Reflections: Tetra-Amelia

Last week in our Developmental Biology class, we did presentations on different topics. I did my presentation on Tetra-Amelia. Tetra-Amelia is an autosomal recessive disorder that has the phenotypic results of absence of all four limbs. Tetra-Amelia causes severe malformations in the face, head, heart, nervous system,skeleton, genitalia and lungs. It is caused by a mutatio on the WNT3 gene.
In class we studied the WNT pathway. The WNT genes play a critical role in development before birth. It gives instructions to make proteins that will be a part of the WNT chemical signaling pathway. The WNT3 gene is specific to creating certain genes that are responsible for the development of limbs.

The WNT proteins are ligands and are able to bidn to receptors on other proteins. They bind to the receptor frizzled protein. This binding to frizzled causes the activation of the disheveled protein. Disheveled then inhibits glycogen synthase kinase 3 (GSK3). When GSK3 is inactive, B-catenin is free to associate with an LEF or TCF protein. This association with the two proteins acts like and becomes a transcription factor. These cascade of effects causes growth and division of cells that will later determine what those cells will differentiate into. The WNT3 gene is critical for outgrowth of limbs and is critical for determining the anterior-posterior axis. IT has five exons and encodes for a protein that has 355 amino acids. When the sequence of WNT3 was done, a nonsense mutation was found. The nonsense mutation at codon 83 created a premature stop codon. This causes only 82 amino acids to be produced instead of 355 amino acids

Dictionary: Cell Signaling

How do cells know where to go and how do they communicate with each other? This process is done by induction, which is an interaction between tissues and or cells within close proximity of each other. Induction has two steps, the inducer (what produces the signal) and the responder (the tissue or cell being induced). In order for the cell to respond to the inducer, must be able to respond to the signal. This ability to respond to a signal is called competence. Each cell has a receptor for the signaling pathways. There are four types of ways cells signal each other.

1. Autocrine --> affecting itself
2. Paracrine --> adjacent to each other
1. FGF
2. Hedgehog
3. WNT
4. TGF-B
3. Juxtacrine --> no diffusion; adjacent to each other (CONTACT)
4. Endocrine --> far from each other
1. Ex: Hormones

Together these different signals work together in development processes. If there is a mutation in a receptor, then the correct protein will not produced or may not be produced at all. This can cause many developmental issues in the organism.

Encounters: Zebrafish

Unfortunately, our zebrafish did not lay any eggs, so we were not able to observe the development of the zebrafish. I was very interested to see the development of the zebrafish, since their embryos are see through. I went online and found a youtube video of the developmental stages from zygote to the larval period.

The stages of the zebrafish development begins with the zygote period, in which the zygote reaches its morula stage and then reaches the 2 cell stage.

 

Within about 0.75 to 2.25 hours, it reaches the cleveage period where it will divide into the 64 cell stage. Meroblastic cleavage occurs in the zebrafish.

Between 2.25 and 5.25 hours, the embryo reaches the blastula stage. After the mid-blastula transition stage

Gastrulation begins between 5.25 10.33 hours. The tailbud begins to form and 2 somites can be observed.

Betwen 10.33 and 24 hours, segmentation begins to happen. This the period in which the folding of the embryo begins to occur and the formation of the somites begins to continue. The embryo begins to elongate and the neural cord and notochord continue to develop. During this stage, the dermis, vertebrae and skeletal muscle are formed as well.

The next stage that happens is the pharyngula period, which occurs between 24-48 hours. During this time period, the notochord is fully developed, the pectoral fins begin development and the cirgulatory system can be observed along with a heart beat.



The next step is the hatching period in which the olfactor palcodes are fully developed, the pectoral fins are elongated and the development of cartilage begins. This stage usually occurs between 48 and 72 hours.

The last stage of development of the zebrafish is the larval period.

