Close

Ribosomal DNA and the rDNA-binding protein Indra mediate non-random sister chromatid segregation in Drosophila male germline stem cells

George Watase, Yukiko Yamashita

Posted on: 20 December 2018

Preprint posted on 16 December 2018

Sisters are not always identical: Chromosomal immortality in germline stem cells rests on rDNA loci and their binding partner Indra

Selected by Maiko Kitaoka

Categories: cell biology, genetics

Background

In a canonical cell cycle, replicated sister chromatids are assumed to be identical and segregated randomly into daughter cells. However, sisters can be epigenetically distinct and can undergo non-random segregation. This has thought to contribute to asymmetric cell divisions, particularly in stem cells where one daughter maintains a stem cell state and the other can differentiate.

Here, Watase and Yamashita use the Drosophila male germline stem cells to investigate the non-random sister segregation of X and Y chromosomes. The group has previously shown that autosomes segregate randomly, while X and Y chromosomes do not, but how and why this phenomenon occurs is still unknown.

Key findings

The authors first identified ribosomal DNA (rDNA) to be a key locus on the X and Y chromosomes. D. melanogaster autosomes do not contain any rDNA loci and also segregate randomly, suggesting that this feature on the sex chromosomes is an important aspect. Deletion strains with no rDNA loci on the X or Y chromosomes showed random sister chromatid segregation, demonstrating the requirement of rDNA loci for non-random segregation.

Sex chromosomes segregate non-randomly, as the red and blue strands are inherited with a bias in germ cell divisions. The red strand ends up in the GSC (closest to the asterisk hub) in 80% of divisions, rather than an even 50/50 split (left images). However, when rDNA is perturbed on the X (bb158) or Y (Ybb) chromosomes, segregation becomes random (right graph). From Figure 1.

 

Since rDNA loci are very large and contain several individual and distinct elements, the authors compared D. melanogaster to D. simulans, whose Y chromosome still segregates non-randomly despite lacking several rDNA elements. Interestingly, both species had intergenic spacer sequence (IGS) repeats, so they attempted to identify any potential IGS-binding proteins by mass spectrometry. This allowed them to uncover 18 proteins enriched for IGS sequence binding, including an uncharacterized zinc finger protein. They named the gene indra after a Hindu god who lost immortality. Consistent with its proposed role with rDNA, Indra localizes to the nucleolus and to the rDNA loci on metaphase chromosomes.

In characterizing indra’s function, Watase and Yamashita discovered that RNAi knockdown of indra led to random sister chromatid segregation. A stronger loss of indra in the germline revealed severe fertility defects due to the rapid loss of germ cells (and loss of cellular immortality). Using DNA FISH, they found that X and Y chromosomes frequently have inter-homolog exchange at the rDNA loci when indra is depleted, indicating indra’s role in preventing recombination between the sex chromosomes. This could be accomplished by preventing DNA double stranded breaks at rDNA loci or by encouraging sister chromatid DNA repair, rather than homolog repair.

In indra knockdown mutants, the X and Y chromosomes recombine at the IGS region of the rDNA loci, likely leading to catastrophic mitoses and cell death. From Figure 4.

 

Interestingly, when indra is depleted from male germline, progeny exhibited a bobbed phenotype, where the stripes on the adult fly’s back are not continuous and straight across, which has been shown to be a hallmark of rDNA insufficiency. This further implicates the role of rDNA, so how does Indra help to maintain rDNA copy number? Unequal sister chromatid exchange is a proposed mechanism for rDNA copy number expansion, where one chromatid gains copy number at the expense of the other. The authors propose that non-random sister chromatid segregation may reflect non-random segregation of higher vs. lower rDNA copy number after unequal sister chromatid exchange. While they could not measure the absolute copy number at rDNA loci, the authors observed multiple sister chromatid exchanges at rDNA loci in indra-depleted GSCs, potentially equalizing the rDNA copy number between sister chromatids. This indicates that indra limits the number of sister chromatid exchanges, pointing to a mechanism where indra acts to ensure that unequal exchange is productive and allows for unequal expansion of rDNA in the stem cell.

Model describing how indra may mediate unequal sister chromatid exchange at rDNA loci to allow for differences in rDNA copy number between sisters. This inequality leads to the non-random segregation of sister chromatids in germ cells. From Figure 5.

