Overview of Gametogenesis in Mammals through

Observations of Spermatocytes in Albino mouse (Mus

musculus) and Oocytes in Pig (Sus scrofa domesticus)

Kristine Mae L. Valenzuela, Billy A. Chan, Febbie Faye Baylon,

Maria Chelo G. Pavericio, Ara May Bataque

Biology Department, College of Science Bicol University 4500, Albay, Philippines

ABSTRACT

Aims: To expound on the concepts and processes of gametogenesis among mammals Study design: Dissection and microscopy Place and Duration of Study: Biology Department Laboratory 106, Bicol University, Legazpi City, Philippines; November 13 and 20, 2012. Methodology: Male albino mice was dissected and epididymis and testis were removed and macerated together with 0.9% NSS. Sperm motility was observed. Prepared slides of other testis of other mammals were observed. Oocytes in pig ovaries were aspirated and observed under the microscope. Prepared slides of oocytes of other mammals were also observed. Results: No sperm movement was observed which may be due to prolonged preparation. No oocyte were also observed which is also mainly due to the young age of the experimental animal. Conclusion: The gametogenesis among mammals have the same stages. Histology of the reproductive tissues of mammals also has similar features Both undergo meiotic divisions and cell differentiation in order to produce gametes with 1n chromosomes. There are also a few types of sperm motility and oocytes. Keywords: Gametogenesis, oocyte, spermatogenesis, epididymis, testis, ovary, mammals, oogenesis

1. INTRODUCTION

Gametogenesis is the process by which diploid or haploid precursor cell undergo cell division

and differentiation to develop and produce mature male and female germ cell which is the

gametes, gametogenesis is also referred to as alternation of generations.

The gametes in males are produced by the testes, two globe-shaped organs which are found in

the reproductive system; usually male gametes are what most referred to as sperm. Gametes in

females are produced by the ovaries, two oblong organs on each side of the uterus in the lower

abdomen. Female gametes are what most people refer to as eggs or ova. There are two types

of processes involved in gametogenesis the oogenesis and the spermatogenesis. Female

organisms produce eggs or oocytes in a process known as oogenesis, while male organisms

make sperm in spermatogenesis. Oogenesis is the production of an ovum or egg cell, the

female gamete or sex cell. It is one type of gametogenesis, or sex cell

production. Oogenesis happens in all sexually reproductive species. It includes all of the

immature stages of the ovum. As it matures, the ovum passes through five stages in mammals:

the oogonium, the primary oocyte, the secondary oocyte, the ootid, and the ovum. The other

type of gametogenesis is the spermatogenesis; it is initiated in the male testis with the beginning

of puberty. This comprises the entire development of the spermatogonia up to sperm cells. The

basic function of spermatogenesis is to turn each one of the diploid spermatogonium into four

haploid sperm cells.

The experiment was performed for two (2) laboratory meetings in the Principles of Embryology class. On the first part, the epididymis of the mouse was taken so as to observe sperm motility. Moreover, histology of the human and mouse testis were also observed with the use of prepared slides. On the second part, pig ovaries were obtained to observe pig oocytes as well as prepared slides of the oocytes of other mammals.

2. MATERIALS AND METHODS / EXPERIMENTAL DETAILS / METHODOLOGY

2.1 Spermatogenesis

Adult male Albino mice, Mus musculus, approximately 8 weeks old was procured from the Bureau of Animal Industry, Quezon City. It was acclimatize for two weeks prior to the actual experiment. The mouse was sacrificed using cervical dislocation. By surgical incision, the testes and epididymis were taken out of the body (Rashid et.al., 2012). The male reproductive parts were added with 1 mL of NSS and macerated using the mortar and pestle. A drop of the sample was placed in the glass slide and a cover slip was put on top of it. The sperms’ motility was later on viewed under the microscope.

Prepared slides of human testes were available. Thus, gametogenic stages in the prepared slides were identified and compared with the observation s in the mouse’s testes sample.

Figure 2. Testes and epididymis removed from the male albino mice

Figure 1. Dissection of the male albino mice on the lower ventral side to obtain testes and epididymis.

2.2 Oogenesis

Pig ovaries were obtained from San Roque slaughter house in Legazpi City on the day of experiment. The ovaries were stored in a thermal cup with 100mL of NSS on it prior to experimentation. A 5mL syringe with 18-gauge needle, that must contain 1mL of distilled water, was used to obtain the oocytes from the follicles of the ovaries (Hua et.al., 2011). The follicular fluid was put in a watch glass. When the particles of the sample were settled down, it was decanted instead of subjecting the sample for centrifugation at 1600r for 20 minutes at 4°C (Hua et.al., 2011); the histology and the quality of oocyetes in the aspirates were viewed under the microscope.