VIDEO OF ZEBRAFISH DEVELOPMENT

Investigations: KG5

Thousands of people die from cancer each year. Those who survive still have a risk of the cancer returning again in later years. There might just be hope for those with cancer thanks to the many time, energy, and dollars put into finidng a cure or better treatment. Researchers from University of San Diego created a drug that is able to change the shape of the protein RAF. RAF is a protein that regulates cell proliferation and survival in normal cells, but in tumor cells, its regulation becomes irregular. The KG5 drug has only been tested on animals and tissue samples from patients with cancer. This drug is very primitive and scientists are hoping that they can use it for cancers that are invasive and have developed resistance to treatment.

Encounters: Turkey Day!

As many of you know, yesterday was Thanksgiving Day! Millions of American families sat down at the table yesterday evening and feasted upon the turkey and many many other dishes. It seems as if all the turkeys in America are fed well year round, preparing them for this one day special occasion. Being that in class we studied the development of chick eggs, I wondered if the development of turkey eggs would be the same? I mean it would make sense that most of the development of turkey eggs would be similar to that of chicken eggs. After-all, they both develop into birds...right?
Cleavage in chick eggs occurs through discoidal cleavage. Discoidal cleavage is a type of meroblastic cleavage that happens when a disk of cells are produced at the animal pole of the zygote. Cleavage only occurs in the blastodisc. Cleavage in the turkey egg is asynchronous and asymmetrical unlike the chick embryo. 
Have you ever thought about why we only chick eggs and not turkey eggs? The reason is because it takes a turkey a longer time to to lay the egg and it takes a longer time to hatch. Therefore chicken eggs are widely used, because they lay eggs at a faster rate and they take a shorter amount of time to hatch.

Reflections: Chick Embryology

Last week our class did a lab on the embryology of the chick. We had a chance to observe the development stages from the 13-18 hour chi to the 96 hour chick embryo. It was very interesting to follow one part of development and observe the changes as the chick embryo matured. I decided to follow the brain through its development. The brain begins its development at the 33-hour chick embryonic stage. It is at this stage that you can see the development of the telencephalon which will later be associated with the olfactory organs such as the smell and taste. The telencephalon will later develop into what we know as the cerebrum, which is important for intelligence. The diencephalon will give rise to the hypothalamus and the infundibulum which store the hormones oxytocin and antidiuretic hormone. The mesencephalon will become the process center of what can be seen and what is heard. The myelencephalon will give rise to what we know as the medulla oblongata which is reponsible for balance. As the chick moves onto its next stages, the brain becomes more and more mature and you can see the head folding. Below you can see the different parts in the developing 33-hour, 48-hour, 72-hour, and 96-hour chick embryo.

Encounters: Genotype XO

I work at a pediatrician's office, and about one to two weeks ago, a patient was born with a genotype of XO. This type of genotype is referred to as Turner Syndrome. It occurs when there is only one X chromosome and the other chromosome is not there at all. The patient's parents were very distraught, because they didn't know what to tell their friends and family members what the sex of the baby was. I found this very interesting because I have never knew of anyone with a genotype other than XX or XY. The doctor stated that in order for the infant to grow into a girl, she would need estrogen shots/pills to boost external female characteristics once she reaches puberty. It is not known whether she will be fertile or infertile, because that will be determined once she reaches the age of puberty.

Investigations: Nature vs. Nurture

Many scientists, mostly geneticists, have argued for years whether it is our genetics that determine our personality and development versus whether it is our environment that determines our personality and development. According to the Proceedings of the National Academy of Sciences (PNAS), the issue of nature versus nurture can finally but be put to rest, because there is evidence to show that there is an interaction between biology and environment in early life that determines and greatly influences human development. According to Marla Sokolowski, a genetiscist from University of Toronto, biologists used to believe that our differences between each other are pre-programmed within our genes while psychologists believed that each person was born with a clean slate and over time, each experience molded us into the person we are today.
A study was done by Sokolowski and her colleagues to see how a stressor in early life can affect adult life. They did this study by taking fruit flies and giving them a malnourished diet and observed their behavior later on as they reached the adult stage.Their results showed that the malnourished fruit flies at an early stage had a great impact upon their adult stage. When they gave another group of fruit flies a well nourished diet at an early stage and observed their adult life, they realized the well nourished diet had a great impact upon their adult life. This is due to the fact that the foraging gene made an enzyme called PKG. When the fruit fly is malnourished, there is a low level of PKG produced, hence the not so health fruit flies that resulted. But when the fruit fly is well nourished, the PKG level is high. This proves that genes work hand in hand with the environment.

http://www.redorbit.com/news/science/1112721044/impact-adversity-early-life-development-102612/

Investigations: Brain Disease Treatment?

