Gonocytes Assignment: Cell Profile Report

Question

Task: Write a Cell Profile Report (Introduction and Discussion)on Gonocytes which are found in male testis developed from Germ Cells. The key points are provided which are to be followed when writing each section and starting references been provided.

I have also attached a sample cell profile report on different cell type. The marking rubric for the assignment is also attached.

Further detailed instructions are provided below:

Introduction:

Cell type – Gonocytes ( brief slides about what is gonocytes is attached in a pdf).

This section should be around 3 pages long including images.

• Provide an introductory paragraph summarising about Gonocytes.
• What is the function of Gonocytes? Is the function different in the embryo and adult?

3) Where are Gonocytes located?
Choose region in which Gonocytes are found and focus on that and mention where else it is found in the embryo?

4) What processes does it go through during embryogenesis (and later) to become

the final, functional Gonocyte ? Outline how Gonocytes are developed fertilisation onwards? (eg: Process of how germ cells are developed w/n testis)

5) With what other tissues must Gonocytes interact in order to function? Keep in mind not only proximal tissues, but also important distal interactions eg hormones produced by various glands. (example: Signalling – FGF-2/notch signalling in seminiferous epithelium; LH- aid for apoptosis; FSH- produce ABH by Sertoli cells.)

6) Outline aspects of cell-cell adhesion, proliferation, apoptosis and/or migration

important for the development of this cell type (example: Sertoli cells, Leydig cells, Apoptosis- maintain ratio of Sertoli cells; SSC undergo proliferation.)

7) Provide some introductory information to your Discussion topic.( example: Cryptorchidism Definition, % affected, 1-2 lines relate to infertility and how male reproductive health needs attention.)

Topic – Cyptorchidism

This section should be around 3 pages long, and have a focus on the developmental

biology of Gonocytes including images.

Few key points of how what should the discussion consist of: (can add in more).

• How Cyptorchidism relates to Gonocytes/primordial germ cells at least half a page
• Comparison b/w normal & UD testis; Mention in brief about Diseases(cancer), health conditions(diabetes) disorders (ADHD, ASD) can cause.
• No presence of BAXprotein, gonadotrophins (LH, TSH) – due to low sperm count not allow apoptosis/ self-renewal/high temperature in testis of Gonocytes.
• Importance of Mini-puberty
• Mention of surgery – orchiopexy in children to fix testicles
• Impact on infertility – comparing % Fertility rates between countries; Discuss the health conditions mentioned at above; how society ignores male reproduction.

Answer

Gonocytes
The report of Gonocytes assignment examines the several aspects of Gonocytes which are the precursors of spermatogonia. Before getting differentiated into spermatogonial stem cells, these can be found from week 7 of the embryonic development till the neonatal stage. Male germ cells serve as the mode of inheritance via transfer of epigenetic and genetic information between generations. Spermatogonia are central to fertility in males, which in turn depends on high population of stem cells. (1) Hence, it can be said that the quality and function and quality of a sperm cell depends on its origination, i.e. spermatogonial stem cell (SSC).

Germ cells are represented by Gonocytes during the migratory developmental stages which are short-term and successive. These stages happen from the time of inhibition of formation of gonads on the genital region by them till the time of their migration to the seminiferous cords’ basement membrane. The development of Gonocytes is divided into various phases: cell proliferation, differentiation, migration, and apoptosis. (2) Any abnormality during any of these stages may lead to some disease related to fertility.

Before settling into gonads, Primordial Germ Cells (PGC) undergoes proliferation several times in testes before being differentiated into gonocytes. The proliferation of gonocytes continues even after colonization, a burst of apoptosis happens in parallel to the proliferation. Cyclin B1 is a critical factor for the proliferation of gonocytes, which is required for a proper spermatogenesis. Various research show that a shortage of cyclin B1 during the postanatal stages leads to a decrease in the germ cells due to increased apoptosis and mitotic arrest. (3) Proliferation is inhibited in a majority of gonocytes when the spermatogonial stem cells after 17-days of conception and they resume mitosis after birth. During this phase as mentioned in the section of Gonocytes assignment, proliferative post-natal and fetal gonocytes die but no other gonocyte dies. Transforming Growing Factor ? (TGF?) signaling plays an important role in the spermatogenesis process as it is involved in the regulation of various processes linked to germ cells like apoptosis, differentiation and proliferation.

Interestingly, DNA-damage-inducible-45-alpha (Gadd45?) and growth arrest is expressed in germ cells in particular. Research on the case scenario of Gonocytes assignment has shown that along with somatic cytochrome c (Cycs), Gadd45? expression upregulates the differentiating gonocytes. Any deactivation in expression of these two genes may lead to uncontrolled proliferation, and proneness to cancer. These genes are also found to play an important role in the initiation of germ cell apoptosis and gonocytes differentiation.