 

To conclude, Watase and Yamashita have discovered a mechanistic explanation to non-random sister chromatid segregation in asymmetric cell division, proving not only the importance of rDNA loci and the newly-named IGS binding protein Indra but also shedding light on the unique identities of sister chromatids. This exciting work opens many more questions for future investigation. Most immediately, it would be interesting to see whether an Indra binding site/IGS repeats are sufficient to induce non-random segregation on the D. melanogaster autosomes. Although, given that the rDNA locus is already very large, artificially adding it to autosomes may prove to be a technical challenge. Second, and more physiologically, what advantage do GSCs maintain by inheriting the sister chromatid with an expanded rDNA copy number? Perhaps the ability of GSCs to undergo repeated rounds of asymmetric cell division may contribute to this, since they would add rDNA copies gradually over time instead of all at once. Finally, the mass spectrometry pull-down experiment identified several other proteins as well that bound to IGS repeats. While some candidates are probably essential for cell survival, it will be interesting to investigate these further and see how they also interact with the rDNA loci and/or Indra.

Questions for the authors

The D. simulans Y chromosome has the Indra binding site and IGS repeats, but no other rDNA loci elements, so do they still show rDNA expansion? If not, how might the sister chromatids segregate non-randomly without the unequal rDNA expansion?

Can you speculate on Indra’s mechanism of action after binding to IGS repeats? How does the binding prevent inter-homolog exchange and/or multiple sister chromatid exchanges?

In somatic stem cells, do the sex chromosomes segregate non-randomly and the autosomes randomly as well?

Tags: asymmetric cell division, cell biology, drosophila, genetics, rdna, ribosomal dna, stem cells

doi: https://doi.org/10.1242/prelights.6514

Read preprint (No Ratings Yet)

Have your say

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Sign up to customise the site to your preferences and to receive alerts

Register here

Also in the cell biology category:

Platelet-derived LPA16:0 inhibits adult neurogenesis and stress resilience in anxiety disorder

Thomas Larrieu, Charline Carron, Fabio Grieco, et al.

Selected by 04 December 2024

Harvey Roweth

Neuroscience

Investigating Mechanically Activated Currents from Trigeminal Neurons of Non-Human Primates

Karen A Lindquist, Jennifer Mecklenburg, Anahit H. Hovhannisyan, et al.

Selected by 04 December 2024

Vanessa Ehlers

Neuroscience

Motor Clustering Enhances Kinesin-driven Vesicle Transport

Rui Jiang, Qingzhou Feng, Daguan Nong, et al.

Selected by 16 November 2024

Sharvari Pitke

Biophysics

Also in the genetics category:

Intracellular diffusion in the cytoplasm increases with cell size in fission yeast

Catherine Tan, Michael C. Lanz, Matthew Swaffer, et al.

Selected by 18 October 2024

Leeba Ann Chacko, Sameer Thukral

Cell Biology

HIF1A contributes to the survival of aneuploid and mosaic pre-implantation embryos

Estefania Sanchez-Vasquez, Marianne E. Bronner, Magdalena Zernicka-Goetz

Selected by 11 October 2024

Anchel De Jaime Soguero

Developmental Biology

Significantly reduced, but balanced, rates of mitochondrial fission and fusion are sufficient to maintain the integrity of yeast mitochondrial DNA

Brett T. Wisniewski, Laura L. Lackner

Selected by 30 August 2024

Leeba Ann Chacko

Cell Biology

preLists in the cell biology category:

November in preprints – the CellBio edition

This is the first community-driven preList! A group of preLighters, with expertise in different areas of cell biology, have worked together to create this preprint reading lists for researchers with an interest in cell biology. Categories include: 1) cancer cell biology 2) cell cycle and division 3) cell migration and cytoskeleton 4) cell organelles and organisation 5) cell signalling and mechanosensing 6) genetics/gene expression

 



List by Felipe Del Valle Batalla et al.

BSCB-Biochemical Society 2024 Cell Migration meeting

This preList features preprints that were discussed and presented during the BSCB-Biochemical Society 2024 Cell Migration meeting in Birmingham, UK in April 2024. Kindly put together by Sara Morais da Silva, Reviews Editor at Journal of Cell Science.

