Multiplicity of Buc copies in Atlantic salmon contrasts with loss of the germ cell determinant in primates, rodents and axolotl

Secondary growth ovarian follicles of the pigmented sterlet sturgeon Acipenser ruthenus L. 1758 (Acipenseriformes, Chondrostei, Actinopterygii, Osteichthyes) - Microscopic study of oocytes, egg envelope and diversification of follicular cells

The individual ovarian follicle of sturgeons (Acipenseriformes, Acipenseridae) contains an oocyte surrounded by follicular cells (FCs), basal lamina, and thecal cells. The late stages of the secondary growth of follicles (mid- and advanced vitellogenic) are not fully explained in Acipenseriformes. To explore and discuss the ultrastructure of oocytes, FCs, an egg envelope, and explain how micropylar cells differentiate and the canals of a multiple micropyle are formed, the samples of ovaries of the mature sterlet sturgeon Acipenser ruthenus were examined. The oocytes are polarized, the nucleus is located in the animal hemisphere, contains lampbrush chromosomes and multiple nucleoli. In the ooplasm three regions are present: a perinuclear (contains the mitochondria), an endoplasm (contains the lipid droplets and yolk platelets), and a periplasm (contains the cortical granules, melanosomes, endocytotic and exocytotic vesicles). The melanosomes in animal hemisphere form two concentric rings separated by a lighter region between them. The FCs are differentiated into bright and dark cells that are both translationally and secretory active. Diversification of FCs involves repeated and cytoskeleton-dependent change of shape. In the advanced follicles the FCs are diversified into micropylar, the animal and vegetal regions cells, and the cells that delaminated from the epithelium in the animal region. The egg envelope is present in the perioocytic space and consists of three layers: (1) an inner layer or vitelline envelope, (2) a middle layer, and (3) an outer layer. The inner layer consists of four sublayers: (a) a filamentous sublayer composed of filaments released from the oocytes, (b) a trabecular 1 sublayer and (c) a trabecular 2 sublayer named due to the sequence of the deposition, and composed of filaments, fibres and trabecules, (d) a homogeneous sublayer located between the trabecular 1 and trabecular 2 sublayers composed of filaments that adhere to each other closely. The middle layer contains two sublayers: a porous 1 and a porous 2 (composed of granular material) which are released by the oocyte and FCs. The outer layer consists of fibrillar material released by the FCs. The egg envelope is pierced by radial canals formed around the microvilli of the oocyte and the microvilli-like processes of FCs. A micropylar field in the egg envelope that covers the animal pole of the oocyte contains 1 - 4 micropylar canals. Micropylar cells are involved in their formation. The shape of these cells is icicle-like and the cytoplasm is differentiated into two regions (a basal and apical bearing a projection) equipped with different sets of organelles.

RNA localization during early development of the axolotl

The asymmetric localization of biomolecules is critical for body plan development. One of the most popular model organisms for early embryogenesis studies is Xenopus laevis but there is a lack of information in other animal species. Here, we compared the early development of two amphibian species-the frog X. laevis and the axolotl Ambystoma mexicanum. This study aimed to identify asymmetrically localized RNAs along the animal-vegetal axis during the early development of A. mexicanum. For that purpose, we performed spatial transcriptome-wide analysis at low resolution, which revealed dynamic changes along the animal-vegetal axis classified into the following categories: profile alteration, de novo synthesis and degradation. Surprisingly, our results showed that many of the vegetally localized genes, which are important for germ cell development, are degraded during early development. Furthermore, we assessed the motif presence in UTRs of degraded mRNAs and revealed the enrichment of several motifs in RNAs of germ cell markers. Our results suggest novel reorganization of the transcriptome during embryogenesis of A. mexicanum to converge to the similar developmental pattern as the X. laevis.

