FOXO3 Knockdown Accelerates Development of Bovine Primordial Follicles

Abstract

Abstract. The objective of the present study was to elucidate the involvement of FOXO3 in the activation of bovine primordial follicles. In immunohistochemistry, FOXO3 was detected in all of the oocytes in primordial and primary follicles. The FOXO3 decreased after treatment with FOXO3 small interfering RNAs (siRNAs). Ovarian tissues containing dominantly primordial follicles were treated with FOXO3 siRNAs and then xenografted to severe combined immune deficiency (SCID) mice. Two months after xenografting, some primordial follicles developed to the secondary and tertiary stages, and the total percentage of these developing follicles (secondary and tertiary follicles: 18 ± 7%) was higher than in the control grafts treated with control siRNA (7 ± 1%). It is thought that bovine primordial follicle activation is regulated by the FOXO3-dependent mechanism and that knockdown of FOXO3 induces the release of primordial follicles from FOXO3 suppression, initiating their growth. Key words: Bovine, FOXO3, Primordial follicle, Severe combined immune deficiency (SCID) mouse, Xenografting (J. Reprod. Dev. 57: [475][476][477][478][479][480] 2011) he mammalian ovary contains a large number of primordial follicles. The primordial follicle consists of a nongrowing oocyte arrested at the diplotene stage of meiosis I and a surrounding single layer of flat-shaped granulosa cells. Ruminant primordial follicles are formed during fetal life [1], which is earlier than in rodents, whose primordial follicles are formed around the time of birth [2,3]. Flat-shaped granulosa cells change their morphology into a cuboidal shape [4] to form primary follicles, and oocytes start to grow. This change is called primordial follicle activation. During the female reproductive life, only small proportions of oocytes in primordial follicles enter the growth phase, while the others remain quiescent [5]. The mechanism of primordial follicle activation is not well understood.Bovine primordial follicles from fetal ovaries initiate growth within 2 days of culture [6]. Development of fetal bovine follicles to the antral stage (tertiary follicle) 15 weeks after xenografting to nude mice has been reported [7]. However, it has also been reported that bovine primordial follicles from adult animals do not develop 4-6 weeks after xenografting to severe combined immune deficiency (SCID) mice [8]. We recently showed that primordial follicles from 15-day-old piglets developed to the tertiary stage 2 months after xenografting, whereas those from 6-month-old animals did not develop [9], suggesting that neonatal pig ovaries contained a mixed population of activated and quiescent primordial follicles, while primordial follicle activation was perhaps negatively regulated by some factors in adult animals, since the follicles had the ability to initiate development 4-6 months after xenografting [10].Castrillon et al. [11] reported that global activation of primordial follicles occurred in Foxo3 -/-mice. FOXO3 is one of the forkhead transcription factors, which are charact...

Lipopolysaccharide Reduces the Primordial Follicle Pool in the Bovine Ovarian Cortex Ex Vivo and in the Murine Ovary In Vivo1

“…Similarly, in the present study, follicle activation in bovine ovarian cortex was associated with reduced expression of the PTEN protein following 6 days' treatment with LPS. While PTEN has not been studied in the bovine ovary, FOXO3 knockdown in bovine ovarian cultures has been shown to promote the activation of primordial follicles [36]. In the present study, the primordial follicle activation following treatment of ovarian cortex with LPS was also associated with translocation of FOXO3 out of the nucleus.…”

Foxo3 negatively regulates the activation of mouse primordial oocytes

“…After knockdown of FOXO3, a proportion of primordial oocytes from prepubertal pigs became activated and entered the growth phase in the xenografts [9]. The similar results have been obtained in bovine primordial oocytes [15]. In the present study, the role of Foxo3 in survival of mouse primordial oocytes was not elucidated.…”

“…Since, mouse oocytes start to grow after birth, this pattern of Foxo3 expression indicates its possible involvement in the growth of primordial oocytes in mice. RNA interference by siRNAs is a well-established method for gene knockdown in cultured cells [12,13], and has been applied for oocytes [14], cortical slices of porcine and bovine ovaries [9,15] and mouse ovaries [16]. Since siRNA mediates sequence-specific mRNA degradation, the Foxo3 siRNAs worked to knock down the target Foxo3 protein in the present experiment.…”

164. Gonadal Expression of Foxo1, but Not Foxo3, Is Conserved in Diverse Mammalian Species.

“…We systematically analyzed the expression and distribution of Foxo1 and Foxo3 in the gonads of diverse mammalian species, including rodents, companion animals, farm animals, nonhuman primates, and humans. There is considerable interest in the roles of the Foxos in gametogenesis and reproduction in diverse mammalian species [14][15][16][17], including their use as targets and/or biomarkers in contraception and advanced reproductive technologies [18][19][20][21]. Therefore, these analyses are an important step toward understanding the potential conservation (and practical applications) of Foxo gonadal functions in mammals.…”