In eukaryotes, many cells can assemble a spindle in the absence of centrosomes as in the case of plant cells during mitosis, and animal cells during meiosis in females. In this context, centrosome-free mitotic extracts from frog oocytes, when supplied with beads covered with DNA, are sufficient to assemble the mitotic spindle. Listed below are a few proteins that could be involved in spindle assembly in such a setting:
A. Ran GTPase
B. Ran-GEF
C. TPX2
D. Myosin V
Which one of the following options has all proteins that are directly involved in controlling spindle assembly without centrosomes?

Correct option is C

Correct Answer:
(c) A, B, and C only
Explanation:
Centrosome-independent spindle assembly relies on a Ran-GTP–mediated pathway around chromatin. Ran-GEF (RCC1) generates Ran-GTP near DNA, Ran GTPase establishes a Ran-GTP gradient, and TPX2 is released from importins to promote microtubule nucleation and spindle formation. Together, A, B, and C directly regulate spindle assembly without centrosomes.
Information Booster :
· DNA-dependent spindle assembly is prominent in oocytes and plant cells.
· A high Ran-GTP concentration near chromatin promotes microtubule stabilization.
· TPX2 is a key spindle assembly factor activated by Ran-GTP signaling.
· This mechanism bypasses the need for centrosomal microtubule organizing centers.
Additional Information (Incorrect Options):
Myosin V (D): An actin-based motor protein involved in vesicle transport, not microtubule organization or spindle assembly.
Options (a) and (b): Incomplete because spindle assembly requires not just Ran signaling but also downstream effectors like TPX2.