Development of somatic cell nuclear transfer biotechnology for cloning of animals: a mini-review

ABSTRACT


INTRODUCTION
In general, several reproductive biotechnology techniques such as artificial insemination (AI), embryo transfer (ET), in vitro fertilization (IVF), and animal cloning (Ciptadi, 2007) can help preserve animals, one of which includes the cloning of the somatic cell nucleus transfer. Somatic Cell Nuclear Transfer (SCNT) cloning is important biotechnology evidence for the conservation of endangered wild animals and preventing the loss of genetic resources of a species (Fatira et al., 2019;Hajian et al., 2011;Holt et al., 2004) as well as for conservation efforts (preservation) of superior local livestock genetic resources (Ciptadi, 2007).
SCNT provides reprogramming somatic cells into totipotent embryos and generates viable animals, such as cloned amphibians and mammalians . To cloned one individual, must from the egg cells. First, must be removed nuclear of egg cells that would become a targeted cell. Then, the nuclear of the clone's egg cell passed towards targeted egg cell before (it doesn't have nuclear anything), it called by cloned egg cells. Cloned egg cells must be transferred to the uterus to develop the embryos. Some somatic cell has the chance to create clone embryos that totipotent specifically (Tajuddin et al., 2015).
SCNT techniques to reprogram somatic cells that have more benefits. Such as so many treatments during the process of nuclear transfer, the donor can be from any other types of somatic cells , the potential of targeted (cloned) egg cell can load all of the genetic resources. Besides, SCNT techniques also provide good livestock products with high genetic resources, so they can increase the productivity of agricultural products (Tajuddin et al., 2015). So, SCNT more potent than any other reproductive biotechnological technique.
Cloning is an organism that is genetically identical to one another (aggregates), either a group of cells, tissue, or an individual produced asexually (in vitro). Cloning can take the form of cloning of cells, tissues, or whole individuals (Tajuddin et al., 2015). Cloning can also be in the form of embryo cloning, which is obtained from the results of nucleus transfer donors that have the potential for applications in various fields, including medical, livestock production, and conservation of threatened wildlife. The success of animal cloning began with the cloning of Dolly's sheep, a clone resulting from the transfer of somatic cell nuclei to each other. Since then, several animals, such as livestock, rats, pigs, and goats, have been cloned (Ciptadi, 2007;Rojas et al., 2005).
The large numbers of publications that show the success of animal cloning for various purposes, as well as the development of animal cloning methods, make it necessary to compare any existing research to provide an evaluation of the success of animal cloning methods. The success of animal cloning depends on the treatment given before, during, and after the cloning process. Based on the study of existing literature, this paper will attempt to review the results of successful and limited animal cloning research on the needs of non-threatened (livestock and wild animals) and threatened wildlife.

METHODS
This research was a kind of literature review. The research method refers to Putri et al. (2018), consists of several stages which are carried out comprehensively. These stages are carried out to get the results of an in-depth review based on the selected articles. The flow diagram of this research is described in more detail in Figure 1. The research flow begins with a literature study of the Scopus indexed journals, Google Scholar, and we get 50 articles. These articles are based on further searches based on the keywords in each article. The search was limited to the keywords "cloning; somatic cell nuclear transfer; animal cloning". Subsequent searches identify titles that match the scope of the minireview in this article. Identify the title in terms of the keywords for each article chosen. Of the 50 articles, the titles identified for further stages were carried out based on the suitability of the title with the topic of cloning reproduction biotechnology with the SCNT method.
After the appropriate article titles are selected, screening for each selected title is based on the abstract to obtain 20 suitable articles. The abstract of each article becomes a detailed description of the article's discussion. The selected abstract was adapted to the purpose of writing this mini-review, which discusses the success of animal cloning using the SCNT method from time to time. The next step is to read the full text of each article and a mini-review process. These 20 articles have gone through comprehensive stages in their selection. Limitation of the scope of discussion in this mini-review had done by selecting the article that has the recent coverage of the success of animal cloning by the SCNT method. This mini-review article only discusses briefly the various previous studies (20 articles) related to the success of animal cloning using the SCNT method, but it would be better to understand that each article that is made into a mini-review can be searched for the article in question and then carried out full-text reading for a thorough understanding of the article.

