Sophie Bennett
Spermatogenesis in grasshopper frogs and chickens differs in several ways. Frogs have cystic spermatogenesis, where sperm develops in large numbers of spermatogonial cysts, while chickens have non-cystic spermatogenesis. Frogs also have two phases of spermatogenesis: prespermatogenesis, when gonocytes proliferate in developing tadpole testes, and active spermatogenesis, when spermatogonial stem cells self-renew or enter meiotic cycles. In addition, the sex of frog germ cells depends on the sex of the developing gonads, and meiosis is delayed until after metamorphosis. On the other hand, chickens, as birds, have Leydig cells that are difficult to distinguish and may only be seen with an electron microscope. Evolutionary analyses of transcriptome data for chicken testes have also unveiled ancestral and species-specific characteristics of spermatogenesis.
| Characteristics | Values |
|---|---|
| Spermatogenesis in grasshopper frog | Consists of two phases: prespermatogenesis and active spermatogenesis |
| Prespermatogenesis in grasshopper frog | Gonocytes proliferate in developing tadpole testes |
| Active spermatogenesis in grasshopper frog | Spermatogonial stem cells (SSCs) either self-renew or enter into meiotic cycles within cysts formed by Sertoli cells |
| Spermatogenesis in chicken | No specific information found |
| General process of spermatogenesis | Involves the invasion of the differentiating male gonad by primordial germ cells (PGCs) that give rise to gonocytes, which are arranged in testicular cords surrounded by precursor Sertoli cells and peritubular myoid cells |
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What You'll Learn
- Sertoli cells in grasshopper frogs, chickens, and other vertebrates are responsible for providing the correct environment for germ cell proliferation, meiosis, and sperm differentiation
- Frogs have solid seminiferous cords composed of gonocytes surrounded by somatic cells
- Frogs have two phases of spermatogenesis: prespermatogenesis and active spermatogenesis
- Frogs have cystic spermatogenesis, which supports the development of more spermatogonia, producing a higher amount of spermatozoa
- In chickens, Leydig cells are a primary source of androgens, or male hormones, and may only be seen under an electron microscope
Sertoli cells in grasshopper frogs, chickens, and other vertebrates are responsible for providing the correct environment for germ cell proliferation, meiosis, and sperm differentiation
Sertoli cells, first observed in 1865 by Italian physician Enrico Sertoli, are present in the seminiferous tubules of the male gonads, the testes. They are one of the two types of cells in the germinal epithelium, the other being of the spermatogonia lineage. Sertoli cells are crucial for sperm production and play a key physiological role in supporting, nourishing, and protecting germ cells. They are also responsible for facilitating spermiogenesis and secreting vital molecules like androgen-binding protein (ABP), inhibin, and activin.
In grasshopper frogs, specifically the Levantine frog (Pelophylax bedriagae), Sertoli cells are located within the seminiferous tubules and exhibit various forms, including pyramid, column, or irregular shapes. Frogs, as amphibians, occupy a unique position in vertebrate evolution, serving as a transitional group between amniotes and anamniotes. The onset of meiosis in amphibians depends on the developmental pathway of the gonad, with germ cells entering meiosis in the larval ovary and typically delaying meiosis until after metamorphosis in males.
In chickens, Sertoli cells support, nourish, and protect germ cells, similar to their role in other vertebrates. Chicken Sertoli cells have been studied in vitro, and they share morphological similarities with mammalian Sertoli cells. Additionally, they express the specific Sertoli marker, anti-Müllerian hormone, and the 3β-hydroxysteroid dehydrogenase enzyme, which is not observed in mammals.
Across different vertebrate groups, Sertoli cells are essential for providing the appropriate environment for germ cell proliferation, meiosis, and sperm differentiation. They form tight junctions and connective adhesion molecules with neighboring Sertoli cells, creating the blood-testes barrier. This barrier plays a crucial role in maintaining the necessary conditions for spermatogenesis, including ion regulation, testosterone concentration, immune system evasion, and barrier protection. The number of Sertoli cells in a given cyst increases with the mitotic division of germ cells, and they undergo turnover in the transient germinal epithelium characteristic of cystic spermatogenesis.
