You are an MD/PhD student studying left-right laterality defects in humans. You are monitoring a pregnancy...

You are an MD/PhD student studying left-right laterality defects in humans. You are monitoring a pregnancy in which the heart and stomach are positioned on the incorrect side of the body, while the rest of the organs are positioned normally.

a) [2pts] What would be the name of this type of visceral organ defect?

You are able to perform corrected surgery on the infant soon after birth. You perform a genetic analysis and discover this child had a mutation in a stretch activated calcium channel.

b) [2pts] What are the normal roles of stretch activated calcium channels?

c) [4pts] Why might this mutation cause the left-right laterality defects you observed?

d) [4pts] Assuming that mouse and human left-right patterning are achieved through similar mechanisms what would you predict Nodal expression in the LPM would have looked like in this human patient during early development? Explain your thinking.

Expert Solution

1. This visceral organ defect is known as Situs inversus in which major visceral organs are position is reverse direction to their normal position or simply are mirrored from their normal positions. It is an autosomal recessive genetic condition

2. The normal function of stretch-activated ion channels (SACs) is to increase ion transients upon activation by mechanical strain to rapidly alter cardiac electrical activity. These ion channels are located in the plasma membrane and several cells such as cardiomyocytes. SACs are activated in tens of milliseconds.

3. Splitting of a fertilized embryo later than usual during pregnancy also known postimplantation turning leads to left-right asymmetry. This late splitting occurs because of the delayed cardiac electrical activity induced by an insertional mutation effects the gene controlling embryonic turning and visceral left-right polarity.

4. In general the role of notch signaling in establishing LR axis is conserved in case of mammals such as human. Also a subsequent notch signaling is required for Nodal expression along with perinodal expression for activation in the LPM

If the system of humans have been similar to that of mouse then mutation inversus viscerum (iv) would have disrupted the gene encoding the ciliary motor “left–right” dynein thereby causing LR asymmetry. This also causes ramdomised nodal expression in the LPM of iv mutants

gladiator answered 1 year ago

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