Earlier within my blog posts, I talked about the benefits of cloning and how cloning can help those who have diseases such as Alzheimer's, Huntington's, and Parkinson's. There is still a lot of debate on using techniques to clone, but in the mean time is there another way to help treat these degenerative diseases? According to Science  Daily, scientists transplanted embryonic neurons into the brains of newborn mice and to their astonishment, these embryonic neurons survived. It turns out that a type of brain cell linked to many different neurological disorders (GABA-secreting interneurons) can be added in significant numbers into the brain and can survive without causing any harmful affects. What the scientists found to be most amazing is that these embryonic neurons survived even when added in large numbers. For years they thought that the brain could only hold a certain amount or had a limited capacity for these cells, but this experiment done with the mice proved their theory wrong.
In laboratory rats, the insertion of these GABA-secreting interneurons showed that transplanting these cells into the brain can increase plasticity, reduce seizures, and reduce Parkinson's-like symptoms in rats. They can also help to decrease pain sensation.
If research is pursued within this area, maybe we won't need to use cloning for nerve degenerative diseases. Even though these experiments show that transplanting GABA-secreting interneurons in rats can treat degenerative diseases in rats, this does not mean that it can do the same in humans.There is a chance that it will.

Dictionary: Spermatogenesis

Our bodies are constantly replacing old cells with new cells through the process of mitosis. But how does the human body develop our sex cells? This process is done through meiosis. In males, the production of sperm is known as spermatogenesis and the production of eggs is known as oogenesis. In spermatogenesis, the gametes produced by the male are known as spermatozoa or sperm. In oogenesis, females produce ova, or eggs.
Spermatogenesis begins at puberty and occurs within the testes. Within the testes are seminiferous tubules. The walls of the seminiferous tubules are filled with cells called Sertoli cells. Sertoli cells provide nutrients and protection for the developing sperm. In between the seminiferous tubules are Leydig cells. Leydig cells are responsible for the hormone productino of testosterone. There are five steps that are needed for the developing sperm to turn into mature sperm. The first stage is known as the spermatogonium which happens within the outer region of the seminiferous tubules. The spermatogonium is where the cells replicate DNA in the S phase of meiosis. Next the primary spermatocyte is produced through Meiosis I. The secondary spermatocyte is produced through Meiosis II. As the developing sperm get closer to the lumen, the spermatid is formed. Lastly, the spermatozoan is formed and heads out the lumen (inner region of the seminiferous tubules) and through the epididymis.

Dictionary: Bipotential Gonads

Everyone is born with the potential to be either male or female. Everyone is born with both the Wolffian duct (male duct system) and the Mullerian duct (female duct system). What determines maleness is the the presence of the SRY gene. The SRY gene is what allows testis to develop. Once the testis are developed, the male duct system begins to form.When a male is about to be formed, a hormone called the anti-Mullerian duct hormone is released so that the Mullerian duct system which would develop into a female, would be destroyed. Once the Mullerian duct is destroyed, the formation of the testis, including the epididymus, the vas deferns, seminal vesicle and seminiferous tubules can develop. Within females, they too are born with both the Mullerian and Wolffian duct systems. But what is different within females is that the Wolffian duct system begins to decrease when it realizes that the SRY gene is not there to tell it to develop into testis. Thus the Mullerian duct can now develop into the uterus, the fallopian tubes, cervix and parts of the vagina.
There are two part sex determination stages. One stage determines the sex internally and one stage determines the sex externally. When something goes wrong, you could have internal male sex organs but have external female organs, or vice versa. This is why you could have a person with the outer apperance of a female, but internally their organs are male, and they are not able to produce because they do not have a uterus.

