In vitro production of canine blastocysts

Current knowledge in the biology of gametes and embryos from Carnivora

In addition to companion animals and laboratory species, about 270 carnivore species play fundamental ecological roles in different ecosystems. However, almost 40% of carnivore species are now threatened or endangered in the wild because of human activities. While protection of natural habitats is critical, it is equally important to better understand carnivore reproduction, including a solid knowledge in sperm, oocyte, and embryo biology, to maintain sustainable populations in the wild and in conservation breeding centers. Characterizing gamete and embryo biology is also needed to develop cryopreservation and assisted reproductive technologies to enhance conservation efforts. The objective of this review is to provide the most recent knowledge in the biology of sperm cells, oocytes, and early embryos across all carnivore families. Overall, most data originate from populations maintained in breeding centers or zoos. Characterizations of sperm biology and cryopreservation are far more advanced than for oocytes and embryos. Currently, sperm biology is mainly studied in Canids, Felids, Ursids, and Mustelids, with more emphasis on structural than functional properties. Importantly, fundamental studies of gamete and embryo biology in domestic dogs, cats, and ferrets have paved the way for more precise characterizations in wild counterparts as well as the development of cryopreservation and assisted reproductive technologies. A striking feature of spermatozoa across a wide range of Canids and Felids is the presence of teratospermia (>60% of abnormal sperm cells), which is related to the loss of genetic diversity in some populations. Although sperm structures differ across carnivore families, sperm biology remains difficult to compare because of the small amount of data in many species. Regarding oocyte biology and embryology, data are much scarcer than in sperm cells, with too few studies going beyond structural descriptions. More carnivore species and more individuals (especially from wild populations in addition to captive ones) must be studied to improve our understanding about comparative germplasm biology and develop adequate conservation breeding strategies including the use of cryobanking and assisted reproductive technologies.

First deliveries of felines by transcervical transfer of in vitro-cultured embryos

Transcervical transplantation of embryos has been wildly used in several species. However, it has not been successful in feline species because of their unique cervix structure combined with poor in vitro culture systems for embryos. In the present study, a simple device to guide the embryo transfer (ET) tube through the cervix and into the uterus was developed. To supply better blastocysts for ET, the in vitro culture system of feline embryos was also optimized. Results showed that 91.67 ± 4.17% of embryos developed to the blastocyst stage in QAU-4 medium compared with 49.17 ± 6.51% in KSOM medium. The total cell number of blastocysts reached 87.1 ± 22.1 in QAU-4 medium compared with 29.8 ± 2.1 in KSOM. Embryoid body formation was also observed in QAU-4 medium. Finally, by the improved technical scheme, CRX (Cone-Rod Homeobox) gene-edited kittens were successfully bred. To date, this is the first report, to our knowledge, of knockout kittens successfully delivered after transcervical ET with a simple transfer tube.

A diverse English keyword search reveals the value of scriptaid treatment for porcine embryo development following somatic cell nuclear transfer

CONTEXT

Incomplete epigenetic reprogramming of histone deacetylation (HDAC) is one of the main reasons for the low efficiency of somatic cell nuclear transfer (SCNT). Scriptaid is a synthetic HDAC inhibitor (HDACi) that may improve the efficiency of porcine SCNT.

AIMS

This study aimed to determine whether scriptaid increases the number of blastocyst cells or the cleavage rate.

METHODS

We conducted a meta-analysis of the pertinent literature published over the past decade.

KEY RESULTS

A total of 73 relevant papers were retrieved using a diverse English keyword search, and 11 articles were used for the meta-analysis. Scriptaid was positively correlated with blastocyst rate but had no effect on cleavage rate or blastocyst cell number. A subgroup analysis of blastocyst cell number showed that the staining method was the source of the heterogeneity.

CONCLUSIONS

In SCNT embryos, scriptaid treatment after activation can promote embryonic development, but there may be adverse effects on early development.

IMPLICATIONS

HDACi research should focus on SCNT birth efficiency.

Strategies to Improve the Efficiency of Somatic Cell Nuclear Transfer

Mammalian oocytes can reprogram differentiated somatic cells into a totipotent state through somatic cell nuclear transfer (SCNT), which is known as cloning. Although many mammalian species have been successfully cloned, the majority of cloned embryos failed to develop to term, resulting in the overall cloning efficiency being still low. There are many factors contributing to the cloning success. Aberrant epigenetic reprogramming is a major cause for the developmental failure of cloned embryos and abnormalities in the cloned offspring. Numerous research groups attempted multiple strategies to technically improve each step of the SCNT procedure and rescue abnormal epigenetic reprogramming by modulating DNA methylation and histone modifications, overexpression or repression of embryonic-related genes, etc. Here, we review the recent approaches for technical SCNT improvement and ameliorating epigenetic modifications in donor cells, oocytes, and cloned embryos in order to enhance cloning efficiency.