Neonatal gonocytes proliferation is stimulated by the 17?-estradiol (E2) and paracrine fashion platelet derived growth factor (PDGF) which are synthesized and secreted by sertoli cells. PDGFR is involved in the proliferation and apoptosis modulation in neonatal gonocytes. (18) E2 acts as a pro-apoptic and an anti-mitotic agent for the neonatal murine gonocytes.

Spermatogonia from Gonocytes:
Gonocytes get relocated to the basement of testicular cords from the lumen after birth. Migration on one hand is required for proper differentiation to spermatogonia, while on the other hand it helps in establishing a strong interaction between pre-spermatogonia and Sertoli cells. After migration, apoptosis happens on the pre-spermatogonia which are left at the center of the cord.

A protein complex known as ADAM-integrin-tetraspanin complex is organized in a sophisticated complex of microdomain membrane known as the tetraspanin web. (17) The attachment of Sertoli cells and pre-spermatogonia is stabilized by binding of tetraspanin web by F-actin. This binding is such that upon detachment, it leads to fragmentation and structural changes of F-actin. Sertoli cells mentioned in this section of Gonocytes assignment clarifies that subsequently release Fas-ligand which is locally soluble and binds FasR in the pre-spermatogonium which is detached. (4)This in turn leads to apoptosis which is extrinsically induced. This apoptotic signaling is evaded by the gonocytes which have timely migrated to the basement membrane, mainly because of their new microenvironment. Hence, it can be established that there is an active communication between Setoli cells and germ cells. And the numbers of germ cells that are supported are guaranteed correct physiology through induced paracrine apoptosis.

Gonocytes are differentiated into type-A spermatogonia after birth. Interstingly in humans, the amount of germ celss are reduced to less than half. And by the end of 2 years, no gonocytes are left through the removal of non-differentiated gonocytes via apoptosis. In humans, by the age of 3-4, type-A spermatogonia get converted into Type-B spermatogonia, which mature into primary spermatocytes after migrating to center of testicular cord. (5)

The investigation carried on the Gonocytes assignment mentions that approximately 75 percent of the germ cells in a healthy male are redundant from spermatogonia to mature spermatozoa. In simpler terms, apoptosis bursts are primarily responsible for selection of such severity. From the above arguments, it can be deduced that the better the understanding of spermatogenesis and the development of the male germ cells, the higher is the potential for them to be used for infertile testis reconciliation. Apoptosis forms an essential part of the process of germ cells development, starting from early stages of embryo till the spermatogenesis completion. The fertility of the male and their delivery of perfect genetic message to the offspring is dependent on the apoptosis at right time and right place of gonads.

Results:
Effect of FGF on Testicular Sertoli and Leydig Cells
Throughout the testis, it is noted herein Gonocytes assignment that the FGFs gets localized to many cells, like Leydig, germ cells and Sertoli. DNA synthesis and cell multiplication, along with their phenotypic expression, have been seen to be stimulated due to the FGFs in cultured Sertoli cells of pig. Upon 3 to 6 days culturing of the cells in isolated 3-day-old, newborn or fetal rats, FGF-2 was found to increase the Sertoli cell numbers. FGF-2 displayed a survival factor for these cells in vitro as they did not lead to an increase in the Sertoli cells’ [³H] thymidine labeling index. (6)

The readings used in the context of Gonocytes assignment illustrates that FGF-2, as a mitogenic factor, may also be required during the immature testis development. Through various immune histochemical evidences, presence of FGF-2 in Leydig cells of fetus has been established. Purified cultures of porcine Leydig cells were taken from the animals, to form a basis of primary model in order to study the mechanism and effect of FGF-2 on steroidogenesis of testis. (16) FGF-2 was found to increase the accumulation of chorionic gonadotropin (hCG)-induced testosterone in human, in the intermediate to a long term treatment of the cultured Leydig cells. Its pleiotropic role is suggested strongly due to its ability to affect the maximal steroidogenic capacity of the Leydig cells.

It was also found in the studies utilized to prepare this Gonocytes assignment that the Leydig cell function’s regulation also involves factors that are locally produced. These factors also include the members of FGF family. Research on Leydig cells isolated from rats of various ages was done in order to understand the effects of FGF-1 and FGF-2. It was shown in the research that FGF-1and 2 stimulated the production of basal 17?-diol and 5?-androstane-3? through immature Leydig cells and production of Luteinizing Hormone-stimulated testosterone by fetal Leydig cells. (7) FGF-1 and FGF-2 had no impact on the production of testosterone by adult Leydig cells, but FGF-1 alone was found to inhibit the production of LH-stimulated testosterone by mature Leydig cells. The research on the case of Gonocytes assignment demonstrates that the effects of FGF-1 and FGF-2 are Leydig cell development and differentiation dependent.

