scholarly journals Osmolarity-regulated swelling initiates egg activation in Drosophila

2021 ◽  
Author(s):  
Anna H. York-Andersen ◽  
Benjamin W. Wood ◽  
Elise L. Wilby ◽  
Alexander S. Berry ◽  
Timothy T. Weil
Keyword(s):  
Mature Oocyte ◽  
Posterior Pole ◽  
Vitelline Membrane ◽  
Egg Activation ◽  
Calcium Wave ◽  
Environmental Cues ◽  
Meiotic Cell ◽  
Volume Increase ◽  
Initiation Factors ◽  
Maternal Mrnas

ABSTRACTEgg activation is a series of highly coordinated processes that prepare the mature oocyte for embryogenesis. Typically associated with fertilisation, egg activation results in many downstream outcomes, including the resumption of the meiotic cell cycle, translation of maternal mRNAs and cross-linking of the vitelline membrane. While some aspects of egg activation, such as initiation factors in mammals and environmental cues in sea animals, have been well-documented, the mechanics of egg activation in insects are less well understood. For many insects, egg activation can be triggered independently of fertilisation. In Drosophila melanogaster, egg activation occurs in the oviduct resulting in a single calcium wave propagating from the posterior pole of the oocyte.Here we use physical manipulations, genetics and live imaging to demonstrate the requirement of a volume increase for calcium entry at egg activation in mature Drosophila oocytes. The addition of water, modified with sucrose to a specific osmolarity, is sufficient to trigger the calcium wave in the mature oocyte and the downstream events associated with egg activation. We show that the swelling process is regulated by the conserved osmoregulatory channels, aquaporins (AQPs) and DEGenerin/Epithelial Na+ (DEG/ENaC) channels. Furthermore, through pharmacological and genetic disruption, we reveal a concentration-dependent requirement of Trpm channels to transport calcium, most likely from the perivitelline space, across the plasma membrane into the mature oocyte.Our data establishes osmotic pressure as the mechanism that initiates egg activation in Drosophila and is consistent with previous work from evolutionarily distant insects, including dragonflies and mosquitos, and shows remarkable similarities to the mechanism of egg activation in some plants.

scholarly journals Osmolarity-regulated swelling initiates egg activation in Drosophila

Open Biology ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 210067
Author(s):  
Anna H. York-Andersen ◽  
Benjamin W. Wood ◽  
Elise L. Wilby ◽  
Alexander S. Berry ◽  
Timothy T. Weil
Keyword(s):  
Transient Receptor Potential ◽  
Ex Vivo ◽  
Receptor Potential ◽  
Mature Oocyte ◽  
Posterior Pole ◽  
Vitelline Membrane ◽  
Egg Activation ◽  
Calcium Wave ◽  
M Channels ◽  
Transient Receptor

Egg activation is a series of highly coordinated processes that prepare the mature oocyte for embryogenesis. Typically associated with fertilization, egg activation results in many downstream outcomes, including the resumption of the meiotic cell cycle, translation of maternal mRNAs and cross-linking of the vitelline membrane. While some aspects of egg activation, such as initiation factors in mammals and environmental cues in sea animals, have been well-documented, the mechanics of egg activation in insects are less well-understood. For many insects, egg activation can be triggered independently of fertilization. In Drosophila melanogaster , egg activation occurs in the oviduct resulting in a single calcium wave propagating from the posterior pole of the oocyte. Here we use physical manipulations, genetics and live imaging to demonstrate the requirement of a volume increase for calcium entry at egg activation in ex vivo mature Drosophila oocytes. The addition of water, modified with sucrose to a specific osmolarity, is sufficient to trigger the calcium wave in the mature oocyte and the downstream events associated with egg activation. We show that the swelling process is regulated by the conserved osmoregulatory channels, aquaporins and DEGenerin/Epithelial Na + channels. Furthermore, through pharmacological and genetic disruption, we reveal a concentration-dependent requirement of transient receptor potential M channels to transport calcium, most probably from the perivitelline space, across the plasma membrane into the mature oocyte. Our data establish osmotic pressure as a mechanism that initiates egg activation in Drosophila and are consistent with previous work from evolutionarily distant insects, including dragonflies and mosquitos, and show remarkable similarities to the mechanism of egg activation in some plants.

