In vitro spermatogenesis as a method to bypass pre-meiotic or post-meiotic barriers blocking the spermatogenetic process: genetic and epigenetic implications in assisted reproductive technology

Abstract

Pregnancies achieved by assisted reproduction technologies and particularly by ooplasmic injections of either in vivo or in vitro generated immature male germ cells are susceptible to genetic risks inherent to the male population treated with assisted reproduction and additional risks inherent to these innovative procedures. The documented, as well as the theoretical risks, are discussed in this review. These risks represent mainly the consequences of genetic abnormalities underlying male infertility and may become stimulators for the development of novel approaches and applications in the treatment of infertility. Recent data suggest that techniques employed for in vitro spermatogenesis, male somatic cell haploidization, stem cell differentiation in vitro and assisted reproductive technology may also affect the epigenetic characteristics of the male gamete, the female gamete, or may have an impact on early embryogenesis. They may be also associated with an increased risk for genomic imprinting abnormalities. Production of haploid male gametes in vitro may not allow the male gamete to undergo all the genetic and epigenetic alterations that the male gamete normally undergoes during in vivo spermatogenesis.

Implications of epigenetics and genomic imprinting in assisted reproductive technologies

“…In azoospermic men, ART options may include injection of immature sperm into oocytes (e.g., round spermatid injection [ROSI], round spermatid nucleus injection [ROSNI], or secondary spermatocyte injection [SECSI]), or in vitro spermatogenesis and spermiogenesis (Yanagimachi, 2005;Georgiou et al, 2007). ROSI, ROSNI, and SECSI have had few successes in humans; therefore, it is not possible to adequately assess potential risks of these procedures to resultant offspring.…”

“…Indeed, in the mouse, embryos generated by ROSI displayed normal expression of six genes (three maternally expressed, three paternally expressed), indicating that spermatids have normal imprinting patterns (Shamanski et al, 1999). On the other hand, use of immature haploid gametes, either recovered from the testis or matured in vitro, for oocyte injection often results in embryos with chromosomal abnormalities, presumably due to inadequacies in the in vitro development culture system (Georgiou et al, 2007). Other anomalies which may occur with the use of in vitro matured sperm include: (1) unfavorable effects on the male generated centrosome, (2) lack of oocyte activating factors, and (3) alteration of the histone to protamine transition (Georgiou et al, 2007).…”

“…On the other hand, use of immature haploid gametes, either recovered from the testis or matured in vitro, for oocyte injection often results in embryos with chromosomal abnormalities, presumably due to inadequacies in the in vitro development culture system (Georgiou et al, 2007). Other anomalies which may occur with the use of in vitro matured sperm include: (1) unfavorable effects on the male generated centrosome, (2) lack of oocyte activating factors, and (3) alteration of the histone to protamine transition (Georgiou et al, 2007). In regard to the latter, any epigenetic modifications that would occur during in vivo spermatogenesis (e.g., histone to protamine transition or epigenetic reprogramming in the epididymis) may not proceed normally in vitro, thereby raising questions about the risk of LOI when using these techniques (Georgiou et al, 2007).…”

“…Other anomalies which may occur with the use of in vitro matured sperm include: (1) unfavorable effects on the male generated centrosome, (2) lack of oocyte activating factors, and (3) alteration of the histone to protamine transition (Georgiou et al, 2007). In regard to the latter, any epigenetic modifications that would occur during in vivo spermatogenesis (e.g., histone to protamine transition or epigenetic reprogramming in the epididymis) may not proceed normally in vitro, thereby raising questions about the risk of LOI when using these techniques (Georgiou et al, 2007).…”

“…Similarly, the injection of a male somatic nucleus into an oocyte may result in haploidization of the male nucleus by the oocyte cytoplasm, thereby restoring diploidy (Fulka et al, 2002). Yet, this too has its drawbacks (Georgiou et al, 2007). Alternatively, the generation of haploid gametes from cloned human embryonic stem cells offers yet another option for biological parentage.…”