Close

Rapid embryonic cell cycles defer the establishment of heterochromatin by Eggless/SetDB1 in Drosophila

Charles A Seller, Chun-Yi Cho, Patrick H O'Farrell

Preprint posted on 22 November 2018 https://www.biorxiv.org/content/early/2018/10/22/450155

Article now published in Genes & Development at http://dx.doi.org/10.1101/gad.321646.118

Cell cycle speed sets the pace for heterochromatin formation

Selected by Gabriel Aughey

Background

Regulation of gene expression is controlled by chromatin environments that are either permissive to transcription or else transcriptionally silent. The formation of heterochromatin, characterised by presence of the protein HP1 and H3K9 histone methylation, is required to establish and maintain cell identity. Heterochromatin is largely absent in the earliest stages of a developing embryo in which transcription is minimal and cell fate is not yet firmly established. Therefore, heterochromatin formation can be viewed as one of the first steps in initiating the transcriptional programme that decides a cell’s developmental trajectory.

Although heterochromatin is well studied, very little is currently known about the mechanisms by which the naïve cells of the early embryo establish heterochromatin. Furthermore, it is difficult to use genetics to study the early embryo due to the presence of a large amount of maternally contributed material. In this preprint, Seller et al. use innovative approaches to identify a key factor involved in deposition of heterochromatin, and point towards a mechanism that implicates cell cycle rate in the regulation of this process.

 

Key findings

Jabba-trap can be used to mislocalise nuclear proteins in early development

The early stages of embryogenesis are difficult to study using classical genetics as a large amount of maternally contributed proteins coordinate the majority of developmental processes before the start of zygotic transcription. These proteins can be removed by creating germline mutants, but this is not feasible if the gene is required for oogenesis. To circumvent these problems, Seller et al. explore a nanobody-mediated mis-localisation system (Jabba-trap). This approach relies on a previously published observation that histone proteins (initially present in excess due to maternal contribution), are stored in lipid droplets during early embryogenesis to overcome toxicity until their redistribution to the nucleus later in development (Li et al. 2012). The authors use a nanobody fused to a lipid droplet targeting protein (Jabba) to sequester proteins of interest to these lipid droplets. The authors use Jabba trap to successfully target nuclear proteins to lipid droplets either when injected into embryos or supplied transgenically. As the nanobody targets GFP, this approach could be used to mislocalise any GFP fused protein of interest.

eggless is required to establish heterochromatin

The authors then apply their new technique to the question of heterochromatin formation in early embryogenesis. Of three known histone methyltransferases, the authors observe that one in particular, eggless (egg), is required for heterochromatin formation, whilst the other two (G9a and Su(var)3-9) are dispensable. Satellite repeats associated with constitutive heterochromatin are shown to colocalise with egg and display a loss of HP1 and H3K9 methylation when egg is mislocalised. An egg cofactor, windei (wde) is also shown to colocalise at these regions and is similarly mislocalised when egg is sequestered from the nucleus, indicating that wde forms a complex with egg at heterochromatin. egg localisation in the nucleus preceded HP1 foci formation, indicating that egg is initiating the formation of heterochromatin.

eggless mediated heterochromatin formation is regulated by interphase duration

One of the authors’ most interesting findings comes from the observation that more egg protein is seen to accumulate as the length of cell cycles increases during embryogenesis (cell cycle 14 is approximately 6-7-fold longer than cell cycle 11, and a concomitant increase of egg is observed at stage 14). The authors hypothesise that longer cell cycles later in embryogenesis allow for greater accumulation of egg, which therefore allows for the formation of more heterochromatin. This hypothesis is tested by using RNAi against cell cycle regulators to artificially alter cell cycle duration. Shortening interphase resulted in less egg and heterochromatin formation, whereas cell cycle arrest resulted in greater accumulation of egg and corresponding heterochromatin markers.

(Fig 6. from Seller et al. – Model depicting heterochromatin formation in relation to interphase duration.)

