Oocyte quality is the limiting factor in female fertility. It is well known that maternal nutrition plays a role in reproductive function, and manipulating nutrition to improve fertility in livestock has been common practice in the past, particularly with respect to negative energy balance in cattle. A deficiency in nicotinamide adenine dinucleotide (NAD⁺) production has been associated with increased incidences of miscarriage and congenital defects in humans and mice, while elevating NAD⁺ through dietary supplements in aged subjects improved oocyte quality and embryo development. NAD⁺ is consumed by Sirtuins and poly-ADP-ribose polymerases (PARPs) within the cell and thus need constant replenishment in order to maintain various cellular functions. Sirtuins and PARPs play important roles in oocyte maturation and embryo development, and their activation may prove beneficial to in vitro embryo production and livestock breeding programs. This review examines the roles of NAD⁺, Sirtuins and PARPs in aspects of fertility, providing insights into the potential use of NAD⁺-elevating treatments in livestock breeding and embryo production programs.

In mammals, the corpus luteum (CL) is a transient organ that secretes progesterone (P4). In the absence of pregnancy, the CL undergoes regression (luteolysis), which is a crucial preparation step for the next estrous cycle. Luteolysis, initiated by uterine prostaglandin F_2α (PGF) in cattle, is usually divided into two phases, namely functional luteolysis characterized by a decline in P4 concentration and structural luteolysis characterized by the elimination of luteal tissues from the ovary. Programmed cell death (PCD) of luteal cells, including luteal steroidogenic cells (LSCs) and luteal endothelial cells (LECs), plays a crucial role in structural luteolysis. The main types of PCD are caspase-dependent apoptosis (type 1), autophagic cell death (ACD) via the autophagy-related gene (ATG) family (type 2), and receptor-interacting protein kinase (RIPK)-dependent programmed necrosis (necroptosis, type 3). However, these PCD signaling pathways are not completely independent and interact with each other. Over the past several decades, most studies on luteolysis have focused on apoptosis as the principal mode of bovine luteal cell death. Recently, ATG family members were reported to be expressed in bovine CL, and their levels increased during luteolysis. Furthermore, the expression of RIPKs, which are crucial mediators of necroptosis, is reported to increase in bovine CL during luteolysis and is upregulated by pro-inflammatory cytokines in bovine LSCs and LECs. Therefore, apoptosis, ACD, and necroptosis may contribute to bovine CL regression. In this article, we present the recent findings regarding the mechanisms of the three main types of PCD and the contribution of these mechanisms to luteolysis.

NANOS3 is an evolutionarily conserved gene expressed in primordial germ cells that is important for germ cell development. Germ cell deletion by NANOS3 knockout has been reported in several mammalian species, but its function in pigs is unclear. In the present study, we investigated the germline effects of NANOS3 knockout in pigs using CRISPR/Cas9. Embryo transfer of CRISPR/Cas9-modified embryos produced ten offspring, of which one showed wild-type NANOS3 alleles, eight had two mutant NANOS3 alleles, and the other exhibited mosaicism (four mutant alleles). Histological analysis revealed no germ cells in the testes or ovaries of any of the nine mutant pigs. These results demonstrated that NANOS3 is crucial for porcine germ cell production.

Oogenesis depends on close interactions between oocytes and granulosa cells. Abnormal signaling between these cell types can result in infertility. However, attempts to manipulate oocyte-granulosa cell interactions have had limited success, likely due to the blood-follicle barrier (BFB), which prevents the penetration of exogenous materials into ovarian follicles. Here, we used adenoviruses (AVs) to manipulate the oocyte-granulosa cell interactions. AVs penetrated the BFB and transduced granulosa cells through ovarian microinjection. Although AVs caused transient inflammation, they did not impair fertility in wild-type mice. Introduction of Kitl-expressing AVs into congenitally infertile Kitl^Sl-t/Kitl^Sl-t mutant mouse ovaries, which contained only primordial follicles because of a lack of Kitl expression, restored fertility through natural mating. The offspring showed no evidence of AV integration and exhibited normal genomic imprinting patterns for imprinted genes. These results demonstrate the usefulness of AVs for manipulating oogenesis and suggest the possibility of gene therapies for human female infertility.

The effect of confirmation of ovulation by rectal palpation and ultrasonography after artificial insemination (AI) on the development of the corpus luteum (CL) and conception rate was investigated in cows. A total of 90 clinically healthy Holstein-Friesian dairy cows were examined in this study. After AI, the cows were divided into three groups (30 cows per group). In Group I, ovulation was confirmed by rectal palpation at 24 h after AI. In Group II, ovulation was confirmed using transrectal ultrasonography 24 h after AI. In Group III, ovulation was not confirmed after AI. Day 0 was defined as the day when ovulation was confirmed in Groups I and II, and as the day after AI was performed in group III. Transrectal ultrasonography was performed on days 3, 5, 7, and 14 to measure the CL diameter, tissue area, and CL blood flow area, and the ratio of CL blood flow area to CL tissue area was calculated. On the day of CL measurement, blood samples were collected to determine the plasma concentrations of progesterone (P₄) and estradiol-17β (E₂). Pregnancy was diagnosed at 28 and 60 days after AI. A high conception rate of approximately 80% was achieved in Groups I and II, in which confirmation of ovulation was conducted. There were no differences in the diameter, tissue area, or blood flow area of the CL between the three groups. These results indicate that the confirmation of ovulation by rectal palpation and transrectal ultrasonography did not affect the formation and function of the CL or conception rate.