scholarly journals Actin Filament Cables in Drosophila Nurse Cells Are Composed of Modules That Slide Passively Past One Another during Dumping

1997 ◽  
Vol 138 (4) ◽  
pp. 783-797 ◽  
Author(s):  
Gregory M. Guild ◽  
Patricia S. Connelly ◽  
Michael K. Shaw ◽  
Lewis G. Tilney
Keyword(s):  
Plasma Membrane ◽  
Cell Surface ◽  
Actin Filaments ◽  
Nurse Cell ◽  
Cell Spreading ◽  
Growth Cones ◽  
Retrograde Flow ◽  
Nurse Cells ◽  
Modular Construction ◽  
Actin Cables

At a late stage in Drosophila oogenesis, nurse cells rapidly expel their cytoplasm into the oocyte via intracellular bridges by a process called nurse cell dumping. Before dumping, numerous cables composed of actin filaments appear in the cytoplasm and extend inward from the plasma membrane toward the nucleus. This actin cage prevents the nucleus, which becomes highly lobed, from physically blocking the intracellular bridges during dumping. Each cable is composed of a linear series of modules composed of ∼25 cross-linked actin filaments. Adjacent modules overlap in the cable like the units of an extension ladder. During cable formation, individual modules are nucleated from the cell surface as microvilli, released, and then cross-linked to an adjacent forming module. The filaments in all the modules in a cable are unidirectionally polarized. During dumping as the volume of the cytoplasm decreases, the nucleus to plasma membrane distance decreases, compressing the actin cables that shorten as adjacent modules slide passively past one another just as the elements of an extension ladder slide past one another for storage. In Drosophila, the modular construction of actin cytoskeletons seems to be a generalized strategy. The behavior of modular actin cytoskeletons has implications for other actin-based cytoskeletal systems, e.g., those involved in Listeria movement, in cell spreading, and in retrograde flow in growth cones and fibroblasts.

scholarly journals Regulated Actin Cytoskeleton Assembly at Filopodium Tips Controls Their Extension and Retraction

1999 ◽  
Vol 146 (5) ◽  
pp. 1097-1106 ◽  
Author(s):  
Aneil Mallavarapu ◽  
Tim Mitchison
Keyword(s):  
Actin Cytoskeleton ◽  
Growth Cone ◽  
Actin Filaments ◽  
Neuroblastoma Cell ◽  
Initial Step ◽  
Growth Cones ◽  
Neuroblastoma Cell Line ◽  
Dominant Factor ◽  
Retrograde Flow ◽  
Assembly Rate

The extension and retraction of filopodia in response to extracellular cues is thought to be an important initial step that determines the direction of growth cone advance. We sought to understand how the dynamic behavior of the actin cytoskeleton is regulated to produce extension or retraction. By observing the movement of fiduciary marks on actin filaments in growth cones of a neuroblastoma cell line, we found that filopodium extension and retraction are governed by a balance between the rate of actin cytoskeleton assembly at the tip and retrograde flow. Both assembly and flow rate can vary with time in a single filopodium and between filopodia in a single growth cone. Regulation of assembly rate is the dominant factor in controlling filopodia behavior in our system.

Drosophila quail, a villin-related protein, bundles actin filaments in apoptotic nurse cells

Development ◽  
1999 ◽  
Vol 126 (24) ◽  
pp. 5645-5657 ◽  
Author(s):  
N. Matova ◽  
S. Mahajan-Miklos ◽  
M.S. Mooseker ◽  
L. Cooley
Keyword(s):  
Actin Filaments ◽  
Nurse Cell ◽  
Calcium Concentration ◽  
Developmental Model ◽  
Free Calcium ◽  
Nurse Cells ◽  
Filamentous Actin ◽  
Actin Bundle ◽  
High Calcium ◽  
Egg Chambers

