Question

Compare and contrast using 2 two model organisms: a) the major signaling pathways, mechanisms and roles of genes that give rise to left-right asymmetry in vertebrates.b) Describe how some major organs are affected by L-R asymmetry in both your model organisms?

Answer 1

ANSWER :- In the above question, let's take the model organism of vertebrates as mouse and human.

Morphological asymmetry is a common feature of animal body parts, from snails to organ placement in humans. The signalling protein in Nodal is key for determining this laterally. Many vertebrates, including humans, use cilia for breaking symmetry during embryonic development: rotating cilia produce a lettward flow of extracelluar fluids that induces the asymmetric expression of Nodal. By, contrast, Nodal symmetry can be induced flow-independently in invertebrates.

a.) In vertebrates, Viscera and abdominal organs are asymmetrically positioned with respect to the two main body axes. This arrangement is termed situs solitus, is rarely altered. Asymmetric organ morphogenesis and placement bis initiated during embryogenesis. In the early vertebrates neural embryo, three genes - these encoding Nodal, it's feedback inhibitor lefty and the homeobox transcription factor Pitx2- become asymmetrically experessed in the left lateral plate mesoderm (LPM). This is also called Nodal cascade is a covered feature of vertebrate left-right (LR) axis formation. The functional importance of this asymmetric expression has been demonstrated in all classes of vertebrates. However, the mechanism of symmetry breakage, i.e., how Nodal, the first asymmetric gene is initially in the left LPM, remains a matter of much debate.

b.) Some major organs that are affected by L-R asymmetry are chest(heart, lung), and abdomen(stomach, spleen, liver, small and large intestine). The apex of the heart, which is placed at the midline, points to the left side. Lungs differ with respect to location: two lobes are found on the left and three lobes on the right side. The stomach and spleen are positioned on the left, whereas the liver and appendix are found on the right. In addition to this the small intestine and colon coil are asymmetrically.