Impact of germ cell ablation on the activation of the brain-pituitary-gonadal axis in precocious Atlantic salmon (Salmo salar L.) males

The germ cells are essential for sexual reproduction by giving rise to the gametes, but the importance of germ cells for gonadal somatic functions varies among vertebrates. The RNA-binding dead end (Dnd) protein is necessary for the specification and migration of primordial germ cells to the future reproductive organs. Here, we ablated the gametes in Atlantic salmon males and females by microinjecting dnd antisense gapmer oligonucleotides at the zygotic stage. Precocious maturation was induced in above 50% of both germ cell-depleted and intact fertile males, but not in females, by exposure to an off-season photoperiod regime. Sterile and fertile males showed similar body growth, but maturing fish tended to be heavier than their immature counterparts. Pituitary fshβ messenger RNA levels strongly increased in maturing sterile and fertile males concomitant with the upregulated expression of Sertoli and Leydig cell markers. Plasma concentrations of 11-ketotestosterone and testosterone in maturing sterile males were significantly higher than the basal levels in immature fish, but lower than those in maturing fertile males. The study demonstrates that germ cells are not a prerequisite for the activation of the brain-pituitary-gonad axis and sex steroidogenesis in Atlantic salmon males, but may be important for the maintenance of gonadal somatic functions.

Primordial germ cell identification and traceability during the initial development of the Siluriformes fish Pseudopimelodus mangurus

Primordial germ cells (PGCs) are responsible for generating all germ cells. Therefore, they are essential targets to be used as a tool for the production of germline chimeras. The labeling and route of PGCs were evaluated during the initial embryonic development of Pseudopimelodus mangurus, using whole-mount in situ hybridization (WISH) and mRNA microinjection in zygotes. A specific antisense RNA probe constituted by a partial coding region from P. mangurus nanos3 mRNA was synthesized for the WISH method. RNA microinjection was performed using the GFP gene reporter regulated by translation regulatory P. mangurus buc and nanos3 3'UTR sequences, germline-specific markers used to describe in vivo migration of PGCs. Nanos3 and buc gene expression was evaluated in tissues for male and female adults and initial development phases and larvae from the first to seventh days post-hatching. The results from the WISH technique indicated the origin of PGCs in P. mangurus from the aggregations of nanos3 mRNA in the cleavage grooves and the signals obtained from nanos3 probes corresponded topographically to the migratory patterns of the PGCs reported for other fish species. Diffuse signals were observed in all blastomeres until the 16-cell stage, which could be related to the two sequences of the nanos3 3'UTR observed in the P. mangurus unfertilized egg transcriptome. Microinjection was not successful using GFP-Dr-nanos1 3'UTR mRNA and GFP-Pm-buc 3'UTR mRNA and allowed the identification of potential PGCs with less than 2% efficiency only and after hatching using GFP-Pm-nanos3 3'UTR. Nanos3 and buc gene expression was reported in the female gonads and from fertilized eggs until the blastula phase. These results provide information about the PGC migration of P. mangurus and the possible use of PGCs for the future generation of germline chimeras to be applied in the conservation efforts of Neotropical Siluriformes species. This study can contribute to establishing genetic banks, manipulating organisms, and assisting in biotechnologies such as transplanting germ cells in fish.

The germ plasm is anchored at the cleavage furrows through interaction with tight junctions in the early zebrafish embryo

The zebrafish germline is specified during early embryogenesis by inherited maternal RNAs and proteins collectively called germ plasm. Only the cells containing germ plasm will become part of the germline, whereas the other cells will commit to somatic cell fates. Therefore, proper localization of germ plasm is key for germ cell specification and its removal is crucial for the development of the soma. The molecular mechanism underlying this process in vertebrates is largely unknown. Here, we show that germ plasm localization in zebrafish is similar to that in Xenopus but distinct from Drosophila. We identified non muscle myosin II (NMII) and tight junction (TJ) components, such as ZO2 and claudin-d (Cldn-d) as interaction candidates of Bucky ball (Buc), which is the germ plasm organizer in zebrafish. Remarkably, we also found that TJ protein ZO1 colocalizes with germ plasm, and electron microscopy of zebrafish embryos uncovered TJ-like structures at the cleavage furrows where the germ plasm is anchored. In addition, injection of the TJ receptor Cldn-d produced extra germ plasm aggregates, whereas expression of a dominant-negative version inhibited germ plasm aggregate formation. Our findings support for the first time a role for TJs in germ plasm localization.