 



List by Reinier Prosee

‘In preprints’ from Development 2022-2023

A list of the preprints featured in Development's 'In preprints' articles between 2022-2023

 



List by Alex Eve, Katherine Brown

preLights peer support – preprints of interest

This is a preprint repository to organise the preprints and preLights covered through the 'preLights peer support' initiative.

 



List by preLights peer support

The Society for Developmental Biology 82nd Annual Meeting

This preList is made up of the preprints discussed during the Society for Developmental Biology 82nd Annual Meeting that took place in Chicago in July 2023.

 



List by Joyce Yu, Katherine Brown

CSHL 87th Symposium: Stem Cells

Preprints mentioned by speakers at the #CSHLsymp23

 



List by Alex Eve

Journal of Cell Science meeting ‘Imaging Cell Dynamics’

This preList highlights the preprints discussed at the JCS meeting 'Imaging Cell Dynamics'. The meeting was held from 14 - 17 May 2023 in Lisbon, Portugal and was organised by Erika Holzbaur, Jennifer Lippincott-Schwartz, Rob Parton and Michael Way.

 



List by Helen Zenner

9th International Symposium on the Biology of Vertebrate Sex Determination

This preList contains preprints discussed during the 9th International Symposium on the Biology of Vertebrate Sex Determination. This conference was held in Kona, Hawaii from April 17th to 21st 2023.

 



List by Martin Estermann

Alumni picks – preLights 5th Birthday

This preList contains preprints that were picked and highlighted by preLights Alumni - an initiative that was set up to mark preLights 5th birthday. More entries will follow throughout February and March 2023.

 



List by Sergio Menchero et al.

CellBio 2022 – An ASCB/EMBO Meeting

This preLists features preprints that were discussed and presented during the CellBio 2022 meeting in Washington, DC in December 2022.

 



List by Nadja Hümpfer et al.

Fibroblasts

The advances in fibroblast biology preList explores the recent discoveries and preprints of the fibroblast world. Get ready to immerse yourself with this list created for fibroblasts aficionados and lovers, and beyond. Here, my goal is to include preprints of fibroblast biology, heterogeneity, fate, extracellular matrix, behavior, topography, single-cell atlases, spatial transcriptomics, and their matrix!

 



List by Osvaldo Contreras

EMBL Synthetic Morphogenesis: From Gene Circuits to Tissue Architecture (2021)

A list of preprints mentioned at the #EESmorphoG virtual meeting in 2021.

 



List by Alex Eve

FENS 2020

A collection of preprints presented during the virtual meeting of the Federation of European Neuroscience Societies (FENS) in 2020

 



List by Ana Dorrego-Rivas

Planar Cell Polarity – PCP

This preList contains preprints about the latest findings on Planar Cell Polarity (PCP) in various model organisms at the molecular, cellular and tissue levels.

 



List by Ana Dorrego-Rivas

BioMalPar XVI: Biology and Pathology of the Malaria Parasite

[under construction] Preprints presented at the (fully virtual) EMBL BioMalPar XVI, 17-18 May 2020 #emblmalaria

 



List by Dey Lab, Samantha Seah

1

Cell Polarity

Recent research from the field of cell polarity is summarized in this list of preprints. It comprises of studies focusing on various forms of cell polarity ranging from epithelial polarity, planar cell polarity to front-to-rear polarity.

 



List by Yamini Ravichandran

TAGC 2020

Preprints recently presented at the virtual Allied Genetics Conference, April 22-26, 2020. #TAGC20

 



List by Maiko Kitaoka et al.

3D Gastruloids

A curated list of preprints related to Gastruloids (in vitro models of early development obtained by 3D aggregation of embryonic cells). Updated until July 2021.

 



List by Paul Gerald L. Sanchez and Stefano Vianello

ECFG15 – Fungal biology

Preprints presented at 15th European Conference on Fungal Genetics 17-20 February 2020 Rome

 



List by Hiral Shah

ASCB EMBO Annual Meeting 2019

A collection of preprints presented at the 2019 ASCB EMBO Meeting in Washington, DC (December 7-11)

 



List by Madhuja Samaddar et al.

