Spermiogenesis

Spermiogenesis is the final stage of spermatogenesis, which sees the maturation of spermatids into mature, motile spermatozoa. The spermatid is a more or less circular cell containing a nucleus, Golgi apparatus, centriole and mitochondria. All these components take part in forming the spermatozoon.

Spermatogenesis
The process of spermatogenesis. 1. Primary spermatocyte 2. Secondary spermatocytes 3. Spermatids 4. Sperm

Phases

Complete diagram of a human spermatozoa en
Complete diagram of a human spermatozoon

The process of spermiogenesis is traditionally divided into four stages: the Golgi phase, the cap phase, formation of tail, and the maturation stage.[1]

Golgi phase

The spermatids, which up until now have been mostly radially symmetrical, begin to develop polarity.

  • The head forms at one end, and the Golgi apparatus creates enzymes that will become the acrosome.
  • At the other end, it develops a thickened mid-piece, where the mitochondria gather and the distal centriole begins to form an axoneme.

Spermatid DNA also undergoes packaging, becoming highly condensed. The DNA is first packaged with specific nuclear basic proteins, which are subsequently replaced with protamines during spermatid elongation. The resultant tightly packed chromatin is transcriptionally inactive.

Cap/Acrosome phase

The Golgi apparatus surrounds the condensed nucleus, becoming the acrosomal cap.

Gray1150
Note how the tails of the sperm point inward. This orientation occurs during the acrosomal phase.

Formation of Tail

One of the centrioles of the cell elongates to become the tail of the sperm. A temporary structure called the "manchette" assists in this elongation.

During this phase, the developing spermatozoa orient themselves so that their tails point towards the center of the lumen, away from the epithelium.

Maturation phase

The excess cytoplasm, known as residual body of regaud, is phagocytosed by surrounding Sertoli cells in the testes.

Spermiation

The mature spermatozoa are released from the protective Sertoli cells into the lumen of the seminiferous tubule and a process called spermiation then takes place, which removes the remaining unnecessary cytoplasm and organelles.[2]

The resulting spermatozoa are now mature but lack motility, rendering them sterile. The non-motile spermatozoa are transported to the epididymis in testicular fluid secreted by the Sertoli cells, with the aid of peristaltic contraction.

Whilst in the epididymis, they acquire motility. However, transport of the mature spermatozoa through the remainder of the male reproductive system is achieved via muscle contraction rather than the spermatozoon's motility. A glycoprotein coat over the acrosome prevents the sperm from fertilizing the egg prior to traveling through the male and female reproductive tracts. Capacitation of the sperm by the enzymes FPP (fertilization promoting peptide, produced in the prostate gland) and heparin (in the female reproductive tract) removes this coat and allows sperm to bind to the egg.[3]

References

  1. ^ ANAT D502 – Basic Histology
  2. ^ O'Donnell, Liza; Nicholls, Peter K.; O'Bryan, Moira K.; McLachlan, Robert I.; Stanton, Peter G. (2011). "Spermiation". Spermatogenesis. 1 (1): 14–35. doi:10.4161/spmg.1.1.14525. PMC 3158646. PMID 21866274.
  3. ^ Fraser, L. R. (September 1998). "Fertilization promoting peptide: an important regulator of sperm function in vivo?". Reviews of Reproduction. 3 (3): 151–154. doi:10.1530/ror.0.0030151. ISSN 1359-6004. PMID 9829549.

External links

Acroplaxome

Spermatozoa develop in the seminiferous tubules of the testes. During their development the spermatogonia proceed through meiosis to become spermatozoa. Many changes occur during this process: the DNA in nuclei becomes condensed; the acrosome develops as a structure close to the nucleus. The acrosome is derived from the Golgi apparatus and contains hydrolytic enzymes important for fusion of the spermatozoon with an egg cell. During spermiogenesis the nucleus condenses and changes shape. Abnormal shape change is a feature of sperm in male infertility.

The acroplaxome is a structure found between the acrosomal membrane and the nuclear membrane. The acroplaxome contains structural proteins including keratin 5, F-actin and profilin IV.

CAMP responsive element modulator

cAMP responsive element modulator is a protein that in humans is encoded by the CREM gene, and it belongs to the cAMP-responsive element binding protein family. It has multiple isoforms, which act either as repressors or activators. CREB family is important for in regulating transcription in response to various stresses, metabolic and developmental signals. CREM transcription factors also play an important role in many physiological systems, such as cardiac function, circadian rhythms, locomotion and spermatogenesis.

Chimaericola leptogaster

Chimaericola leptogaster is a species of polyopisthocotylean monogenean in the family Chimaericolidae. It is ectoparasitic on the gills of the chimaera Chimaera monstrosa.

Dinophilidae

Dinophilidae is a family of annelids of uncertain phylogenetic affinity comprising the two genera Dinophilus and Trilobodrilus, first linked based on their sperm morphology.

Fecampiida

Fecampiida is an order of flatworms in the class Rhabditophora. It is a considerably recent clade, erected after molecular studies.

