Loredana Ricchiari

An ultrastructural study on the vitellogenesis in the spotted ray Torpedo marmorata

The present investigation strongly suggests that in Torpedo the oocyte growth is not only due to the uptake of exogenous molecules, but also by the oocyte itself and the granulosa cells. The oocyte, starting from the early previtellogenic follicles (see also Mol. Reprod. Dev. 61 (2002) 78), synthesizes large amounts of glycogen. Later, as the oocyte growth goes on, the cytoplasm of granulosa cells progressively bears numerous islets of glycogen, which are also evident inside the intercellular bridges and in the oocyte cortex, suggesting that they may flow from granulosa cells to the oocyte. The contribution of granulosa cells seems to become most relevant during the vitellogenesis. In vitellogenic follicles, both small, intermediate, and pyriform-like cells bear numerous vacuoles containing vitellogenin-like material, suggesting strongly that in Torpedo, differently from other vertebrate species, granulosa cells could be engaged in vitellogenesis. The present investigation does not allow us to know if such a material is due to a transcytosis process and/or is synthesized inside them. The organization of granulosa seems to exclude the possibility that it is transferred to granulosa via transcytosis. On the contrary, granulosa cells, especially in vitellogenic follicles, display the morphological organization of metabolically active cells, so they could be engaged in vitellogenin synthesis. This interpretation is consistent with the observation that granulosa cells are positively stained by OZI (osmium tetroxide-zinc iodide) and that the same positivity is evident on intercellular spaces, containing vitellogenin-like material, and on nascent yolk globules.

An ultrastructural study of germ cells during ovarian differentiation in Torpedo marmorata

An ultrastructural investigation, performed on embryos, neonates, subadult and adult females, demonstrated that in Torpedo marmorata oogenesis occurs very early in life and continues, in its proliferative phase, also after birth. Clusters of early meiotic cells were already evident in the ovarian cortex of 6‐cm‐long embryos, as well as in the ovary of newborns and three‐month‐old young. Conversely, in the ovaries of subadult and adult females, all the germ cells present were organized into follicles, and no clusters of oogonia and early meiotic cells were generally found in the cortex, except for one adult female where clusters of germ cells not organized in follicles were found in the cortex. These data demonstrated that, in Torpedo marmorata, oogenesis is immediate, and, as oogonia persist after birth, more similar to that of mouse, monkey, rabbit, and ferret (Mauleon Arch Anat Microsc, 1967; 56:125–150; Byskov and Hoyer 1994 ) than to that of human, rat, pig, and guinea pig (Byskov and Hoyer 1994 ). Such a pattern is in agreement with the reproductive strategy of Torpedo, a scantly prolific species with low uterine fecundity. The presence of meiotic cells that are not organized in follicles in one adult female might be consistent with the large individual variability characterizing cartilaginous fishes. The possibility that such a character is typical of mature females should be rejected as oogonia and early meiotic cells were not found inside the totally sectioned gonads of subadult and adult females. Anat Rec 263:237–245, 2001.

Distribution of PACAP in the brain of the cartilaginous fish Torpedo Marmorata

Abstract:  In this article, we investigated the distribution of pituitary adenylate cyclase‐activating polypeptide (PACAP) and its mRNA by immunohistochemistry, in situ hybridization, and RT‐PCR techniques, in the central nervous system of the elasmobranch Torpedo marmorata. RT‐PCR analysis showed that the CNS of T. marmorata expresses a messenger encoding PACAP. The immunohistochemistry and in situ hybridization patterns were partly overlapping, with a major expression in the hypothalamo–pituitary region and, surprisingly, in the saccus vasculosus. Our results show that, in T. marmorata, PACAP is synthesized and widely distributed in the CNS, suggesting an as yet unidentified role for this peptide in elasmobranch brain physiology.

Organization of the Vitelline Envelope in Ovarian Follicles of Torpedo marmorata Risso, 1810 (Elasmobranchii: Torpediniformes)

In Torpedo marmorata, the vitelline envelope (VE), an extracellular envelope surrounding the growing oocyte, consists of fibrils and amorphous materials that are deposited in the perivitelline space starting from the initial steps of oocyte growth. SDS-PAGE analysis of the isolated and purified VE reveals that it consists of different glycoproteins. Furthermore, our investigations showed that the 120 and 66 kDa glycoproteins are positive to an antibody directed against gp69/64 of the Xenopus laevis VE and are synthesized under the control of 17beta-estradiol in the liver, that, together follicle cells and the oocyte, is the biosynthetic site of VE components.