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.