The Function of the “Dorsal Protein” in Patterning the Dorsoventral Body Axis of the Drosophila Embryo
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Introduction
It has been previously well established that the patterning of the body axis in the developing embryo of the Dipteran fruit fly Drosophila melanogaster employs a mechanism, in which the positional location of cells along the axis of the embryo are established through the use of morphogenic proteins that exhibit concentration gradients which either activate or represses certain genes within the nucleic DNA of the cells.
This phenomenon has previously been best described in the arrangement of the anterior/posterior axis, in which the transcription factor encoded by maternal effect gene Bicoid is positioned in the anterior of the ovum during oogenesis and diffuses through the developing embryo along a concentration gradient from anterior to posterior that will ultimately position the cells along the axis, from which the relevant body structures of the larvae and future imago will form.
The arrangement of the dorsoventral patterning structure also utilises a transcription factor that is encoded by a maternal effect gene. Known as “Dorsal” it employs a different mechanism other than a simple diffusion path to establish a concentration gradient. Accordingly in this essay I will attempt to address the role of “Dorsal” in the establishment of the dorsoventral axis in Drosophila melanogaster and whether “Dorsal” functions as a morphogenic protein.
The Road to Dorsal: Paying the Toll
The earliest stages of dorsoventral axis development are dependent upon a series of processes that begin during oogenesis. It is triggered by the transportation of the oocyte nucleus to the anterior-dorsal margin along microtubules from t...
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...erm stage the wild type embryo will display a nuclear “Dorsal” gradient over the entire ventral half of the embryo which will present a concentration maximum in the nuclei at the ventral pole, which decreases as it moves dorsally towards the embryo equator.
However a dl-mutant embryo will not display the same concentration gradient patterning as the wild type embryo, instead the concentration of the “Dorsal” protein has not been localised at the ventral pole by the “Toll” signal and accordingly the dl-mutant embryo will present a clearly defined band of staining in the nuclei around the entire circumference of the embryo.
The Effects of Dorsal: Establishing a Pattern
Upon entering the nuclei of the syncytial blastoderm, “Dorsal” begins affecting gene expression in distinctly defined regions along the dorsoventral axis as the differing germ layers become established.
Barlow (1953) first postulated the existence of feature-sensitive ganglion cells in a frog’s retina based on an inhibitory-surround structure of the receptive field. He maintained that the “on-off” units of these cells triggered by the presence of a particular stimulus corresponded to certain behaviour in the frog. For example, presenting a spot of light in the visual field would cause certain neurons to fire in a particular ganglion cell, and in a live frog, would cause the frog to snap at the stimulus. Barlow concluded that these cells must be “fly detectors”. Lettvin et al. (1959) further examined the visual mechanisms of the frog and discerned fo...
Ross Wolff, Jennifer, and David Zarkower. "Somatic Sexual Differentiation in Caenorhabditis Elegans." Current Topics in Developmental Biology 83 (2008): 1-39. Web. 28 Feb. 2014. .
All references and resources are taken from the Public Library of Science, Biology March 2004 issue and from Science March 16, 2004
Fox, R. 2001. Invertebrate Anatomy OnLine: Artemia Franciscana. Lander University. http://webs.lander.edu/rsfox/invertebrates/artemia.html, retrieved February 13, 2011.
17. Fruit flies normally have eight chromosomes. The diagram below shows the result of meiosis in three fruit flies to produce gametes with the number of chromosomes indicated. The male then mates with both female A and female B to produce three zygotes (1, 2, and 3).
The white (w) eye color gene is located on the X chromosome at 1.5 genetic map units (1). The mutation is also recessive, meaning that each fly has different copies of the gene if they are either male or female (2). In wild-type Drosophila, the brick red color is visible due to the combination of two pigments, brown and scarlet. The synthesis of drosopterin for bright red pigments is controlled by the (bw+) gene and the synthesis of ommochromes for brown pigments is controlled by the (st+) gene (7). Therefore, there are two pigment synthesis pathways that must be working in order for the flies to express the brick red eye color. In addition, transport proteins are responsible for transporting both pigments into the eye in order to express the color (8). Thus, both the pathways responsible for the synthesis of brown and red pigments must work properly as well as the genes that encode for transport proteins. Despite having white eyes, Drosophila flies with this mutation still experience normal eyesight
The F2 punnett square shows that there should not be a female fly that has apterous wing mutation. Our observed experiment showed that female flies are capable of forming in the F2 Generation. Therefore, the mutation is located on autosomal chromosomes. In trial 1, the p value is not significant. This could be due to the fact that the male to female ratio in the F1 generation was unequal. In trial 2, the p value is significant and likely due to chance. The probability error is between 1 % and 5%.