scholarly journals Calcium waves occur as Drosophila oocytes activate

2015 ◽  
Vol 112 (3) ◽  
pp. 791-796 ◽  
Author(s):  
Taro Kaneuchi ◽  
Caroline V. Sartain ◽  
Satomi Takeo ◽  
Vanessa L. Horner ◽  
Norene A. Buehner ◽  
...  
Keyword(s):  
Reproductive Tract ◽  
Cytosolic Calcium ◽  
Mature Oocyte ◽  
Egg Activation ◽  
Calcium Wave ◽  
Calcium Stores ◽  
S Wave ◽  
Downstream Signaling ◽  
Vitelline Envelope

Egg activation is the process by which a mature oocyte becomes capable of supporting embryo development. In vertebrates and echinoderms, activation is induced by fertilization. Molecules introduced into the egg by the sperm trigger progressive release of intracellular calcium stores in the oocyte. Calcium wave(s) spread through the oocyte and induce completion of meiosis, new macromolecular synthesis, and modification of the vitelline envelope to prevent polyspermy. However, arthropod eggs activate without fertilization: in the insects examined, eggs activate as they move through the female’s reproductive tract. Here, we show that a calcium wave is, nevertheless, characteristic of egg activation in Drosophila. This calcium rise requires influx of calcium from the external environment and is induced as the egg is ovulated. Pressure on the oocyte (or swelling by the oocyte) can induce a calcium rise through the action of mechanosensitive ion channels. Visualization of calcium fluxes in activating eggs in oviducts shows a wave of increased calcium initiating at one or both oocyte poles and spreading across the oocyte. In vitro, waves also spread inward from oocyte pole(s). Wave propagation requires the IP3 system. Thus, although a fertilizing sperm is not necessary for egg activation in Drosophila, the characteristic of increased cytosolic calcium levels spreading through the egg is conserved. Because many downstream signaling effectors are conserved in Drosophila, this system offers the unique perspective of egg activation events due solely to maternal components.

scholarly journals The GNU subunit of PNG kinase, the developmental regulator of mRNA translation, binds BIC-C to localize to RNP granules

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Emir E Avilés-Pagán ◽  
Masatoshi Hara ◽  
Terry L Orr-Weaver
Keyword(s):  
Translational Regulation ◽  
Mrna Translation ◽  
Mature Oocyte ◽  
Early Embryogenesis ◽  
Egg Activation ◽  
Maternal Mrna ◽  
Rnp Granules

Control of mRNA translation is a key mechanism by which the differentiated oocyte transitions to a totipotent embryo. In Drosophila, the PNG kinase complex regulates maternal mRNA translation at the oocyte-to-embryo transition. We previously showed the GNU activating subunit is crucial in regulating PNG and timing its activity to the window between egg activation and early embryogenesis (Hara et al., 2017). In this study, we find associations between GNU and proteins of RNP granules and demonstrate that GNU localizes to cytoplasmic RNP granules in the mature oocyte, identifying GNU as a new component of a subset of RNP granules. Furthermore, we define roles for the domains of GNU. Interactions between GNU and the granule component BIC-C reveal potential conserved functions for translational regulation in metazoan development. We propose that by binding to BIC-C, upon egg activation GNU brings PNG to its initial targets, translational repressors in RNP granules.

Temporal and spatial correlation of fertilization current, calcium waves and cytoplasmic contraction in eggs of Ciona intestinalis

1990 ◽  
Vol 239 (1296) ◽  
pp. 321-328 ◽  
Keyword(s):  
Ciona Intestinalis ◽  
Egg Activation ◽  
Calcium Wave ◽  
Calcium Waves ◽  
Cytoplasmic Calcium ◽  
Animal Pole ◽  
Calcium Indicator ◽  
Temporal And Spatial ◽  
Contraction Wave ◽  
Normal Fertilization