EMBL Seeing is Believing – Imaging the Molecular Processes of Life

Preprints discussed at the 2019 edition of Seeing is Believing, at EMBL Heidelberg from the 9th-12th October 2019

 



List by Dey Lab

Autophagy

Preprints on autophagy and lysosomal degradation and its role in neurodegeneration and disease. Includes molecular mechanisms, upstream signalling and regulation as well as studies on pharmaceutical interventions to upregulate the process.

 



List by Sandra Malmgren Hill

Lung Disease and Regeneration

This preprint list compiles highlights from the field of lung biology.

 



List by Rob Hynds

Cellular metabolism

A curated list of preprints related to cellular metabolism at Biorxiv by Pablo Ranea Robles from the Prelights community. Special interest on lipid metabolism, peroxisomes and mitochondria.

 



List by Pablo Ranea Robles

BSCB/BSDB Annual Meeting 2019

Preprints presented at the BSCB/BSDB Annual Meeting 2019

 



List by Dey Lab

MitoList

This list of preprints is focused on work expanding our knowledge on mitochondria in any organism, tissue or cell type, from the normal biology to the pathology.

 



List by Sandra Franco Iborra

Biophysical Society Annual Meeting 2019

Few of the preprints that were discussed in the recent BPS annual meeting at Baltimore, USA

 



List by Joseph Jose Thottacherry

ASCB/EMBO Annual Meeting 2018

This list relates to preprints that were discussed at the recent ASCB conference.

 



List by Dey Lab, Amanda Haage

Also in the genetics category:

BSDB/GenSoc Spring Meeting 2024

A list of preprints highlighted at the British Society for Developmental Biology and Genetics Society joint Spring meeting 2024 at Warwick, UK.

 



List by Joyce Yu, Katherine Brown

BSCB-Biochemical Society 2024 Cell Migration meeting

This preList features preprints that were discussed and presented during the BSCB-Biochemical Society 2024 Cell Migration meeting in Birmingham, UK in April 2024. Kindly put together by Sara Morais da Silva, Reviews Editor at Journal of Cell Science.

 



List by Reinier Prosee

9th International Symposium on the Biology of Vertebrate Sex Determination

This preList contains preprints discussed during the 9th International Symposium on the Biology of Vertebrate Sex Determination. This conference was held in Kona, Hawaii from April 17th to 21st 2023.

 



List by Martin Estermann

Alumni picks – preLights 5th Birthday

This preList contains preprints that were picked and highlighted by preLights Alumni - an initiative that was set up to mark preLights 5th birthday. More entries will follow throughout February and March 2023.

 



List by Sergio Menchero et al.

Semmelweis Symposium 2022: 40th anniversary of international medical education at Semmelweis University

This preList contains preprints discussed during the 'Semmelweis Symposium 2022' (7-9 November), organised around the 40th anniversary of international medical education at Semmelweis University covering a wide range of topics.

 



List by Nándor Lipták

20th “Genetics Workshops in Hungary”, Szeged (25th, September)

In this annual conference, Hungarian geneticists, biochemists and biotechnologists presented their works. Link: http://group.szbk.u-szeged.hu/minikonf/archive/prg2021.pdf

 



List by Nándor Lipták

2nd Conference of the Visegrád Group Society for Developmental Biology

Preprints from the 2nd Conference of the Visegrád Group Society for Developmental Biology (2-5 September, 2021, Szeged, Hungary)

 



List by Nándor Lipták

EMBL Conference: From functional genomics to systems biology

Preprints presented at the virtual EMBL conference "from functional genomics and systems biology", 16-19 November 2020

 



List by Jesus Victorino

TAGC 2020

Preprints recently presented at the virtual Allied Genetics Conference, April 22-26, 2020. #TAGC20

 



List by Maiko Kitaoka et al.

ECFG15 – Fungal biology

Preprints presented at 15th European Conference on Fungal Genetics 17-20 February 2020 Rome

 



List by Hiral Shah

Autophagy

Preprints on autophagy and lysosomal degradation and its role in neurodegeneration and disease. Includes molecular mechanisms, upstream signalling and regulation as well as studies on pharmaceutical interventions to upregulate the process.

 



List by Sandra Malmgren Hill

Zebrafish immunology

A compilation of cutting-edge research that uses the zebrafish as a model system to elucidate novel immunological mechanisms in health and disease.

 



List by Shikha Nayar
Close