Endosomes transfer yolk proteins to lysosomes in the vitellogenic oocyte of the trout

Abstract

The internalization of the yolk proteins has been investigated by electron microscopy and cytochemistry in the oocyte of the trout which stores up large quantities of yolk. The oocyte evolution has been followed for 18 months in a homogeneous group of animals. Anionic ferritin has been injected during vitellogenesis. The results indicate that as in other oocytes the yolk proteins are absorbed by coated vesicles during vitellogenesis. But unlike most other oocytes the yolk proteins are then transferred via typical endosomes to a conspicuous lysosomal compartment built up very early at the onset of the cytoplasmic differentiation of the oocyte e.i. 10 months earlier. During vitellogenesis yolk progressively accumulates in this lysosomal compartment. Injected anionic ferritin follows the same pathway of internalization. These findings indicate that in this oocyte, the whole yolk cycle presumably represents an adaptation of a general cellular activity, the receptor-mediated endocytosis, largely amplified, sequenced and spread over several months.

Particularities of reproduction and oogenesis in teleost fish compared to mammals

“…After leaving the blood vessels, vtg goes through the follicle wall and is selectively incorporated into the oocyte [105], by receptor-mediated endocytosis [106,107]. Vtg is then transferred into multivesicular bodies from the lysosomial compartment [108] where it is colocalised with a proteolytic enzyme, cathepsin D [109], which is probably responsible for its cleavage into yolk proteins.…”

An unusual lysosome compartment involved in vitellogenin endocytosis by Xenopus oocytes.

“…Morphological observation of yolk deposition in trout oocytes has revealed the presence of an acid phosphatase-positive MVB compartment in previtellogenic cells (3). As these oocytes enter the vitellogenic phase of their development, internalized vitellogenin appears to accumulate in the MVB compartment, concomitant with a loss of histochemically demonstrable acid phosphatase activity.…”

The reproductive cycle of male and female brown trout (Salmo trutta fario): a quantitative study

“…More specific work on vitellogenesis, especially at the earliest stage of oocyte development, has been carried out by Beams and Kessel (1973), Upadhyay (1977), Upadhyay et al (1978), Van den Hurk and Peute (1979), Breton et al (1983), Busson-Mabillot (1984) and Sumpter et a/. (1984).…”