Spermatozoa: one of the reasons for our existence

Louis du Gardin, in 1623, hypothesized the sperm cells as “fertilizing particles” (Holstein, 2009). In 1677, Leeuwenhoek proposed the sperm cell formally known as “animalcules” penetrates the female eggs. However, the discovery was not published. Huygens observed a tiny animal in semen samples; afterward, Nicolas confirmed a tadpole-like organism in cockerel’s semen. As Huygens and Nicolas acknowledged the work of Leeuwenhoek in a letter to the Royal Society, hence, Leeuwenhoek was equally credited for the discovery (Pitnick et al., 2008).

SPERM CELL ANATOMY: A MASTERPIECE OF NATURAL CELLULAR ENGINEERING

Sperm cell comprises chiefly three elements including head, midpiece, and flagella. Each element has unique executions in the fertilization process.

Head of sperm cell

Head encompasses the essential genomes in tightly bind elliptical morphology (~ [4–6 um] major and ~3 minor axis). The head also contained a crescent shape organelle denoted as an acrosome, which contains enzymes and receptors and its interaction with follicular fluid (FF) induces chemo-kinesis (Ralt et al., 1994) and chemotaxis (Guidobaldi et al., 2017).

Midpiece of sperm cell

The midpiece of the sperm cell contains an axoneme at the center diffused in internal fibers and surrounded by an array of mitochondria that actualizes the energy transfer for flagellar swimming (Mao et al., 2013).

Sperm flagella

Sperm flagellum is a significant component in male DNA transportation towards female oocytes. Sperm flagellum drives the physiological basics of sperm motility and energetics alike cilia in many eukaryotic cells (Inaba, 2003). Flagella comprises the motor proteins which induce the motility of the sperm cell. The motile machinery of sperm cell is activated through a synergistic interplay of cytoskeleton and motor proteins accompanying other supplementary molecules. The sperm flagellum includes the outer coarse fibers, which embeds the 9 doublet microtubules with dynein arms steering clockwise, the radial spokes are the cytoskeletal proteins that establish the synergies between the outer and 2 central microtubules for the proper beating of the filaments (9+2 arrangement) (Inaba, 2003; Lindemann and Lesich, 2016; Nicastro et al., 2006; Porter and Sale, 2000; Sironen et al., 2020).

Male infertility

The morphological or functionality deficiencies of the sperm elements leads to male infertility. The modern-day lifestyle including nicotine (Lotti et al., 2015) and alcohol consumption (Vellani et al., 2013), anxiety (Vellani et al., 2013), and obesity (Sermondade et al., 2013) also influence male reproductive health. click here to see sperm cell anatomy

References

Inaba, K., 2003. Molecular Architecture of the Sperm Flagella: Molecules for Motility and Signaling. Zoolog. Sci. https://doi.org/10.2108/zsj.20.1043

Shiva K Shukla is H2020 MSCA IF Fellow at Cherry Biotech. Dr. Shukla's research aim is to facilitate lab-ready-solutions to human reproductive clinics.