Biology subjects

Dunleavy, E. M.

Publications and source records attributed to Dunleavy, E. M..

5 recordsLinked to original sources

bioRxiv2026

Distinct pools of CENP-A and CENP-C support unique phases of centromere assembly in spermatogenesis.

The centromere is the chromosomal site of kinetochore assembly, defined by the histone H3 variant CENP-A. Each cell cycle, the assembly and maintenance of CENP-A is functionally critical for chromosome segregation. In Drosophila male meiosis, CID (fly CENP-A) is assembled in two phases; prophase of meiosis I and post-meiosis II. Here we investigate the dynamics of the assembly components CAL1 and CENP-C in prophase I and determine the requirements for the second assembly phase. In early prophase I, CENP-C functions with CAL1 to maintain the centromere. In late prophase I, CAL1 is undetectable at centromeres and CENP-C no longer functions in centromere maintenance. Instead CENP-C is critical for meiotic kinetochore recruitment and function. This CENP-C pool also functions in CID assembly post-meiosis II, which is independent of CAL1. In addition to different functional pools of CENP-C, distinct pools of CID protein persist in the male germline, and the synthesis of each pool is uncoupled from its cell cycle deposition timing.

cell biology↗

bioRxiv2022

Asymmetric distribution of centromere proteins between germline stem and daughter cells maintains a balanced niche in Drosophila males.

In the germline, stem cells undergo asymmetric cell division (ACD) to give rise to one new stem cell as well as one daughter cell that differentiates and eventually gives rise to the gamete (egg or sperm). The silent sister hypothesis proposes the selective inheritance of one set of sister chromatids carrying specific epigenetic marks to explain how genetically identical stem and daughter cells can adopt different fates. It also proposes that centromeres of sister chromatids might differ epigenetically. In Drosophila germline stem cells (GSCs), the centromeric histone CENP-A - CID in flies - is asymmetrically distributed between sister chromatids such that chromosomes that end up in the GSC harbour more CID at centromeres. In this system, a model of mitotic drive has been proposed. According to this model, stronger and earlier centromere and kinetochore interactions with microtubules bias sister chromatid segregation during ACD. Here we show that in Drosophila males, CID, CENP-C and CAL1 are asymmetrically distributed between newly divided GSCs and daughter cells that have entered S-phase of the next cell cycle. We find that overexpression of CID, overexpression of CID together with CAL1 or CENP-C depletion disrupts CID asymmetry, with an increased pool of GSCs relative to daughter cells detectable in the niche. This result suggests a shift toward GSC self-renewal rather than differentiation, which is important to maintain tissue homeostasis. Over-expression of CAL1 does not disrupt asymmetry, nor does it affect the GSC and daughter cell balance, but instead drives germ cell proliferation in the niche. Our results in male GSCs are closely aligned with previous observations in female GSCs, indicating that despite differences in signaling, organisation and niche composition, centromere asymmetry and its effects on GSC maintenance are conserved between the sexes.

developmental biology↗

bioRxiv2020

CENP-C regulates centromere assembly, asymmetry and epigenetic age in Drosophila germline stem cells.

Germline stem cells divide asymmetrically to produce one new daughter stem cell and one daughter cell that will subsequently undergo meiosis and differentiate to generate the mature gamete. The silent sister hypothesis proposes that in asymmetric divisions, the selective inheritance of sister chromatids carrying specific epigenetic marks between stem and daughter cells impacts cell fate. To facilitate this selective inheritance, the hypothesis specifically proposes that the centromeric region of each sister chromatid is distinct. In Drosophila germ line stem cells (GSCs), it has recently been shown that the centromeric histone CENP-A (called CID in flies) - the epigenetic determinant of centromere identity - is asymmetrically distributed between sister chromatids. In these cells, CID deposition occurs in G2 phase such that sister chromatids destined to end up in the stem cell harbour more CENP-A, assemble more kinetochore proteins and capture more spindle microtubules. These results suggest a potential mechanism of mitotic drive that might bias chromosome segregation. Here we report that the inner kinetochore protein CENP-C, is required for the assembly of CID in G2 phase in GSCs. Moreover, CENP-C is required to maintain a normal asymmetric distribution of CID between stem and daughter cells. In addition, we find that CID is lost from centromeres in aged GSCs and that a reduction in CENP-C accelerates this loss. Finally, we show that CENP-C depletion in GSCs disrupts the balance of stem and daughter cells in the ovary, shifting GSCs toward a self-renewal tendency. Ultimately, we provide evidence that centromere assembly and maintenance via CENP-C is required to sustain asymmetric divisions in female Drosophila GSCs.

cell biology↗

bioRxiv2019

CENP-A drives asymmetric cell division and maintains stem identity

Centromeres, chromosomal loci essential for genome integrity, are epigenetically defined by CENP-A-containing chromatin. Recent studies suggest that parental CENP-A is asymmetrically distributed upon stem cell asymmetric division. However, a direct link between centromeres and stem cell identity has not been demonstrated. We show that Drosophila female germline stem cells (GSCs) and neuroblasts assemble centromeres between G2-phase and prophase, requiring CYCLIN A. Intriguingly, chromosomes that will be inherited by GSCs incorporate more CENP-A and capture more spindle fibers at pro-metaphase. Furthermore, over-expression of CAL1 (Drosophila CENP-A assembly factor) causes GSC-like tumours, while over-expression of both CENP-A and CAL1 promotes stem cell self-renewal. Finally, once centromeres have been assembled in GSCs, continued CENP-A assembly is not required in differentiating cells outside of the niche and CAL1 becomes dispensable. According to our results CENP-A regulates stem cell identity/maintenance. Moreover, crucial centromere assembly occurs in the niche prior to oocyte meiosis.

cell biology↗

bioRxiv2019

RNA transcribed from heterochromatic simple-tandem repeats are required for male fertility and histone-protamine exchange in Drosophila melanogaster

Long arrays of simple, tandemly repeated DNA sequences (known as satellites) are enriched in centromeres1 and pericentromeric regions2, and contribute to chromosome segregation and other heterochromatin functions3,4. Surprisingly, satellite DNAs are expressed in many multicellular eukaryotes, and their aberrant transcription may contribute to carcinogenesis and cellular toxicity5-7. Satellite transcription and/or RNAs may also promote centromere and heterochromatin activities 8-12. However, we lack direct evidence that satellite DNA transcripts are required for normal cell or organismal functions. Here, we show that satellite RNAs derived from AAGAG tandem repeats are transcribed in many cell types throughout Drosophila melanogaster development, enriched in neuronal tissues and testes, localized within heterochromatic regions, and important for viability. Strikingly, we find that AAGAG transcripts are necessary for male fertility and are specifically required for normal histone-protamine exchange and sperm chromatin organization. Since AAGAG RNA-dependent events happen late in spermatogenesis when the transcripts are not detected, we speculate that AAGAG RNA functions in primary spermatocytes to prime post-meiosis steps in sperm maturation. In addition to demonstrating specific essential functions for AAGAG RNAs, comparisons between closely related Drosophila species suggest that satellite repeats and their transcription evolve quickly to generate new functions.

cell biology↗