Microscopic study of the primary growth ovarian follicles of the pike-perch Sander lucioperca (Linnaeus 1758) (Actinopterygii, Perciformes)

The ovaries of Sander lucioperca (Actinopterygii, Perciformes) are made up of the germinal epithelium and ovarian follicles, in which primary oocytes grow. Each follicle is composed of an oocyte surrounded by flattened follicular cells, the basal lamina, and thecal cells. The early stages of oocyte development (primary growth = previtellogenesis) are not fully explained in this species. The results of research with the use of stereoscopic, light, fluorescence, and transmission electron microscopes on ovarian follicles containing developing primary oocytes of S. lucioperca are presented. The polarization and ultrastructure of oocytes are described and discussed. The deposition of egg envelopes during the primary growth and the ultrastructure of the eggshell in maturing follicles of S. lucioperca are also presented. Nuclei in primary oocytes comprise lampbrush chromosomes, nuclear bodies, and nucleoli. Numerous additional nucleoli arise in the nucleoplasm during primary growth and locate close to the nuclear envelope. The Balbiani body in the cytoplasm of oocytes (ooplasm) is composed of nuage aggregations of nuclear origin and mitochondria, endoplasmic reticulum (ER), and Golgi apparatus. The presence of the Balbiani body was reported in oocytes of numerous species of Actinopterygii; however, its ultrastructure was investigated in a limited number of species. In primary oocytes of S. lucioperca, the Balbiani body is initially located in the perinuclear ooplasm on one side of the nucleus. Next, it surrounds the nucleus, expands toward the plasma membrane of oocytes (oolemma), and becomes fragmented. Within the Balbiani body, the granular nuage condenses in the form of threads, locates near the oolemma, at the vegetal oocyte pole, and then dissolves. Mitochondria and cisternae of the rough endoplasmic reticulum (RER) are present between the threads. During primary growth micropylar cells differentiate in the follicular epithelium. They contain cisternae and vesicles of the RER and Golgi apparatus as well as numerous dense vesicles suggesting high synthetic and secretory activity. During the final step of primary growth several follicular cells delaminate from the follicular epithelium, migrate toward the oocyte and submerge in the most external egg envelope. In the ooplasm, three regions are distinguished: perinuclear, endoplasm, and periplasm. Cortical alveoli arise in the perinuclear ooplasm and in the endoplasm as a result of the fusion of RER vesicles with Golgi ones. They are evenly distributed. Lamellar bodies in the periplasm store the plasma membrane and release it into a space between the follicular cells and the oocyte. The developing eggshell in this space is made up of two egg envelopes (the internal one and the external) that are pierced by canals formed around the microvilli of oocytes and the processes of follicular cells. In the deposition of egg envelopes the oocyte itself and follicular cells are engaged. In maturing ovarian follicles the eggshell is solid and the internal egg envelope is covered with protuberances.

Balbiani body formation and cytoplasmic zonation during early oocyte development in two Clupeiform fishes

The Balbiani body (Bb) was examined in primary growth phase oocytes for the first time in two clupeoid fish species, the Mediterranean sardine, Sardina pilchardus, and the European anchovy, Engraulis encrasicolus, which belong to different families, Clupeidae and Engraulidae, respectively. Cytoplasmic morphological changes of early secondary growth oocytes were also investigated using confocal laser scanning microscopy, light and transmission electron microscopy. The ultrastructural observations showed that the two species develop a distinct spherical Bb. However, differences in the cytoplasm, mainly in the perinuclear area, were observed. Briefly, in sardine the Bb coexists with a thick perinuclear ring containing mitochondria, nuage, endoplasmic reticulum and small vesicles, while in anchovy this perinuclear ring is thinner, consisting of complexes of nuage and mitochondria. After the disassembly of the Bb, a prominent cytoplasmic zonation develops in the secondary growth oocytes of sardine and anchovy, although with different organelle distribution between the two species. Sardine oocytes exhibit a thick zone of endoplasmic reticulum around the nucleus, whereas in those of anchovy, a thick mitochondria-rich ring surrounding the nucleus was observed. The cytoplasmic characteristics, such as the perinuclear ring in primary oocytes in sardine and the mitochondria-rich ring of early secondary oocytes in anchovy, are also discernible in histological sections by standard procedures and could thus be used as indicators of maturity or imminent spawning period in routine light microscopy observations, providing a valuable tool for applied fisheries biology.

