Prolactin-induced termination of obligate diapause of mink (Mustela vison) blastocysts in vitro and subsequent establishment of embryonic stem-like cells

Selected Aspects of Reproductive Behavior of American Mink (Neovison vison) under Artificial Conditions

Observation and behavioral analysis of animals can be one of the factors taken into consideration when assessing the welfare of animals kept in artificially created breeding conditions. Disturbed welfare and prolonged exposure to stress can lead to the emergence of abnormal behaviors, including reproductive issues. The aim of this study was to examine the mating behavior of male American mink, with regard to the duration of mating and any potential differences with regard to time of day, mating period, number of mating attempts, and time spent with the female. The study material consisted of 12 one-year-old male American minks with pearl coloring and 60 two-year-old females. Observations were conducted using images captured using externally mounted cameras. The video material capturing the activity of males and females during the mating period was analyzed using the Behawior program. The obtained results indicate the presence of individual differences in copulation duration. It was observed that the copulation time increases with successive days of the breeding season and with number of copulations. It was also observed that a longer time spent with the female to initiate copulation, and behaviors such as rubbing or sniffing the female, were associated with a shorter copulation time. The above-mentioned studies provide specific guidelines regarding the management of matings on the farm, demonstrating the feasibility of conducting matings both in the hours before and after noon.

An Ethogram of the Reproductive Behaviour of the American Mink (Neovison vison) in Farmed Conditions

Ethograms can serve as benchmarks against which abnormal animal behaviour can be identified, and then normal behaviour can be restored by appropriately modifying the environment in which an individual resides. The aim of the present study was to create an ethogram of the reproductive behaviour of American mink kept in farmed conditions. The research material consisted of 12 one-year-old male American mink, pearl coloured, selected randomly from among the varieties of coloured mink on the farm, and 60 two-year-old females. The animals participating in the study were grouped into two breeding sets, each consisting of 30 females and 6 males. Reproductive rituals included chasing the female, grasping her neck with the teeth, marking the local area, mounting the partner, and sniffing the neck, anal and genital areas. The copulation times recorded in this study varied greatly, ranging from several minutes to over two hours. The obtained results indicate that the American mink can express some natural reproductive behaviour in breeding conditions, which may also be an indicator of the welfare of these animals.

Prolactin from Pluripotency to Central Nervous System Development

Prolactin (PRL) is a versatile hormone that exerts more than 300 functions in vertebrates, mainly associated with physiological effects in adult animals. Although the process that regulates early development is poorly understood, evidence suggests a role of PRL in the early embryonic development regarding pluripotency and nervous system development. Thus, PRL could be a crucial regulator in oocyte preimplantation and maturation as well as during diapause, a reversible state of blastocyst development arrest that shares metabolic, transcriptomic, and proteomic similarities with pluripotent stem cells in the naïve state. Thus, we analyzed the role of the hormone during those processes, which involve the regulation of its receptor and several signaling cascades (Jak/Mapk, Jak/Stat, and PI3k/Akt), resulting in either a plethora of physiological actions or their dysregulation, a factor in developmental disorders. Finally, we propose models to improve the knowledge on PRL function during early development.

Dynamics of small non-coding RNAs in bovine scNT embryos through the maternal-to-embryonic transition

The efficiency of somatic cell nuclear transfer (scNT) for production of viable offspring is relatively low as compared to in vitro fertilization (IVF), presumably due to deficiencies in epigenetic reprogramming of the donor cell genome. Such defects may also involve the population of small non-coding RNAs (sncRNAs), which are important during early embryonic development. The objective of this study was to examine dynamic changes in relative abundance of sncRNAs during the maternal-to embryonic transition (MET) in bovine embryos produced by scNT as compared to IVF by using RNA sequencing. When comparing populations of miRNA in scNT versus IVF embryos, only miR-2340, miR-345, and miR34a were differentially expressed in morulae, though many more miRNAs were differentially expressed when comparing across developmental stages. Also of interest, distinct populations of piwi-interacting like RNAs (pilRNAs) were identified in bovine embryos prior to and during embryonic genome activation (EGA) as compared bovine embryos post EGA and differentiated cells. Overall, sncRNA sequencing analysis of preimplantation embryos revealed largely similar profiles of sncRNAs for IVF and scNT embryos at the 2-cell, 8-cell, morula and blastocyst stages of development. However, these sncRNA profiles, including miRNA, piRNA and tRNA fragments, were notably distinct prior to and after completion of the MET.