Drosophila Quail protein is required for the completion of fast cytoplasm transport from nurse cells to the oocyte, an event critical for the production of viable oocytes. The abundant network of cytoplasmic filamentous actin, established at the onset of fast transport, is absent in quail mutant egg chambers. Previously, we showed that Quail is a germline-specific protein with sequence homology to villin, a vertebrate actin-regulating protein. In this study, we combined biochemical experiments with observations in egg chambers to define more precisely the function of this protein in the regulation of actin-bundle assembly in nurse cells. We report that recombinant Quail can bind and bundle filamentous actin in vitro in a manner similar to villin at a physiological calcium concentration. In contrast to villin, Quail is unable to sever or cap filamentous actin, or to promote nucleation of new actin filaments at a high calcium concentration. Instead, Quail bundles the filaments regardless of the calcium concentration. In vivo, the assembly of nurse-cell actin bundles is accompanied by extensive perforation of the nurse-cell nuclear envelopes, and both of these phenomena are manifestations of nurse-cell apoptosis. To investigate whether free calcium levels are affected during apoptosis, we loaded egg chambers with the calcium indicator Indo-1. Our observations indicate a rise in free calcium in the nurse-cell cytoplasm coincident with the permeabilization of the nuclear envelopes. We also show that human villin expressed in the Drosophila germline could sense elevated cytoplasmic calcium; in nurse cells with reduced levels of Quail protein, villin interfered with actin-bundle stability. We conclude that Quail efficiently assembles actin filaments into bundles in nurse cells and maintains their stability under fluctuating free calcium levels. We also propose a developmental model for the fast phase of cytoplasm transport incorporating findings presented in this study.

scholarly journals Polymerizing Microtubules Activate Site-directed F-Actin Assembly in Nerve Growth Cones

1999 ◽  
Vol 10 (7) ◽  
pp. 2309-2327 ◽  
Author(s):  
M. William Rochlin ◽  
Michael E. Dailey ◽  
Paul C. Bridgman
Keyword(s):  
Plasma Membrane ◽  
Actin Filaments ◽  
Cytochalasin B ◽  
Membrane Surface ◽  
Growth Cones ◽  
Actin Assembly ◽  
Electron Microscopic ◽  
Early Step ◽  
Microscopic Studies ◽  
Nerve Growth Cones

We identify an actin-based protrusive structure in growth cones termed “intrapodium.” Unlike filopodia, intrapodia are initiated exclusively within lamellipodia and elongate in a continuous (nonsaltatory) manner parallel to the plane of the dorsal plasma membrane causing a ridge-like protrusion. Intrapodia resemble the actin-rich structures induced by intracellular pathogens (e.g.,Listeria) or by extracellular beads. Cytochalasin B inhibits intrapodial elongation and removal of cytochalasin B produced a burst of intrapodial activity. Electron microscopic studies revealed that lamellipodial intrapodia contain both short and long actin filaments oriented with their barbed ends toward the membrane surface or advancing end. Our data suggest an interaction between microtubule endings and intrapodia formation. Disruption of microtubules by acute nocodazole treatment decreased intrapodia frequency, and washout of nocodazole or addition of the microtubule-stabilizing drug Taxol caused a burst of intrapodia formation. Furthermore, individual microtubule ends were found near intrapodia initiation sites. Thus, microtubule ends or associated structures may regulate these actin-dependent structures. We propose that intrapodia are the consequence of an early step in a cascade of events that leads to the development of F-actin-associated plasma membrane specializations.

Presence of Clathrin at Adhesion Sites in Phagocytosing Macrophages

1982 ◽  
Vol 40 ◽  
pp. 114-117
Author(s):  
J. Aggeler ◽  
J.E. Heuser ◽  
Z. Werb
Keyword(s):  
Plasma Membrane ◽  
Actin Filaments ◽  
Binding Proteins ◽  
Binding Protein ◽  
Cell Spreading ◽  
Actin Binding ◽  
Dense Network ◽  
Actin Binding Protein ◽  
Adhesion Sites ◽  
Cytoplasmic Surface

Phagocytosis of particles by macrophages may be similar to cell spreading on a substratum, in that a dense network of actin filaments appears beneath the plasma membrane in both cases. When viewed in broken-open or detergent- extracted cells, cytoskeletal filaments are observed to form focal attachments to the plasma membrane and to the cytoplasmic surface of phagosomes. Hartwig et al. have presented a model of phagocytosis in which an actin-binding protein alters the organization of subplasmalemma1 actin filaments in such a way that the plasma membrane is forced up over the particle to form the phagosome. Their evidence indicates that similar actin-binding proteins may function during cell spreading.

scholarly journals The 110-kD protein-calmodulin complex of the intestinal microvillus (brush border myosin I) is a mechanoenzyme.

