FELLOWSHIP IN EMBRYOLOGY IN INDIA: SPERMATOGENESIS

Fellowship in Embryology in India: Spermatogenesis

Fellowship in Embryology in India: Spermatogenesis

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Sperm is a unique cell having a specialized ability to migrate through the female genital tract and fertilize the egg, carry genetic material for zygote formation, and carry centrosome to enable cell division. What exactly happens and how are the, mitotic divisions, meiotic divisions, and how does the, the spermatogenesis happens, and how many days does it take for the entire process? We’ll know about this in the article.

Spermatogenesis is a process wherein the metro sperm from the spermatogonia, the mature sperm is being formed. The entire process takes about sixty-four days. And, how is it being divided? The process of proliferation and differentiation takes place of the male germ cells within the seminiferous tubules. What exactly happens?

There is mitotic division, which is happening - that is meiosis one and meiosis two, which has been taking place, and metamorphic, changes wherein, the spermatid undergoes some changes with respect to the nucleus, Golgi complex, centrioles to form the mature spermatozoa, which is ready to fertilize an egg. The purpose is to produce mature sperms, which can fertilize the oocyte.

Location?


  • Somniferous tubule of the testis

  • Epididymis


When it passes through the tail region, it gains up the motility. It's about sixty-four days in humans, and 64-70 days to form a spermatozoa. And then, it begins at puberty and continues till death. The sperm production keeps happening till a person stops breathing.

Development:

  • The testis begins its differentiation at 6-7 weeks by appearance of Sertoli cells and spermatogonia from the primordial germ cells.

  • Development of male phenotype depends on production of AMH and testosterone.

  • Sertoli cell differentiation begins at 7 weeks and is a site for production of androgen binding protein (ABP) to maintain high local androgen environment and inhibin.

  • Leydig cells appear at 8 weeks from the interstitial component

  • Leydig cells produce testosterone and the secretion increases with increase in number and peaks at 15-18 weeks.

  • Male primordial germ cells unlike in the female do not start with the meiotic division before the onset of puberty.

  • The testosterone production in the local tissues causes the differentiation of the local tissues causes the differentiation of the Wolffian system.

  • Testis is an oval-shaped organ that is in the scrotum and has a volume of about 15mL (measured with Prader Orchidometer), length of about 5 cm, and rubbery in consistency.

  • Testis needs a temperature of 2-3 degree lower than the body temperature for normal functioning.

  • Each testis contains 200-300 seminiferous tubules are lined by stratified germinal epithelium and contain germ cells and supporting cells/ Sertoli cells.

  • 5% of the total testicular tissue consist of the Leydig cells, and they are responsible for testosterone production.


Understanding the concept:

  • Spermatogenesis is the process of sperm cell development, that is, from spermatogonia to spermatozoa.

  • Spermatocytogenesis is the development of spermatogonia to spermatocyte.

  • Spermogenesis is the maturation of spermatids into spermatozoa, and spermeation is the process of release of metro spermatozoa from the satellite cells into the lumen.


Different phases of spermatogenesis:

  • Proliferation and differentiation of spermatogonia

  • Meiosis that gives rise to haploid gametes

  • Spermiogenesis which is the maturation of round spermatids to the spermatozoan


How exactly does the sperm DNA condensation occur?

The answer is protamines. These are proteins with high content of positively charged amino acids. About 48% of the rich's arginine. So protamines are a highly condensed complex with its formed DNA. DNA has a strong negative charge. Cysteine allows the formation of disulfide bonds between the protamines thereby stabilizing the nucleoprotamine complex. The main function of protamines is DNA condensation and protection of the sperm's DNA damage by mutagen and other factors. Proteins also cause the reprogramming of the genome. They remove the transcription factor and other proteins from the sperm DNA, thereby creating a blank genetic message that can be reprogrammed by the egg. It gives an epigenetic imprinting to the sperm DNA, and protein can also leave an epigenetic mark on some regions of the sperm DNA, which can affect how it's reactivated during fertilization or once the sperm enters into the egg.

What are the most relevant applied aspects of protamines that we should be aware of?

Mature sperm DNA is 85% protamine bound and the rest 15% is histamine bound. Any deficiency in protamine makes sperm DNA more susceptible to damage by ROS. Infertile men have a higher ratio of histone to protamine, and five to ten percent of infertile men have complete protamine deficiency. This can be checked by performing sperm chromatin assay using toluidine blue and chromonychia a test.

FSH and testosterone are both very important to achieve proper spermatogenesis, and the role of zed cells are more apparent in case of FSH. Exogenous testosterone and progesterone act on the cortex, hypothalamus, and the pituitary. Polar tropins act different directly on pituitary to give it a signal to release SH and LH that can act on satellite cells and lading cells respectively to cause sperm maturation and production of testosterone. Testosterone production is in turn regulated by a feedback mechanism that sends a signal to hypothalamus to stop the GnRH release. Now coming to the intrinsic mechanism that regulates spermatozoa. The sertralized cells provide factors such as substrates for glycolysis and it does so by modulating the entry of substrates into the adnominal compartment of the testis. In primary spermatocytes, the preferred substrate for glycolysis is lactose and not glucose. Now, under the influence of FSH, lactate is generated in the sertralized cells. Production of lactate causes a change in pH. This results in alteration of the processing of stem cells, of stem cell factors from a soluble cell bound form, and this influences its action on spermatogonium stimulation.

Testicular transferrin is an iron binding protein that is regulated by FSH, and it delivers iron to primary spermatocytes. Celluloplasmin is a copper binding protein that delivers copper to germ cells. Now all cells require iron to maintain respiration and cytoplasm function, and copper acts as a coenzyme for a number of protein production. Some other factors controlling for mitogenesis are immotile celiac syndrome or Cartagena syndrome that lacks specific proteins called dynein, which hamper the motility of the sperm. If there is a genetic inactivation of gene encoding for a sperm calcium ion channel, even a morphologically normal sperm will be immortal. The advanced evaluation of male infertility mandates for sound knowledge of the various factors of spermatogenesis.

To conclude, spermatogenesis is a complex process involving various intrinsic, autocrine, paracrine mechanisms and gene. A normal sperm analysis cannot reveal the functional complexity of the sperm. An advanced evaluation of male fertility mandates a sound knowledge of various factors and processes which are involved in spermatogenesis.

Want to learn more about Spermatogenesis? Join our comprehensive Fellowship in Embryology Program at Medline Academics. With the increasing demand for trained reproductive specialists in India, the need for continued medical education is also increasing. But, with a regular practice, it is difficult to cope with continuous lectures. Medline Academics with its hybrid courses has come to solve this recurring issue for all the practising clinicians. With the hybrid Fellowship in Reproductive Medicine in India, mentees can refer to the theory modules as per their convenience and comfort. The live classes are conducted weekly and right after half of the syllabus is over, the midterm exams are conducted online. Students enrolled for the fellowship program in Medline Academics have to only attend the simulation training, clinical attachment and the final examinations in person.

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