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Ovaries of Tubificinae (Clitellata, Naididae) resemble ovary cords found in Hirudinea (Clitellata).

Urbisz AZ, Krodkiewska M, Swiątek P - Zoomorphology (2010)

Bottom Line: During late previtellogenesis/early vitellogenesis, the oocytes detach from the cytophore and float in the coelom; they are usually enveloped by the peritoneal epithelium and associated with blood vessels.Generally, the organization of ovaries in all of the Tubificinae species studied resembles the polarized ovary cords found within the ovisacs of some Euhirudinea.The organization of ovaries and the course of oogenesis between the genera studied and other clitellate annelids are compared.

View Article: PubMed Central - PubMed

ABSTRACT
The ultrastructure of the ovaries and oogenesis was studied in three species of three genera of Tubificinae. The paired ovaries are small, conically shaped structures, connected to the intersegmental septum between segments X and XI by their narrow end. The ovaries are composed of syncytial cysts of germ cells interconnected by stable cytoplasmic bridges (ring canals) and surrounded by follicular cells. The architecture of the germ-line cysts is exactly the same as in all clitellate annelids studied to date, i.e. each cell in a cyst has only one ring canal connecting it to the central, anuclear cytoplasmic mass, the cytophore. The ovaries found in all of the species studied seem to be meroistic, i.e. the ultimate fate of germ cells within a cyst is different, and the majority of cells withdraw from meiosis and become nurse cells; the rest continue meiosis, gather macromolecules, cell organelles and storage material, and become oocytes. The ovaries are polarized; their narrow end contains mitotically dividing oogonia and germ cells entering the meiosis prophase; whereas within the middle and basal parts, nurse cells, a prominent cytophore and growing oocytes occur. During late previtellogenesis/early vitellogenesis, the oocytes detach from the cytophore and float in the coelom; they are usually enveloped by the peritoneal epithelium and associated with blood vessels. Generally, the organization of ovaries in all of the Tubificinae species studied resembles the polarized ovary cords found within the ovisacs of some Euhirudinea. The organization of ovaries and the course of oogenesis between the genera studied and other clitellate annelids are compared. Finally, it is suggested that germ-line cysts formation and the meroistic mode of oogenesis may be a primary character for all Clitellata.

No MeSH data available.


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a Zone I of Limnodrilus claparedeanus ovary. All germ cells (GC) enter meiosis prophase I; synaptonemal complexes (arrows) are visible. Germ cells are connected to the initial cytophore (CY) via ring canals (star). b Zones II/III of L. claparedeanus ovary. The nurse cells (NC) withdraw from meiosis; their nuclei (NU) show an interphase organization of chromatin. Each nurse cell is connected to the cytophore (CY) via a ring canal (stars). c, d Zone III of Potamothrix bavaricus ovary. Nurse cells (NC) are still connected to the cytophore (CY) via ring canals (stars). Note nuage accumulations (arrows) associated with mitochondria (M); NU nuclei of nurse cells. eL. claparedeanus. Early previtellogenic oocyte (O) connected to the cytophore (CY) via a ring canal (star). Oocyte has an irregularly shaped nucleus (NU); its oolemma forms microvilli (MI). f A fragment of a previtellogenic oocyte (O) and cytophore (CY) in P. bavaricus. The ring canal is broad (arrows); mitochondria (M) and lipid droplets (LD) can be seen passing the ring canal; NU oocyte nucleus. g Detail of cytophore (CY) structure in L. claparedeanus. An accumulation of microtubules (MT) is visible; NU nurse cell nucleus. a–g Transmission electron microscopy (TEM)
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Fig3: a Zone I of Limnodrilus claparedeanus ovary. All germ cells (GC) enter meiosis prophase I; synaptonemal complexes (arrows) are visible. Germ cells are connected to the initial cytophore (CY) via ring canals (star). b Zones II/III of L. claparedeanus ovary. The nurse cells (NC) withdraw from meiosis; their nuclei (NU) show an interphase organization of chromatin. Each nurse cell is connected to the cytophore (CY) via a ring canal (stars). c, d Zone III of Potamothrix bavaricus ovary. Nurse cells (NC) are still connected to the cytophore (CY) via ring canals (stars). Note nuage accumulations (arrows) associated with mitochondria (M); NU nuclei of nurse cells. eL. claparedeanus. Early previtellogenic oocyte (O) connected to the cytophore (CY) via a ring canal (star). Oocyte has an irregularly shaped nucleus (NU); its oolemma forms microvilli (MI). f A fragment of a previtellogenic oocyte (O) and cytophore (CY) in P. bavaricus. The ring canal is broad (arrows); mitochondria (M) and lipid droplets (LD) can be seen passing the ring canal; NU oocyte nucleus. g Detail of cytophore (CY) structure in L. claparedeanus. An accumulation of microtubules (MT) is visible; NU nurse cell nucleus. a–g Transmission electron microscopy (TEM)