1989 ◽  
Vol 108 (6) ◽  
pp. 2395-2400 ◽  
Author(s):  
M S Mooseker ◽  
T R Coleman
Keyword(s):  
Skeletal Muscle ◽  
Plasma Membrane ◽  
Brush Border ◽  
Actin Filaments ◽  
Average Rate ◽  
Skeletal Muscle Myosin ◽  
Intestinal Brush Border ◽  
Myosin I ◽  
Actin Cables ◽  
Muscle Myosin

The 110-kD protein-calmodulin complex (110K-CM) of the intestinal brush border serves to laterally tether microvillar actin filaments to the plasma membrane. Results from several laboratories have demonstrated that this complex shares many enzymatic and structural properties with myosin. The mechanochemical potential of purified avian 110K-CM was assessed using the Nitella bead motility assay (Sheetz, M. P., and J. A. Spudich. 1983. Nature (Lond.). 303:31-35). Under low Ca2+ conditions, 110K-CM-coated beads bound to actin cables, but no movement was observed. Using EGTA/calcium buffers (approximately 5-10 microM free Ca2+) movement of 110K-CM-coated beads along actin cables (average rate of approximately 8 nm/s) was observed. The movement was in the same direction as that for beads coated with skeletal muscle myosin. The motile preparations of 110K-CM were shown to be free of detectable contamination by conventional brush border myosin. Based on these and other observations demonstrating the myosin-like properties of 110K-CM, we propose that this complex be named "brush border myosin I."

scholarly journals Vps13 is required for timely removal of nurse cell corpses

Development ◽  
2020 ◽  
Vol 147 (20) ◽  
pp. dev191759
Author(s):  
Anita I. E. Faber ◽  
Marianne van der Zwaag ◽  
Hein Schepers ◽  
Ellie Eggens-Meijer ◽  
Bart Kanon ◽  
...  
Keyword(s):  
Cell Death ◽  
Plasma Membrane ◽  
Programmed Cell Death ◽  
Nurse Cell ◽  
Close Association ◽  
Follicle Cells ◽  
Nurse Cells ◽  
Lipid Transfer ◽  
Membranous Structure ◽  
Membrane Contact Sites

ABSTRACTProgrammed cell death and consecutive removal of cellular remnants is essential for development. During late stages of Drosophila melanogaster oogenesis, the small somatic follicle cells that surround the large nurse cells promote non-apoptotic nurse cell death, subsequently engulf them, and contribute to the timely removal of nurse cell corpses. Here, we identify a role for Vps13 in the timely removal of nurse cell corpses downstream of developmental programmed cell death. Vps13 is an evolutionarily conserved peripheral membrane protein associated with membrane contact sites and lipid transfer. It is expressed in late nurse cells, and persistent nurse cell remnants are observed when Vps13 is depleted from nurse cells but not from follicle cells. Microscopic analysis revealed enrichment of Vps13 in close proximity to the plasma membrane and the endoplasmic reticulum in nurse cells undergoing degradation. Ultrastructural analysis uncovered the presence of an underlying Vps13-dependent membranous structure in close association with the plasma membrane. The newly identified structure and function suggests the presence of a Vps13-dependent process required for complete degradation of bulky remnants of dying cells.

