Functional equivalence of germ plasm organizers

Me31B is a protein component of Drosophila germ granules and plays an important role in germline development by interacting with other proteins and RNAs. To understand the dynamic changes that the Me31B interactome undergoes from oogenesis to early embryogenesis, we characterized the early embryo Me31B interactome and compared it to the known ovary interactome. The two interactomes shared RNA regulation proteins, glycolytic enzymes, and cytoskeleton/motor proteins, but the core germ plasm proteins Vas, Tud, and Aub were significantly decreased in the embryo interactome. Our follow-up on two RNA regulations proteins present in both interactomes, Tral and Cup, revealed that they colocalize with Me31B in nuage granules, P-bodies/sponge bodies, and possibly in germ plasm granules. We further show that Tral and Cup are both needed for maintaining Me31B protein level and mRNA stability, with Tral's effect being more specific. In addition, we provide evidence that Me31B likely colocalizes and interacts with germ plasm marker Vas in the ovaries and early embryo germ granules. Finally, we show that Me31B's localization in germ plasm is likely independent of the Osk-Vas-Tud-Aub germ plasm assembly pathway although its proper enrichment in the germ plasm may still rely on certain conserved germ plasm proteins. Germ cells are essential for sexual reproduction and the survival of many species, and species-specific strategies exist to form germ cells 1-5. Drosophila melanogaster uses maternally inherited germ granules to determine germ cell fate. Germ granules are heterogeneous aggregates of ribonucleoprotein (RNP) complexes 6 that undergo dynamic positional, morphological, and compositional changes during germline development, a process that spans oogenesis and early embryogenesis 7-11. Me31B, a conserved germ granule component 9,12 , is expressed in nurse cells, oocytes, and early embryos 13. In these cells, Me31B exists in different types of RNP granules, including nuage granules, P-bodies, sponge bodies, and germ plasm granules 12-15. In these granules, Me31B has been suggested to function as a putative ATP-dependent RNA helicase that interacts with other germline proteins and RNAs to exert post-transcriptional regulation on those RNAs 10,11,13,16,17. As an important example, Me31B associates with osk mRNA to ensure its proper translation into Osk protein only at the posterior pole of developing oocytes. Then, the Osk protein initiates a step-wise assembly pathway that recruits downstream proteins including Vas, Tud, and Aub to form the germ plasm and eventually dictates germ cell formation 13,18-21. Me31B exhibits changes in its localization pattern, aggregation status, and even function as germline cells develop during the ovary-to-embryo transition 13,17. It is believed that these changes are correlated with the different biological contexts in which Me31B exists 17. Therefore, to understand the role of Me31B during germ

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“…3E,G). Similar phenotypes were observed in three other cup mutants, cup 1 /Df, cup 21 /Df, and cup 27 /Df (data not shown and Fig. 3E).…”

Section: Me31b's Aggregation Into the Germ Granules And Me31b Proteinsupporting

confidence: 86%

“…osk-bcd 3′UTR strain was received from Dr. Ruth Lehmann lab and was previously described 19 . cup 1 , cup 16 , cup 21 , and cup 27 strains were received from Dr. Akira Nakamura lab.…”

Section: Methodsmentioning

confidence: 99%

Comparative Proteomics Reveal Me31B’s Interactome Dynamics, Expression Regulation, and Assembly Mechanism into Germ Granules during Drosophila Germline Development

McCambridge

Solanki

Olchawa

et al. 2020

Sci Rep

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“…The Balbiani body is a non-membrane bound super-organelle consisting mostly of mitochondria but also Golgi complexes, endoplasmic reticulum (ER), other vesicles and RNA (Boke et al, 2016; Cox and Spradling, 2003; Hertig, 1968; Kloc et al, 2004). The Balbiani body is held together by an amyloid-like matrix formed by an intrinsically disordered protein in frogs and in zebrafish (Boke et al, 2016; Krishnakumar et al, 2018). The Balbiani body is only present in early, non-growing oocytes and dissociates upon oocyte activation, thus is closely associated with oocyte dormancy.…”

