The Drosophila fusome, a germline-specific organelle, contains membrane skeletal proteins and functions in cyst formation

Development ◽  
1994 ◽  
Vol 120 (4) ◽  
pp. 947-956 ◽  
Author(s):  
H. Lin ◽  
L. Yue ◽  
A.C. Spradling
Keyword(s):  
Cyst Formation ◽  
Nurse Cells ◽  
Germline Stem Cells ◽  
Cytoplasmic Structure ◽  
Ring Canals ◽  
Alpha Spectrin ◽  
Polarized Transport ◽  
Form Ring ◽  
Molecular Components ◽  
Number Of Cells

Oogenesis in Drosophila takes place within germline cysts that support polarized transport through ring canals interconnecting their 15 nurse cells and single oocyte. Developing cystocytes are spanned by a large cytoplasmic structure known as the fusome that has been postulated to help form ring canals and determine the pattern of nurse cell-oocyte interconnections. We identified the adducin-like hts product and alpha-spectrin as molecular components of fusomes, discovered a related structure in germline stem cells and documented regular associations between fusomes and cystocyte centrosomes. hts mutations completely eliminated fusomes, causing abnormal cysts containing a reduced number of cells to form. Our results imply that Drosophila fusomes are required for ovarian cyst formation and suggest that membrane skeletal proteins regulate cystocyte divisions.

scholarly journals Differentiating Drosophila female germ cells initiate Polycomb silencing by regulating PRC2-interacting proteins

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Steven Z DeLuca ◽  
Megha Ghildiyal ◽  
Liang-Yu Pang ◽  
Allan C Spradling
Keyword(s):  
Interacting Proteins ◽  
Nurse Cells ◽  
Germline Stem Cells ◽  
Developmentally Regulated ◽  
Canonical Distribution ◽  
Polycomb Repressive Complex 2 ◽  
Animal Development ◽  
Target Sites ◽  
Female Germline ◽  
Inactive Chromatin

Polycomb silencing represses gene expression and provides a molecular memory of chromatin state that is essential for animal development. We show that Drosophila female germline stem cells (GSCs) provide a powerful system for studying Polycomb silencing. GSCs have a non-canonical distribution of PRC2 activity and lack silenced chromatin like embryonic progenitors. As GSC daughters differentiate into nurse cells and oocytes, nurse cells, like embryonic somatic cells, silence genes in traditional Polycomb domains and in generally inactive chromatin. Developmentally controlled expression of two Polycomb repressive complex 2 (PRC2)-interacting proteins, Pcl and Scm, initiate silencing during differentiation. In GSCs, abundant Pcl inhibits PRC2-dependent silencing globally, while in nurse cells Pcl declines and newly induced Scm concentrates PRC2 activity on traditional Polycomb domains. Our results suggest that PRC2-dependent silencing is developmentally regulated by accessory proteins that either increase the concentration of PRC2 at target sites or inhibit the rate that PRC2 samples chromatin.

scholarly journals A novel pattern of germ cell divisions in the production of hymenopteran insect eggs

2020 ◽  
Vol 16 (5) ◽  
pp. 20200137
Author(s):  
Katherine J. Eastin ◽  
Austin P. Huang ◽  
Patrick M. Ferree
Keyword(s):  
Germ Cell ◽  
Germ Cells ◽  
Radial Direction ◽  
Fruit Fly ◽  
Cell Number ◽  
Nurse Cells ◽  
Insect Eggs ◽  
Ring Canals ◽  
Cytoplasmic Bridges ◽  
Higher Eukaryotes

