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The union of male and female gametes creates offspring. The production of these vital reproductive cells occurs in the testis and the ovary during spermatogenesis and oogenesis, respectively.[1] The primary male reproductive organs, the testes, are located in the scrotum and produce sperm cells and the primary male hormone, testosterone. As mentioned above, spermatogenesis is the process by which sperm cells are produced; germ cells give rise to haploid spermatozoa. Sperm production takes place inside the seminiferous tubules, which are a convoluted cluster of tubes located inside the testes. Testosterone is produced by Leydig cells, which surround the seminiferous tubules. After being formed, sperm cells travel outside of the tubules into the epididymis, where they mature and prepare for ejaculation. The complex process of spermatogenesis occurs in 3 steps. The first step involves mitotic cell division, which allows the early cell stage, spermatogonia, to multiply. The second step requires meiosis, in which the diploid cells form haploid cells. A division occurs until a round spermatid formation occurs. The final stage of spermatogenesis includes the production of mature, motile sperm cells from round spermatids through a process called spermiogenesis.[2] Diminished fertility or infertility may result from a decrease in spermatozoa number, alteration in shape, and inefficient motility.[3] The 3 steps represent the foundation of spermatogenesis. Functional abnormalities may occur in any of them, leading to the entire process failing. These abnormalities can lead to defective or reduced sperm production. In more severe conditions, a complete absence of spermatozoa can result, leading to infertility. Therefore, we must expand our knowledge of spermatogenesis as a whole to provide essential information regarding the regulatory mechanisms. The testicular environment is complex; therefore, studying spermatogenesis can be quite tricky in most species. To achieve this understanding, experimental studies completed in rodents and primates are the cornerstone of this crucial knowledge.[2]

Occasionally, the seminiferous tubules may contain tumor cells in the basal compartment rather than healthy spermatogonia. They can be seen on histological sections, differing from spermatogonia due to their noticeably larger size, prominent nucleolus, increased glycogen content, and characteristic peripheral border. The presence of these neoplastic cells contributes to carcinoma in situ and can lead to hypospermatogenesis. Carcinomatous cells characterize the stem cell population in many, if not most, germ cell tumors. Examples include seminomatous and teratomatous tumor types. During active spermatogenesis, the tubules may give rise to sporadic tumor cells. However, spermatogenesis ceases as the cancer cells increase in number, leading to detachment of the remaining spermatogonia, which then enter the tubular lumen. As cancer cells proliferate, they are eventually released into the tubular lumen or penetrate the lamina propria of the seminiferous tubules, forming intertubular tumor cell clusters.[3] PLAP, which is placental-like alkaline phosphatase, is an immunohistochemical marker used to diagnose preinvasive carcinoma in situ. It is manifested exclusively in these carcinoma-in-situ cells. A score-count system evaluates the histology of cancer cells and other techniques used to assess protein and mRNA expression. Testicular biopsies are also recommended and should be completed in specialist centers.[8] Meiosis is a convoluted process that is vulnerable to many faults and defects. Apoptotic spermatocytes can arise in the process and are known to be frequent. Megalospermatocytes, which are very large spermatocytes, can sometimes appear. In these cells, homologous chromosomes fail to pair in a process called asynapsis, causing the cells to become abortive. Moreover, spermatogenesis can halt at the primary spermatocyte stage, preventing morphological changes in the cells. Primary spermatocytes are seen to border the lumen of seminiferous tubules. They do not develop further, leading to cell disintegration and a failure to produce spermatids.[3]

Meiosis is a convoluted process that is vulnerable to many faults and defects. Apoptotic spermatocytes can arise in the process and are known to be frequent. Megalospermatocytes, which are very large spermatocytes, can sometimes appear. In these cells, homologous chromosomes fail to pair in a process called asynapsis, causing the cells to become abortive. Moreover, spermatogenesis can halt at the primary spermatocyte stage, preventing morphological changes in the cells. Primary spermatocytes are seen to border the lumen of seminiferous tubules. They do not develop further, leading to cell disintegration and a failure to produce spermatids.[3] The structure of the sperm tail closely resembles the motile cilium in that the axoneme has a 9+2 microtubular arrangement. Therefore, genetic defects detected in motile cilia can significantly affect the formation of the sperm tail. A genetic disease called PCD (primary ciliary dyskinesia), due to the malformation of motile cilia, causes pulmonary disease, increased risk of infections, and male infertility. Many genes are associated with PCD; however, the exact effects of mutations in these genes on spermatogenesis remain under investigation.[9] A study using testicular histology to determine the effects of aging on spermatogenesis revealed various alterations, including basal membrane thickening, decreased germinal and Sertoli cell numbers, and individual variation. Upon examination of post-meiotic cells, the aneuploidy rate was higher than average during the arrest of spermiogenesis. However, they concluded that spermatogenesis could still be possible until the male is 95 years old.[10]