Chapter 12 Part 3: Bird Development: Axis Specification Flashcards
Although formation of the chick body axes is accomplished during gastrulation, axis specification begins EARLIER WHEN THE EMBRYO IS STILL UNDERGOING CLEAVAGE
Therefore, axis specification occurs BEFORE PRIMITIVE STREAK FORMATION AND CELL MIGRATION AND GASTRULATION
What force is important for converting a radially symmetric blastoderm to a bilateral structure?
gravity
before laying, the ovum is rotated as it moves through the oviduct. What does this do?
causes the yolk to shift so that the lighter determinants lie on one side of the blastoderm. This causes the blastoderm to “tip up” to induce posterior marginal zone formation, next to where the primitive streak will form.
When a marginal zone forms, cells of the posterior marginal zone initiatise ____
initiates gastrulation, and prevents other regions of the marginal zone from forming a primitive streak. The PMZ is essentially the nieukwoop center for chickens because ti can initiate gastrulation
the entire marginal zone around the area pellucida secretes ____, which induces ____ accumulation
secretes Wtn8, which induces beta catenin accumulation.
posterior marginal zone secretes ____, and it works together with the Wnt8 in the rest of the marginal zone to induce ____ near the Koller’s sickle and PMZ in the future embryonic epiblast.
posterior marginal zone secretes VG1, and it works together with the Wnt8 in the rest of the marginal zone to induce NODAL near the Koller’s sickle and PMZ in the future embryonic epiblast.
posterior marginal zone secretes VG1, and it works together with the Wnt8 in the rest of the marginal zone to induce NODAL near the Koller’s sickle and PMZ in the future embryonic epiblast. Why is nodal so important?
nodal in the posterior marginal zone, which is induced by Vg1 and Wnt8, is important for primitive streak formation.
How do other areas of the marginal zone prevent primitive streak formation?
nodal activity is required for further formation of the primitive streak later on. Primary hypoblast cells in the anterior side of the blastoderm (recall these were islands) prevent primitive streaks by secreting CEREBRUS: a nodal antagonist.
Once the primitive streak is formed in the posterior margianl zone because nodal is not being repressed by anterior cerebrus, the posterior epiblast secretes its own nodal antagonist, ____, to prevent further primitive streak formation.
Once the primitive streak is formed in the posterior margianl zone because nodal is not being repressed by anterior cerebrus, the posterior epiblast secretes its own nodal antagonist, LEFTY, to prevent further primitive streak formation. cerebrus in the anterior region of the blastoderm that is secreted by primary hypoblast cells are continued to be secreted, ensuring that these cells in this region become the forebrain rather than more posterior structures of the nervous system.
like amphibians, left and right distinction in birds is primarily regulated via left-sided expression of ___, a paracrine factor, and ___, a transcription factor.
like amphibians, left and right distinction in birds is primarily regulated via left-sided expression of NODAL, a paracrine factor, and PITX2, a transcription factor.
Left-right axis formation: ___ ( a nodal type of paracrine factor), and ___ expression causes ___ gene expression to be restricted to the left side of the embryo.
At the same time, these two molecules activate ____ on the RIGHT side of the embryo, while activin inhibits SHH on the right side. Why is this so important?
Left-right axis formation: ACTIVIN ( a nodal type of paracrine factor), and BMP4 expression causes SHH gene expression to be restricted to the left side of the embryo, because activin suppresses SHH activity on the right side.
Activin and BMP4 on the right side ACTIVATES Fgf8. Fgf8 blocks cerebrus (paracrine factor) on the right side, and activates mesodermal signalling cascade that instructs the mesoderm to have right-sided capacities.
*on the left side, cerebrus is activated by SHH because there is no activin suppressing SHH. Cerebrus activates BMPS, which stimulates the prouction of Nodal. Nodal then can activate Pitx2, and repress Snail. This allows for Pitx2 to be expressed only on the left side.
During left-right axis formation, what prevents cerberus on the left (which activates BMPs, which activates nodal, which allows for Pitx2 expression) from acting on the right side?
there is lefty being expressed in the midline, which suppresses cerberus.
