ORIGINAL RESEARCH
Exploration of the femtosecond laser pulse thermal effects on the mouse embryos during the assisted hatching procedure
1 Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
2 Joint Institute for High Temperatures of the Russian Academy of Sciences, Moscow, Russia
Correspondence should be addressed: Marina V. Kubekina
Vavilova, 34/5, 119334, Moscow, Russia; moc.liamg@ymukyram
Funding: the procedures involving manipulating embryos using a laser and assessment of expression of the genes responsible for synthesis of heat shock proteins were supported by RSF (project 23-19-00424) and conducted using the equipment of the UNU "Laser Terawatt Femtosecond Complex", which was a part of the Center for Collective Usage "Laser Femtosecond Complex" of the Joint Institute for High Temperatures RAS. The procedures to acquire embryos were supported by the UNU “Transgenbank” grant (№ 075-15-2021-668 of July 29, 2021).
Author contribution: Kubekina MV — immunofluorescence staining and assessment of the heat shock protein expression levels, manuscript writing; Filatov MA — handling embryos, statistical processing, manuscript writing; Silaeva YuYu — general management of the experiment; Sitnikov DS — laser miscrosurgery, data processing, manuscript writing; all authors — discussion and manuscript editing.
Compliance with ethical standards: the study was approved by the Ethics Committee of the Institute of Gene Biology RAS (protocol № 1 dated 25 September 2023) and conducted in strict compliance with the provisions of the Directive 2010/63/EU of the European Parliament and of the Council of 22 September 2010 on the protection of animals used for scientific purposes.
Impaired hatching of the embryo from the zona pellucida (ZP), the specialized protective shell, immediately before implantation is one of the factors of infertility. Hatching impairment is often due to the ZP hardening or thickening. In such cases, the laser assisted hatching procedure is used to overcome infertility. During this procedure a hole is drilled in the ZP facilitating the embryo release. The question of the safe use of laser for assisted hatching remains open, since laser beam can heat the environment and cause thermal shock in embryos. The study was aimed to assess safety of the mouse embryo femtosecond laser exposure during the assisted hatching procedure using the embryo viability and HSP gene expression assessment methods. A new type of pulsed laser was used in the study for the ZP dissection — the femtosecond laser. The energy of such pulses was two orders of magnitude lower than the energy of laser dissectors currently used in the clinics. To assess the femtosecond laser exposure to the embryo, the house mouse (Mus musculus) embryos were stained with fluorescence dyes, and expression of the genes encoding heat shock proteins (Hsp90aa1 and Hspa5) was assessed. The embryonic cells remained viable after the laser assisted hatching procedure involving the use of a femtosecond laser, while expression levels of the genes encoding heat shock proteins were slightly increased compared to the negative control group (p = 0.408).
Keywords: heat shock proteins, blastocyst, laser assisted hatching, femtosecond laser pulses, embryo, mouse, zona pellucida