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Title: X chromosome as a polarising signal in asymmetric cell division
Author: Al Yazeedi, Talal Ali Mohammed
ISNI:       0000 0004 9357 9882
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2020
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In the nematode genus of Auanema, sex is determined by X chromosome dosage, females and self-fertilising hermaphrodites are XX and males are XO. Surprisingly, cross between XX female and XO male results in mostly XX progeny. This occurs because males only produce one functional sperm bearing an X chromosome, whereas nullo-X sperm is discarded. The exclusive formation of X-bearing sperm by males is attributed to the asymmetric segregation of essential sperm components, necessary for sperm function and motility, with the X chromosome. Whereas non-essential cytoplasmic materials (e.g., Golgi complex, ribosomes) disposed of in the nullo-X cell that takes the role of a residual body. This unique system permits easy-to-score phenotype on the organismal level to study asymmetric cell division; because the sex ratio of a cross-progeny can be used to monitor the type of divisions occurring during male spermatogenesis. Here I report that during Auanema spermatogenesis, the X chromosome acts as a polarising signal for sperm components to segregate with the cell inheriting the X chromosome. Sperm components also segregate with the X chromosomes in other A. rhodensis spermatogenesis models. During the spermatogenesis of A. rhodensis XX hermaphrodites, sperm components segregate to the cell inheriting the X chromosome. Similarly, I identified that during the spermatogenesis of A. rhodensis masculiniser mutant Arh-mas-1 (Genetically XX but with a male morphology), sperm components co-segregate with X chromosomes in asymmetric division or equally with X chromosomes to both daughter cells in symmetric division. I demonstrated that shuffling X chromosome haplotype blocks in A. freiburgensis RIAILs from two strains with different genetic background resulted in a new transgressive phenotype. Where, males from RIAILs produced a high number of males, due to their ability to form a functional nullo-X sperm. Genetic mapping using BSA analysis identified four candidate regions on the X chromosome involved in the spatial localisation of cytoplasmic components. Those findings led to hypothesised that interaction between a group of polygenes on the X chromosome in Auanema polarises sperm components to segregate with the X chromosome. Mechanisms describing how intrinsic factors regulate cell polarity are poorly understood, mostly because it is difficult to establish in the absence of extrinsic factors influence. Here, I present a novel mechanism for an intrinsic polarisation of asymmetrically dividing cells initiated by the X chromosome.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QH Natural history