Section: Introductionmentioning

confidence: 99%

Mouse oocytes do not contain a Balbiani body

Dhandapani

Salzer

Durán

et al. 2021

Preprint

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Poor oocyte quality accounts for majority of female fertility problems, however, we know little about how oocytes can remain healthy for many years or why they eventually decline with age. An oocyte spends majority of its lifetime in primordial state. Unlike many somatic cell types or mature oocytes, the cellular and molecular biology of primordial oocytes are largely unexplored. Yet, studying these aspects is necessary to understand the remarkable lifespan of oocytes and their eventual decline.A hallmark of primordial oocytes in many species is the Balbiani body, a non-membrane bound compartment that contains majority of mitochondria in oocyte cytoplasm. The Balbiani body was shown to be held together by an amyloid-like matrix in Xenopus oocytes. It has been proposed to be essential for maintaining mitochondria in a healthy state during long-lasting dormancy.Here, we develop enabling methods that allow live-imaging based comparative characterisation of Xenopus, mouse and human primordial oocytes. We show that human and Xenopus oocytes have a Balbiani body, characterised by an intense accumulation of mitochondria. Our results suggest that amyloid-like features of Balbiani bodies are conserved in humans and Xenopus. However, despite previous reports, we could not find a conventional Balbiani body in mouse oocytes. We demonstrate what was mistaken for a Balbiani body in mouse primordials is an unconventionally shaped Golgi apparatus. Our work provides the first insights into the organisation of the cytoplasm in mammalian primordial oocytes, and clarifies relative advantages and limitations of different model systems for studying female (in)fertility.Significance StatementWorld-wide data suggest that >25% of female fertility problems are undiagnosed, pointing to a huge gap in our understanding of female reproduction. Our findings help fill this gap by studying the cell biology of primordial oocytes. Having optimised methods for isolation and live-imaging of oocytes, we show that oocytes of evolutionary more distant species, Xenopus and human have a conserved super-organelle, a Balbiani body, in their cytoplasm whereas mouse oocytes do not have one. We propose that the shorter lifespan in mice obviates the need for a Balbiani body. Our results also suggest that primordial oocytes have active organelles, and thus call for a re-examination of the concept of dormancy in these long-lived cells.

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“…It is likely that the maternal provision mode of germ plasm evolved multiple times among the animals, and this is reflected in the highly variable, and often novel, molecular basis of germ plasm determinants across animals [6]. For example, germ plasm in vertebrates (where it exists) is dependent on the maternal localization of bucky ball [7] a novel gene found only in vertebrates without clear homologs in other lineages [8]. Similarly, the gene products of oskar ( osk ), another novel gene that appears to have originated as a chimera between a LOTUS domain-containing gene and a bacterial lipase [9, 10], are both necessary and sufficient to induce germ plasm and, thus, primordial germ cells (PGCs) in the fly Drosophila [11–14].…”

Section: Introductionmentioning

confidence: 99%

Transcriptomic and functional analysis of the oosome, a unique form of germ plasm in the wasp Nasonia vitripennis

2019

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Background The oosome is the germline determinant in the wasp Nasonia vitripennis and is homologous to the polar granules of Drosophila. Despite a common evolutionary origin and developmental role, the oosome is morphologically quite distinct from polar granules. It is a solid sphere that migrates within the cytoplasm before budding out and forming pole cells. Results To gain an understanding of both the molecular basis of oosome development and the conserved essential features of germ plasm, we quantified and compared transcript levels between embryo fragments that contained the oosome and those that did not. The identity of the differentially localized transcripts indicated that Nasonia uses a distinct set of molecules to carry out conserved germ plasm functions. In addition, functional testing of a sample of localized transcripts revealed potentially novel mechanisms of ribonucleoprotein assembly and pole cell cellularization in the wasp. Conclusions Our results demonstrate that the composition of germ plasm varies significantly within Holometabola, as very few mRNAs share localization to the oosome and polar granules. Some of this variability appears to be related to the unique properties of the oosome relative to the polar granules in Drosophila, and some may be related to differences in pole formation between species. This work will serve as the basis for further investigation into the patterns of germline determinant evolution among insects, the molecular basis of the unique properties of the oosome, and the incorporation of novel components into developmental networks.

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Functional equivalence of germ plasm organizers

Cited by 42 publications

References 124 publications

Comparative Proteomics Reveal Me31B’s Interactome Dynamics, Expression Regulation, and Assembly Mechanism into Germ Granules during Drosophila Germline Development

Comparative Proteomics Reveal Me31B’s Interactome Dynamics, Expression Regulation, and Assembly Mechanism into Germ Granules during Drosophila Germline Development

Mouse oocytes do not contain a Balbiani body

Transcriptomic and functional analysis of the oosome, a unique form of germ plasm in the wasp Nasonia vitripennis

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