User:Tphelpsdu/C. elegans Development/sandbox

Life Cycle (Kyanna)

The C. elegans life cycle has an embryonic stage, a set of four larval stages and an adult stage as the last stage. First, the C. elegans embryos are and left to hatch. After hatching, the larval stage begins. Within the larval stage, there are four molts that take place for the organism to enter the adult stage.

During the development of the embryo following fertilization, two meiotic divisions take place and the cytoplasm that was within the cell moves towards the posterior and the cortical cytoplasm is moved to the anterior region. After cleavage continues, and the cells continue to divide, gastrulation begins to take place. Gastrulation is marked by the stage where two cells move into the interior as part of the invagination process.

Fertilization (Kyanna)

The fertilization process in C. elegans begins with an amoeboid sperm cell. The sperm enters any part of the outer surface of the oocyte. While the point of entry of the sperm is known to be random, it later determines the posterior of the zygote. In the C. elegans that contain hermaphrodite oocytes, the mature oocyte goes through ovulation and travels to the spermatheca. This results in fertilization.

When fertilization takes place in the hermaphrodite C. elegans, the process begins near either the intestine or anus portion of the worm. The oocytes mature in a single file line depending on their stages in development. They are formed by budding from the syncytial gonad. Every oocyte bud created contains one nucleus. The oocytes are fertilized once they enter the spermatheca. After passing through the spermathecal, the embryos develop in the uterus and get discharged through the vulva.

Another route of fertilization occurs when a male nematode inseminates a hermaphrodite. The male sperm found in C. elegans is used to fertilized oocytes. The sperm of the C. elegans consists of a nucleus with mitochondria tightly packed around it. There are no flagellum on the sperm of C. elegans.

Cleavage(Alex)

C. elegans exhibit rotational holoblastic cleavage. When cleavage begins 4 founder cells are created. The cell division in C. elegans is Asymmetrical. This means that during the first cleavage the cleavage furrow is located asymmetrically along the axis of the egg. Axis determination in C. elegans is determined by elongated axis found during cell division. The decision of which end of the cell will become anterior or posterior is determined by which end the sperm cell enters the egg. When the sperm enter the oocyte Cytoplasm the centriole pushes the male nucleus to the nearest end of the oblong oocyte this end is the posterior pole. The second anterior to posterior asymmetry is seen shortly after this. P-granules move towards the posterior end of the zygote, so they can only enter the blastomere. P-granules are ribonucleoprotein that function in specifying the germ cells.

Gastrulation(Alex)

Gastrulation in C. Elegans starts early compared to other organisms, it begins just after the formation of the P4 generation in 24-cell Embryos. After the 28 cell stage, 2 daughter cells will migrate from the ventral side of C. elegans into the center of the embryo. When this occurs they will divide and cause the formation of a gut consisting of 20 cells. The inward migration of Ea and Ep cells creates a tiny blastopore.

Neurulation(Alicia)

Neurulation is the stage in which the nervous system begins development following gastrulation. The beginning of neurulation occurs when the cells that will later make up the nervous system become internalized.4 The cells of the ventral epidermis begin invagination into the gastrula and division occurs in order to produce neuroblasts. The ventral surface of the embryo is comprised mainly of neuroblasts at this point and the neuroblasts continue to undergo division. The neuroblasts then form organized groups of cells within the embryo to create the structure of the nervous system. Following the last round of divisions of the neuroblasts, the surface of the embryo begins to be covered by the hypodermis that makes up the chitinous outer layer of C. elegans6. The end of neurulation is called the comma stage which occurs 300 minutes after the beginning of fertilization.

Axis Signaling (Alicia)

Axis development in c. elegans is crucial in determining how differentiation will take place. To determine the anterior-posterior axis in C. elegans, the cortical PAR genes are needed. PAR-1 and PAR-2 proteins determine the posterior potion of embryo while PAR-3 and PAR-6 determine the anterior. Both of these are present following the first mitotic division of the C. elegans embryo. The dorsal-ventral axis of C. elegans is formed following the division of the AB cell during cleavage. The dorsal/ventral axis is determined following the second mitotic division when the AB cell changes orientation of the mitotic spindle. The dorsal and ventral axis of the C. elegans embryo is determined by maternal genes apx-1 and glp-1. Glp-1 is used to determine the ABp and Aba cell fates during cleavage along with the maternal gene apx-1 .11 The left right axis of the C. elegans embryo is determined as a result of the anterior-posterior and dorsal-ventral determination. This occurs after the division of the 4-cell embryo and involves rotational cellular rearrangement and Wnt signaling.

Advantages/ Disadvantages as a Model Organism

Before you can get to the advantages and disadvantages of using the C. elegans as a model organism, it is important to understand why this organism was first chosen for these specific studies and experiments. Specifically, Sydney Brenner was the scientist responsible for the discovery of C. elegans. Brenner proposed that biological research would need to require a model system that could grow in vast quantities in the lab, were cheap to maintain and had a simple body plan.

When performing experiments on the C. elegans, the advantages of using this species as a model organism vary with each specific scenario. So many questions about C. elegans development and its close relation to that of human developmental processes have been answered when specific analyzes are performed on these organisms. These advantages range from simple knowledge about cellular structure and development to getting answers to vaccine possibilities for neurodegenerative diseases. Because humans and the C. elegans organism both possess similar molecular signaling responsible for development control, many of the organism’s genes have been studied and manipulated. The C. elegans genes have proved to be useful as a prime model for human diseases research. Benefits of C. elegans also include that the entire genome is sequenced and annotated, the availability of an RNAi library comprising approx. 80% of the genes in the genome, the ease of generating transgenic strains and the recent development of gene-targeting approaches. Lifespan has also been an element that has been studied in close relation between C. elegans and overall human development.

While there are many advantages of using C. elegans as model organisms, the organism is not without disadvantages. Because the organism has a very simple body plan, its structure may lack many defined organs/tissues including a brain, blood, a defined fat cell, internal organs, and is evolutionary from humans. The size of the C. elegans organism is also a disadvantage when being used in an experiment as a model organism. The organism’s small size leads to questions about whether the size would be appropriate for biochemistry experiments. Biochemistry covers so many aspects of these studies and it is important that those aspects are similar on both small and large scale. Because of this size difference, it has led to a limited understanding of any tissue-specific signaling such as whether a gene is expressed in the hypodermis or the intestine. Lab experiments with these simple organisms is also very limited due to lack of space and nutrients in cell cultures.

1� Klass, M. R. (1977). “Aging in the nematode Caenorhabditis elegans: major biological and environmental factors influencing life span.” Mechanisms of ageing and development, 6: 413-429.

2� Klass, M. R. (1977). “Aging in the nematode Caenorhabditis elegans: major biological and environmental factors influencing life span.” Mechanisms of ageing and development, 6: 413-429.

4� Harrell, J. R., & Goldstein, B. (2011). Internalization of multiple cells during C. elegans gastrulation depends on common cytoskeletal mechanisms but different cell polarity and cell fate regulators. Developmental Biology, 350(1), 1–12. http://doi.org/10.1016/j.ydbio.2010.09.012

6� Sulston, J., & Horvitz, H. (1977). Post-embryonic cell lineages of the nematode, Caenorhabditis elegans. Developmental Biology,56(1), 110-156. doi:10.1016/0012-1606(77)90158-0