Mentions: Like all of the clitellate annelids studied so far (see Świątek et al. 2009 and references herein), the germ cells in all of the species studied are united into syncytial cysts. The pattern of the organization of the cysts is also the same as in other Clitellata. Each germ cell in a cyst has only one stable cytoplasmic bridge (usually referred to as a ring canal) connecting it to a central, anuclear cytoplasmic core, the cytophore (Figs. 1b–d; 2a, b, e, f; 3a–g). Germ-line cysts are formed before germ cells enter meiosis. The last mitotic divisions of oogonia are not followed by full cytokineses; instead the cleavage furrow is stabilized and forms a broad cytoplasmic channel, a ring canal (Fig. 3a–f). The formation of germ-cell cysts has not been observed in the Tubificinae studied; however, the organization of the cysts suggests that they develop in the same manner as in other clitellate annelids (see Świątek et al. 2009). In zones I and II of the ovary, the germ cells within a cyst (cystocytes) are morphologically identical (Figs. 2d; 3a, b). All germ cells in this region of the ovary enter meiotic prophase I; the synaptonemal complexes are easy to see within the nuclei of these cells (Fig. 3a). Beneath this region the majority of germ cells cease meiosis, their nuclei return to an interphase organization of chromatin, and these cells become nurse cells (Figs. 2a, b, d–f; 3b–d). Several cells continue meiosis and grow; their nuclei contain meiotic chromosomes in the form of lampbrush chromosomes and start to grow as oocytes (Fig. 1c, d).Fig. 3


Ovaries of Tubificinae (Clitellata, Naididae) resemble ovary cords found in Hirudinea (Clitellata).

Urbisz AZ, Krodkiewska M, Swiątek P - Zoomorphology (2010)

