Soma/Germline Interactions In Caenorhabditis Elegans Gonad

Abstract

<jats:p>A combination of microscopical methods (TEM, SEM, freeze fracture, confocal, immunoEM) are utilized to demonstrate functional interactions between somatic cells and the germline in the model organism, <jats:italic>C. elegans.</jats:italic>A variety of signaling mechanisms are required to coordinate activity of maturing oocytes and the somatic sheath of the gonad. Communication via gap junctions allows direct coordination of sheath cell motility and oocyte development. Gap junctions link adjoining sheath cells, and link the sheath to the most mature oocyte. Yolk protein produced in the intestine passes from the pseudocoelom through the basal lamina of the proximal gonad and then through fenestrations (sheath pores) in the gonad sheath before being endocytosed into the most mature oocytes. Myoepithelial specializations anchored by hemi-adherens junctions in the proximal sheath act to squeeze the primary oocyte out of the gonad to the spermatheca for fertilization.</jats:p>

Control of oocyte meiotic maturation and fertilization

“…In diakinesis, six discrete highly condensed bivalents, corresponding to the homologous chromosome pairs, are readily visualized ( Figure 2B). Oocytes develop in close association with proximal gonadal sheath cells ( Figure 2), smooth muscle-like cells that regulate meiotic maturation and contract to drive ovulation (McCarter et al, 1997;Hall et al, 1999;Miller et al, 2003). Meiotic maturation takes place in an assembly line fashion, such that the most proximal oocyte (often referred to as the -1 oocyte) matures, enters the spermatheca at ovulation, and is fertilized ( Figure 2; Movie 1).…”

“…The vitellogenins, protein components of yolk particles, are synthesized in the intestine (Kimble and Sharrock, 1983) and secreted into the Control of oocyte meiotic maturation and fertilization pseudocoelom. Yolk lipoprotein particles appear to pass through the gonadal basal lamina, move through pores in the gonadal sheath cells (Figure 2E), are endocytosed, and stored in membrane-bounded granules within oocytes (Hall et al, 1999). Endocytosis, of yolk lipoprotein particles requires the RME-2 yolk receptor, a member of the low-density lipoprotein receptor superfamily (Grant and Hirsh, 1999).…”

“…Oocyte meiotic maturation can be viewed by time-lapse videomicroscopy of living animals (Ward and Carrel, 1979; Movie 1). The timing of landmark events during meiotic maturation (McCarter et al, 1999) and the ultrastructure of the proximal gonad (Hall et al, 1999) have been described. The nuclear envelope of the most proximal oocyte breaks down~5 min prior to ovulation as it enters meiotic M-phase from prophase (McCarter et al, 1999).…”

“…(D) Gap junction (gj) between oocyte and proximal sheath cell. Photograph modified fromHall et al (1999) with permission. (E) High magnification view of a freeze-fracture replica of sheath cell 4 covering the -2 oocyte.…”

“…Irregular sheath pores (p) form fenestrae through which the oocyte surface is visible. Photograph modified fromHall et al (1999) with permission. Movie 1.…”