Blog Assignment: Part Three

Long Distance Communication (Endocrine)

Endocrine signalling involves the transfer of information from one cell to another, where an endocrine hormone is transported from the signal-producing cell to the receiving cell through the circulatory system. This can be achieved via the blood plasma, lymph or cerebrospinal fluid since the signal producing cells and the signal receiving cells are distant to each other, therefore communication over long distance.


This process occurs, for example, between the basophil cell of pituitary gland and the oocyte cell of the reproductive system. Generally, hormones are chemicals that are released into the blood stream to perform a specific function with respect to its target cell. Basically, they function in facilitating the regulation of body functions by either stimulating or inhibiting other cells. The ovaries are just one of the many organs in the body regulated by hormones. Initially, a follicle grows within one of the ovaries; a follicle consists of the developing egg cell and the support cells that surround, providing the required nourishments. As this occurs, a small structure in the brain, the pituitary gland (specifically the basophil cell) releases hormones, mostly FSH which induces the follicles to begin growth.



The dominant follicle releases a hormone, estrogen which prepares the lining of the uterus for the egg. As this occurs, the estrogen in the blood stream enables the brain to release a surge of LH which results in the rapid enlargement of the follicle. Approximately 24 to 36 hours after the LH exposure, the follicle disintegrates and thus releases the egg cell (ovulation).



Cell Type – Oocyte (Egg) Cell of Xenopus Laevis

This is my life…. I am an Oocyte (EGG) Cell!



          In research and development, the oocytes and embryos of Xenopus Laevis are widely used as model systems as their handling and manipulation is easily achieved. Oocytes are tetraploid cells (having four sets of chromosomes) located within the ovarian lobe of adult female frogs and are surrounded by a layer of follicle cells. The large nucleus within the oocyte is called a germinal vesicle and contains genetic information and mitochondrial DNA.

            It is the largest single cell in the body (filling up the ovarian volume) and has many similar structures to that of a somatic cell. Oocytes have two poles, the animal pole and the vegital pole. There are permeable to small molecues but when fertiliztion does not occur, they convert to impermeable molecules. 

         The oocyte is an active site for mRNA and protein snythesis as they provide an important expression system used extensively in molecular biology. They play a massive role in reproduction of the Xenopus Laevis species, together with the sperm of their male counterparts. Their fate, upon fertilization is to grow and develop into a full functioning  organism, therefore providing a continuation of their respective species. 







Choice of Model Organism – Xenopus Laevis (African Clawed Frog)

For this assignment, I chose the Xenopus laevis (African clawed frog) as the model organism for my research.

As defined in the previous post, a model organism is a species that has been extensively analyzed and studied due to the fact that it is easy to maintain and breed in a laboratory setting.

The African clawed Frog is a species of  aquatic frogs found mostly in Sub-Suharan Africa. They are greenish-grey in colour and can grow up to a length of thirteen (13cm) with both it’s head and body flattened. However they posses no ear and tongue but instead have lateral lines along their bodies used to sense vibrations and movement in the water. One characteristic feature of this organism is their clawed feet (present only on their hind feet) hence the name African clawed Frog. They use these to tear up any large pieces of food before eating it. 

African clawed frogs reproduce via eggs.

The females are easily identified since they are approximately 20 percent larger than their male counterparts. In research and development, these respective eggs and embryos are used as model systems due to their experimental tractability and evolution alongside human beings.  They take between one to two years to achieve maturity, being tetraploid (4x) like others of its genus.

Because their embryo is large and easy to manipulate, they are extensively used in developmental Biology. 





Model Organism: Yeast (Saccharomyces Cerevisiae) by Professor Rhona Borts.

After viewing this respective video, I was amazed by the extent to which model organisms can be used to study and development cures for human diseases. Hope it was as educating to you as it was for me!

This video provides a thorough explanation on reproduction of a specific type of yeast known as Saccharomyces cerevisiae (found in baking and brewing). It illustrates why yeast is used as a model organism and the respective advantages related to its structure and function. Professor Borts uses this model organism to study how gametes (sperm and egg) are generated, and by extension, DNA replication. She also relates numerous human diseases that are modeled into yeast; Infertility and Colon Cancer.

What are Model Organisms? Why are they useful in Scientific Research?


 A model organism is a species that has been extensively analyzed and studied due to the fact that it is easy to maintain and breed in a laboratory setting. Models are those organisms with a wealth of biological data that make them attractive to study as examples for other species and/or natural phenomena that are more difficult to study directly. 

These specific organisms possess particular experimental advantages which can be further utilized in many research projects. Therefore, this mechanism provides an efficient method of investigating these respective organisms.

Model Organisms can further be classified into three categories:

1) Genetic Model Organism: These are species that are amenable to genetic analysis, i.e. they breed in large numbers and have a short generation time so large-scale crosses can be set up and followed over several generations. Examples include the fruit fly (Drosophila melanogaster) and the nematode worm (Caenorhabditis elegans) 

2) Experimental Model Organisms: These species may not necessarily be genetically amenable (i.e. they may have long generation intervals and poor genetic maps) but they have other experimental advantages. For example, the chicken and the African clawed frog Xenopus laevis have many disadvantages in terms of genetics but they produce robust embryos that can be studied and manipulated with ease.

3) Genomic Model Organisms: Regardless of their genetic or experimental advantages and disadvantages, certain species are chosen as model organisms because they occupy a pivotal position in the evolutionary tree or because some quality of their genome makes them ideal to study. An example is the puffer fish (Fugu Rubripes) which has a similar gene repertoire to humans but a much smaller genome (400 million base pairs instead of 3000 million). 



In classrooms, Model Organisms are widely used to demonstrate to students important concepts in various disciplines. This method of teaching is effective in that the information relayed to these students is done so in a fun and productive manner. There are three main advantages:

1) In a laboratory setting, the model organism’s immediate response to the change of environment will enhance students’ learning and serve to hold their attention and interest.

2) Secondly, the use of model organisms involves hands-on activities that provide a unique experience that could not be obtained with other teaching methods.

3)Thirdly, by working with model organisms, students are able to explore scientific methods and concepts themselves. Moreover, they will come to understand about the investigative nature of the scientific enterprise, including how conclusions are drawn from data.





Cell and Developmental Biology…

And so the blogging continues but in a different perspective…. From Biochemistry to Cell and Development Biology. Be sure to look out for more posts and discussions. 


List of Model Organisms:

1) Drosophila Melanogaster (Fruit Fly)


2) Xenopus Laevis (African Clawed Frog)

3) Caenorhabditis Elegans (Nematode Worm)

4) Arabidopsis Thaliana (Mustard Plant)

5) Zebrafish

6) Mouse

7) Tomato (Solanum Lycopersicum)