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Frogs have solid seminiferous cords composed of gonocytes surrounded by somatic cells
The presence of solid seminiferous cords composed of gonocytes surrounded by somatic cells is a characteristic feature of the early stages of frog development. During this phase, known as prespermatogenesis, the gonocytes proliferate in developing tadpole testes. Prespermatogenesis is restricted to the larval and early juvenile periods, equivalent to the fetal and prepubertal periods in mammals. It is during this stage that the gonocytes, also known as prespermatogonia or prospermatogonia, start their mitotic divisions and give rise to a pool of transient (T) gonocytes. These transient gonocytes remain dormant until puberty when they transform into stem cells, specifically spermatogonial stem cells (SSCs).
The SSCs are mitotically active and can either renew the adult spermatogonial pool or differentiate into several generations of secondary spermatogonia. The secondary spermatogonia then enter meiosis, leading to sperm production. This process is known as active spermatogenesis, which occurs in adult frogs. During active spermatogenesis, the SSCs, or descendants of gonocytes, either self-renew or enter into meiotic cycles within cysts formed by Sertoli cells.
The Sertoli cells play a crucial role in both prespermatogenesis and active spermatogenesis. They provide structural support and create a protective barrier for the developing germ cells. In the adult testis, the Sertoli cells form a single-cell layer epithelium through which the spermatogonia pass as they transform into spermatocytes and commence meiosis. The integrity and functionality of Sertoli cells are vital for male fertility, and their proper development is influenced by the transcription factor DMRT1.
The solid seminiferous cords observed in the earliest tadpole testes undergo differentiation to form seminiferous tubules. These tubules are filled with cysts containing germ cells at different stages of spermatogenesis. The cysts are situated along the walls of the seminiferous tubules, which are constituted by Sertoli cells and their basement membranes. This transformation from solid seminiferous cords to seminiferous tubules with cysts reflects the progression of spermatogenesis in frogs.
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Frogs have two phases of spermatogenesis: prespermatogenesis and active spermatogenesis
Spermatogenesis in frogs was first divided into two phases: prespermatogenesis and active spermatogenesis. Prespermatogenesis occurs when gonocytes proliferate in developing tadpole testes. Active spermatogenesis, on the other hand, occurs when spermatogonial stem cells (SSCs), or descendants of gonocytes, either self-renew or enter meiotic cycles within cysts formed by Sertoli cells.
The earliest stages of spermatogenesis in frogs are observed in two species of water frogs: Pelophylax lessonae and Pelophylax ridibundus. However, the process may be extrapolated to other anuran amphibians with the same pattern of differentiation and development of testes. The completion of metamorphosis in amphibians is considered equivalent to birth in mammals. Thus, amphibian larval primary spermatogonia are homologous to mammalian gonocytes, while primary spermatogonia in adult frogs are SSCs.
In the larval and early juvenile period, prespermatogenesis is restricted to the formation of testicular cords that are surrounded by precursor Sertoli cells (pSCs) and peritubular myoid cells. This is equivalent to the foetal and prepubertal periods in mammals. During prespermatogenesis, there is a proliferation of supporting cells, while gonocytes only proliferate from the fifteenth to the seventeenth day of gestation. The percentage of gonocytes in the total number of cells in the sex cords or seminiferous tubules decreases from 70% on the fifteenth day of gestation to 4% on the fourth postnatal day.
During active spermatogenesis, SSCs are mitotically active and can either renew the adult spermatogonial pool or give rise to several generations of secondary spermatogonia. The lowest number of secondary spermatogonia inside a cyst is eight, indicating the minimum number of cell cycles (three) necessary to enter meiosis. This number is similar to that recorded for mammals as the result of a single As proliferation. The number of secondary spermatogonia correlates with the volume of a cyst.
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Frogs have cystic spermatogenesis, which supports the development of more spermatogonia, producing a higher amount of spermatozoa
Spermatogenesis in frogs has been divided into two phases: prespermatogenesis and active spermatogenesis. During prespermatogenesis, gonocytes proliferate in developing tadpole testes. Active spermatogenesis, on the other hand, involves spermatogonial stem cells (SSCs) that are descendants of gonocytes. These SSCs either self-renew or enter meiotic cycles within cysts formed by Sertoli cells.