a Zone I of Limnodrilus claparedeanus ovary. All germ cells (GC) enter meiosis prophase I; synaptonemal complexes (arrows) are visible. Germ cells are connected to the initial cytophore (CY) via ring canals (star). b Zones II/III of L. claparedeanus ovary. The nurse cells (NC) withdraw from meiosis; their nuclei (NU) show an interphase organization of chromatin. Each nurse cell is connected to the cytophore (CY) via a ring canal (stars). c, d Zone III of Potamothrix bavaricus ovary. Nurse cells (NC) are still connected to the cytophore (CY) via ring canals (stars). Note nuage accumulations (arrows) associated with mitochondria (M); NU nuclei of nurse cells. eL. claparedeanus. Early previtellogenic oocyte (O) connected to the cytophore (CY) via a ring canal (star). Oocyte has an irregularly shaped nucleus (NU); its oolemma forms microvilli (MI). f A fragment of a previtellogenic oocyte (O) and cytophore (CY) in P. bavaricus. The ring canal is broad (arrows); mitochondria (M) and lipid droplets (LD) can be seen passing the ring canal; NU oocyte nucleus. g Detail of cytophore (CY) structure in L. claparedeanus. An accumulation of microtubules (MT) is visible; NU nurse cell nucleus. a–g Transmission electron microscopy (TEM)
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Fig3: a Zone I of Limnodrilus claparedeanus ovary. All germ cells (GC) enter meiosis prophase I; synaptonemal complexes (arrows) are visible. Germ cells are connected to the initial cytophore (CY) via ring canals (star). b Zones II/III of L. claparedeanus ovary. The nurse cells (NC) withdraw from meiosis; their nuclei (NU) show an interphase organization of chromatin. Each nurse cell is connected to the cytophore (CY) via a ring canal (stars). c, d Zone III of Potamothrix bavaricus ovary. Nurse cells (NC) are still connected to the cytophore (CY) via ring canals (stars). Note nuage accumulations (arrows) associated with mitochondria (M); NU nuclei of nurse cells. eL. claparedeanus. Early previtellogenic oocyte (O) connected to the cytophore (CY) via a ring canal (star). Oocyte has an irregularly shaped nucleus (NU); its oolemma forms microvilli (MI). f A fragment of a previtellogenic oocyte (O) and cytophore (CY) in P. bavaricus. The ring canal is broad (arrows); mitochondria (M) and lipid droplets (LD) can be seen passing the ring canal; NU oocyte nucleus. g Detail of cytophore (CY) structure in L. claparedeanus. An accumulation of microtubules (MT) is visible; NU nurse cell nucleus. a–g Transmission electron microscopy (TEM)
Mentions: Like all of the clitellate annelids studied so far (see Świątek et al. 2009 and references herein), the germ cells in all of the species studied are united into syncytial cysts. The pattern of the organization of the cysts is also the same as in other Clitellata. Each germ cell in a cyst has only one stable cytoplasmic bridge (usually referred to as a ring canal) connecting it to a central, anuclear cytoplasmic core, the cytophore (Figs. 1b–d; 2a, b, e, f; 3a–g). Germ-line cysts are formed before germ cells enter meiosis. The last mitotic divisions of oogonia are not followed by full cytokineses; instead the cleavage furrow is stabilized and forms a broad cytoplasmic channel, a ring canal (Fig. 3a–f). The formation of germ-cell cysts has not been observed in the Tubificinae studied; however, the organization of the cysts suggests that they develop in the same manner as in other clitellate annelids (see Świątek et al. 2009). In zones I and II of the ovary, the germ cells within a cyst (cystocytes) are morphologically identical (Figs. 2d; 3a, b). All germ cells in this region of the ovary enter meiotic prophase I; the synaptonemal complexes are easy to see within the nuclei of these cells (Fig. 3a). Beneath this region the majority of germ cells cease meiosis, their nuclei return to an interphase organization of chromatin, and these cells become nurse cells (Figs. 2a, b, d–f; 3b–d). Several cells continue meiosis and grow; their nuclei contain meiotic chromosomes in the form of lampbrush chromosomes and start to grow as oocytes (Fig. 1c, d).Fig. 3

Bottom Line: During late previtellogenesis/early vitellogenesis, the oocytes detach from the cytophore and float in the coelom; they are usually enveloped by the peritoneal epithelium and associated with blood vessels.Generally, the organization of ovaries in all of the Tubificinae species studied resembles the polarized ovary cords found within the ovisacs of some Euhirudinea.The organization of ovaries and the course of oogenesis between the genera studied and other clitellate annelids are compared.

View Article: PubMed Central - PubMed

ABSTRACT
The ultrastructure of the ovaries and oogenesis was studied in three species of three genera of Tubificinae. The paired ovaries are small, conically shaped structures, connected to the intersegmental septum between segments X and XI by their narrow end. The ovaries are composed of syncytial cysts of germ cells interconnected by stable cytoplasmic bridges (ring canals) and surrounded by follicular cells. The architecture of the germ-line cysts is exactly the same as in all clitellate annelids studied to date, i.e. each cell in a cyst has only one ring canal connecting it to the central, anuclear cytoplasmic mass, the cytophore. The ovaries found in all of the species studied seem to be meroistic, i.e. the ultimate fate of germ cells within a cyst is different, and the majority of cells withdraw from meiosis and become nurse cells; the rest continue meiosis, gather macromolecules, cell organelles and storage material, and become oocytes. The ovaries are polarized; their narrow end contains mitotically dividing oogonia and germ cells entering the meiosis prophase; whereas within the middle and basal parts, nurse cells, a prominent cytophore and growing oocytes occur. During late previtellogenesis/early vitellogenesis, the oocytes detach from the cytophore and float in the coelom; they are usually enveloped by the peritoneal epithelium and associated with blood vessels. Generally, the organization of ovaries in all of the Tubificinae species studied resembles the polarized ovary cords found within the ovisacs of some Euhirudinea. The organization of ovaries and the course of oogenesis between the genera studied and other clitellate annelids are compared. Finally, it is suggested that germ-line cysts formation and the meroistic mode of oogenesis may be a primary character for all Clitellata.

No MeSH data available.


Related in: MedlinePlus