The Domestic Dog and Cat as Models for Understanding the Regulation of Ovarian Follicle Development In Vitro

Abstract

The culture of ovarian follicles is an important tool for understanding of the mechanisms controlling follicle development and differentiation of its oocyte. The benefit of recovering meiotically and developmentally competent oocytes from early stage follicles (primordial, primary, preantral and early antral) also would be significant, ranging from rescue of genomes from endangered species to preserving fertility in women facing cancer treatments. This field of research is at an early stage of scientific discovery. To-date, live offspring from cultured primordial follicles that produced fertilizable oocytes has occurred only in the mouse. Progress in other more complex species has been limited because larger animals have longer durations of natural folliculogenesis, thereby requiring more culture time to generate fully grown follicles and oocytes. We believe the dog and cat are excellent models for understanding more about folliculogenesis in vitro. This review highlights what is known about this topic for these two species as well as future priorities. In brief, it is more challenging to maintain viability of primordial follicles within ovarian tissues in vitro in the dog than the cat. Nonetheless, it is possible to grow both isolated cat and dog preantral follicles in culture. Although the follicles of both species have the capacity to increase in size and produce steroids, only cat oocytes are morphologically normal. This striking difference between the dog and cat is an area of high research priority. While much more fundamental data are required, we envision advanced technology that will allow harvesting oocytes from the vast, unused follicle stores sequestered within carnivore ovaries. These gametes have utility for reproducing genetically valuable dogs and cats that are ‘companions’ or biomedical models for investigating human disorders or for salvaging the genomes of rare canid and felid species that die before contributing to genetic management programs.

Mammalian fertility preservation through cryobiology: value of classical comparative studies and the need for new preservation options

“…Yet the information required to achieve these milestones remains rudimentary at best, even for livestock and common laboratory species (Paris et al 2004; Cleary et al 2004; Songsasen et al 2012). For example, it has been projected that it will be necessary to maintain living follicles in culture for up to 6 months to allow the recovery of viable oocytes in carnivores (Songsasen et al 2012). Such approaches will require an array of pre-emptive comparative studies within and across species to determine the influence of a host of microenvironmental factors.…”

Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) pre-exposure ensures follicle integrity during in vitro culture of ovarian tissue but not during cryopreservation in the domestic cat model

“…These options also are particularly interesting in endangered species conservation to bank ovarian tissue containing an abundant amount of preantral and primordial follicles for individuals undergoing surgical ovarian removal or dying unexpectedly [2][3][4]. In this type of studies, the domestic cat represents an excellent biomedical model for nondomestic cats and human [3,5,6]. In association with the freezing techniques, culture of the ovarian tissue in vitro is a fundamental approach to reanimate the tissue and grow more oocytes to an advanced stage [5,7,8].…”

“…In this type of studies, the domestic cat represents an excellent biomedical model for nondomestic cats and human [3,5,6]. In association with the freezing techniques, culture of the ovarian tissue in vitro is a fundamental approach to reanimate the tissue and grow more oocytes to an advanced stage [5,7,8]. However, there may be several hours between the ovarian tissue collection and the cryopreservation process itself which compromises (through ischemia and oxidative stress) the viability and developmental competence of the germ cells within the gonads [3,9,10].…”

The role of TGF superfamily gene expression in the regulation of folliculogenesis and oogenesis in mammals: a review

“…In all mammalian species, the proper course of folliculogenesis and oogenesis is the main factor that influences the growth and development of cumulus-oocytes complexes, the maturation of oocytes to reach the MII stage and subsequently monospermic fertilisation (Chaves et al 2012;Songsasen et al 2012;Jovanovic et al 2013;Linke et al 2013;Sobinoff et al 2013). Developing from the preantral into the antral stage, the follicle is finally morphologically modified to three separate populations of somatic cell: theca cells, granulosa cells and cumulus oophorus (Figure 1).…”