Exam 2 Flashcards
- Describe the formation of body axes. Tips on what to focus. Why do animals present body axes? Are all animal body structures symmetric? Do you know any molecular mechanism involved in generating symmetry/asymmetry? Do you know any disease related to this?
In animals the correct position of tissues, organs and appendages is essential, the correct of position of these are defined by the body axes. The formation of body axes occurs during gastrulation. The formation of the body axes is through expression of specific sets of genes that regulate which cells will develop into specific structures during gastrulation.
During gastrulation the formation of the primitive streak occurs, cells will migrate to the midline of the gastrula and cause a thickening, this is what the primitive streak is. At the cranial end of the primitive streak the primitive pit is formed by epiblast cells forming a circular cavity, then migrating epiblast cells will join the primitive streak at the cranial end forming the primitive node, this is what becomes the primary tissue organizer where transcription factors (TGFB, Nodal, WNT, BMPs) further induce tissue formation in later stages.
Epiblast cells in the lateral edge of the epiblast layer will undergo epithelial to mesenchymal transition (EMT) to be able to migrate into the primitive streak. The first cells of epiblastic EMT to move into the primitive streak will transform into the endoderm. The second cells that do this will transform into the mesoderm. Multiple mesodermal structures such as the notochord (cells that pass through the primitive pit become notochord) will develop. The formation of the notochord is very important during embryonic development as it provides structural support, defining the midline of the embryo as well as providing chemical and physical interactions with the dorsal lying ectoderm to differentiate. It is the notochord that defines the anterior-posterior axis.
The notochord will secrete Sonic hedgehog ligands in a morphogenic gradient pattern which causes the formation of the ventral/dorsal axis. The formation of the left-right axis is caused by Nodal flow. Nodal flow is the leftward movement of fluid across the anterior-posterior plane, this is caused by movement of the cilia within the embryo. Nodal flow causes a morphogenic gradient which determines the left-right axis, this is the cause of asymmetry in our body.
Holt-Oram syndrome is a disease where the septum that separates the right and left sides fail to grow normally, leading to absence in wrist or thumb bones.
- What are induced pluripotent cells? Tips: Explain their discovery and why they are important both for defining tour knowledge of development as well as a medical tool.
Somatic cells, cells that are fully differentiated, can be reprogrammed into an embryonic-like state by the transfer of nuclear contents into oocytes or by fusion with embryonic stem cells (ES). There are factors that induce this somatic cell reprogramming and those factors are known as the Yamanaka factors, the factors are Oct3/4, Sox2, c-Myc, Klf4.
John B Gordon was the one that discovered that cell differentiation is reversible through nuclear transplantation. He replaced the immature cell nucleus in an egg of a xenopus with a mature intestinal cell, the xenopus egg would grow into in a normal xenopus, it showed that the DNA of a mature cell still had all the information needed to develop all cells in the xenopus. This technique is known as somatic cell nuclear transfer.
Shinya Yamanaka discovered how somatic mice cells could be reprogrammed into pluripotent
stem cells through the introduction of 4 genes. During his experiment there was 24 factors that was suspected of conducting pluripotency. What he did was that he used mice embryonic fibroblasts which are differentiated cells with no stem cell properties, he then took the 24 suspected pluripotency factors and induced it back into fibroblasts which resulted in growth of colonies on a petri dish, meaning they had become pluripotent. They then took this cocktail of 24 factors and removed 1 at a time eventually leading to the discovery that c-Myc, Klf4, Oct3/4 and Sox2 were the factors responsible for the pluripotent induction.
- How many model organisms could you list> For each of them, explain a good reason why they could be chosen and describe a milestone experiment that was performed with their use.
Dorosophilia, mouse, C elegance, ANSWER THIS
- Describe the concept of differential gene expression. Why is it important, and how can it be studied?
We share 60% homologus genes with the dorosophilia yet we look and are completely different from it. It’s the same with many other animal species such as mice for example, we have a lot of DNA that is eqvivalent in both of us but it’s the gene expression that makes us so different. Gene expression is how the DNA is expressed, what DNA gets transcribed and what doesn’t and how much of the DNA is transcribed some will have enhancers so it will be big a lot of gene transcritpion for that DNA while some doesn’t so they will still be transcribed but not as much.
Gene expression measurement is usually achieved by quantifying levels of the gene product, which is often a protein. Two common techniques used for protein quantification include Western blotting and enzyme-linked immunosorbent assay or ELISA.
- Describe what signalling pathways are, and how the different components of a signalling cascade could be discovered.
Signalling pathways are the way cells communicate with each other and there are different types of signalling pathways. Depending on the signal received, the cells may reorganize their metabolic activities, divide, migrate, or even undergo apoptosis. The functions of these signaling proteins can be studied with the help of classical biochemical approaches, such as western blotting, pull-down assays, and immunoprecipitation.
- Describe the Spemann Organizer: how was it discovered and what is its molecular nature? Why was the latter elucidated only ca. 80 years after its discovery?
The Spemann-Mangold organizer, also known as the Spemann organizer, is a cluster of cells in the developing embryo of an amphibian that induces development of the central nervous system. This discovery also introduced the concept of induction in embryonic development, which is the process by which the identity of certain cells influences the developmental fate of surrounding cells.