Egg development is a defining process of reproduction in higher eukaryotes. In the fruit fly, Drosophila melanogaster , this process begins with four mitotic divisions starting from a single germ cell, producing a cyst of 16 cystocytes; one of these cells will become the oocyte and the others supporting nurse cells. These mitotic divisions are exceptional because cytokinesis is incomplete, resulting in the formation of cytoplasmic bridges known as ring canals that interconnect the cystocytes. This organization allows all cystocytes to divide synchronously during each mitotic round, resulting in a final, power-of-2 number of germ cells. Given that numerous insects obey this power-of-2 rule, we investigated if strict cell doubling is a universal, underlying cause. Using confocal microscopy, we found striking departures from this paradigm in three different power-of-2 insects belonging to the Apocrita suborder (ants, bees and wasps). In these insects, the earliest-formed cystocytes cease to divide during the latter mitotic cycles while their descendants undergo further division, thereby producing a ‘radial’ direction of division activity. Such cystocyte division patterns that depart from strict cell doubling may be ‘fine-tuned’ in order to maintain a final, power-of-2 germ cell number.

scholarly journals A Dual Role for Actin and Microtubule Cytoskeleton in the Transport of Golgi Units from the Nurse Cells to the Oocyte Across Ring Canals

2009 ◽  
Vol 20 (1) ◽  
pp. 556-568 ◽  
Author(s):  
Emmanuelle Nicolas ◽  
Nicolas Chenouard ◽  
Jean-Christophe Olivo-Marin ◽  
Antoine Guichet
Keyword(s):  
Embryonic Development ◽  
Transport Process ◽  
Myosin Ii ◽  
Nurse Cells ◽  
Transport Mechanisms ◽  
Step Process ◽  
Actin Networks ◽  
Ring Canals ◽  
Cytoplasmic Bridges ◽  
Active Transport Process

Axis specification during Drosophila embryonic development requires transfer of maternal components during oogenesis from nurse cells (NCs) into the oocyte through cytoplasmic bridges. We found that the asymmetrical distribution of Golgi, between nurse cells and the oocyte, is sustained by an active transport process. We have characterized actin basket structures that asymmetrically cap the NC side of Ring canals (RCs) connecting the oocyte. Our results suggest that these actin baskets structurally support transport mechanisms of RC transit. In addition, our tracking analysis indicates that Golgi are actively transported to the oocyte rather than diffusing. We observed that RC transit is microtubule-based and mediated at least by dynein. Finally, we show that actin networks may be involved in RC crossing through a myosin II step process, as well as in dispatching Golgi units inside the oocyte subcompartments.

scholarly journals Myosin Light Chain–activating Phosphorylation Sites Are Required for Oogenesis in Drosophila

1997 ◽  
Vol 139 (7) ◽  
pp. 1805-1819 ◽  
Author(s):  
Pascale Jordan ◽  
Roger Karess
Keyword(s):  
Amino Acids ◽  
Heavy Chain ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Germ Line ◽  
Myosin Ii ◽  
Oocyte Development ◽  
Nurse Cells ◽  
Ring Canals

The Drosophila spaghetti squash (sqh) gene encodes the regulatory myosin light chain (RMLC) of nonmuscle myosin II. Biochemical analysis of vertebrate nonmuscle and smooth muscle myosin II has established that phosphorylation of certain amino acids of the RMLC greatly increases the actin-dependent myosin ATPase and motor activity of myosin in vitro. We have assessed the in vivo importance of these sites, which in Drosophila correspond to serine-21 and threonine-20, by creating a series of transgenes in which these specific amino acids were altered. The phenotypes of the transgenes were examined in an otherwise null mutant background during oocyte development in Drosophila females. Germ line cystoblasts entirely lacking a functional sqh gene show severe defects in proliferation and cytokinesis. The ring canals, cytoplasmic bridges linking the oocyte to the nurse cells in the egg chamber, are abnormal, suggesting a role of myosin II in their establishment or maintenance. In addition, numerous aggregates of myosin heavy chain accumulate in the sqh null cells. Mutant sqh transgene sqh-A20, A21 in which both serine-21 and threonine-20 have been replaced by alanines behaves in most respects identically to the null allele in this system, with the exception that no heavy chain aggregates are found. In contrast, expression of sqh-A21, in which only the primary phosphorylation target serine-21 site is altered, partially restores functionality to germ line myosin II, allowing cystoblast division and oocyte development, albeit with some cytokinesis failure, defects in the rapid cytoplasmic transport from nurse cells to cytoplasm characteristic of late stage oogenesis, and some damaged ring canals. Substituting a glutamate for the serine-21 (mutant sqh-E21) allows oogenesis to be completed with minimal defects, producing eggs that can develop normally to produce fertile adults. Flies expressing sqh-A20, in which only the secondary phosphorylation site is absent, appear to be entirely wild type. Taken together, this genetic evidence argues that phosphorylation at serine-21 is critical to RMLC function in activating myosin II in vivo, but that the function can be partially provided by phosphorylation at threonine-20.