Profiles of maternal origin factors during transition from embryonic diapause to implantation in roe deer

The aim was to evaluate in female roe deer: (a) PAG mRNA relative abundance in endometrial uterine tissue for determination of the duration of embryonic diapause, (b) mRNA relative abundance of progesterone, estradiol, and prolactin (P4, E2, and PRL) receptors (PGR, ESR, and PRLR) during diapause and after implantation in the endometrium; (c) concentration of P4, E2, and PRL in the blood, and (d) a noninvasive method of hormone detection by measurement of P4 and E2 concentrations in feces. A total of fifteen individuals were obtained post mortem during hunting seasons and divided into three experimental groups (November, December, January). The results did not reveal mRNA relative abundance for PAGs in the endometrium or detectable PAG concentrations in the serum of all examined females. Concentration of PRL and mRNA relative abundance for PRLR long isoform in the endometrium was the highest in January (p < .01). mRNA relative abundance for PGR, P4 concentration in the endometrium, serum, and feces was the highest in January (p < .01). Endometrial origin PRL and P4 may be responsible for the termination of this process and pregnancy development after implantation.

Culture of Mink Preimplantation Embryos

The reproduction of the mink, Neovison vison, has been extensively studied over the past 70 years. The endocrine control of pregnancy is reasonably well understood, but our understanding of early embryo development is limited. The mink is one of the best characterized mammals for the study of embryonic diapause, but in order to unravel the complex interactions that occur between the blastocyst and the uterus during diapause and reactivation, a defined culture media system that supports growth is essential. Until recently, culture of the mink blastocyst has been relatively unsuccessful. This chapter will describe a method for successfully obtaining and culturing mink blastocysts and will highlight some of the unique challenges in working with this species. Methods to age match prediapause embryos in a mammal that exhibits superfetation, and to synchronize collection of reactivation from diapause stages using prolactin will be discussed. Finally, a quantitative method to determine the extent of cell proliferation in the blastocyst, a hallmark of reactivation from diapause, will be detailed.

The Escape of the Mink Embryo from Obligate Diapause1

The obligate embryonic diapause that characterizes gestation in mink engenders a developmental arrest at the blastocyst stage. The characteristics of escape from obligate diapause were investigated in embryos reactivated by treatment of the dams with exogenous prolactin. Protein and DNA synthesis showed marked increases within 72 h after the reinitiation of development, and embryo diameter increased thereafter. Trophoblast cells from embryos at Day 5 after activation proliferated more readily in vitro than trophoblasts from diapause or from Day 9 after activation, while in Day 9 embryos, cells from the inner cell mass (ICM) replicated comparatively more readily in vitro. There was evidence of expression of fibroblast growth factor-4 (FGF4) in both diapause and activated embryos and in ICM, but not the trophoblast. FGF receptor-2 was present in embryos from Day 5 after reactivation in both trophoblast and ICM cell lines. Trophoblast cell lines established from mink embryos proliferated in culture in the presence of FGF4 with a doubling time of 1.4 days, while in its absence, the doubling time was 4.0 days. We conclude that, during reinitiation of embryogenesis in the mink after diapause, embryo growth is characterized by gradual increases in protein synthesis, accompanied by mitosis of the trophoblast and ICM. There appears to be a pattern of differential proliferation between cells derived from these embryonic compartments, with the trophoblast phase of replication occurring mainly in the early reactivation phase, while the ICM proliferates more rapidly nearer to the time of implantation.

Long-term culture and transplantation of murine testicular germ cells

The objectives of this study were to develop an in vitro culture system to optimize germ cell proliferation and to measure the potential of the cultured germ cells to produce mature spermatozoa after transplantation into a recipient. Donor germ cells isolated from ROSA26 male mice were cultured with a STO feeder cell layer in Dulbecco's minimal essential medium (DMEM) supplemented with fetal bovine serum (FBS), stem cell factor, leukemia inhibitory factor, basic fibroblast growth factor, insulin-like growth factor 1, interleukin-11, L-glutamine, sodium pyruvate, 2-mercaptoethanol, murine oncostatin M, and platelet-derived growth factor. Donor germ cells formed colonies in the primary cultures after 8-21 days. These cultured colonies were maintained for 4 weeks or longer without subculture and proliferated for up to 8 passages over a period of 3 months. These colonies had alkaline phosphatase activity and incorporated 5-bromo-2'-deoxyuridine. These colonies were positive partially when screened with antibody for germ cell nuclear antigen and c-kit. Germ cells cultured with this supplemented medium showed enhanced colonization vs controls cultured with DMEM and FBS. Cultured germ cells from Rosa26 donors were transplanted into testes and were identified by X-gal staining and histological screening. The cells cultured in the supplemented medium colonized the tubules and initiated spermatogenesis in the recipient mice. This is an improved method for culturing germ cells and may be useful in gene therapy and the production of transgenic animals.

