Centromere function in asymmetrically dividing Drosophila germline stem cells
Kochendoerfer, Antje Maria
Kochendoerfer, Antje Maria
Loading...
Repository DOI
Publication Date
2023-03-28
Type
Thesis
Downloads
Citation
Abstract
Germline stem cells (GSCs) undergo asymmetric cell division (ACD) to give rise to one stem cell residing in the niche and one differentiating daughter cell. The daughter cell subsequently divides through mitosis and meiosis to finally form mature gametes (eggs or sperm). In 2007, Peter Lansdorp postulated the ‘silent sister hypothesis’ (SSH) according to which ACD can impact on cell fate. It proposes the centromere as a key chromosomal locus capable of distinguishing sister chromatids carrying distinct epigenetic marks and gene expression profiles. Centromeres are the constricted site of chromosomes to which the microtubules of the spindle attach during cell division. For most eukaryotes, including the fruit fly Drosophila melanogaster, the centromere is defined epigenetically by the histone H3 variant CENP-A (CID in Drosophila). CID assembly is facilitated through its chaperone and assembly factor CAL1, as well as CENP-C. Previous studies in Drosophila GSCs have demonstrated that CID is asymmetrically distributed between sister centromeres. In this cell type, sister chromatids that end up in the stem cell have more CID, more kinetochore proteins and capture more spindle fibres. This was described as the ‘mitotic drive’ phenomenon, contributing to a mechanism of non-random sister chromatid segregation. This thesis shows that Drosophila male GSCs are labelled with 40% more CID, CENP-C and CAL1, compared to daughter cells, measured at S-phase. Through depletion and overexpression of CID, CAL1 and CENP-C we show that disrupted centromeres (and potentially asymmetry) impacts on cell fate, in both Drosophila male and female GSCs. A disrupted centromeric core in GSCs, perturbs the balance of stem and daughter cells in the niche, shifting GSCs to more self-renewal. As part of this thesis, we developed three functional assays to measure cell fate in the testes stem cell niche and further an anti-CAL1 antibody. Ultimately, we identify CID level as a stem cell marker and demonstrate that CAL1 functions in germ cell proliferation. In addition, we find that CENP-C is important for centromere asymmetry and stem cell maintenance in the male testes niche.
Funder
Publisher
NUI Galway