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.
-All of the following findings in sperm would cause lower fertilization rates in IVF EXCEPT:

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.
-All of the following findings in sperm would cause lower fertilization rates in IVF EXCEPT:

Quizplus · Accepted Answer

11ecba2d_0fc7_ce5a_a3bf_abc4ee21b242_MD0008_00 A human sperm cell is divided into three segments: a head, a midpiece, and a tail (flagellum). The head contains an acrosome and the nucleus. The acrosome is a flattened structure that encapsulates the tip of the nucleus and is rich in lysosome-like enzymes specialized for piercing the outer shell of an oocyte during fertilization. The midpiece section is packed with mitochondria, essential organelles that produce the ATP required for flagellum-driven sperm motility. This section also contains a pair of central microtubules that are anchored to the cytoskeleton and extend down the length of the flagellum (tail region). The tail, or flagellum, is a singular elongated structure specialized for wavelike movements to propel sperm through a fluid environment. Flagellum-driven motility is derived from the action of ATP-dependent motor proteins that act on the central microtubules. In this experiment, in vitro fertilization (IVF) was used to introduce sperm cells into BCB⁻ and BCB⁺ oocytes. IVF involves introducing numerous sperm into a dish containing an oocyte. Fully developed sperm generally have little to nonexistent cytoplasm; therefore, reporting that the cytoplasm is reduced in sperm used for IVF would be a normal finding that is unlikely to impact fertilization rate. (Choice A) Microtubule dysfunction would likely result in failure of the sperm cell's flagellum. Lacking a functional flagellum would impair IVF because the sperm cell still needs to be able to swim to the oocyte to fertilize it. (Choice B) Mitochondria, the powerhouses of the cell, produce the majority of ATP used to propel the sperm cell to the oocyte. If the sperm cells used in IVF had a mitochondrial deficiency, they would not have sufficient energy (ATP) to swim to the oocyte, resulting in lower fertilization rates. (Choice D) Even fully motile sperm cells will remain trapped outside the oocyte if they lack the necessary acrosomal enzymes to break through the oocyte surface (ie, the corona radiata cells and zona pellucida). Misfolding of acrosomal enzymes would therefore present a major barrier to successful fertilization in IVF. Educational objective: A human sperm cell is composed of a head (contains the acrosome and nucleus), a midpiece (contains mitochondria that generate the ATP required for flagellum-driven sperm motility), and a tail (ie, the flagellum necessary for motility through a fluid environment).