H1FNT

H1 histone family, member N, testis-specific is a member of the histone family of nuclear proteins which are a component of chromatin. In humans, this protein is encoded by the H1FNT gene.The H1FNT protein is essential for nuclear formation in spermatozoa, and is involved in the replacement of histones with protamines during spermiogenesis.

PRDX4

Peroxiredoxin-4 is a protein that in humans is encoded by the PRDX4 gene. It is a member of the peroxiredoxin family of antioxidant enzymes.

Perineal raphe

The perineal raphe is a visible line or ridge of tissue on the human body that extends from the anus through the perineum. It is found in both males and females, and arises from the fusion of the urogenital folds.

In males, this structure continues through the midline of the scrotum (scrotal raphe) and upwards through the posterior midline aspect of the penis (penile raphe). It also exists deeper through the scrotum where it is called the scrotal septum. It is the result of a fetal developmental phenomenon whereby the scrotum and penis close toward the midline and fuse.It has been argued that the "rib" in the biblical story of Adam and Eve is actually a mistranslation of a Biblical Hebrew euphemism for baculum (penis bone), and that its removal from Adam in the Book of Genesis is a creation narrative to explain its absence in humans, as well as the presence of the raphe– as a resultant 'scar'.

Peripatopsis capensis

Peripatopsis capensis is a species of velvet worm in the Peripatopsidae family. The type locality is in South Africa.

Peripatopsis moseleyi

Peripatopsis moseleyi is a species of velvet worm in the Peripatopsidae family. The type locality is in South Africa.

Rhabdocoela

Rhabdocoela is an order of flatworms in the class Rhabditophora with about 1700 species described worldwide. Most of rhabdocoels are free-living organisms, but some live symbiotically with other animals.

SLC4A2

Anion exchange protein 2 (AE2) is a membrane transport protein that in humans is encoded by the SLC4A2 gene. AE2 is functionally similar to the Band 3 Cl−/HCO3− exchange protein.

Mice have been used to explore the function of AE2. AE2 contributes to basolateral membrane HCO3− transport in the gastrointestinal tract. AE2 is required for spermiogenesis in mice. AE2 is required for normal osteoclast function. The activity of AE2 is sensitive to pH.AE3 has been suggested as a target for prevention of diabetic vasculopathy.

Sebileau's muscle

Sebileau's muscle is the deep muscle fibres of the dartos tunic which pass into the scrotal septum. It is named after French anatomist Pierre Sebileau (1860–1953).

Spermatid

The spermatid is the haploid male gametid that results from division of secondary spermatocytes. As a result of meiosis, each spermatid contains only half of the genetic material present in the original primary spermatocyte.

Spermatids are connected by cytoplasmic material and have superfluous cytoplasmic material around their nuclei.

When formed, early round spermatids must undergo further maturational events to develop into spermatozoa, a process termed spermiogenesis (also termed spermeteliosis).

The spermatids begin to grow a living thread, develop a thickened mid-piece where the mitochondria become localised, and form an acrosome. Spermatid DNA also undergoes packaging, becoming highly condensed. The DNA is packaged firstly with specific nuclear basic proteins, which are subsequently replaced with protamines during spermatid elongation. The resultant tightly packed chromatin is transcriptionally inactive.

In 2016 scientists at Nanjing Medical University claimed they had produced cells resembling mouse spermatids artificially from stem cells. They injected these spermatids into mouse eggs and produced pups.

Spermatogenesis

Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules. These cells are called spermatogonial stem cells. The mitotic division of these produces two types of cells. Type A cells replenish the stem cells, and type B cells differentiate into spermatocytes. The primary spermatocyte divides meiotically (Meiosis I) into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. The spermatids are transformed into spermatozoa(sperm) by the process of spermiogenesis. These develop into mature spermatozoa, also known as sperm cells. Thus, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa and four haploid cells.Spermatozoa are the mature male gametes in many sexually reproducing organisms. Thus, spermatogenesis is the male version of gametogenesis, of which the female equivalent is oogenesis. In mammals it occurs in the seminiferous tubules of the male testes in a stepwise fashion. Spermatogenesis is highly dependent upon optimal conditions for the process to occur correctly, and is essential for sexual reproduction. DNA methylation and histone modification have been implicated in the regulation of this process. It starts at puberty and usually continues uninterrupted until death, although a slight decrease can be discerned in the quantity of produced sperm with increase in age (see Male infertility).

TNP1

Spermatid nuclear transition protein 1 is a protein that in humans is encoded by the TNP1 gene.

TNP2

Nuclear transition protein 2 is a protein that in humans is encoded by the TNP2 gene.

TSSK2

Testis-specific serine/threonine-protein kinase 2 is an enzyme that in humans is encoded by the TSSK2 gene.

Transition nuclear protein

Transition nuclear proteins (TNPs) are proteins that are involved in the packaging of sperm nuclear DNA during spermiogenesis. They take the place of histones associated with the sperm DNA, and are subsequently themselves replaced by protamines.

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