Primordial Germ Cell Specification in Vertebrate Embryos: Phylogenetic Distribution and Conserved Molecular Features of Preformation and Induction

The differentiation of primordial germ cells (PGCs) occurs during early embryonic development and is critical for the survival and fitness of sexually reproducing species. Here, we review the two main mechanisms of PGC specification, induction, and preformation, in the context of four model vertebrate species: mouse, axolotl, Xenopus frogs, and zebrafish. We additionally discuss some notable molecular characteristics shared across PGC specification pathways, including the shared expression of products from three conserved germline gene families, DAZ (Deleted in Azoospermia) genes, nanos-related genes, and DEAD-box RNA helicases. Then, we summarize the current state of knowledge of the distribution of germ cell determination systems across kingdom Animalia, with particular attention to vertebrate species, but include several categories of invertebrates - ranging from the "proto-vertebrate" cephalochordates to arthropods, cnidarians, and ctenophores. We also briefly highlight ongoing investigations and potential lines of inquiry that aim to understand the evolutionary relationships between these modes of specification.

Bucky ball induces primordial germ cell increase in medaka

Balbaini body (Bb) plays a vital role in germ plasm (GP) assembly and dorsoventral pattern, which is of critical important in germline specification and development. Bucky ball (buc) is reported to be essential for boosting primordial germ cell (PGC) through Bb in previous research. In the present study, a buc homolog (Olbuc) was identified in medaka (Oryzias latipes), and the roles of Olbuc on PGC development were further elucidated. The full length of Olbuc was 2148 bp, which contains a 1724 bp CDS (Coding sequence), a 167 bp 5' UTR (Untranslated region), and a 257 bp 3' UTR. By RT-PCR, the Olbuc RNA expression was maternally provided during embryogenesis and was restricted in the ovary of adult tissues. By in situ hybridization, Olbuc RNA was abundant in oocyte of meiotic stage, but gradually decreased as the oogenesis proceeded. Surprisingly, Olbuc was not co-localized with dazl, the marker gene of Bb. Interestingly, GFP can be specifically and stably expressed through the induction of Olbuc 3'UTR in PGCs. Furthermore, overexpression of Olbuc mRNA could increase PGC number and generate ectopic PGC in medaka and zebrafish embryos. In summary, our results showed that Olbuc performs a conserved function in PGC development in medaka.

Asymmetry in the cytoplasm of oocytes of largescale yellowfish Labeobarbus marequensis Smith 1841 (Teleostei: Cypriniformes: Cyprinidae)

The ovaries of the largescale yellowfish, Labeobarbus marequensis (Teleostei: Cypriniformes: Cyprinidae), are made up of the germinal epithelium, nests of late chromatin nucleolus stage oocytes, and ovarian follicles. Each follicle is composed of a single oocyte, which is surrounded by somatic follicular cells and a basal lamina covered by thecal cells. We describe polarization and ultrastructure of oocytes during the primary growth stage. The oocyte nucleus contains lampbrush chromosomes, nuclear bodies and fibrillar material in which multiple nucleoli arise. Nuage aggregations composed of material of a nuclear origin are present in the perinuclear cytoplasm. The Balbiani body (Bb) contains aggregations of nuage, rough endoplasmic reticulum, individual mitochondria and complexes of mitochondria with nuage (cement). Some mitochondria in the Bb come into close contact with endoplasmic reticulum cisternae and vesicles that contain granular material. At the start of primary growth, the Bb is present in the cytoplasm close to the nucleus. Next, it expands towards the oocyte plasma membrane. In these oocytes, a spherical structure, the so-called yolk nucleus, arises in the Bb. It consists of granular nuage in which mitochondria and vesicles containing granular material are immersed. Later, the Bb becomes fragmented and a fully grown yolk nucleus is present in the vegetal region. It contains numerous threads composed of granular nuage, mitochondria, lysosome-like organelles and autophagosomes. We discuss the formation of autophagosomes in the cytoplasm of primary growth oocytes. During the final step of primary growth, the cortical alveoli arise in the cytoplasm and are distributed evenly. The eggshell is deposited on the external surface of the oocyte plasma membrane and is made up of two egg envelopes that are pierced by numerous pore canals. The external egg envelope is covered in protuberances. During primary growth no lipid droplets are synthesized or stored in the oocytes.