Successfully Animal Cloned
a. Importance of SCNT Cloning Somatic cell nuclear transfer (SCNT) has a major role in animal reproduction biotechnology, namely as a reproductive biotechnology method that can increase livestock yields (Selokar et al., 2019), bio-conservation strategies for endangered animals, critically endangered animals, and safeguarding animal genetic resources (Fatira et al., 2019;Hajian et al., 2011). SCNT is carried out in several mammals. With the help of reproductive technology, genetic copies are obtained from individual single somatic cell donors. SCNT can be done to maintain the genetics of an existing species and epigenetically (Ogura, 2020).
Reproductive cloning, the production of identical offspring through SCNT, can save endangered wildlife species. Cloning of endangered mammals, including species with external embryonic development, is possible (Holt et al., 2004). Cloning of differentiated SCNT to previously enucleated oocytes is a promising technique for producing cloned embryos with high genetic value (Rojas et al., 2005).

b. Evidence of the Success of SCNT Cloning Technique
A suitable SCNT cloning technique can produce embryos from endangered species. Huemul is a native Andean deer that has been declared as an endangered species, has great patrimonial value, and is Chile's national emblem. The use of assisted reproductive and procreation biotechnology can assist conservation programs oriented towards protecting endangered species of deer (Rojas et al., 2005).
Cloning with SCNT can be intraspecific and interspecific (iSCNT; interspecific Somatic Cell Nuclear Transfer) for the conservation of wild mammals' biodiversity of germplasm; nuclei cell reprogrammed to produce cells induced by pluripotent cells. Many wild mammals are cloned, but due to the difficulty of obtaining cytoplasmic (or cytoplasm) donor cells, it becomes a major problem in the cloning process. Donor cell nuclei (karyoplast) are obtained from the skin of live or post-mortem individuals, then stored in somatic cell banks. Cloning of different species, such as wild carnivores and ungulates, can be successful through the iSCNT technique even though it is not easy (Borges & Pereira, 2019).

Development of Cloned Animals
Since Dolly cloned, the first cloned mature animal in 1996 from 6 years old mammary gland cell Finn Dorset (white sheep) in lowest nutrition medium, so the cell stopped divided, research of cloned animals has increased. We provide the successfully cloned animals with authors, years, and results. It can be seen in Table 1.

a.Cow
Researchers have successfully cloned farm animals such as Anatolian Gray's endemic cow cloning, according to Arat et al. (2011) using different types of donor cells (fibroblasts, cartilage, and granulosa cells) cryopreserved in a gene bank and oocytes aspirated from the ovaries of Holstein Cows as the source of the recipient cytoplasm. The cloning results consisted of one male from fibroblasts, three females from granulosa cells, and one female from the cloned cartilage cells, which were born healthy with normal birth weight. No calf is lethal after birth. The results showed that the cloned calves had the same microsatellite alleles in 11 loci with their nucleus cell donors. However, the mtDNA from five cloned calves Anatolian Gray had a different haplotype from the donor cells, and mtDNA heteroplasmy could not be detected in any of the clones. The birth of healthy clones indicated that haplotype differences between the cells and the donor oocytes did not affect development before or after implantation of SCNT-derived embryos. This study proves that the Anatolian Gray Cattle, which is a critically endangered species, can be preserved (Arat et al., 2011).
According to Ciptadi (2007), for the successful birth of a B. taurus bull male, which was the result of iSCNT cloning on B. taurus cow oocyte gaur, which was transferred to the recipient broodstock of domestic cattle. The production method of embryo cloning using somatic cell donors in various livestock species was reconstituted using mammary gland somatic cell donors and fetal fibroblast epithelial cells. One of the advantages of this technology is that it can be used to implement genome resource banks, which are very useful for conserving the genetic diversity of endangered animal species or accelerate the improvement of the genetic quality of superior livestock (Ciptadi, 2007). Cloning of 15 cattle (10 females, 5 males) was also successfully carried out (Dantas et al., 2020).
According to Wells et al. (1999), they have cloned Friesian dairy cows with high livestock genetic resources. The SCNT technique uses mural granulosa cells, which are totipotent. This cloning succeeded in producing ten calves performed by cesarean section, and all of them survived. After the transfer of 16 chronographed blastocysts, embryo survival was monitored at day 60 by 38%. DNA analysis said the calves were genetically identical to the donor cattle. Missed chances of survival during pregnancy may be due to placental dysfunction at some stage. Further research is needed to modify specific genetics for biomedical or livestock purposes (Wells et al., 1999).
b. Goat Deng et al. (2020) cloned goat embryos with control of DNA and histone methylation. The cloned goat embryo is still in the development stage to become an individual born whole and normal. It is necessary to further develop this research to produce cloned filial (small goats) that are intact and can survive.
c. Pig Boquest et al. (2002) report successfully cloning piglets from fetal fibroblast cells that have been cultured in liquid nitrogen for two years by inducing the donor cell nucleus to the oocyte cytoplasm for approximately three days before chemical activation. The cultured fibroblast cells were mixed in a calcium-free medium to become enucleated oocytes excreted from superovulation. This research focuses on the presence of the α(1,3)-galactosyltransferase gene, which can be used for transplantation in humans in the future.
d. Sheep Hajian et al. (2011) explained that in vitro ripened and enucleated oocytes in domestic sheep can be used to clone the Esfahan mouflon Ovis orientalis isphahanica, which is vulnerable to extinction. Cryofibroblast deflected from the mouflon (derived from the genome bank), and domestic sheep were prepared and cultured in vitro and used as a karyotype. The somatic cells used from Ovis orientalis isphahanica and domestic sheep have been frozen for two years. The freezone SCNT technique used domestic sheep oocytes ripened and enucleated in vitro induced by donor nuclei Ovis orientalis isphahanica and domestic sheep nuclei cells. The cloned blastocyst of Ovis orientalis isphahanica was then transferred into the uterus of a domestic sheep by dissection (Hajian et al., 2011). The cloned sheep need to be considered for their health. Since the incident of Dolly's sheep, it is important to pay attention to monitoring the health of sheep; such as Sinclair et al. (2016) conducted research related to musculoskeletal monitoring, metabolic tests, and blood pressure of 13 cloned sheep aged 7-9 years, including four from Dolly's lineage.