Prepared slide of a cat Felis domesticus ovary was also available and was viewed under the microscope.

3. RESULTS AND DISCUSSION

3.1 Gametogenesis

Gametogenesis is the process by which the gametes or sex cells are produced. There are

definitely different stages between the male and female gametes. Spermatogenesis refers to

the production and differentiation of spermatozoa or the male gametes while oogenesis is the

production and differentiation of the ovum or the female gametes. It is noted that in each stage

the gametes are named differently.

Figure 3. Pig ovaries obtained from slaughterhouse. Figure 4. Aspiration of oocytes from pig ovary using 18-Gauge needle and syringe.

3.2 Spermatogenesis

In order to observe the mammalian sperm, the sperm from the male albino mice was observed

under the microscope. Sperm motility was specifically taken into consideration. Sperm motility

under the microscope was seen as wriggling movements of the tail. However, there are actually

three types of sperm motility: (a) Progressive, (b) Non-progressive and (c) Immotility.

Progressive motility refers to linear movement of the sperm. Therefore, movement from location

to the other is observed. Non-progressive motility is referred to as only the wriggling movement

of spermatozoa, without shifting location. Immotility refers to no movement at all.

Figure 5. Comparison of Human Testes (A) 400x and Mouse Testes (B) 400x

According to Johnson, et. al (1980), only 42% of the testicular parenchyma consisted of

seminiferous epithelium in humans while 64% in rats. Moreover, only 64% of the seminiferous

epithelium was occupied by germinal cells in humans while 89% in rats.

The primordial germ cells of the embryo travel to the gonads and differentiate to form diploid

spermatogonia. Mitotic divisions occur afterwards to produce more spermatogonia.

Differentiation takes place and start of meiosis I occurs. The diploid spermatocyte undergoes

first meiosis follows to produce four haploid secondary spermatocytes. The second meiosis

occurs to produce early spermatids. Another differentiation stage occurs to produce the

spermatozoa while the sertoli cells provide nourishment for the sperm cells.

3.3 Oogenesis

The second part of the experiment included the aspiration of the oocytes from the pig ovaries.

The activity aimed for the researchers to view Grade A, Grade B and Grade C oocytes.

However, no oocyte was observed by the group though others groups were able to observe

Grades A and C oocytes. This was for the reason that the source of the ovary was a piglet

therefore the oocytes were most probably not yet fully developed.

The pig ovaries are located peripheral to the fallopian tubes of the female reproductive system.

Its average length is about 3-4 centimeters. Its surface is smooth but corrugated. It has a

pinkish color.

On the prepared slides, it is seen that the mammalian oocytes show similarities. Moreover, the

ovum itself is surrounded by smaller follicular cells.

4. CONCLUSION

Gametogenesis is divided into two categories: spermatogenesis for the male and oogenesis for

the female. The endoderm is the origin of the primordial germ cells which later travel into the

gonads then differentiation takes place so that gametogenesis continues.

Male gametogenesis starts at puberty and is a continuous process. It starts in prophase I until

the second meiosis and differentiation occurs so that mature sperm cells ready for fertilization

are formed.

The mammalian oocyte begins meiosis during fetal development but is arrested part-way

through meiosis I (MI). The first division is completed only until ovulation. Meanwhile, the

second division (MII) is completed only if the egg is fertilized. Starting from primordial germ

cells, an oogonium, which is a diploid is later formed. This later becomes a primary oocyte then

division is arrested. Oocyte reaches resting state or the dictyate. When first ovulation occurs,

first meiotic division occurs to produce a secondary oocyte and the first polar body. A secondary

meiotic division follows so that an ootid, now a haploid and the second polar body are

produced.the ootid later becomes an ovum, a haploid.

In the differentiation of the histology of mammalian testis, 22% of the human testis are occupied

by germinal cells while 54% of which occupy those of the rat testis.

REFERENCES

Rashid A, Nabihazara A, Ara C. “Testicular toxicity induced by deltamethrin in Albino mice”. Pakistan Journal Zoology. Vol 44(5). 2012. pp 1349-1353. Hua Z, Zheng X, Qiao X, Qing X, Xu H, Xiao H, Liu X, Li L. “A new tool for in vitro culture of porcine eggs”. African Journal of Biotechnology. Vol 10(14). 4 April 2011. pp. 2780-2784. Johnson, L., Petty, C. and Neaves, W. “A Comparative Study of Daily Sperm Production and Testicular Composition in Humans and Rats.” Biology of Reproduction 22, 1233-1243 (1980).