Oogenesis in four species of Piscicola (Hirudinea, Rhynchobdellida)

Abstract

Piscicola has a pair of elongated sac-shaped ovaries. Inside the ovaries are numerous small somatic cells and regularly spherical egg follicles. Each follicle is composed of three types of cells: many (average 30) germ cells (cystocytes) interconnected by intercellular bridges in clones (cysts), one intermediate cell, and three to five outer follicle cells (envelope cells). Each germ cell in a clone has one intercellular bridge connecting it to the central anucleate cytoplasmic mass, the cytophore. Each cluster of germ cells is completely embedded inside a single huge somatic follicle cell, the intermediate (interstitial) cell. The most spectacular feature of the intermediate cell is its development of a system of intracytoplasmic canals apparently formed of invaginations of its cell membrane. Initially the complex of germ cell cluster + intermediate cell is enclosed within an envelope composed of squamous cells. As oogenesis progresses the envelope cells gradually degenerate. All the germ cells that have terminated their mitotic divisions are of similar size and enter meiotic prophase, but one of the cystocytes promptly starts to grow faster and differentiates into the oocyte, whereas the remaining cystocytes withdraw from meiosis and become nurse cells (trophocytes). Numerous mitochondria, ER, and a vast amount of ribosomes are transferred from the trophocytes via the cytophore toward the oocyte. Eventually the oocyte ingests all the content of the cytophore, and the trophocytes degenerate. Little vitellogenesis takes place; the oocyte gathers nutrients in the form of small lipid droplets. At the end of oogenesis, an electron-dense fibrous vitelline envelope appears around the oocyte, among short microvilli. At the same time, electron-dense cortical granules occur in the oocyte cortical cytoplasm; at the end of oogenesis they are numerous, but after fertilization they disappear from the ooplasm. In the present article we point out many differences in the course of oogenesis in two related families of rhynchobdellids: piscicolids and glossiphoniids.

Ovary cord structure and oogenesis in Hirudo medicinalis and Haemopis sanguisuga (Clitellata, Annelida): remarks on different ovaries organization in Hirudinea

“…• egg follicles developing in ovaries of Piscicolidae (Pérez 1907;Jörgensen 1913;Heath 1925;Fischer and Weigelt 1975;Spaiek-Woiczyjska et al 2008 (Jörgensen 1908;Van Damme 1974;Urbajska-Jasik 1988).…”

“…For all species of the Piscicolidae each egg follicle is composed of a clone of germ cells embedded within one huge follicular cell (intermediate cell); this group is additionally surrounded by several envelope cells (Pérez 1907;Jörgensen 1913;Fischer and Weigelt 1975;Spaiek-Woiczyjska et al 2008). A detailed analysis of egg follicle organization in four species of Piscicola, with a comparison to ovary cords found in glossiphoniids, has recently been presented (Spaiek-Woiczyjska et al 2008). Ovary organization and some aspects of oogenesis in the leech families studied so far are compared in Fig.…”

“…In Piscicolidae there are no ovary cords; instead, egg follicles are formed in early oogenesis. Each follicle is composed of one cyst of interconnected germ cells surrounded by one follicular cell (intermediate cell) and several Xattened cells (Jörgensen 1913;Fischer and Weigelt 1975;Spaiek-Woiczyjska et al 2008). In Erpobdellidae, several rod-like bodies, the so-called ovarian bodies, occur within the ovisac (Jörgensen 1908;Van Damme 1974;Urbajska-Jasik 1988).…”

“…In Hirudinea in each cyst one cell diVerentiates into an oocyte, and the rest become nurse cells which communicate with the developing oocyte via a speciWc anuclear cytoplasmic mass, the cytophore (Fernández et al 1992;Eckelbarger 2006). However, an examination of earlier and recent literature devoted to ovary organization and the course of oogenesis in Hirudinea (Brumpt 1900;Pérez 1907;Jörgen-sen 1908Jörgen-sen , 1913Heath 1925;Aisenstadt 1964;Damas 1964Damas , 1977Aisenstadt et al 1967;Gruzova and Zaichikova 1967;Van Damme 1974;Fischer and Weigelt 1975;UrbajskaJasik 1988;Fernández et al 1992;Klimaszewska-Guzik 2000;Jwiatek 2005a, b;Jwiatek 2006;Spaiek-Woiczyjska et al 2008) suggests that in these clitellates at least four systems of internal ovary organization occur.…”

Similarities between oocytes and macrophages. An overview

“…In leeches, nurse cells, which are also called trophocytes, provide cytoplasmic organelles to the oocytes by way of transport through the oolemma, and some of them are even sacrificed for this purpose [13,14].…”