A spermatogonium (plural: spermatogonia) is an undifferentiated male germ cell. Spermatogonia undergo spermatogenesis to form mature spermatozoa in the seminiferous tubules of the testicles.

Subtypes

Spermatogonia are often classified into different types depending on their stage in the differentiation process. In humans and most mammals, spermatogonia are divided into two types, A and B, but this can differ for other organisms.

There are three subtypes of spermatogonia in humans:

  • Type A (dark) cells, with dark nuclei. These cells are reserve spermatogonial stem cells which do not usually undergo active mitosis.
  • Type A (pale) cells, with pale nuclei. These are the spermatogonial stem cells that undergo active mitosis. These cells divide to produce Type B cells.
  • Type B cells, which undergo growth and become primary spermatocytes.

These 3 different subtypes get distinguished based on nuclear morphology: A<sub>dark</sub> has a homogeneously dense, deeply stained chromatin with at least one chromatin-free cavity, occasionally presenting nuclear rarefraction zones. A<sub>pale</sub> have a less dense chromatin, while type B spermatogonia can be recognized by nucleolar localization, their position to the basement membrane and the presence of several flakes or granules.

Spermatogenesis

Spermatogenesis is the process in which sperm cells are produced and formed into mature spermatozoa from spermatogonia. Males mature spermatozoa (sperm) are produced to later join with a female oocyte (egg) to create offspring. Throughout the process of spermatogenesis, there are many different parts of the male anatomy, accessory organs, and hormones. However, spermatogenesis can be broken down in the following steps, which are initiated at the start of puberty:

  • Spermatogenesis occurs in the germinal epithelium of the seminiferous tubules. Spermatogonia undergo meiosis to produce spermatids that later mature into spermatozoa. The spermatogonia duplicate their DNA to obtain 46 chromosomes in preparation for the primary division. At this stage, the germ cells are now referred to as primary spermatocytes.
  • The primary spermatocytes undergo a primary division, yielding two secondary spermatocytes each with 23 chromatids. The secondary spermatocytes then undergo a second division to produce two spermatids, each with 23 chromosomes.
  • Follicle-stimulating hormone (FSH): FSH is in charge of stimulating Sertoli cells with testosterone to produce regulatory molecules and nutrients needed for the cells. The nutrients are a needed factor for the maintenance of spermatogenesis.
  • Luteinizing hormone (LH): LH stimulates Leydig cells to produce testosterone.

Sperm structure

The overall structure of spermatozoa is very specialized as the cell has fully differentiated and matured. As spermatozoa, the cell no longer undergoes division. It consists of a head, midpiece, and flagella tail for motility.

  • Head: As the head of the sperm, it is an ovular shape consisting of the nucleus and the acrosome.

Diseases that cause infertility

There are many diseases and causes of infertility experienced in males.

  • Cystic fibrosis
  • Cystic fibrosis is a genetic condition that changes proteins in the body. It causes mucus to become thick and sticky leading to blockages and damage as it builds up.
  • The vast majority of Men with cystic fibrosis suffer from infertility issues. The main cause of infertility is due to obstructive azoospermia (OA). OA is a condition where there is a blockage in a male's reproductive tract, resulting in a lack of sperm in a male's ejaculate. This is mostly due to an absence of the vas deferens, which is thought to be caused by CFTR mutations. In most males with CF, spermatogenesis does occur, but the males have a lower ejaculate volume.
  • Klinefelter syndrome
  • Klinefelter syndrome is the most common chromosomal abnormality associated with male infertility. Klinefelter's is due to a trisomy of XXY on the 23rd chromosome, giving males an extra X chromosome. The cause of infertility is related to the replacement of normal testicular architecture with tubular atrophy, sclerosis, or maturation arrest, which degenerates into fibrosis.

Cystic fibrosis and Klinefelter syndrome are just two examples of ways diseases and genetic mutations can lead to infertility in men.

Anticancer drugs

Anticancer drugs such as doxorubicin and vincristine can adversely affect male fertility by damaging the DNA of proliferative spermatogonial stem cells. Experimental exposure of rat undifferentiated spermatogonia to doxorubicin and vincristine indicated that these cells are able to respond to DNA damage by increasing their expression of DNA repair genes, and that this response likely partially prevents DNA break accumulation. In addition to a DNA repair response, exposure of spermatogonia to doxorubicin can also induce programmed cell death (apoptosis).

Additional images

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File:Gray1150.png|Transverse section of a tubule of the testis of a rat. X 250.

File:Spermatocytogenesis.png|Schematic diagram of Spermatocytogenesis Wandimu Geneti

</gallery>

See also

  • List of distinct cell types in the adult human body

References