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The Special Issue features one review and three research articles focusing on mechanisms regulating dog oocyte maturation and development. A review paper presented in this Special Issue summarizes the latest findings on germ cell development, the methods available for obtaining germ cells in vitro, and their potential applications in canid species. Germ cell development: Primordial germ cells are specialized cells that give rise to gametes (sperm and eggs). [Extracted from the article]

The maned wolf is a threatened canid species native to South America. Previous studies have suggested the species exhibits induced ovulation. In captive breeding facilities, reproductive success is low while rates of neonatal mortality are high. Females that are not recommended for breeding are frequently housed together. However there has never been a systematic study of the reproductive consequences of co-housing females. This study was conducted for three purposes, to: (1) corroborate the presence of induced ovulation, (2) determine whether elevated cortisol is implicated in neonatal pup mortality, and (3) evaluate the endocrine correlates of group housed females. Using fecal hormone monitoring for estrogen, progesterone, and cortisol, 43 cycles from 33 female maned wolves were studied from 2002 to 2015. Females were categorized by their reproductive status: pregnant and successfully raised pups (PR; n = 11), pregnant with neonatal pup demise within 3 days (PL; n = 7), housed with a male but no signs of breeding or pregnancy (PP; n = 10), housed singly (S; n = 8), or housed with related females (F; n = 7). Estrogen and progestagen remained at baseline for all females not housed with a male (S, F), while elevations consistent with ovulation were seen in females housed with a male (PP, PL, PR). Compared to PR females, PL individuals showed similar cortisol levels throughout the cycle and slightly lower progesterone levels during gestation. As for the effect of co-housing related females, F females showed estrogen and progesterone levels lower even than S females while cortisol levels were elevated compared to all other groups. These findings support the previous evidence of induced ovulation in the maned wolf. Although elevated cortisol does not seem to be implicated in pup loss, a non-significant trend towards lower progesterone during gestation could be implicated. Future studies should assess depressed progesterone levels as a correlate to neonatal pup mortality. Female maned wolves housed with related females experience suppressed reproductive hormones and elevated adrenal hormones. Therefore, a more systematic study of hormonal and behavioral correlates to co-housing with related females is warranted. [ABSTRACT FROM AUTHOR]

Understanding stage-specific requirements of mammalian folliculogenesis is limited in the domestic dog. The present study examined the effects of two potential regulators of dog follicle growth and survival in vitro, namely the original stage of the follicle (i.e. preantral (≤230 µm diameter) vs early antral (diameter from >230 to ≤330 µm) and FSH and/or LH concentrations. After isolation and alginate encapsulation, follicles were cultured in 0, 1, 10 or 100 µg mL-1 FSH and 0, 1 or 10 ng mL-1 LH for 20 days. Regardless of stage, FSH promoted growth, but LH did the same only in the absence of FSH. Production of 17β-oestradiol and progesterone was detectable, indicating theca cell activity. The greatest growth occurred in preantral (mean (± s.d.) 61.4 ± 25.9%) versus antral (42.6 ± 20.3%) follicles, but neither developmental stage nor gonadotropin affected survival. Antrum detection was minimal due, in part, to antral collapse, and oocytes exhibited an increasingly pale appearance and chromatin degeneration over time. The results demonstrate that pre-and early antral stage dog follicles encapsulated in alginate grow significantly in vitro. However, because FSH and LH alone or in combination fail to promote antrum development, the next step is identifying factors that enhance antral expansion. [ABSTRACT FROM AUTHOR]

Development of assisted reproductive technologies (ART) in the dog has resisted progress for decades, due to their unique reproductive physiology. This lack of progress is remarkable given the critical role ART could play in conserving endangered canid species or eradicating heritable disease through gene-editing technologies—an approach that would also advance the dog as a biomedical model. Over 350 heritable disorders/traits in dogs are homologous with human conditions, almost twice the number of any other species. Here we report the first live births from in vitro fertilized embryos in the dog. Adding to the practical significance, these embryos had also been cryopreserved. Changes in handling of both gametes enabled this progress. The medium previously used to capacitate sperm excluded magnesium because it delayed spontaneous acrosome exocytosis. We found that magnesium significantly enhanced sperm hyperactivation and ability to undergo physiologically-induced acrosome exocytosis, two functions essential to fertilize an egg. Unlike other mammals, dogs ovulate a primary oocyte, which reaches metaphase II on Days 4–5 after the luteinizing hormone (LH) surge. We found that only on Day 6 are oocytes consistently able to be fertilized. In vitro fertilization of Day 6 oocytes with sperm capacitated in medium supplemented with magnesium resulted in high rates of embryo development (78.8%, n = 146). Intra-oviductal transfer of nineteen cryopreserved, in vitro fertilization (IVF)-derived embryos resulted in seven live, healthy puppies. Development of IVF enables modern genetic approaches to be applied more efficiently in dogs, and for gamete rescue to conserve endangered canid species. [ABSTRACT FROM AUTHOR]

Simple Summary: As the dog shows unique and peculiar reproductive characteristics, assisted reproductive techniques such as in vitro maturation and in vitro fertilization have not been well-established compared with those of other mammals. Our recent work demonstrated the interplay between in vitro oviductal cell-derived extracellular vesicles (OC-EVs) and cumulus-oocyte complexes in dogs. Here, we provided for the first time a comprehensive proteomic analysis of OC-EVs. A total of 398 proteins were identified in all OC-EVs samples. A functional enrichment analysis indicated that these core proteins were involved in the key cellular metabolic process related to oocyte maturation and embryonic development. The current comprehensive description of the canine OC-EVs proteome would provide a fundamental resource for further understanding canine reproductive physiology, the interaction of sperms with female counterparts during fertilization, early pregnancy, and establishing an efficient system of in vitro embryo production. Dogs (Canis lupus familiaris) have unique and peculiar reproductive characteristics. While the interplay between in vitro oviductal cell-derived extracellular vesicles (OC-EVs) and cumulus-oocyte complexes in dogs has begun to be elucidated, no study has yet provided extensive information on the biological content and physiological function of OC-EVs and their role in canine oocyte development. Here, we aimed to provide the first comprehensive proteomic analysis of OC-EVs. We identified 398 proteins as present in all OC-EVs samples. The functional enrichment analysis using Gene Ontology terms and an Ingenuity Pathway Analysis revealed that the identified proteins were involved in several cellular metabolic processes, including translation, synthesis, expression, and protein metabolism. Notably, the proteins were also involved in critical canonical pathways with essential functions in oocyte and embryo development, such as ERK/MAPK, EIF2, PI3K/AKT, and mTOR signaling. These data would be an important resource for studying canine reproductive physiology and establishing a successful in vitro embryo production system in dogs. [ABSTRACT FROM AUTHOR]