The ovary of Lagostomus maximus (Mammalia, Rodentia): an analysis by confocal microscopy.

Lagostomus maximus is a notable mammalian model for reproductive studies. Females have an extremely high ovulation rate, which is due to down-regulation of the follicular apoptosis pathway, which ensures a large pool of developing follicles. This large pool is supported by the convoluted anatomy of the mature ovary, whose germinal tissue is found in irregularly curved ridges throughout the cortex. Medullary tissue is restricted to a minimum. Lyso Tracker Red reconstruction under confocal laser scanning microscopy was used to recognize and measure all follicular stages from primordial to antral. Unlike most mammals in which early primordial follicles are just found in fetal life, the adult ovary shows regions packed with early primordial follicles. Follicle size ranged from 24 to 316 microm. We discuss the relationships of L. maximus follicles size with regard to other species of mammals and propose that the physiology of the adult viscacha ovary obeys to a neoteny process in the evolution of this species.

The ovary of Lagostomus maximus (Mammalia, Rodentia): an analysis by confocal microscopy

Lagostomus maximus is a notable mammalian model for reproductive studies. Females have an extremely high ovulation rate, which is due to down-regulation of the follicular apoptosis pathway, which ensures a large pool of developing follicles. This large pool is supported by the convoluted anatomy of the mature ovary, whose germinal tissue is found in irregularly curved ridges throughout the cortex. Medullary tissue is restricted to a minimum. Lyso Tracker Red reconstruction under confocal laser scanning microscopy was used to recognize and measure all follicular stages from primordial to antral. Unlike most mammals in which early primordial follicles are just found in fetal life, the adult ovary shows regions packed with early primordial follicles. Follicle size ranged from 24 to 316 µm. We discuss the relationships of L. maximus follicles size with regard to other species of mammals and propose that the physiology of the adult viscacha ovary obeys to a neoteny process in the evolution of this species.

The developing human ovary: immunohistochemical analysis of germ-cell-specific VASA protein, BCL-2/BAX expression balance and apoptosis.

BACKGROUND: Germ cell number during ovarian organogenesis is regulated through programmed cell death. We investigated the expression of germ-cell-specific VASA protein, apoptosis-related proteins BAX and BCL-2 and DNA fragmentation in developing human ovaries from gestation week 12 to term. METHODS: Human fetal ovaries from 13 women undergoing spontaneous abortion were fixed, paraffin-embedded and processed for immunohistochemistry to analyse temporal and cellular localization of VASA, BCL-2 and BAX, and to detect apoptosis by TUNEL assay. RESULTS: VASA showed a differential pattern of expression throughout the differentiation and proliferative phase and prophase I to finally associate with Balbiani's body in primordial and primary follicles. BCL-2 was detected from week 12 to 17 and became undetectable thereafter. Strong BAX signal was detected in oogonia and oocytes from week 12 to term. Low levels (

The ovary of the gestating South American plains vizcacha (Lagostomus maximus): suppressed apoptosis and corpora lutea persistence.

The South American plains vizcacha, Lagostomus maximus, displays an exceptional ovulation rate of up to 800 eggs per cycle, the highest rate recorded for a mammal. Massive polyovulation arises from the overexpression of the apoptosis-inhibiting BCL2 gene leading to a suppression of apoptotic pathways responsible for follicular atresia in mammals. We analyzed the ovarian histology, ovarian apoptosis, and apoptosis-related protein expression with special emphasis in corpora lutea throughout the 5-mo-long gestation period, at parturition day and early postpartum, in L. maximus. Corpora lutea were abundant throughout gestation with no sign of structural regression even at the end of gestation. Both immunohistochemistry and Western blot analysis showed strong signals for apoptosis-inhibiting BCL2 protein, whereas the proapoptotic BAX protein was just detected in isolated luteal cells in gestating females and postpartum females. Apoptosis-associated DNA fragmentation detected by TUNEL was very scarce and occasional and correlated with BAX detection in luteal cells. Marked expression of progesterone and alpha-estrogen receptors in luteal cells was found at early, mid-, and late gestation as well as at parturition day and early postpartum samples. Additionally, serum level of progesterone increased markedly to reach maximal values at late gestation and decreasing at parturition to levels found at early gestation, suggesting that corpora lutea remained functional throughout gestation. These results point out that the unusual ovarian environment of L. maximus in which germ cell demise is abolished through antiapoptotic BCL2 gene overexpression also preserves structural integrity and functionality of corpora lutea during the whole gestation. Overexpression of antiapoptotic BCL2 gene may represent a strategy for an essential need of ovary and corpora lutea in order to maintain pregnancy until term.

Naturally suppressed apoptosis prevents follicular atresia and oocyte reserve decline in the adult ovary of Lagostomus maximus (Rodentia, Caviomorpha).

It has been widely accepted that mammalian females are born with a non-renewing, finite pool of oocytes that will be continuously cleared by atresia, with only a small proportion of them reaching ovulation. Apoptosis regulates this mass germ cell death, especially through the balance between pro- and anti-apoptotic proteins encoded by the BCL-2 gene family. The caviomorph rodent Lagostomus maximus, the South American plains viscacha, displays the highest ovulation rate known for a mammal releasing 400-800 eggs per cycle. We tested the hypothesis that in L. maximus massive polyovulation is a consequence of reduced apoptosis resulting in suppressed follicular atresia. We found that anti-apoptotic BCL-2 gene is markedly expressed in all kind of follicles from primordial to fully mature antral stages in the adult ovary of L. maximus. On the other hand, pro-apoptotic BAX gene showed weak signals or was undetectable by immunohistochemical examination. Western blot against both proteins confirmed immunohistochemical results. Screening for DNA fragmentation by TUNEL assay was conspicuously negative in ovaries from both pregnant and non-pregnant females. In addition, alpha-oestrogen receptor also showed an enhanced expression from primordial stage to fully mature antral follicles. Our results show that natural preferential expression of BCL-2 and restricted BAX expression greatly suppresses apoptosis in the ovary of L. maximus. This prevents the decline of the oocyte reserve by abolishing follicular atresia and enables the highest ovulation rate known for a mammal, 400-800 or more eggs per cycle.