Eggs of the ascidian Ciona intestinalis were loaded with the calcium indicator fura-2 via whole-cell clamp electrodes and changes in cytoplasmic calcium and cell currents were monitored during fertilization either in separate eggs or simultaneously in the same egg. The first indication of egg activation was the fertilization current; which reached peak values around 1 nA after 30 s. A wave of elevated calcium was detectable between 5 s and 30 s (mean = 21 s) after the start of the fertilization current. This wave spread across the egg increasing cytoplasmic calcium levels to at least 10 μm. When the fertilization current and calcium wave were complete and cytoplasmic calcium levels were decreasing to pre-fertilization levels, a cortical contraction wave spread across the egg surface. In eggs showing normal fertilization current, the calcium wave and the contraction wave were in the same direction. A region of elevated calcium persisted at the animal pole. Changing cytoplasmic calcium levels locally by local application of ionophorre A23187 caused a contraction wave originating at the site of ionophore application. Increasing cytoplasmic calcium uniformly by facilitating calcium entry through voltage-regulated channels did not result in a contraction wave.

The eggshell of Drosophila melanogaster. II. New staging characteristics and fine structural analysis of choriogenesis

1986 ◽  
Vol 64 (10) ◽  
pp. 2152-2175 ◽  
Author(s):  
Lukas H. Margaritis
Keyword(s):  
Electron Microscopy ◽  
Light And Electron Microscopy ◽  
Dark Field ◽  
Posterior Pole ◽  
Follicle Cells ◽  
Vitelline Membrane ◽  
Simultaneous Formation ◽  
Last Stage ◽  
Flocculent Material ◽  
Factor C

The characteristics of the stages of choriogenesis have been identified using light and electron microscopy. Nine stages have been discerned (11A, 11B, 12A, 12B, 12C, 13A, 13B, 14A, 14B), replacing the four stages used so far (11, 12, 13, 14). Characteristics used to determine the stage of the choriogenesis include (a) the size of oocyte as compared with the whole follicle, (b) the length of the chorionic appendages, and (c) the fine structure of the chorionic layers at the main shell and at the specialized regions. Factors a and b were detected by dark-field light microscopy on living follicles, whereas factor c was studied with electron microscopy. At stage 11A the vitelline membrane has just been completed. At stage 11B the follicle cells secrete the wax layer and the respiratory appendages start to form. Stage 12A follicles secrete endochorion at the anterior pole and the appendages elongate, whereas at stage 12B the main shell follicle cells start to secrete endochorion complex. Stage 12C shows initiation of pillar formation at the main shell and 150 μm long appendages. Stage 13A is characterized by 200 μm long appendages and formation of endochorionic cavities at the main shell, through the participation of a "flocculent" material. At stage 13B the endochorionic "roof is formed, which is completed at stage 14A by the simultaneous formation of the "roof network." The last stage, 14B, exhibits 300 μm long appendages and the secretion of exochorion over the entire follicle. The above stages are accompanied by region-specific formation of specialized structures which include the respiratory appendages, the operculum, the posterior pole, the micropyle, and the collar.

The eggshell of Drosophila melanogaster. I. Fine structure of the layers and regions of the wild-type eggshell

1980 ◽  
Vol 43 (1) ◽  
pp. 1-35 ◽  
Author(s):  
L.H. Margaritis ◽  
F.C. Kafatos ◽  
W.H. Petri
Keyword(s):  
Drosophila Melanogaster ◽  
Fine Structure ◽  
Freeze Fracture ◽  
Central Area ◽  
Ventral Side ◽  
Dorsal Side ◽  
Posterior Pole ◽  
Optical Diffraction ◽  
Vitelline Membrane ◽  
Freeze Fracture Electron Microscopy

