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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, b Organization of ovaries in Limnodrilus claparedeanus. Growing oocytes (O), nurse cells (NC), and cytophore (CY) with accumulations of cytoskeletal elements (stars) are visible; NU oocyte nuclei. cPotamothrix bavaricus. Vitellogenic oocytes (O) are in close contact with blood vessels (BV) and are surrounded by coelomic epithelium (arrows). d Zones I and II of the Tubifex tubifex ovary. Within this part of the ovary, the germ cells (GC) are undifferentiated, and all are in meiotic prophase I. Some degenerating cells (arrows) are also visible; BV blood vessel. e, f Details of the organization of a germ-line cyst in L. claparedeanus. The cytophore (CY) occupies the cyst center, whereas the nurse cells (NC) and oocytes (O) are located peripherally and are connected to the cytophore via ring canals (arrow). Within the cytophore, accumulations of cytoskeletal elements are visible (stars). a–f Light microscopy, Epon semithin sections stained with methylene blue
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Fig2: a, b Organization of ovaries in Limnodrilus claparedeanus. Growing oocytes (O), nurse cells (NC), and cytophore (CY) with accumulations of cytoskeletal elements (stars) are visible; NU oocyte nuclei. cPotamothrix bavaricus. Vitellogenic oocytes (O) are in close contact with blood vessels (BV) and are surrounded by coelomic epithelium (arrows). d Zones I and II of the Tubifex tubifex ovary. Within this part of the ovary, the germ cells (GC) are undifferentiated, and all are in meiotic prophase I. Some degenerating cells (arrows) are also visible; BV blood vessel. e, f Details of the organization of a germ-line cyst in L. claparedeanus. The cytophore (CY) occupies the cyst center, whereas the nurse cells (NC) and oocytes (O) are located peripherally and are connected to the cytophore via ring canals (arrow). Within the cytophore, accumulations of cytoskeletal elements are visible (stars). a–f Light microscopy, Epon semithin sections stained with methylene blue

Mentions: The ovaries are paired structures, conically shaped, with the narrow end connected to the intersegmental septum between segments X and XI. Each ovary is joined to the septum via a thin ligament (Fig. 1a), whereas the broad end of the ovary extends freely into the coelom of segment XI. The ovaries are composed of cysts of germ-line cells (see below) enveloped by a layer of elongated follicular cells, which are almost undetectable on whole-mounted preparations (Fig. 1a, b), but their nuclei are visible on the semithin sections (Fig. 1c–d). The germ cells in the ovaries are represented by oogonia, undifferentiated germ cells united into cysts (cystocytes), oocytes at different stages of oogenesis (from the onset of oogenesis to early vitellogenic ones) and nurse cells (Fig. 1a–d). The oocytes that intensively absorb the yolk (vitellogenic ones) have lost contact with the cytophore and float freely in the coelom. Vitellogenic oocytes and oocytes that have completed vitellogenesis, i.e. oocytes arrested in meiotic metaphase I, are in close contact with blood vessels and the coelomic epithelium (Fig. 2c).Fig. 1


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

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

a, b Organization of ovaries in Limnodrilus claparedeanus. Growing oocytes (O), nurse cells (NC), and cytophore (CY) with accumulations of cytoskeletal elements (stars) are visible; NU oocyte nuclei. cPotamothrix bavaricus. Vitellogenic oocytes (O) are in close contact with blood vessels (BV) and are surrounded by coelomic epithelium (arrows). d Zones I and II of the Tubifex tubifex ovary. Within this part of the ovary, the germ cells (GC) are undifferentiated, and all are in meiotic prophase I. Some degenerating cells (arrows) are also visible; BV blood vessel. e, f Details of the organization of a germ-line cyst in L. claparedeanus. The cytophore (CY) occupies the cyst center, whereas the nurse cells (NC) and oocytes (O) are located peripherally and are connected to the cytophore via ring canals (arrow). Within the cytophore, accumulations of cytoskeletal elements are visible (stars). a–f Light microscopy, Epon semithin sections stained with methylene blue
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2991200&req=5

Fig2: a, b Organization of ovaries in Limnodrilus claparedeanus. Growing oocytes (O), nurse cells (NC), and cytophore (CY) with accumulations of cytoskeletal elements (stars) are visible; NU oocyte nuclei. cPotamothrix bavaricus. Vitellogenic oocytes (O) are in close contact with blood vessels (BV) and are surrounded by coelomic epithelium (arrows). d Zones I and II of the Tubifex tubifex ovary. Within this part of the ovary, the germ cells (GC) are undifferentiated, and all are in meiotic prophase I. Some degenerating cells (arrows) are also visible; BV blood vessel. e, f Details of the organization of a germ-line cyst in L. claparedeanus. The cytophore (CY) occupies the cyst center, whereas the nurse cells (NC) and oocytes (O) are located peripherally and are connected to the cytophore via ring canals (arrow). Within the cytophore, accumulations of cytoskeletal elements are visible (stars). a–f Light microscopy, Epon semithin sections stained with methylene blue
Mentions: The ovaries are paired structures, conically shaped, with the narrow end connected to the intersegmental septum between segments X and XI. Each ovary is joined to the septum via a thin ligament (Fig. 1a), whereas the broad end of the ovary extends freely into the coelom of segment XI. The ovaries are composed of cysts of germ-line cells (see below) enveloped by a layer of elongated follicular cells, which are almost undetectable on whole-mounted preparations (Fig. 1a, b), but their nuclei are visible on the semithin sections (Fig. 1c–d). The germ cells in the ovaries are represented by oogonia, undifferentiated germ cells united into cysts (cystocytes), oocytes at different stages of oogenesis (from the onset of oogenesis to early vitellogenic ones) and nurse cells (Fig. 1a–d). The oocytes that intensively absorb the yolk (vitellogenic ones) have lost contact with the cytophore and float freely in the coelom. Vitellogenic oocytes and oocytes that have completed vitellogenesis, i.e. oocytes arrested in meiotic metaphase I, are in close contact with blood vessels and the coelomic epithelium (Fig. 2c).Fig. 1

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