Germline cysts and asymmetry in early previtellogenic ovarian follicles in cultured albino females of sterlet Acipenser ruthenus L. 1758 (Chondrostei, Acipenseriformes)

It is a first report on the structure of germline cells in ovaries of albino sterlet Acipenser ruthenus L. 1758. Ovarian nests, follicles, and germinal epithelium have been examined in gynogenetic and control specimens of this species. The structure of oogonia (named the cystoblasts) and of germline cysts in the nests has been described in detail. Also, the asymmetry in the cytoplasm and early growth of cystocytes in the cysts and of early previtellogenic oocytes has been described. In the cytoplasm of cystoblasts and in all cystocytes, a precursor of granular cytoplasm (Balbiani cytoplasm) is present and defines future vegetal region in the oocytes. Interestingly, the nuclei in cystoblasts comprise a large dense body that contains deoxyribonucleic acid (DNA). The role of this body in formation of multiple nucleoli has been explained. During the zygotene and pachytene stages, massive extrachromosomal amplification of DNA begins in the nucleoplasm of all cystocytes. As a result of the accumulation of extra DNA, an irregularly shaped DNA-body is formed. Multiple nucleoli arise in this DNA-body and around fragments of dense bodies. The asymmetry of the early previtellogenic oocyte cytoplasm is well marked by the presence of the granular cytoplasm. Moreover, the cisternae of the rough endoplasmic reticulum, dictyosomes, mitochondria, complexes of mitochondria with cement, nuage accumulations, and lipid droplets are located in specific zones in the granular cytoplasm. The follicular epithelium is composed of two subpopulations of somatic follicular cells (FCs): the main body cells and future micropylar cells.

Functional equivalence of germ plasm organizers

The proteins Oskar (Osk) in Drosophila and Bucky ball (Buc) in zebrafish act as germ plasm organizers. Both proteins recapitulate germ plasm activities but seem to be unique to their animal groups. Here, we discover that Osk and Buc show similar activities during germ cell specification. Drosophila Osk induces additional PGCs in zebrafish. Surprisingly, Osk and Buc do not show homologous protein motifs that would explain their related function. Nonetheless, we detect that both proteins contain stretches of intrinsically disordered regions (IDRs), which seem to be involved in protein aggregation. IDRs are known to rapidly change their sequence during evolution, which might obscure biochemical interaction motifs. Indeed, we show that Buc binds to the known Oskar interactors Vasa protein and nanos mRNA indicating conserved biochemical activities. These data provide a molecular framework for two proteins with unrelated sequence but with equivalent function to assemble a conserved core-complex nucleating germ plasm.

Multicellular organisms use gametes for their propagation. Gametes are formed from germ cells, which are specified during embryogenesis in some animals by the inheritance of RNP granules known as germ plasm. Transplantation of germ plasm induces extra germ cells, whereas germ plasm ablation leads to the loss of gametes and sterility. Therefore, germ plasm is key for germ cell formation and reproduction. However, the molecular mechanisms of germ cell specification by germ plasm in the vertebrate embryo remain an unsolved question. Proteins, which assemble the germ plasm, are known as germ plasm organizers. Here, we show that the two germ plasm organizers Oskar from the fly and Bucky ball from the fish show similar functions by using a cross species approach. Both are intrinsically disordered proteins, which rapidly changed their sequence during evolution. Moreover, both proteins still interact with conserved components of the germ cell specification pathway. These data might provide a first example of two proteins with the same biological role, but distinct sequence.

Molecular characterization, tissue distribution, localization and mRNA expression of the bucky ball gene in the Dabry's sturgeon (Acipenser dabryanus) during oogenesis

In many organisms, germ cells are specified during embryogenesis by the inheritance of maternally deposited RNAs and proteins termed germ plasm. In vertebrates, the bucky ball (buc) gene plays an essential role in the germ plasm aggregation. In this study, the full-length cDNA of buc homologue in Dabry's sturgeon, Adbuc, was isolated and characterized. Multiple sequence alignments showed that the BUVE domain of Buc was highly conserved in vertebrates, despite exhibiting low identities with each other across the whole protein. By quantitative real-time PCR analysis, we found that Adbuc RNAs were only detected in the gonad with a high level in the ovary and a very low level in the testis. During embryogenesis, these RNAs were highly expressed from the unfertilized eggs to blastula, declined dramatically from the gastrula stage, and hardly found after the neurula stage. Moreover, with the development of ovary, the expression level of Adbuc was increasing. By in situ hybridization, the signal of Adbuc was not found in the oogonia, increased slightly in the stage I oocytes, and extremely strong in the stage II oocytes, suggesting that the signal became much stronger with increasing size of oocytes. Additionally, Adbuc co-localized with the mitochondrial cloud. Thus, we conclude that Dabry's sturgeon buc gene might also function in germplasm formation.

