Question

Question 1 topic: Gene regulatory networks. Use the figure and information in the figure legend to answer the questions. (20 points) a) What genes in this network are expressed in the skeletogenic lineage? b) If you knockdown Rp1, what gene(s) is/are expressed in all cells? What would be the resulting phenotype of the sea urchin embryo? c) If you knockdown Rp2, what gene(s) is/are expressed in all cells? What would be the resulting phenotype of the sea urchin embryo? d) If you use MOE of Rp2, what gene(s) is/are expressed in all cells? What would be the resulting phenotype of the sea urchin embryo? Rp1 Rp2 Figure 1. illustrates a hypothetical gene regulatory network necessary for production of the early urchin skeleton. Sk1 Sk2 Sk3 Rp1 is normally expressed only in the skeletogenic cell lineage. Sk4

Answer 1

According to gene regulatory network,

• Rp1 inhibits rp2
• Rp2 inhibits sk1, sk2, and sk3
• Sk1 and sk3 activates sk4
• U activates rp1, sk1, sk2 and sk3

From the above, if rp1 is activated, it will inhibits rp2. So, rp2 will not be able to inhibit sk1, sk2 and sk3, that means all these skeletogenic genes will be activated. If sk1 and sk3 is activated then sk4 will be activated. So when rp1 is activated, all the sk genes will be activated.

If rp1 is inhibited may be due to mutation, then rp2 will not be inhibited by rp1, so it will be actived. Thus it will inhibit the sk 1, sk2 and sk3.and is sk1 and sk3 is not active it won't activate sk4. So when rp1 is mutated only rp2 will be activated.

Sk genes are the skeletogenic genes of sea urchins, if these are active, it will direct the micromere specification and results in transformation of much of the embryo into skeletogenic mesenchyme cells that express skeletogenic markers.

If sk genes are inactive, it will direct the macromere and mesomere specification and results in transformation of much of the embryo into non skeletogenic mesenchyme cells.

In the question, it is clearly mentioned that rp1 is express in only skeletogenic cell, so

a) in skeletogenic lineage, rp1, sk1, sk2, sk3 and sk4 will be expressed.

b) if rp1 is knockdwon, it means it's expression is reduced, then rp2 will be activated and all the skeletogenic genes will be inhibited. So most of embryo will be of non skeletogenic mesenchyme cells.

c) if rp2 is knockdown, then rp1 and all the skeletogenic genes will be activated. So most of the embryo will be of skeletogenic mesenchyme cells.

d) if rp2 is overexpressed, MOE (mRNA overexpression), then even if rp1 is present it won't be able to inhibit rp2 as it's gene is mutated, it will continuously get expressed. So it will inhibit skeletogenic genes, therefore fate will be non skeletogenic mesenchyme cells.