Expressed widely in embryonic tissues, FGF-8 plays an important role in the morphogenesis of central nervous system, face and limbs, and elongation of body axis. But in an adult mouse, expression of FGF-8 m-RNA has been detected in the testis through Northern blotting. (15) Due to the decrease in the proliferation of murine Sertoli cells after birth and it ceasing while puberty, a very low level of FGF-8 expression can be expected in adult testis. The stage of expression of FGF-8 illustrated in this segment of Gonocytes assignment shows its specific function in the testis’ seminiferous epithelium’s maturation.

Figure: Immunofluorescent detection of expression of GFRA1 and FOXO1 protein treated without and with signal inhibitors. (6)

Effect of FGF on Testicular Germ Cells:
A wide range of cellular activities like cell differentiation and proliferation during embryonic development of various organs are regulated by FGFs. Fully functional sperm depends heavily on the testis’ environment and cannot develop on its own. Regulating the testicular cell growth is necessary for the spermatogenesis maintenance in the adult testis. The study examined in the Gonocytes assignment mentions that presence of specific growth factor is required for the high rate of germinal cell proliferation in the adult testis.

Paracrine regulation of the growth of testis germ cell also involves some members of FGF. FGF-2 supplement led to a significant increase in the gonocytes number, which were cultured for 6 days and separated from animals which were newly born or 3-day-old. (14) The germ cells’ numbers were found to be doubled as compared to the control cultures. Research have also shown that spermatogenic meiosis and mitotic proliferation of spermatogonia is stimulated by FGFs partially through FGFRs in order to enhance the activity of mitogen activated protein kinase (MAPK). (1)

Figure: (A) GST characterization in the murine testes. GST is initiated in gonocytes. (B) GST regulation in the murine testes. FGF signaling is the basis of signaling mechanism. (4)

Discussion:
The phenomena of Cryptorchidism explored herein Gonocytes assignment is caused when an individual scrotum lacks of one or both the testes. This is one of the common defects in the genital tract of males from their birth. Around 1 to 4% newborn males suffer from undescended testis or Cryptorchidism which eventually leads to infertility and testicular cancer. According to the research, infertility in undescended testis (UDT) is due to the development of abnormal gonocytes that generally during minipuberty (in human 2-6 months and in mice 2-6 days) convert into spermatogonial stem cells (SSC) or undergoes programmed cell death. (8) Throughout minipuberty under the control of FSH ns indirect control of Androgen and LH the hypothalamic–pituitary axis stimulating gonocyte transform. An arrested gonocytes as well as developmental abnormalities in germ cells is the root cause for malignancy in later age of an UDT individual.

Development of the Germ cells:
Development of germ cells is an active process. After the birth (within 1^st year) neonatal gonocytes starts changing into adult dark spermatogonis. These adult stem cells comprise a dark nucleus that differentiates them from the other cells. Adult dark cells does not take part directly in spermatogenesis instead make sure to supply a certain amount of stem cells required for spermatogenesis.Certainly, Adult dark spermatogonia replicate to produce light nuclei comprising adult pale (AP) spermatogonia.(13) By the mitosis process these cells are produce which further become primary spermatocytes by dividing and differentiating (found in 4 year boys).

According to several research data considered to develop this report on Gonocytes assignment, AD is formed in the age of 3 to 9 and this cycle requires an optimum temperature (33⁰C) as well as normal amount of testicular hormones like androgens and gonadotropins. (9) All the neonatal gonocytes does not convert into AD spermatogonia instead undergo involution via apoptosis. Environmental and genetic conditions effect these processes.

Recently the development and modification of germ cell in cryptorchidism is been studied by several researchers. The process by which sperm cells are produced is known a spermatogenesis. During puberty it begins to form with the increase amount of testosterone and gonadotropins. This process involves various complex process in a sequential manner like first mitosis takes place and then followed by meiosis and differentiation. (12) In every steps autocrine, paracrine and endocrine factors participate. The inability to transform gonocytes into AD cells leads to infertility in males.

Figure: Presence of abnormal gonocytes in a boy of 6 months of age with cryptorchidism. The germ cells are indicated with mouse homolog of Drosophila Vasa and the Sertoli cells with MIS/AMH. (3)

As per the readings of the authors considered to develop the study within this Gonocytes assignment, the abnormal high temperature in the cryptorchid males is the main reason for the mal development of these germ cells.

