The X chromosome is a potential polarising signal for asymmetric cell divisions in meiotic cells of a nematode

Abstract

The unequal partition of molecules and organelles during cell division results in daughter cells with different fates. Asymmetric cell divisions have been best characterised in systems in which extrinsic signals polarise the mother cell during cell division. However, the mechanisms of asymmetric cell division mediated by intrinsic signals, and the nature of these signals, are mostly unknown. Here we report an asymmetric cell division in the nematode Auanema rhodensis that may be cued by the X chromosome. In the wildtype XO male, the spermatocyte divides asymmetrically to generate X-bearing spermatids that inherit components necessary for sperm viability, and nullo-spermatids that inherits components to be discarded. We found that in XX mutant pseudomales, sperm components co-segregate with the X chromosome, supporting the hypothesis that the X chromosome is employed as a polarising signal for partitioning essential cytoplasmic components for sperm function.

De novo Genome Assembly of Auanema melissensis, a Trioecious Free-Living Nematode

“…This is in contrast with A. rhodensis XX females for which the X homologs pair and recombine during meiosis ( Tandonnet et al, 2018 ). The X chromosome is also inherited from the father by the son in the event of a cross (female–male or hermaphrodite–male) due to the asymmetric partitioning of the cytoplasm during male spermatogenesis resulting in only X-bearing sperm being produced ( Shakes et al, 2011 ; Tandonnet et al, 2018 ; Al-Yazeedi et al, 2022 ). To this date, the mechanisms controlling the unusual X chromosome segregation are unknown.…”

“…In laboratory cultures, XO males are in lower proportions (typically 5-15%) than XX non-males (females and hermaphrodites) (Félix, 2004;Chaudhuri et al, 2011aChaudhuri et al, , 2015Shakes et al, 2011;Robles et al, 2021). The dynamics of this unusual mating system is poorly understood (Anderson et al, 2020;Rupp, 2020). In the species described so far, Auanema rhodensis (aka Rhabditis sp.…”