scholarly journals The Arp2/3 complex and the formin, Diaphanous, are both required to regulate the size of germline ring canals in the developing egg chamber

2019 ◽  
Author(s):  
Josephine Thestrup ◽  
Marina Tipold ◽  
Alexandra Kindred ◽  
Kara Stark ◽  
Travis Curry ◽  
...  
Keyword(s):  
Fruit Fly ◽  
Actin Binding ◽  
Nurse Cells ◽  
Intercellular Bridge ◽  
Ring Canal ◽  
Contractile Ring ◽  
Intercellular Bridges ◽  
Large Size ◽  
Ring Canals ◽  
Egg Chamber

AbstractIntercellular bridges are an essential structural feature found in both germline and somatic cells throughout the animal kingdom. Because of their large size, the germline intercellular bridges, or ring canals, in the developing fruit fly egg chamber are an excellent model to study the formation, stabilization, and expansion of these structures. Within the egg chamber, the germline ring canals connect 15 supporting nurse cells to the developing oocyte, facilitating the transfer of materials required for successful oogenesis. The ring canals are derived from a stalled actomyosin contractile ring; once formed, additional actin and actin-binding proteins are recruited to the ring to support the 20-fold expansion that accompanies oogenesis. These behaviors provide a unique model system to study the actin regulators that control incomplete cytokinesis, intercellular bridge formation, and expansion. By temporally controlling their expression in the germline, we have demonstrated that the Arp2/3 complex and the formin, Diaphanous (Dia), coordinately regulate ring canal size and expansion throughout oogenesis. Dia is required for successful incomplete cytokinesis and the initial stabilization of the germline ring canals. Once the ring canals have formed, the Arp2/3 complex and Dia cooperate to determine ring canal size and maintain their stability. Our data suggest that the nurse cells must maintain a precise balance between the activity of these two nucleators during oogenesis.

scholarly journals Zebrafish dazl regulates cystogenesis and germline stem cell specification during the primordial germ cell to germline stem cell transition

Development ◽  
2021 ◽  
Vol 148 (7) ◽  
Author(s):  
Sylvain Bertho ◽  
Mara Clapp ◽  
Torsten U. Banisch ◽  
Jan Bandemer ◽  
Erez Raz ◽  
...  
Keyword(s):  
Stem Cells ◽  
Stem Cell ◽  
Rna Binding ◽  
Process Analysis ◽  
Primordial Germ Cell ◽  
Cyst Formation ◽  
Rapid Expansion ◽  
Germline Stem Cell ◽  
Cell Specification ◽  
Ring Canals

ABSTRACT Fertility and gamete reserves are maintained by asymmetric divisions of the germline stem cells to produce new stem cells or daughters that differentiate as gametes. Before entering meiosis, differentiating germ cells (GCs) of sexual animals typically undergo cystogenesis. This evolutionarily conserved process involves synchronous and incomplete mitotic divisions of a GC daughter (cystoblast) to generate sister cells connected by intercellular bridges that facilitate the exchange of materials to support rapid expansion of the gamete progenitor population. Here, we investigated cystogenesis in zebrafish and found that early GCs are connected by ring canals, and show that Deleted in azoospermia-like (Dazl), a conserved vertebrate RNA-binding protein (Rbp), is a regulator of this process. Analysis of dazl mutants revealed the essential role of Dazl in regulating incomplete cytokinesis, germline cyst formation and germline stem cell specification before the meiotic transition. Accordingly, dazl mutant GCs form defective ring canals, and ultimately remain as individual cells that fail to differentiate as meiocytes. In addition to promoting cystoblast divisions and meiotic entry, dazl is required for germline stem cell establishment and fertility.