Changes in sex steroids, gonadotropins, prolactin, and inhibin in pregnant and nonpregnant Japanese black bears (Ursus thibetanus japonicus)

We examined changes in the concentrations of serum progesterone (P4), estradiol-17beta (E2), FSH, LH, prolactin (PRL), and inhibin to determine their interaction and their effect on the reproductive endocrine controls of pregnant and nonpregnant female Japanese black bears. Fourteen female bears were used in this study over a 2-yr period. In the first year, six of the bears were divided into two groups; a pseudopregnant group and a nonpregnant group. In the second year, the remaining eight bears were also divided into two groups; a pregnant group and a nonpregnant group. Pregnant and pseudopregnant bears had similar P4 trends with both groups exhibiting a significant increase in December, which is the suspected time of implantation in pregnant bears. These trends correlated with an increase in PRL levels, whereas low levels of LH were maintained throughout the year. Nonpregnant bears maintained low concentrations of P4, and compared with pregnant and pseudopregnant bears, they also exhibited a delayed elevation in PRL. Luteinizing hormone activity varied among individual animals, but regardless of reproductive status, fluctuation patterns of E2, FSH, and inhibin did not differ among bears. Our results suggest that PRL may play a luteotropic role in both pregnant and pseudopregnant bears, and is possibly responsible for inducing reactivation of the dormant corpus luteum that precedes implantation in the Japanese black bear.

Diapause

Embryonic diapause, or delayed implantation as it is sometimes known, is said to occur when the conceptus enters a state of suspended animation at the blastocyst stage of development. Blastocysts may either cease cell division so that their size and cell numbers remain constant, or undergo a period of very slow growth with minimal cell division and expansion. Diapause has independently evolved on many occasions. There are almost 100 mammals in seven different mammalian orders that undergo diapause. In some groups, such as rodents, kangaroos, and mustelids, it is widespread, whereas others such as the Artiodactyla have only a single representative (the roe deer). In each family the characteristics of diapause differ, and the specific controls vary widely from lactational to seasonal, from estrogen to progesterone, or from photoperiod to nutritional. Prolactin is a key hormone controlling the endocrine milieu of diapause in many species, but paradoxically it may act either to stimulate or inhibit growth and activity of the corpus luteum. Whatever the species-specific mechanisms, the ecological result of diapause is one of synchronization: It effectively lengthens the active gestation period, which allows mating to occur and young to be born at times of the year optimal for that species.

Live birth of a bear cub following nonsurgical embryo collection

In the near future, 6 of 8 bear species will face extinction mainly because of loss of their natural habitat. This loss of habitat will ultimately require some of these bears to be maintained in zoos and wildlife preserves in the hope of conserving genetic diversity. If the giant panda is representative of other bear species, reproductive performance will be inhibited in such an environment. In this study, we used the nonendangered American black bear (Ursus americanus) as the model for developing appropriate embryo transfer procedures. The donor bear mated numerous times between late May and early June. In late July we anesthetized her and used a series of telescoping sheaths to gain access to the uterus Then we passed a catheter through the largest sheath, inflated the balloon, and, using a 20-mL syringe, repeatedly infused into and then aspirated from the uterus PBS + BSA. We emptied the syringe into Petri dishes and observed 2 embryos. We rinsed the embryos, placed them in human tubal fluid + HSA + HEPES and then held them at 35 degrees C for 5 h. The recipient mated during mid-June; in late July we anesthetized her and, with the aid of laparoscopy, transferred an embryo into the cranial portion of the uterine horn ipsilateral to the ovary containing a CL. The recipient delivered 2 cubs in January. Necropsy results indicated that the neonates lived for 6 to 8 wk before succumbing to flooding in the den. The DNA from hair samples belonging to the neonates indicated that the male cub belonged to the donor, the female cub to the recipient. The delayed implantation mechanism in bears probably allowed for the successful development of the embryo in the presence of a substantial asynchrony between the donor and the recipient (13 d). We conclude that embryo transfer is possible in the American black bear and can lead to the birth of live cubs.

Cloning, developmental expression, and immunohistochemistry of cyclooxygenase 2 in the endometrium during embryo implantation and gestation in the mink (Mustela vison)

Cyclooxygenase (COX) is the first rate-limiting enzyme in the biosynthesis of PGs. There are two isoforms, COX-1, a constitutive enzyme and COX-2, the induced form, products of two different genes. In this study, we report COX-2 complementary DNA cloning, uterine expression, and immunohistochemical localization in the mink uterus during postimplantation gestation. The open reading frame of mink COX-2 contains 1812 nucleotides encoding 604 amino acids. The homologies are 86%, 83%, 83%, 83%, 85%, and 84% in nucleotides and 86%, 87%, 87%, 85%, 86%, and 88% in amino acids with human, mouse, rat, guinea pig, sheep, and rabbit, respectively. All domains associated with biological activity are conserved in the mink. Northern analysis revealed a transcript of 4.2 kb for COX-2 in mink uterus and adrenal. Semiquantitative RT-PCR showed that COX-2 messenger RNA is not present during diapause. The abundance of COX-2 messenger RNA reached its maxima (P < 0.05) on days 3-5 of postimplantation, gradually decreased through day 9, and was not present thereafter. By immunohistochemistry, COX-2 was present in uterine epithelium, stroma, and necks of endometrial glands at sites of implantation. COX-2 expression appears to be induced in the endometrium by the embryo and may play a role in implantation and placentation in the mink.