Convergent evolution of germ granule nucleators: A hypothesis

Germ cells have been considered "the ultimate stem cell" because they alone, during normal development of sexually reproducing organisms, are able to give rise to all organismal cell types. Morphological descriptions of a specialized cytoplasm termed 'germ plasm' and associated electron dense ribonucleoprotein (RNP) structures called 'germ granules' within germ cells date back as early as the 1800s. Both germ plasm and germ granules are implicated in germ line specification across metazoans. However, at a molecular level, little is currently understood about the molecular mechanisms that assemble these entities in germ cells. The discovery that in some animals, the gene products of a small number of lineage-specific genes initiate the assembly (also termed nucleation) of germ granules and/or germ plasm is the first step towards facilitating a better understanding of these complex biological processes. Here, we draw on research spanning over 100years that supports the hypothesis that these nucleator genes may have evolved convergently, allowing them to perform analogous roles across animal lineages.

Ovarian nests in cultured females of the Siberian sturgeon Acipenser baerii (Chondrostei, Acipenseriformes)

Ovaries of Acipenser baerii are of an alimentary type and probably are meroistic. They contain ovarian nests, individual follicles, inner germinal ovarian epithelium, and fat tissue. Nests comprise cystoblasts, germline cysts, numerous early previtellogenic oocytes, and somatic cells. Cysts are composed of cystocytes, which are connected by intercellular bridges and are in the pachytene stage of the first meiotic prophase. They contain bivalents, finely granular, medium electron dense material, and nucleoli in the nucleoplasm. Many cystocytes degenerate. Oocytes differ in size and structure. Most oocytes are in the pachytene and early diplotene stages and are referred to as the PACH oocytes. Oocytes in more advanced diplotene stage are referred to as the DIP oocytes. Nuclei in the PACH oocytes contain bivalents and irregularly shaped accumulation of DNA (DNA-body), most probably corresponding to the rDNA-body. The DNA-body is composed of loose, fine granular material, and comprises multiple nucleoli. At peripheries, it is fragmented into blocks that remain in contact with the inner nuclear membrane. In the ooplasm, there is the rough endoplasmic reticulum, Golgi complexes, free ribosomes, complexes of mitochondria with cement, fine fibrillar material containing granules, and lipid droplets. The organelles and material of nuclear origin form a distinct accumulation (a granular ooplasm) in the vicinity of the nucleus. Some of the PACH oocytes are surrounded by flat somatic cells. There are lampbrush chromosomes and multiple nucleoli present (early diplotene stage) in the nucleoplasm. These PACH oocytes and neighboring somatic cells have initiated the formation of ovarian follicles. The remaining PACH oocytes transform to the DIP oocytes. The DIP oocytes contain lampbrush chromosomes and a DNA-body is absent in nuclei. Multiple nucleoli are numerous in the nucleoplasm and granular ooplasm is present at the vegetal region of the oocyte.

Acquisition of Oocyte Polarity

Acquisition of oocyte polarity involves complex translocation and aggregation of intracellular organelles, RNAs, and proteins, along with strict posttranscriptional regulation. While much is still unknown regarding the formation of the animal-vegetal axis, an early marker of polarity, animal models have contributed to our understanding of these early processes controlling normal oogenesis and embryo development. In recent years, it has become clear that proteins with self-assembling properties are involved in assembling discrete subcellular compartments or domains underlying subcellular asymmetries in the early mitotic and meiotic cells of the female germline. These include asymmetries in duplication of the centrioles and formation of centrosomes and assembly of the organelle and RNA-rich Balbiani body, which plays a critical role in oocyte polarity. Notably, at specific stages of germline development, these transient structures in oocytes are temporally coincident and align with asymmetries in the position and arrangement of nuclear components, such as the nuclear pore and the chromosomal bouquet and the centrioles and cytoskeleton in the cytoplasm. Formation of these critical, transient structures and arrangements involves microtubule pathways, intrinsically disordered proteins (proteins with domains that tend to be fluid or lack a rigid ordered three-dimensional structure ranging from random coils, globular domains, to completely unstructured proteins), and translational repressors and activators. This review aims to examine recent literature and key players in oocyte polarity.