each with unique life-history and dispersal characteristics, are conducted to identify areas of high endemism potentially associated with underlying geological features, and also to test for the role that geographic features have played in generating patterns of vertebrate diversity and distribution. My lab also has a significant focus on capacity-building through the education and training of both American and Malagasy students. Research opportunities for American graduate students are enhanced by the formation of Malagasy/American partnerships.

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