Oogenesis and oocytes

Abstract

The morphological features of polychaete ovarian morphology and oogenesis are reviewed. Some basic information on ovarian structure and/or oogenesis is known for slightly more than half of recognized polychaete families although comprehensive studies of oogenesis have been conducted on $0.1% of described species. Relative to other major metazoan groups, ovarian morphology is highly variable in the Polychaeta. While some species appear to lack a defined ovary, most have paired organs that are segmentally repeated to varying degrees depending on the family. Ovaries vary widely in their location but are most frequently associated with the coelomic peritoneum, parapodial connective tissue, or elements of the circulatory system. The structural complexity of the ovary is correlated with the type of oogenesis expressed by the species. In some polychaetes, extraovarian oogenesis occurs in which previtellogenic oocytes are released into the coelom from a simple ovary where differentiation occurs in a solitary fashion or in association with nurse cells or follicle cells. In other species, intraovarian oogenesis occurs in which oocytes undergo vitellogenesis within the ovary, often in association with follicle cells that may provide nutrition. Vitellogenesis probably includes both autosynthetic and heterosynthetic processes; autosynthesis involves the manufacture of yolk bodies via the proteosynthetic organelles of the oocyte whereas heterosynthesis involves the extraovarian production of female-specific yolk proteins that are incorporated into the oocyte through a receptor-mediated process of endocytosis. Variation in the speed of egg production varies widely and appears to be correlated with the vitellogenic mechanism employed. Mature ova display a wide range of egg envelope morphologies that often show some intrafamilial similarities.

Development of polarized female germline cysts in the polychaete, Ophryotrocha labronica

“…The autoradiographic studies mentioned above also demonstrated active transcription and translation within the oocyte (Ruthmann, 1964;Emanuelsson, 1985;Emanuelsson and Anehus, 1985). In this respect, oogenesis in O. labronica is similar to that observed in other polychaetes, in which oocytes are typically transcriptionally active (Eckelbarger, 1992(Eckelbarger, , 2005(Eckelbarger, , 2007. This strategy differs markedly from that of insects with polytrophic ovarioles (i.e., those with nurse cells), in which oocyte nuclei have greatly reduced transcriptional activity, and lack nucleoli for much of the vitellogenic stage of oogenesis (King and Burnett, 1959;Mahowald and Tiefert, 1970).…”

Systematic revision of Sabellariidae (Polychaeta) and their relationships with other polychaetes using morphological and DNA sequence data

“…The morphological features selected for assessing relationships at family level were scored from the literature (e.g. Dales, 1962; Orrhage, 1980; Bartolomaeus, 1995, 1998; Purschke, 1997, 2005; Hausen & Bartolomaeus, 1998; Rouse, 2000a, b; Zhadan & Tzetlin, 2003; Bartolomaeus & Quast, 2005; Eckelbarger, 2005; Hausen, 2005; Orrhage & Müller, 2005; Tzetlin & Filippova, 2005; Purschke & Müller, 2006; Purschke & Hausen, 2007; Suschenko & Purschke, 2009). The list of 99 characters and states is summarized in Table 2 and described in .…”

Ultrastructural study of oogenesis in Phoronopsis harmeri (Phoronida)

“…It is likely that these clusters are a germ plasm which is well known from primordial and early germ cells as well as from the embryos of many metazoans (Extavour and Akam 2003). The germ plasm has been described in many morphological embodiments including groups of dense particles associated with mitochondria (Eddy 1975; Wourms 1987; Eckelbarger 2005) identical to those observed in previtelllogenic oocytes of Ph. harmeri .…”