Recent findings on oogenesis of Drosophila melanogaster

Development ◽  
1977 ◽  
Vol 38 (1) ◽  
pp. 115-124
Author(s):  
F. Giorgi ◽  
J. Jacob
Keyword(s):  
Drosophila Melanogaster ◽  
Plasma Membrane ◽  
Early Stage ◽  
Dense Body ◽  
Superficial Layer ◽  
Coated Vesicles ◽  
Nurse Cells ◽  
External Limiting Membrane ◽  
Ring Canals

The ultrastructure of the developing ooplasm has been examined in 2–3–day-old flies of Drosophila melanogaster with a view to clarifying the origin of the yolk platelets. Previtellogenic ovarian chambers have been shown to exhibit a number of cytolysosomes; these are first formed in the nurse cells and are later brought to the ooplasm after having passed through the ring canals. Just prior to the beginning of vitellogenesis some of the cytolysosomes in the ooplasm acquire in places a yolk-like appearance. As vitellogenesis commences, in early stage-8 chambers, the central ooplasm comes to exhibit a number of inclusions which combine in themselves features of both yolk platelets and cytolysosomes. The onset of vitellogenesis at stage 8 is marked by the appearance of several structural entities on the plasma membrane of the oocyte. At this site, there appear a number of depressions or pits in between the microvilli. Deeper in the cortical ooplasm there are also present a number of coated vesicles and tubules. While the former exhibit a typical threelayered structure similar to that of the pits, the tubules lack the outer spiked layer. Mature yolk platelets appear to be made up of three major components. These are a central homogeneous dense body, an outer superficial layer with a number of small spherules and a rounded body therein, and an external limiting membrane. Instances of fusion between vesicles of sizes progressively larger have been observed with frequency. This observation is discussed in relation to the formation of yolk platelets by means of pinocytotic uptake. A contribution made by the nurse cells to the formation of the yolk platelets is also taken into account.

Morphogenesis of the Drosophila fusome and its implications for oocyte specification

Development ◽  
1998 ◽  
Vol 125 (15) ◽  
pp. 2781-2789 ◽  
Author(s):  
M. de Cuevas ◽  
A.C. Spradling
Keyword(s):  
Stem Cells ◽  
Daughter Cell ◽  
Cyst Formation ◽  
The Other ◽  
Cytoplasmic Organelle ◽  
Ring Canal ◽  
Cell Cycles ◽  
Ring Canals ◽  
Asymmetrically Distributed ◽  
Cyst Growth

The Drosophila oocyte develops within a cyst of 16 germline cells interconnected by ring canals. Polarized, microtubule-based transport of unknown determinants is required for oocyte formation, but whether polarity is established during or after cyst formation is not clear. We have analyzed how polarity develops in stem cells and dividing cysts by following the growth of the fusome, a vesiculated cytoplasmic organelle. Our studies show that the fusome grows by a regular, polarized process throughout the stem cell and cyst cell cycles. Each polarization cycle begins in mitosis, when the fusome segregates to a single daughter cell of each pair. Following mitosis, a ‘plug’ of fusomal material forms in each nascent ring canal and gradually fuses with the pre-existing fusome. In stem cells, the ring canal is transient and closes down after the fusome is partitioned through it. In dividing cysts, as the fusome plugs move toward the pre-existing fusome, their associated ring canals also move, changing the geometry of the cyst. At the end of each cycle of cyst growth, the fusome remains asymmetrically distributed within the cyst; one of the two cells with four ring canals retains a bigger piece of fusome than any other cell, including the other cell with four ring canals. Based on these observations, we argue that the oocyte is specified at the first cyst division.

