Module 14 - Development Flashcards
Mention the three germ layers and the type of tissues they give rise to.
Ectoderm: epidermis and nervous system
Endoderm: lining of gut, liver, pancreas, lung
Mesoderm:connective tissue, muscle, blood, bone
Define the concept of pattern formation and morphogenesis. Mention how these events occur with the Twist gene.
Pattern formation refers to the process by which patterns of gene expression are established.
Morphogenesis refers to the process by which the form/shape of the embryo is established.
(Pattern Formation) A dorsoventral gradient of morphogen, called Dorsal, results in Twist being expressed in the ventral cells of the embryo. (Morphogenesis) Twist then turns on expression of hundreds of genes which affect the behaviour of the cells, causing it to constrict on their apical side, forming a furrow.
Differentiate between asymmetric and symmetric divisions in regards to cell differentiation .
During an asymmetric division, internal factors/signals may be segregated to one cell after division which lead to different sister cells. These are called “cell fate determinants”.
Alternatively, a symmetric division may produce two identical cells, but as a result of external factors/signals acting on them after their birth, the sister cell may be different.
Explain the mechanism of morphogenesis in the transition between mesenchymal and epithelial cells.
Describe the concept of induction.
Induction refers to the signalling action of one group of cells on another that leads to the establishment of the developmental pathway in the responding tissue.
Explain how Bicoid fulfills the definition of a morphogen (gradient and concentration controlling cell fate).
Bicoid mRNA is provided maternally and is localised to the anterior end of the embryo. When it is translated, Bicoid protein diffuses to form a concentration gradient, hence it can be considered to be a morphogen.
Mention examples of how gap gene expression is regulated by egg-polarity genes and other gap genes?
hunchback:
- a gap gene with a similair phenotype to bicoid
- transcription is regulated by Bicoid when above a certain threshold concentration
Krüppel:
- repressed in anterior end by Giant
- repressed in posterior end by Knirps
- activated by intermediate levels of Hunchback
Explain the concept that eve strips (pair-rule genes) are controlled by different enhancers.
Eve stripe expression is modular with each of the multiple stripe enhacers expressing the gene in their respective are, independent of each other.
Explain how the eve-stripe-2 enhancer is controlled by Bicoid, Hunchback, Giant, and Kruppel
Bicoid and hunchback activate expression in a broad domain. Giant and Kruppel repress Eve, thereby defining the anterior and posterior limits of expression.
Explain how the expression of the segment-polarity gene engrailed is established and maintained.
Segement polarity genes:
- are expressed in a subregion within each segment
- expression initiated by pair-rule proteins and maintained by other segment polarity proteins
- establish patterns of cell fate within the segment
How is segment identity determined?
Egg polarity, gap, pair-rule, and segment polarity genes combine to control the expression of the homeotic selector genes (HOX) genes.
These genes determines the identity of the segments, and exhibits colinearity.
Mention 4 key processes during developement.
Cell proliferation (+ apoptosis), cell specialization (differentiation), cell interaction (cell-cell adhesion and signalling), cell movement (morphogenesis)
Activation of ____ can promote migration of cell.
Rac
Explain the concept of differentiation.
Cellular differentiation is the process where a cell changes from one cell type to another. Usually, the cell changes to a more specialized type.
Mention and describe the mutant phenotypes and expression patterns of the four gene classes discovered by Nüsslein-Volhard and Wieschaus.
Egg-polarity gene: expresses in the anterior half, exp. Bicoid
Gap gene: expressed in broad regions, exp. Krüppel, Hunchback
Pair-rule gene: expressed in alternate segments, exp. Even-skipped
Segment-polarity gene: expressed in posterior half of every segment, exp. Hedgehog
Explain the concept of morphogen.
Morphogen is a substance whose non-uniform distribution governs the pattern of tissue development in the process of morphogenesis or pattern formation. Different concentrations result in different cell fates.
Explain the concept of progressive refinement.
Progressive refinement refers to the patterning by sequential induction, where a series of inductive interactions can generate many types of cells, starting from only a few.
What is meant by hierarchical network of gene regulation?
Describe egg polarity genes’ expression pattern.
It establish the overall anterior-posterior pattern of the embryo. This expression pattern is established during formation of the egg.
Describe gap genes’ expression pattern.
They have exprssion pattern that cover large regions of the embryo. Their expression pattern is controlled by egg-polarity genes and by other gap genes.
Give examples of an activation of segment polarity gene expression and how are they maintained.
Two important segment polarity genes are wingless (wg) and engrailed (en).
en expression is activated by high concentrations of Eve or Ftz and repressed by other pair-rule genes. Meanwhile, wg expression is activated where Ftz and Eve are absent.
These gene expressions are maintained by a single postive feedback loop between engrailed and wingless protein.
Define colinearity.
Colinearity refers to the fact that the order of expression along the anterior-posterior axis in the embryo is also the order in which the genes are found in the chromosome.
