Gonadotrophic hormone inEulalia viridis(Polychaeta, Annelida): Stimulation of vitellogenesis

Abstract

Incorporation of 3~-leucine into TCA extracted, water soluble oocyte proteins is significantly enhanced in in vivo cultures of Eulalia viridis which have intact supra-oesophageal ganglia and those which have undergone replacement therapy when compared to decerebrate treatments. This response is gonad specific, with no differences in the rate of uptake of 3~-leucine into gut proteins between treatments. There was no significant difference in the rate of protein synthesis between oocytes cultured in vitro in the presence or absence of supra-oesophageal ganglion homogenate on culture medium containing 3~-leucine. However, oocytes cultured in the presence of supra-oesophageal ganglion homogenate do show a significant increase in the rate of uptake of radiolabel when compared to oocytes cultured in the absence of prostomial homogenate when cultured on medium containing 3~-labelled oocyte protein. These results indicate the presence of a gonadotrophic hormone in the supra-oesophageal ganglion of Eulalia viridis which promotes the uptake of external egg protein into developing oocytes. It is suggested that this is, at least in part, a heterosynthetic process with 3~-leucine being incorporated into an external protein before incorporation into the developing oocytes.

The endocrine control of reproduction in Nereidae: a new multi-hormonal model with implications for their functional role in a changing environment

“…The production of oestradiol-17b or uptake of vitellogenin is also enhanced by a second neurohormone present in the ganglion of mature females. This hormone appears to have a gonadotrophic function similar to that described in a number of iteroparous species (Lawrence & Olive 1995).…”

Oogenesis and oocytes

“…Early morphological and radioactive tracer studies suggested that oocytes manufactured yolk via autosynthetic processes whereas later studies indicated that heterosynthetic uptake of yolk precursors was the predominate mechanism (reviewed in Fischer & Hoeger, 1993;Lawrence & Olive, 1995;Fischer, 1999). There are suggestions that the length of vitellogenesis is closely related to the mechanism of yolk synthesis (auto-vs. heterosynthesis) with relatively slow yolk synthesis being associated with autosynthesis, while rapid yolk synthesis is correlated with heterosynthesis (Eckelbarger, 1983(Eckelbarger, , 1988(Eckelbarger, , 1992(Eckelbarger, , 1994.…”

Endocrine and environmental control of reproduction in Polychaeta

“…This result should be compared with what occurs in Nereidae. Although the nereid brain hormone has an inhibitory effect on sexual maturation, it is also essential for normal oocyte development, even if its action is not a direct one (see above), which led Lawrence and Olive (1995) to hypothesize that in Nereidae, the gonadotrophic role might be the brain hormone's primitive function.…”

“…As vitellogenesis is induced by the spring rise in sea temperatures to 10°C and above, it is likely that the hormone is implicated in the transduction of environmental input. The role of the hormone has been elucidated using bioassays and the incorporation of 3 H-leucine (Lawrence and Olive 1995). Contrary to what occurs in Nephtyidae, the hormone does not stimulate autosynthesis of protein in the oocytes but promotes the uptake of external egg protein into developing oocytes.…”