scholarly journals Drosophila sperm development and intercellular cytoplasm sharing through ring canals do not require an intact fusome

Development ◽  
2020 ◽  
Vol 147 (22) ◽  
pp. dev190140
Author(s):  
Ronit S. Kaufman ◽  
Kari L. Price ◽  
Katelynn M. Mannix ◽  
Kathleen M. Ayers ◽  
Andrew M. Hudson ◽  
...  
Keyword(s):  
Quality Control ◽  
Germ Cells ◽  
Male Fertility ◽  
Intercellular Bridges ◽  
Male Germline ◽  
Cytoplasmic Structure ◽  
Ring Canals ◽  
Sperm Development ◽  
Intercellular Movement ◽  
Endogenous Proteins

ABSTRACTAnimal germ cells communicate directly with each other during gametogenesis through intercellular bridges, often called ring canals (RCs), that form as a consequence of incomplete cytokinesis during cell division. Developing germ cells in Drosophila have an additional specialized organelle connecting the cells called the fusome. Ring canals and the fusome are required for fertility in Drosophila females, but little is known about their roles during spermatogenesis. With live imaging, we directly observe the intercellular movement of GFP and a subset of endogenous proteins through RCs during spermatogenesis, from two-cell diploid spermatogonia to clusters of 64 post-meiotic haploid spermatids, demonstrating that RCs are stable and open to intercellular traffic throughout spermatogenesis. Disruption of the fusome, a large cytoplasmic structure that extends through RCs and is important during oogenesis, had no effect on spermatogenesis or male fertility under normal conditions. Our results reveal that male germline RCs allow the sharing of cytoplasmic information that might play a role in quality control surveillance during sperm development.

scholarly journals Formation of actin filament bundles in the ring canals of developing Drosophila follicles.

1996 ◽  
Vol 133 (1) ◽  
pp. 61-74 ◽  
Author(s):  
L G Tilney ◽  
M S Tilney ◽  
G M Guild
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Actin Binding ◽  
Nurse Cells ◽  
Ring Canal ◽  
Contractile Ring ◽  
Thin Sections ◽  
Development Stages ◽  
Ring Canals ◽  
Filament Bundles

Growing the intracellular bridges that connect nurse cells with each o ther and to the developing oocyte is vital for egg development. These ring canals increase from 0.5 microns in diameter at stage 2 to 10 microns in diameter at stage 11. Thin sections cut horizontally as you would cut a bagel, show that there is a layer of circumferentially oriented actin filaments attached to the plasma membrane at the periphery of each canal. By decoration with subfragment 1 of myosin we find actin filaments of mixed polarities in the ring such as found in the "contractile ring" formed during cytokinesis. In vertical sections through the canal the actin filaments appear as dense dots. At stage 2 there are 82 actin filaments in the ring, by stage 6 there are 717 and by stage 10 there are 726. Taking into account the diameter, this indicates that there is 170 microns of actin filaments/canal at stage 2 (pi x 0.5 microns x 82), 14,000 microns at stage 9 and approximately 23,000 microns at stage 11 or one inch of actin filament! The density of actin filaments remains unchanged throughout development. What is particularly striking is that by stages 4-5, the ring of actin filaments has achieved its maximum thickness, even though the diameter has not yet increased significantly. Thereafter, the diameter increases. Throughout development, stages 2-11, the canal length also increases. Although the density (number of actin filaments/micron2) through a canal remains constant from stage 5 on, the actin filaments appear as a net of interconnected bundles. Further information on this net of bundles comes from studying mutant animals that lack kelch, a protein located in the ring canal that has homology to the actin binding protein, scruin. In this mutant, the actin filaments form normally but individual bundles that comprise the fibers of the net are not bound tightly together. Some bundles enter into the ring canal lumen but do not completely occlude the lumen. all these observations lay the groundwork for our understanding of how a noncontractile ring increases in thickness, diameter, and length during development.

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