Microinsemination and Nuclear Transfer with Male Germ Cells

Abstract

This chapter focuses on microinsemination techniques using spermatozoa, spermatids, and spermatocytes, and on nuclear transfer techniques using male primordial germ cells. Microinsemination generally refers to intracytoplasmic sperm injection (ICSI) in which a sperm cell is injected directly into the cytoplasm of an oocyte, although it also includes techniques such as partial zona dissection and subzonal insemination that aid the passage of spermatozoa through the zona pellucida. Various types of male germ cells, from primordial germ cells in fetal gonads to spermatozoa in adult testes, can participate in the formation of early embryos after microinsemination or nuclear transfer. Microinsemination with mature spermatozoa has already been successful in several mammalian species, including humans. Microinsemination with round spermatids leads to normal births in mice, rabbits, and humans. Moreover, in mice, secondary and primary spermatocytes also support full-term development after incorporation into immature or mature oocytes. Nuclear transfer using mouse primordial germ cells from male fetal gonads during days 12.5 to 16.5 of pregnancy produces cloned fetuses that arrest their development on day 10, probably due to erasure of the parental memory of imprinted genes. The fetal development is highly dependent on the expression of imprinted genes from the correct parental alleles. A bovine embryo produced from the male germ cells of a 52-day-old fetus reportedly developed into a normal calf, although it died of respiratory failure within 24 hours of its birth.