Significant studies observed in various animal models suggest that due to heat stress both direct and indirect effects is applied on the germ cells, initiating impaired transformation, maturation of the cells and inhibiting apoptosis. (2) This injury is caused by heat shock protein and certain reactive oxygen species that damage the Sertoli cells and the germ cells.

Disease associated with cryptorchidism:
Researchers have observed that the precursor cells of testicular cancer are alike to fetal gonocytes. According to a recent study used to develop this Gonocytes assignment, the abnormal high temperature of UD leads to an irregular apoptosis that let some gonocytes to remain arrested and transform in cancerous cells that leads to malignancy and infertility in adulthood via several mutations and cellular unbalance.

Figure: Spermatogenesis and development of cancer: Malignant and normal testicular germ cell development.

The established etiology for germ cell carcinoma is still unknown though instabilities in the microenvironment delivered by the Leydig and Sertoli cells plays an important role. In fact this process of spermatogenesis is influenced and controlled by various signaling pathways those are delivered from the Leydig cells and the local environment. Throughout the development process expression of the insulin-like-3 gene (INSL3)is visible that is responsible for testicular descent and gubernaculum maturation.(11) It has been observed that there is a reasonable relationship in between INSL3 and cryptorchidism males.

What is the role of treatment performed in Cryptorchidism in the context of Gonocytes assignment?
Orchidopexy is one of the most common practice in cryptorchidism treatment. Other two approaches are inguinal operation and laproscopy. (10) Initial surgical treatment may avoid infertility. Orchidopexy surgery is mostly perform before the age of 2 and several recent studies suggest that if this surgery is done before the age of 1, normal spermatogenesis may achieve by inhibiting the progressive changes of the testes and germ cell loss. Though this surgery does not assure normal fertility in later life. According to Hadziselimovic, that despite performing orchidopexy before the age of 6, nearly 35% of boys were found to be infertile irrespective of the total normal germ cell count.

Mini Puberty:
A period in infancy when male fertility recognized (30-90 days after birth) is known as mini puberty. (10) During this puberty period there is a temporary increase in certain hormons like testosterone and gonadotropins that helps the gonocytes to diferenciate into AD germ cells.This AD spermatogonia establish germ cell memory and pathways of DNA methylation specific to the males. According to several studies it has been found that there is a mild primarily disfunction in the boys having cryptorchidism. It is observed herein Gonocytes assignment that early after birth there is a deficiency of androgen and testosterone indicating a disturbing function in the testicles. This hormonal deficiency in 3-month child shows lower amount of production in inhibin B. (3)

Nonetheless, boys having cryptorchidism as found to have low levels of testosterone, luteinizing hormone (LH), abrogated variation of Ad spermatogonia from gonocytes and atrophic Leydig cells. The major difference between the UDT and normal children is the reduce amount of response to human chorionic gonadotropin (hCG) by the leydig cells. Early treatment with hCG in UDT boys can strike out the difference in terms of stimulation. (5) Therefore, the reason behind lower response of testosterone obtained in this aspect of Gonocytes assignment appears to be at the hypothalamic level and perhaps due to insufficient stimulation by the Leydig cells. Several LH-RH tests have confirmed a lower Luteinizing Hormone response by gonadotropin-releasing hormone.

A Normal separated germ cells in newborns with mini-puberty. One Adult dark and two Adult pale germ cells are present. The gonocyte cells is missing. B Compromised mini-puberty leads to a defective conversion of gonocytes into Adult dark spermatogonia. Atrophic Leydig cells are observed between the tubles which proves the presence of impaired gonadotropin stimulation.

Ignorance of society about Male Reproduction:
According to the human fertilization and Embryology Authority report (2014-16) observed in the context of Gonocytes assignment, male infertility (around 37%) is a common problem in recent times. Meanwhile this area of research does not get more priority. This is because of the bizarre and deep rooted perceptions of the society about importance of femaleness in infertility. The way that these problems, pain, ineffective treatment, infertility and ultimate responsibility or blame are often being associated with females is not only a female issue but also a failure of female. On the other hand, with males this issue is a shooting blank. This complex biological and cultural perception of the society towards the females leads to violence and even criminal incidences. According to the research performed by Harvard Medical School in Boston, it is noted herein Gonocytes assignment that the sperm quality of the males reduces with age and create troublesome in fertilization and also potentially affect the infants’ health. Despite the fact even today men can fail in innumerable ways as per the society but a woman is considered as messing up everything and the total blame is put on her of not being able to bear a child.

References