X-treme loss of sequence diversity linked to neo-X chromosomes in filarial nematodes
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by John Mattick, Silvia Libro, Robin Bromley, Wanpen Chaicumpa, Matthew Chung, Darren Cook, Mohammad Behram Khan, Nikhil Kumar, Yee-Ling Lau, Shailja Misra-Bhattacharya, Ramakrishna Rao, Lisa Sadzewicz, Atiporn Saeung, Mohd Shahab, Benjamin C. Sparklin, Andrew Steven, Joseph D. Turner, Luke J. Tallon, Mark J. Taylor, Andrew R. Moorhead, Michelle Michalski, Jeremy M. Foster, Julie C. Dunning Hotopp
The sequence diversity of natural and laboratory populations of Brugia pahangi and Brugia malayi was assessed with Illumina resequencing followed by mapping to identify single nucleotide variants and insertions/deletions. In natural and laboratory Brugia populations, there is a lack of sequence diversity on chromosome X relative to the autosomes (πX/πA = 0.2), which is lower than the expected πX/πA = 0.75). A reduction in diversity is also observed in other filarial nematodes with neo-X chromosome fusions in the genera Onchocerca and Wuchereria, but not those without neo-X chromosome fusions in the genera Loa and Dirofilaria. In the species with neo-X chromosome fusions, chromosome X is abnormally large, containing a third of the genetic material such that a sizable portion of the genome is lacking sequence diversity. Such profound differences in genetic diversity can be consequential, having been associated with drug resistance and adaptability, with the potential to affect filarial eradication.