Gametogenesis of Drosophila melanogaster

Gametogenesis of Drosophila of Drosophila melanogaster melanogaster

Tricia Anne U. Barot Department of Biology College of Science, University of Santo Tomas

 Drosophila melanogaster , commonly known as the fruit fly, is a staple in scientific research. Gametogenesis is a process in which  primordial sex cells differentiate into either sperm or eggs. Sperm formation is called spermatogenesis, egg formation, on the other hand, is called oogenesis.

Figure 2. Sperm cell mitotic division

Figure 1. Sex organs of D. melanogaster 

In  D. melanogaster, spermatogenesis occurs within the testis and starts with the  primordial sex cells, called gonialblasts, gonialblasts, which undergo mitotic amplification divisions to generate a cyst of spermatogonia. The cyst of spermatogonia will then differentiate into spermatocytes, and ultimately, into mature sperm. One gonialblast goes through four rounds of mitotic divisions and two meiotic divisions to yield a total of 64 haploid spermatids. Spermatids undergo further maturation, a process called spermiogenesis, that involves the elongation of the sperm head and tail, and the reduction of the cytoplasmic material found in spermatids. Mature sperm are transported to the seminal vesicle, awaiting release during copulation.

In  D. melanogaster , oogenesis occurs within ovaries of the female fruit fly. The oogonia are called cytoblasts that undergo multiple mitotic divisions, but fail to undergo cytokinesis. Failure to successfully divide into new cells means that all the cytocytes that result from one cytoblast remain connected to the original cell. One cytoblast results into 16 cytocytes, however, only one cytocyte becomes the oocyte while the other 15 become nurse cells.

Figure 3. Egg cell mitotic division

These nurse cells synthesize large amounts of RNA and nutrients for the oocyte to accumulate massive amounts of cytoplasm in order to support the development of the future embryo. A special gene, named the par1 gene, is responsible for the formation of the oocyte in  D. melanogaster ; without the par1 gene, all 16 cytocytes will become nurse cells.

 both ends of the oocyte. The differences of the follicle cells are grounded on its function. Columnar follicle cells are found covering the oocyte instead of squamous follicle cells  because the oocyte needs more protection compared to nurse cells. Border cells, on the other hand, have another special function other than protect and nourish the egg prior to its release during ovulation; it is important in the determination of the anteroposterior pattern of the future embryo. The major production site for the yolk of the egg is the fat body of the female fly; yolk proteins are carried by hemolymph. References [1] Demarco, R.S., Eikenes, A., Haglund, K., & Jones,

Figure 4. Egg cell formation within the ovary of D. melanogaster

The whole cluster of oocyte and nurse cells is surrounded by ovarian follicle cells to form the egg chamber. The follicle cells secrete  both the vitelline membrane and the chorion which is a tough outer coat surrounding the egg. These cells are derived from the gonads and are thus of somatic rather than germ-line in origin. As the oocyte matures, the follicle cells become classified into three groups: namely, squamous, columnar, and border cells.

D.L.

(2014).

 Methods:

 Investigating

Spermatogenesis

 Drosophila

melanogaster. 

in

doi:

http://dx.doi.org/10.1016/j.ymeth.2014 .04.020 [2] eol.org. (n.d.) Drosophila melanogaster. Retrieved from http://eol.org/pages/733739/overview on 29 Aug 2016. [3] Slack, J. (2013). Essential Developmental  Biology. West Sussex, UK: Blackwell

Publishing Ltd. [4] Woodworth, C. (2003). Gametogenesis. Postdam, NY: Clarkson University. Figure 4. Egg chamber of the D. melanogaster egg cell

Squamous follicle cells are found covering the nurse cells, while columnar follicle cells are found covering the oocyte. Border cells, on the other hand, are found at