Reflections: Sea Urchins

Today in lab we studied the development of sea urchins. In order to understand how sea urchins are developed, we need to understand the stages of animal development. The first stage in development is fertilization. Fertilization is the process in which the sperm and egg fuse together. The next stage is cleavage. This is where the cell will begin to have rapid miotic divisions which will form into a sphere called the bastula. Gastrulation is the next stage of animal development. This is the stage where the three germ layers, ectoderm, mesoderm and endoderm are formed. Each layer is specific to which part of the body will arise. The ectoderm will give rise to the epidermis, the mesoderm will give rise to the muscles and the endoderm will give rise to the dermis. The second to last stage of development is organogensis. This is the process in which organs are formed. The last stage is gametogenesis. Gametogenesis is the formation of gametes.

Within the lab today, we observed the first stage of animal development, fertilization. We first started off the process of fertilization by taking the sea urchins out of the tank and placing them into a basin of sea water for about a minute. Next we placed the  sea urchins upside down within the petri dish and took 2 mL of potassium chloride (KCl) and injected it into the bottom of the sea urchin. We then poured the sea water into a container and turne dthe sea urchins over to observe whether it was a male or a female sea urchin. The male sea urchins gametes were white and the female sea urchin's gametes were yellow. After this was done, we looked at the egg under the microscope and the sperm under the microscope. Next we took the slide with the egg and placed a drop of sperm onto the slide and watched the fertilization process begin. At first the egg sat there for a few seconds then out of no where, the many many sperm came out of no where and quickly rushed to the egg. Within a matter of seconds the fertilization envelope was formed such that there will be a block of any more sperm from fertilizing the egg and creating polyspermy. Here is a picture of the sperm trying to enter through the fertilization envelope that has formed.

I really enjoyed this lab. It was the first time I was able to see fertilization done within that amount of time. Although I was not able to observe the rest of the stages, one day I hope to see the cleavage stage within the gametes of the sea urchins. I think it would be amazing if I was able to see the cell divide into many cells and begin to differentiate. Overall I really enjoyed this lab, I just wish we were able to view the sea urchins through the clevagage and gastrulation stage.

Investigation: The Benefits of Cloning

Today we often hear about the many ethical issues about the topic on cloning. Many of Americans believe that cloning is not ethically correct. They believe that God can only create life and that if we tamper with it then we are playing God. However, many people are not aware of the benefits of cloning. For example as we get older, we tend to lose our brain cells and in some people, they lose their brain cells at a faster pace than others. Alzheimer's is a brain disorder that causes brain cells to be destroyed. For people with Alzheimer's, cloning can serve as a way where the damaged nerve cells can be replaced with embryonic stem cells that were grown to produce nerve cells. The best part of cloning is that, the person does not have to worry about rejection by their immune system. A lot of diseases and problems would be cured if human cloning was allowed.
Another great example where cloning would be useful is in babies with birth defects. If we use cloning we can prevent these infants from having that birth defect. For example if you are an older female who would like to have kids, instead of having the risk of having a child with down syndrome, cloning could be used to prevent the child from having down syndrome by altering that gene.
There are many people today who are in need of different transplants, but the problem with transplants are body rejections and there are long lists of people who are on donor lists. Cloning will solve both problems because the cloned body part will not be rejected because it has the same DNA as the original organism. For example, if a patient is in need of a liver transplant, the likelihood that the liver from a donor will be rejected by the patient is at a higher rate than that of a liver from the patient's stem cell.
As you can see, cloning has many benefits. If only cloning were allowed, many people would be cured of diseases such as Alzheimer's and Parkinson's. Because cloning is not allowed on humans, scientists are not able to test and study the long term pros and cons of inserting stem cells into the body to regenerate specific organs or tissues or cells.