Meiosis, also called reduction division, is a distinct type of cell division that is essential for sexual reproduction to occur. It is one in which two successive divisions of diploid cell occur thereby producing four genetically different haploid daughter cells, also called gametes, each with half the number of chromosomes and thus, half the total amount of genetic material as compared to the amount before meiosis began. Interphase precedes meiosis and thus, paves the way for meiosis to eventuate as the cell’s DNA replicates in the S phase yielding corresponding, identical chromosomes. Interphase sparks the marvelous process of meiosis that allows variation to transpire within the organisms it occurs, hence, giving rise to millions of organisms with unique aspects unlike any other on Earth. Because meiosis is a form of sexual reproduction itself, it is the means through which gametes are produced, each with a reduced number of chromosomes, so that when two gametes fuse during fertilization, not only do they form a diploid zygote with 46 chromosomes, but also have manifested differing features due to the rearrangement (crossing-over) of chromosomes.
The reason why I believe figure 2 to be so pertinent to the results is because it shows that there is no mutation of Pitx1 in either the benthic or marine species that affects pelvic development (figure 2). Figure 3, is pertinent to the results because it takes this one step farther and actually shows that indeed the only difference between species that have a pelvic region and have an absence of a pelvic region is due to the regulation of the Pitx1 gene. I believe that the experimental data supports the conclusion of this paper because as I previously explained the results show that there is a major chromosome region that is controlling the presence or absence of pelvic structures. The results also show that there is no actual mutation within the Pitx1 gene between the different stickleback species. Not only that but the strong directional asymmetry seen in pelvic-reduced fish and the altered pattern of Pitx1 gene expression during development also goes to support the conclusion that there is a regulatory mutation. This regulatory mutation is thus responsible for the lack of Pitx1 gene in the benthic stickleback, which results in pelvic reduction and is most likely a cis-acting regulation
Sadler, T. W., and Jan Langman. Langman's Medical Embryology. Philadelphia: Lippincott Williams & Wilkins, 2006. Print.
Evolutionary developmental biology (evo-devo) was instituted in the early 1980s as a distinctive field of study to characterise the new synthesis of evolution hypothesis (Müller, 2007). Evo-devo is regarded as a new rule in evolutionary biology and a complement to neo-Darwinian theories. It has formed from the combination of molecular developmental biology and evolutionary molecular genetics; their integration has helped greatly to understand both of these fields. Evo-devo as a discipline has been exploring the role of the process of individual development and the changes in evolutionary phenotype, meaning the developmental procedure by which single-celled zygotes grow to be multicellular organisms. Alterations in the developmental program frequently cause differences in adult morphology.
In metaphase I, bivalents, each composed of two chromosomes, align at the metaphase plate. The orientation is random, with either parental homologue on a side. This means that there is a 50-50 chance for the daughter cells to get either the mother's or father's homologue for each chromosome.
nuclei was then inactivated and substituted with dead nuclei from the extinct frog. Some eggs started to grow and divide to early embryo stage (a tiny ball of m...
Once the sperm fuses with the ovum both chromosomes will pair up and begin the first stages of cell division.
Sally: Embryonic cells are "undifferentiated." Undifferentiated cells have not gone through changes that make some cells into skin cells or muscle cells or brain cells, for example. Undifferentiated cells can become any cell in the body because it can activate any gene on any chromosome, but as cells develop, the DNA of certain cells fold in particular ways making large portions of the DNA inaccessible. This makes sure that the wrong genes do not get turned on at the wrong time or in the wrong place.