Amit Kumar Kumar

Somatic Cell Nuclear Transfer (SCNT) is an essential process for cloning used in developmental and regenerative medicine. In the current investigation, there is a discussion about the mechanisms involved in genome replication, as well as the factors influencing clone development during SCNT. As a result of the analysis, it was found that cloned embryos have low developmental efficiency due to the insufficient epigenetic reprogramming, improper DNA methylation, problems with mitochondria, high oxidative stress, and insufficient activation of pluripotency genes. Comparing the SCNT embryos with the fertilized ones, there was a difference between the rate of developmental abnormalities and embryo survival. Moreover, the research suggests the possibility to use new techniques, including CRISPR-based epigenetic reprogramming, artificial intelligence-based monitoring of genomes, incorporation of stem cells, and artificial egg activation, to improve the cloning process. Despite some scientific achievements made within SCNT and related areas, many difficulties connected with ethics and biological aspects still do not allow to conduct human reproductive cloning. Therefore, the future research should concentrate only on therapeutic purposes of SCNT.

Conjoined twinning is a very rare congenital disorder that results from partial separation during the development of the embryos in cases of monozygotic twins. Male-female symmetrical conjoined twins with an opposite phenotype in relation to their biological sex are an extremely rare developmental abnormality due to the complications involved, from an embryological, genetic, hormonal, clinical, and ethical standpoint. In this review, we discuss the embryological causes of conjoined twinning, sexual differentiation processes, and the potential causes of discordant phenotypical sex development through chromosomal mosaicism, epigenetics, asymmetry of hormone distribution, or receptors. Furthermore, Disorders of Sex Development (DSD), prenatal diagnosis and molecular analyses, psychosocial impacts, surgery, and ethical issues related to sexual discordance among conjoined twins are evaluated. Our current scientific knowledge is limited since such cases are extremely rare.