The fine structure of the several layers and regional specializations in the Drosophila melanogaster eggshell has been studied by a combination of shell isolation procedures and ultrastructural techniques (conventional TEM, whole-mount TEM, SEM, HVEM, freeze-fracture electron microscopy utilizing rotary replication, shadow casting, optical diffraction and stereo imaging). The main shell consists of 5 layers: the vitelline membrane (300 nm thick), the wax layer, the innermost chorionic layer (40-50 nm), the endochorion (500-700 nm), and the exochorion (300-500 nm). The vitelline membrane consists of irregularly organized particles. The wax layer appears to contain multilayered hydrophobic plates which split tangenitally upon freeze fracturing. The innermost chorionic layer is composed of a crystalling lattice. The endochorion is made of a thin (40 nm) fenestrated floor composed of 40-nm fibres and an outer solid (200 nm) roof covered with a network of 40-nm strands. Intermittently spaced pillar connect these 2 parts. Similarities in the substructure of the floor, pillars and roof suggest that they may be composed of similar or identical structural elements. The specialized regions of the shell are the 2 respiratory appendages, the operculum area and the posterior pole. The appendages exhibit 2 sharply distinct surfaces, a dorsal side with isolated 1.5-micrometer plaques and a ventral side with strands of 40–50 nm connected in a network with openings of 70–80 nm. The operculum area, which includes the micropoyle and the collar, is distinguished by 3 unique types of cell imprints. The posterior pole contains 2 distinctive populations of cell imprints: the central area has very thin intercellular ridges and a thin, perforated, endochorionic roof, while the peripheral area contains mixed, thick and thin, intercellular ridges and serves as a transition zone to the main shell pattern. The pillars in the central area of the posterior pole have a distinct arrangement, forming one peripheral circle within each cell imprint. An analysis utilizing structural and developmental criteria indicates that as many as ten different populations of follicular epithelial cells may be involved in the construction of the various regions of the Drosophila eggshell.

SOME ASPECTS OF MOISTURE ABSORPTION AND LOSS IN EGGS OF MELANOPLUS BIVITTATUS (SAY)

1952 ◽  
Vol 30 (1) ◽  
pp. 55-82 ◽  
Author(s):  
R. W. Salt
Keyword(s):  
Moisture Content ◽  
Moisture Absorption ◽  
Age Groups ◽  
Posterior Pole ◽  
Moisture Loss ◽  
Vitelline Membrane ◽  
Desiccation Rate ◽  
Gradual Onset ◽  
Dry Conditions ◽  
Moisture Conditions

The penetration of moisture into or out of eggs of Melanoplus bivittatus (Say) is assisted or retarded by a variety of envelopes. Proceeding inwardly these are, in the newly laid egg, the chorion, the primary lipoid layer (probably waxy), and the vitelline membrane; later, to these are added the secondary lipoid layer (probably oily), the yellow cuticle, a bonding material, the white cuticle, and the serosa, which secretes all the others of this group. The primary lipoid layer waterproofs the egg in its earliest stages, but its function is soon taken over by the secondary lipoid layer. A specialized moisture-permeable area, the hydropyle, is formed at the posterior pole. Moisture is absorbed from the environment chiefly through the hydropyle, reaching a peak of absorption on the eighth or ninth day at 25 °C. and then decreasing because of the limited expansion of the cuticular layers. The original moisture content of the egg is approximately doubled. Moisture loss in young eggs, up to seven days of age, is restricted at first by the primary lipoid layer and later by the secondary lipoid layer. From the eighth day to the end of anatrepsis, on the 14th day, the desiccation rate is greatly increased. Most of the loss occurs through the hydropyle, which at this time is normally absorbing water; however, the relationship between loss and gain through the hydropyle is not close. After blastokinesis, or after the 14th day of incubation at 25 °C., the desiccation rate is extremely variable. Some of the moisture loss takes place through the hydropyle, and when the rate is low all of it does so; however, in many eggs the general cuticular surface becomes permeable (to desiccation but not to absorption), and the losses are erratic and unpredictable. With the gradual onset of diapause after the 21st day, the desiccation rate declines. Changing the moisture conditions during incubation of the eggs results in changes in the desiccation rates. The variability of the rates in older eggs was not caused by retardation of development, irregular moisture absorption, intermittent drying, or laboratory techniques, but was probably the result of variable cuticular permeability. Most M. bivittatus eggs, regardless of age, survived losses up to one-third of their moisture content, but few survived more than a two-thirds loss. After more than a one-third loss, the collapsing action of the egg frequently produced distorted or abnormal embryos. Though these often lived for some time, they never hatched. Those individuals and those age groups with the lowest desiccation rates naturally survived dry conditions longest.

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