Frogs have cystic spermatogenesis, which is distinct from the acystic spermatogenesis observed in mammals. In cystic spermatogenesis, all spermatogenic stages beyond a single spermatogonial stem cell (SSC) are synchronic and encapsulated by cysts. This encapsulation allows for the development of more spermatogonia, resulting in a higher amount of spermatozoa. The efficiency of cystic spermatogenesis in amphibians is attributed to the ability of Sertoli cells to support germ cells at different developmental stages simultaneously.
The process of cystic spermatogenesis in frogs begins with the formation of cysts by Sertoli cells. Each cyst contains germ cells at the same developmental stage, interacting with a single Sertoli cell. As the number of Sertoli cells in a cyst increases, so does the mitotic division of the germ cells. Once the germ cells enter meiosis, proliferation ceases, and tight junctions form between the Sertoli cells, creating a barrier. After spermiogenesis is complete, the cysts open to release spermatozoa during spermiation.
The Sertoli cells play a crucial role in cystic spermatogenesis by providing the necessary environment for germ cell proliferation, meiosis, and sperm differentiation. The turnover of Sertoli cells is observed in adult amphibians due to the transient nature of the germinal epithelium. This turnover is facilitated by the ability of Sertoli cells to divide when in contact with mitotically active spermatogonia stem cells, leading to the periodic formation of new cysts.
In summary, frogs undergo cystic spermatogenesis, which involves the encapsulation of spermatogenic cells within cysts formed by Sertoli cells. This process supports the development of more spermatogonia, resulting in a higher production of spermatozoa compared to acystic spermatogenesis observed in mammals. The efficiency of cystic spermatogenesis in frogs highlights the importance of understanding the impact of environmental contaminants on the fertility of these species.
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In chickens, Leydig cells are a primary source of androgens, or male hormones, and may only be seen under an electron microscope
Spermatogenesis refers to the process of sperm production in males. In chickens, Leydig cells are a primary source of androgens, or male hormones. Leydig cells are glandular (interstitial) cells present in most, if not all, vertebrates. In some bird species, Leydig cells are so small that they can only be seen under an electron microscope.
Leydig cells play a crucial role in the production of male hormones, which are essential for spermatogenesis and other male reproductive functions. These cells are typically found in the testicular stroma, which fills the spaces between seminiferous tubules or spermatogenic cysts. The testicular stroma consists of connective tissue, blood and lymphatic vessels, and nerves. The specific arrangement and abundance of these components can vary among different vertebrates.
The capillary system of the testis is designed so that blood that has bathed the Leydig cells flows directly to the tubules. This indicates that the hormones produced by Leydig cells are likely to have a direct and immediate impact on the germinal epithelium, which is crucial for sperm development. The proximity of the blood vessels to the Leydig cells suggests a functional relationship between them, highlighting the importance of Leydig cells in the overall process of spermatogenesis.
While Leydig cells are a primary source of androgens, it is important to note that they are not always easily distinguishable. In certain bird species, such as chickens, the small size of Leydig cells makes them difficult to observe without the aid of an electron microscope. This highlights the need for advanced microscopic techniques to fully understand the structure and function of these cells in different species.
In summary, Leydig cells play a vital role in chicken testis by producing male hormones necessary for spermatogenesis. Their small size in birds makes them challenging to study, and the use of electron microscopy has been instrumental in understanding their contribution to the process of sperm production in male chickens.
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Frequently asked questions
Spermatogenesis is the process of producing sperm.
Spermatogenesis in grasshopper frogs occurs in two phases: prespermatogenesis and active spermatogenesis. During prespermatogenesis, gonocytes proliferate in developing tadpole testes. Active spermatogenesis involves spermatogonial stem cells (SSCs) that either self-renew or enter meiotic cycles within cysts formed by Sertoli cells.
Spermatogenesis in chickens, as studied in the red jungle fowl, has been used as an evolutionary outgroup when compared to other species. While specific details of chicken spermatogenesis are not readily available, it is known that they possess Leydig cells, which are thought to be a primary source of androgens or male hormones.