The role of microfilaments in cytoplasmic streaming in Drosophila follicles

1986 ◽  
Vol 80 (1) ◽  
pp. 159-169 ◽  
Author(s):  
H.O. Gutzeit
Keyword(s):  
Cell Membrane ◽  
Nuclear Membrane ◽  
Actin Filaments ◽  
Cytoplasmic Streaming ◽  
Nurse Cell ◽  
Time Lapse ◽  
Nurse Cells ◽  
Cell Nuclei ◽  
Cell Cytoplasm

During the last phase of oogenesis in Drosophila, nurse cell cytoplasm can be seen to be streaming into the growing oocyte when visualized in time-lapse films. This process can be reversibly inhibited by cytochalasins. The distribution of F-actin filaments in the nurse cells has been studied by staining with rhodamine-conjugated phalloidin. At the beginning of cytoplasmic streaming (stage 10B) increasingly thick bundles of microfilaments formed, many of which spanned the nurse cell cytoplasm from the cell membrane to the nuclear membrane. The association of F-actin with the nuclear membrane persisted when nurse cell nuclei were isolated mechanically. The experimental evidence suggests that microfilament contraction in the nurse cells leads to cytoplasmic streaming by pressure flow.

scholarly journals Fusion of Drosophila oocytes with specified germline sister cells

2020 ◽  
Author(s):  
Zehra Ali-Murthy ◽  
Richard D. Fetter ◽  
Thomas B. Kornberg
Keyword(s):  
Plasma Membrane ◽  
Nurse Cell ◽  
Drosophila Species ◽  
Nurse Cells ◽  
Egg Chambers ◽  
Germline Cells ◽  
Egg Chamber ◽  
Two Stages ◽  
Sister Cells

ABSTRACTIn many animals, oocytes develop together with sister germline cells that pass products to the developing oocyte. In Drosophila, fifteen sister germline (nurse) cells in each egg chamber are known to apoptose by stage 12-13, but we discovered that two specific nurse cells that are juxtaposed to the oocyte are eliminated precociously at stage 10B. These nurse cells fuse with the oocyte and their nuclei extrude through an opening that forms in the oocyte. These nuclei extinguish in the ooplasm, and at stage 11, egg chambers have thirteen nucleated nurse cells and the plasma membrane of the oocyte is mostly restored. In infrequent egg chambers in which nurse cells are not eliminated, oocytes do not develop normally and are not fertilized. Precocious elimination is common to other Drosophila species. We conclude that nurse cells are distinguished by position and identity, and that nurse cell dissolution proceeds in two stages.

scholarly journals A Diaphanous and Enabled dependent asymmetric actin cable array repositions nuclei during Drosophila oogenesis

2020 ◽  
Author(s):  
Gregory Logan ◽  
Brooke M. McCartney
Keyword(s):  
Growth Rate ◽  
Nurse Cell ◽  
Cell Cortex ◽  
Nurse Cells ◽  
Nuclear Movement ◽  
Actin Cable ◽  
Rate Asymmetry ◽  
Ring Canals ◽  
Differential Localization ◽  
Actin Cables

AbstractCells reposition their nuclei for a diversity of specialized functions through a wide variety of cytoskeletal mechanisms. To complete oogenesis, Drosophila nurse cells employ novel actin cable arrays to reposition their nuclei. During oogenesis, 15 nurse cells connected by ring canals contract to “dump” their cytoplasmic contents into the oocyte. Just prior to dumping, actin cables initiate from the nurse cell cortex and elongate toward their nuclei, pushing them away from the ring canals to prevent obstruction. How the actin cable arrays generate directional nuclear movement is not known. We found regional differences in the actin cable growth rate that are dependent on the differential localization of the actin assembly factors Enabled (Ena) and Diaphanous (Dia). Mislocalization of Ena resulted in actin cable arrays with a uniform growth rate. In the absence of growth rate asymmetry, nuclear relocation was significantly altered and cytoplasmic dumping was incomplete. This novel mechanism for nuclear repositioning relies on the regulated cortical localization of Dia and Ena producing asymmetric actin cable arrays that push the nuclei away from the ring canals, enabling successful oogenesis.Summary statementThis work demonstrates that an asymmetric actin cable array regulated by the differential localization of Diaphanous and Enabled is necessary to reposition nurse cell nuclei and complete oogenesis in Drosophila.

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