Hans Spemann showed that by transplanting presumptive epidermis into an area of presumptive neural tissue the presumptive epidermis would develop into presumptive neural tissue and likewise when he transplanted presumptive neural tissue into presumptive epidermis. This gave rise to the idea that there were some type of organization center that was determined prior to embryonic development which also influenced differentiation of adjacent cells. He tested this hypothesis together Hilde Mangold resembled the previous experiment but now they used embryos from two different species Triturus taeniatus and Triturus cristatus. Teanitus is pigmented whilst cristatus is not which allowed for easier observation. They were able to see that a transplanted piece of the blastopore lip from the taeniatus into the cristatus and vice versa these developed normally. This experiment concluded that a piece of the upper blastopore lip can be transplanted into indifferent tissues and induce the host tissue into the formation of a secondary embryo, therefore implicating the transplanted tissue as an organization center.
- Eyes have been described as evolving more than 40 times, independently, in the animal kingdom. Do you agree? Motivate your answer.
Complex, image-forming eyes have evolved independently several times. The eye distinctively exemplifies an analogous organ found in many animal forms.
- How many mechanisms of sex determination do you know> why, in your opinion, does sex exist?
Sex determination depends from species to species. In mammals the presence of a chromosomes XX and XY determines sex. The Y chromosome determines male sex because the Y chromosome contains the SRY gene which produces a protein called sex-determining region Y protein that activates a testis-forming pathway which leads to the production of anti-mullerian hormone, testosterone and dyhyrdrotestosterone further leading to male sex characteristics.
Birds have a different sex determination, theirs is dependent on chromosomes ZZ and ZW, there is no counterpart to the SRY gene on the Z or W chromosome, but instead it is dependant on DMRT1 gene, we also have this gene in mammals and they are a member of the testis-forming pathway, but in order for testis development 2 DRMT1 alleles are needed. DMRT1 gene is present on the Z chromosome, making ZZ the male and ZW the female in birds.
Drosophila also have XX and XY as we humans do, but in this case the Y chromosome doesn’t determine sex but rather the sperm production capabilities in Drosophila. The sex determination in drosophila is determined primarily by the ratio of the number of X chromosomes to the number of autosomes. There is a balance between female-determining factors encoded on the X chromosome and male-determining factors on the autosomes that determines the sex-specific pattern of transcription. XX, XXY, XXYY are females, XY and XO are males.
- What is chromatin> Describe the Implication of its structure on Gene Expression.
The defenition of chromatin is the mixture of chromosomes wrapped around the proteins histone to make them more condensed. This also affect gene expression depending on how tightly wrapped and how avaible they then are for transcription factors around the histones. Euchromatin and heterochromatin. Heterochromatin is highly condensed, gene-poor, and transcriptionally silent, whereas euchromatin is less condensed, gene-rich, and more easily transcribed.
- Describe Gastrulation. Why is the developmental stage so important?
During gastrulation the formation of the primitive streak occurs, cells will migrate to the midline of the gastrula and cause a thickening, this is what the primitive streak is. At the cranial end of the primitive streak the primitive pit is formed by epiblast cells forming a circular cavity, then migrating epiblast cells will join the primitive streak at the cranial end forming the primitive node, this is what becomes the primary tissue organizer where transcription factors (TGFB, Nodal, WNT, BMPs) further induce tissue formation in later stages.
Epiblast cells in the lateral edge of the epiblast layer will undergo epithelial to mesenchymal transition (EMT) to be able to migrate into the primitive streak. The first cells of epiblastic EMT to move into the primitive streak will transform into the endoderm. The second cells that do this will transform into the mesoderm. Multiple mesodermal structures such as the notochord (cells that pass through the primitive pit become notochord) will develop. The formation of the notochord is very important during embryonic development as it provides structural support, defining the midline of the embryo as well as providing chemical and physical interactions with the dorsal lying ectoderm to differentiate. It is the notochord that defines the anterior-posterior axis.
Important because: It primes the embryo for organogenesis by creating the three germ layers that are able to differentiate into tissues, it forms the body axis due to morphogenic gradients which allow for the correct position of the organs.
- Define “stem cells”
There are different types of stem cells with various deffentation ability. Totipotent stem cells can become any cell type and unipotent stem cells such found in the liver that can only give rise to new liver cells. But stem cells can generate more of themselved and with the exception of unipotent stem cells they can become different cell types as well.
- Describe the differences between epithelial and mesenchymal cells.
Epithelial cells are specialized cells, which line cavities, organs, and vessels in the body. In contrast, mesenchymal cells are unspecialized cells, which are capable of differentiating into any type of cells in the body at any time.
- What are transcription factors?
Transcription factors are proteins involved in the process of converting, or transcribing, DNA into RNA. Transcription factors (TF) control gene expression by binding to their target DNA site to recruit, or block, the transcription machinery onto the promoter region of the gene of interest.
- Barnacles (Cirripedia) are crustaceans that have been classified among mollusks for many centuries. What evidence made us include them into the right taxon (animal group)?
A scientist working with them thought they were just plants but when he started cutting in them they experienced pain and started having animal like movemeant which made us classify them as animals instead.
- We now possess a complete sequence of the human genome. And that of several other organisms. Why is this important?
It is important because it uses information from DNA to develop new ways to treat, cure, or even prevent the thousands of diseases that afflict humankind.