e. Bull
The cloning of Murrah's superior bull, which is a very high value in livestock production, was successfully carried out through the SCNT technique. Donor cells were derived from a tail skin biopsy and seminal plasma. Development, hematology, plasma biochemistry, and reproductive organs are all normal and intact (Selokar et al., 2019). The transgenic Bubalus bubalis cloning was also successfully carried out using the SCNT technique, according to Lu et al. (2018). f

. Dog and Cat
The birth of the world's first cloned dog, Snuppy, was a huge success in mammal cloning. This study succeeded in giving birth to 3 puppies cloned Snuppy by SCNT from ASCs (adiposederived mesenchymal stem cells) (Kim et al., 2017). Also, cat cloning was successfully by Song et al. (2019) on an SCNT basis. Cytoplasm injection (CICT; cytoplasm injection cloning technology) is performed to develop cloned embryos in vitro.
g. Mice (Mouse) According to Ogura (2020), it was related to mouse cloning by SCNT using female nucleus cell donor B6D2F1-female. Somatic cell donors can come from different cell types and different genotypes. In contrast, Riaz et al. (2011) managed to clone a mouse from a fertilized egg. The cell nuclei were reprogrammed then cultured in vitro and in vivo after transferring chromosomes from embryonic stem cells into tetraploid mouse embryos. The SCNT cloned mice had normal chromosomes and intact genome composition. The possibility to improve the quality of cloned mice with the SCNT technique has been developed and is very useful for biomedical research purposes as an experimental animal (Ogura, 2020). Song et al. (2020) cloned mouse embryos by reprogramming the cloned embryos' cytoplasmic volume. Cytoplasm injection (CICT; cytoplasm injection cloning technology) was developed to increase reprogramming of the SCNT.
h. Fish Cloning primitive Russian sturgeon fish, Acipenser gueldenstaedtii, could save this endangered species. Fatira et al. (2019) tried to clone the primitive fish Acipenser gueldenstaedtii by SCNT with multiple donor somatic cells and the Acipenser ruthenus sterlet as recipient nonenucleated egg cells. Injection of multiple donor somatic cells into single manipulated cells (reprogramming) can promote embryonic development. In the future, similar engineering experiments can save endangered species (Fatira et al., 2019). The cloning of Paralichthys olivaceus, a kind of fish, has also been done by Hou et al. (2016); cloning comes from the induction of meioginogenesis in eggs from homozygous diploid mitoginogenesis. When the clones reached their peak maturity of the gonads, meioginogenesis was re-inducted to produce a second-generation cloning group of Paralichthys olivaceus. After three months, 611 individuals survived.
Besides, the various negative implications that may arise in the development of cloning using the SCNT technique include: 1) cloning can be used to create dominant groups or certain races through the selection of individuals with desired traits. Morally, this is still contradictory; 2) on a large scale, it is possible to reduce genetic diversity; 3) cloned results are susceptible to disease; 4) cloning is possible to shorten the life expectancy of the individual clone; 5) religiously, some people still believe how the cloned zygote is from the "soul" side (Tajuddin et al., 2015). Various studies related to ethics may need to be carried out to discuss the positives and negatives of this SCNT cloning process. On the other hand, the development of SCNT can be a breakthrough for animal husbandry and rescue endangered wild animals.

CONCLUSIONS
Based on the discussion above, it can be concluded that the results of SCNT biotechnology for animal cloning can be used for the preservation of wild animal germplasm genetic resources, increasing the production of superior livestock, and ways of conserving threatened animals. Various suitable and purposeful SCNT methods have had a high success rate in animal cloning