Passage
Domestic pigs have been used as valuable preclinical models for scientific research due to their numerous anatomical, developmental, and physiological similarities to humans. For example, oogenesis and embryonic development in pigs are remarkably similar to the human processes and have facilitated the study of impaired fertilization due to decreased oocyte competence (quality) .Researchers have hypothesized that early termination of embryo development can arise from low mitochondrial DNA (mtDNA) copy number. Because mtDNA replication and reduction events have been extensively mapped in pigs, oocytes and sperm were isolated from their respective porcine gonads to test this hypothesis.Experiment 1To evaluate the developmental competence of porcine oocytes, researchers first measured the activity of glucose-6-phosphate dehydrogenase (G6PD) , an enzyme that is downregulated as the oocyte matures. The oocytes were stained with Brilliant Cresyl Blue (BCB) , a nontoxic blue dye that is converted to a colorless compound by G6PD. After 90 minutes of staining, oocytes were divided into two groups: one contained oocytes with colorless cytoplasm (BCB⁻) and the other contained oocytes with blue cytoplasm (BCB⁺) . Gene expression profiles were compared to evaluate the number of oocytes in the BCB⁺ and BCB⁻ groups that had developed to metaphase II.Experiment 2BCB⁺ and BCB⁻ oocytes underwent in vitro fertilization (IVF) , intracytoplasmic sperm injection (ICSI) , or supplementation with homogeneous mitochondria and ICSI (mICSI) . During IVF, an isolated oocyte was placed in a well plate and incubated with sperm at 39 C for 4 hours. In ICSI, a single sperm was selected and injected directly into the oocyte.Table 1 Developmental Rates for BCB⁺ and BCB⁻ Oocytes Fertilized Subjected to IVF, ICSI, or mICSI
Adapted from Cagnone GL, Tsai TS, Makanji Y, et al. Sci Rep. 2016;6:23229.
-What conclusions can be made about the production of blastocysts by the fertilization methods shown in Table 1?

Question

Passage
Domestic pigs have been used as valuable preclinical models for scientific research due to their numerous anatomical, developmental, and physiological similarities to humans. For example, oogenesis and embryonic development in pigs are remarkably similar to the human processes and have facilitated the study of impaired fertilization due to decreased oocyte competence (quality) .Researchers have hypothesized that early termination of embryo development can arise from low mitochondrial DNA (mtDNA) copy number. Because mtDNA replication and reduction events have been extensively mapped in pigs, oocytes and sperm were isolated from their respective porcine gonads to test this hypothesis.Experiment 1To evaluate the developmental competence of porcine oocytes, researchers first measured the activity of glucose-6-phosphate dehydrogenase (G6PD) , an enzyme that is downregulated as the oocyte matures. The oocytes were stained with Brilliant Cresyl Blue (BCB) , a nontoxic blue dye that is converted to a colorless compound by G6PD. After 90 minutes of staining, oocytes were divided into two groups: one contained oocytes with colorless cytoplasm (BCB⁻) and the other contained oocytes with blue cytoplasm (BCB⁺) . Gene expression profiles were compared to evaluate the number of oocytes in the BCB⁺ and BCB⁻ groups that had developed to metaphase II.Experiment 2BCB⁺ and BCB⁻ oocytes underwent in vitro fertilization (IVF) , intracytoplasmic sperm injection (ICSI) , or supplementation with homogeneous mitochondria and ICSI (mICSI) . During IVF, an isolated oocyte was placed in a well plate and incubated with sperm at 39 C for 4 hours. In ICSI, a single sperm was selected and injected directly into the oocyte.Table 1 Developmental Rates for BCB⁺ and BCB⁻ Oocytes Fertilized Subjected to IVF, ICSI, or mICSI

Adapted from Cagnone GL, Tsai TS, Makanji Y, et al. Sci Rep. 2016;6:23229.
-What conclusions can be made about the production of blastocysts by the fertilization methods shown in Table 1?

Quizplus · Accepted Answer

11ecba2d_0fc9_f13c_a3bf_7bd166a8b991_MD0008_00 In this experiment, oocytes with colorless cytoplasm (BCB⁻) were separated from oocytes with blue cytoplasm (BCB⁺). Both groups of oocytes were subjected to three different fertilization techniques: IVF (live sperm cells were added to a dish containing an oocyte), ICSI (sperm cells were injected into the oocytes directly), and mICSI (oocytes were supplemented with mitochondria and then underwent ICSI). The researchers then measured the success of the fertilization techniques used for each oocyte group by assessing zygote to blastocyst progression. In Table 1, the column showing oocytes fertilized indicates the percentage of oocytes in each trial that were successfully fertilized. The column indicating which zygotes progressed to the blastocyst stage gives the percentage of oocytes that were successfully fertilized and progressed to the blastocyst stage, a measure of early zygote development. In the BCB⁻ group, only ~11% and ~18% of oocytes fertilized by IVF and ICSI made it to the blastocyst stage, respectively. However, once BCB⁻ oocytes were supplemented with mitochondria during mICSI, the fertilization rate increased to ~36%. These results signify that mICSI yields higher rates of zygote development than both IVF and ICSI in the BCB⁻ oocytes group. (Choice A) ICSI is more effective than IVF because it has higher percentages of fertilization success and blastocyst development in both BCB⁺ and BCB⁻ groups. (Choice B) Oocytes (not blastocysts) were supplemented with mitochondria prior to ICSI, not IVF. The passage makes no mention of mitochondrial incorporation in combination with IVF treatment. However, this should have been done to ensure the experiment had improved validity when comparing fertilization methods. (Choice C) The passage provides no information on the fate of blastocysts that continue development. Therefore, the data do not support any statement about the viability of blastocysts produced after fertilization. Educational objective: Following fertilization, the mammalian zygote undergoes cleavage (successive mitotic cell divisions) and forms the blastocyst, a hollow ball of cells that implants into the uterine wall.