The equine ascarids: resuscitating historic model organisms for modern purposes

Cain, Jennifer L.; Nielsen, Martin K.

doi:10.1007/s00436-022-07627-z

Cited by 6 publications

(1 citation statement)

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“…There are two known species of the horse parasitic nematode Parascaris, P. univalens with one pair of germline chromosomes (2n = 2, Figure 1A) and P. equorum with two (2n = 4). 28 P. univalens is the main species currently observed in equines 29 and used in this study. Here we use P. univalens and Parascaris interchangeably.…”

Section: Resultsmentioning

confidence: 99%

Chromosome fusion and programmed DNA elimination shape karyotypes of parasitic nematodes

Simmons,

Estrem,

Zagoskin

et al. 2023

Preprint

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A growing list of metazoans undergo programmed DNA elimination (PDE), where a significant amount of DNA is selectively lost from the somatic genome during development. In some nematodes, PDE leads to the removal and remodeling of the ends of all germline chromosomes. In several species, PDE also generates internal breaks that lead to sequence loss and an increased number of somatic chromosomes. The biological significance of these karyotype changes associated with PDE and the origin and evolution of nematode PDE remain largely unknown. Here, we assembled the single germline chromosome of the horse parasiteParascaris univalensand compared the karyotypes, chromosomal gene organization, and PDE features among ascarid nematodes. We show that PDE inParascarisconverts an XX/XY sex-determination system in the germline into an XX/XO system in the somatic cells. Comparisons ofAscaris, Parascaris,andBaylisascarisascarid chromosomes suggest that PDE existed in the ancestor of these parasites, and their current distinct germline karyotypes were derived from fusion events of smaller ancestral chromosomes. The DNA breaks involved in PDE resolve these fused germline chromosomes into their pre-fusion karyotypes, leading to alterations in genome architecture and gene expression in the somatic cells. Cytological and genomic analyses further suggest that satellite DNA and the heterochromatic chromosome arms play a dynamic role in theParascarisgermline chromosome during meiosis. Overall, our results show that chromosome fusion and PDE have been harnessed in these ascarids to sculpt their karyotypes, altering the genome organization and serving specific functions in the germline and somatic cells.

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Section: Resultsmentioning

confidence: 99%