The specification of sea urchin micromeres involves the activation of a repressor protein Pmar1, which represses the expression of hesC, which also encodes a repressor protein. One of the genes controlled by HesC is Delta, whose expression is used as a marker for micromere lineage. The image below represents a sea urchin embryo on which whole mount in situ hybridization (WMISH) was performed using delta probe, indicated by the area ‘A’. The rest of the embryo is labeled ‘B’.​

​(Image from Revilla-i-Domingo et al (2007), PNAS 104:12383-12386)​

​The table below summarizes a set of experiments (column A) and the area in which hybridization is observed (column B)​

​Which one of the following options is a correct match between columns A and B?​

Correct option is A

Explanation-

A. WMISH with hesC probe
In wild-type embryos, HesC is expressed in all cells except micromeres (Area A). So, WMISH using hesC probe will show signal in B (not in A).
 Correct match: A → ii (B)

B. WMISH with delta probe following microinjection of pmar1 mRNA into fertilized egg
Overexpression of Pmar1 suppresses HesC throughout the embryo. Without HesC, Delta is expressed everywhere (not just A).
Correct match: B → iii (Both A and B)

C. WMISH with delta probe following microinjection of antisense RNA to hesC into fertilized egg
Antisense RNA blocks HesC expression, mimicking the effect of Pmar1 overexpression.
Result:Delta is expressed in both A and B regions.
Correct match: C → iii (Both A and B)

Final Matching :
A → ii
B → iii
C → iii

Correct answer - Option a - A - ii; B - iii; C - iii