Why I like this preprint

This preprint has several features that I admire. Firstly, the authors have pioneered an innovative approach using nanobodies to mislocalise proteins of interest. This allowed them to study a fundamental period of development that was previously relatively inaccessible to experimental interventions of this nature. This technique is one of several recent studies leveraging nanobodies in creative ways to answer interesting questions (Caussinus et al., Harmansa et al.), and I think the principles that underlie these techniques are useful to many researchers.

Secondly, I am struck by the idea that the slowing of cell cycles is sufficient to kick-start heterochromatin formation at this fundamental juncture in development. Often, I think that as biologists we are predisposed to imagining complex mechanisms to explain our observations. In this case, it is pleasing that an idea as simple as a slowing of cell division could be sufficient to result in a fundamental shift in the gene-regulatory programme of a developing animal.

 

Open questions

  • How does the Jabba-trap technique compare to other nanobody mediated methods? For example, what is the advantage of mislocalisation of nuclear proteins over degradation techniques such as the degradFP system (Caussinus et al, 2011)?
  • What is the mechanism by which egg is recruited to heterochromatin regions? Are the physical properties of repeat DNA regions sufficient for recognition by egg? Does egg alone recognise sequence features associated with heterochromatin or is there a preceding cofactor (chicken perhaps!?) that comes before egg?
  • What happens if cell cycle rate is altered by other means? It is well known that the rate of Drosophila development is temperature dependent. If the temperature is decreased, does slowed diffusion of egg result in HP1 recruitment at a proportionally reduced rate?
  • Is early embryogenesis the only developmental stage in which cell cycle speed affects heterochromatin formation? Could increased cell cycle speed or unusual cell cycles such as endoreplication influence heterochromatin later in development?

 

References

Li Z, Thiel K, Thul PJ, Beller M, Kühnlein RP, Welte MA. (2012). Lipid Droplets Control the Maternal Histone Supply of Drosophila Embryos. Current Biology 22:2104–2113.

Caussinus E, Kanca O, Affolter M. (2011). Fluorescent fusion protein knockout mediated by anti-GFP nanobody. Nat Struct Mol Biol. 19(1):117-21.

Harmansa S, Alborelli I, Bieli D, Caussinus E, Affolter M. (2017) A nanobody-based toolset to investigate the role of protein localization and dispersal in Drosophila. Elife. Apr 11;6. pii: e22549. doi: 10.7554/eLife.22549

Tags: drosophila, embryogenesis, fly, heterochromatin

Posted on: 22 November 2018

doi: https://doi.org/10.1242/prelights.5762

Read preprint (No Ratings Yet)

Have your say

Your email address will not be published.

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

preLists in the developmental biology category:

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

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

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

Single Cell Biology 2020

A list of preprints mentioned at the Wellcome Genome Campus Single Cell Biology 2020 meeting.

 



List by Alex Eve

Society for Developmental Biology 79th Annual Meeting

Preprints at SDB 2020

 



List by Irepan Salvador-Martinez, Martin Estermann

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

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

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.

EDBC Alicante 2019

Preprints presented at the European Developmental Biology Congress (EDBC) in Alicante, October 23-26 2019.

 



List by Sergio Menchero 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

SDB 78th Annual Meeting 2019

A curation of the preprints presented at the SDB meeting in Boston, July 26-30 2019. The preList will be updated throughout the duration of the meeting.

 



List by Alex Eve

Lung Disease and Regeneration

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

 



List by Rob Hynds

Young Embryologist Network Conference 2019

Preprints presented at the Young Embryologist Network 2019 conference, 13 May, The Francis Crick Institute, London

 



List by Alex Eve

Pattern formation during development

The aim of this preList is to integrate results about the mechanisms that govern patterning during development, from genes implicated in the processes to theoritical models of pattern formation in nature.

 



List by Alexa Sadier

BSCB/BSDB Annual Meeting 2019

Preprints presented at the BSCB/BSDB Annual Meeting 2019

 



List by Dey Lab

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

Also in the genetics category:

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
Close