Spindle and Cytoplasm 71 



The spindle fibers at anaj^hasc can be destroyed l)y the proper 

 concentration oi colchicine. Ihiis, in addition to an inhibitive action 

 upon a spindle at the start of the mitotic cycle, the spindle fibers can 

 be reduced after they ha\e been formed (Fig. 3.Li(-G) . The destruc- 

 ti\e action at anaphase follows a regular order, and there is a (juan- 

 titati\e as well as a cjualitati\e basis for the change. 



3.5—/: Neuroblast cells uf grasshopper. The technique developed 

 bv Professor J. Carlson, University of Tennessee, and used etfecti\ely 

 in cooperative research with Dr. M. E. Gaulden, Oak Ridge Labora- 

 tories, Tennessee, has given a new insight to the relationship between 

 colchicine and spindle fibers. Continuous observations upon li\ing 

 cells, together with the application of the chemical at a s])ecific stage 

 and in \ariable concentrations, ha\e been a \aluable addition. In fact, 

 the answer to our question about anaphase and colchicine demands 

 this kind of special method foi" watching an action upon the fiber 

 (Figs. 3.1 and 3.2). 



Cells at early, middle, and late anaphase were chosen. Strong 

 concentrations (50 and 25 X 10 "^ M) were used, and in each instance 

 the spindle was "imj^aired almost innnediateh' •'' (Fig. 3.2/) . The 

 chromosomes stopped in ihcir mo\ement to the poles; the two groups 

 intermingled, fused, and formed into a single telophasic nudcus (Fig. 

 S.2s-zi'') . This restitution nucleus was tetraploid, since the anaphasic 

 separation of centromeres had taken place before the drug was ap])lied. 

 Fom- nucleoli appeared instead of two, and the "uncoiling" ])rocesses 

 were only slighth delayed by colchicine (Fig. 3.2it'') . Spindle fibers 

 were destroyed at anaphase. 



When the concentration was reduced to 2.5 X 10 " ^^^ f^^i' the 

 same stage, an anajjhase. no detectable restdts were obser\ed. The 

 chromosomes continued to mo\e to the respective poles. Vet this 

 same concentration in\oked a definite reaction at an earlier mitotic 

 stage, i.e., late prophase or pro-metaphase (Fig. 3.2c) .^' 



Fig 3.2 — Mitotic stage when treatment began, shown in right colurr.n. Concentrations 

 are expressed in molarity. Successive stages are lettered a to i'. a and b: prophase 

 reversions occurring 10 to 20 minutes after treatment with this strong concentration. 

 Chromatin resembles early prophase, c to e: chromosomes lie at random, no spindle 

 formed, exploded c-metophoses, chromosomes continue to shorten, then clump together 

 in groups at bottom of cell, hyaline globules formed in d rise to top of cell, f to h: .he 

 evolution of a star metophase. i to k: star metaphase that becomes increased to mul- 

 tiple star and lost chromosomes. I to m: weak solutions do not fully inhibit spindle but 

 reduce the size, n to q: the metophasic spindle is reduced, hyaline globules form in o, 

 chromosomes settle to bottom and globules rise in cell, r cell divides when concentration 

 is too weak to destroy spindle completely. Compare figure r and c, that received same 

 concentration, but applied at different stages. Anaphase spindles are reduced if con- 

 centration is 25 X 10 ' M or more. Chromosomes fuse and intermingle in t and v, hya- 

 line globule forms in stages t, v, and y. Four nucleoli in w' and i' indicate a tetraploid 

 restitution nucleus. These stages show the interaction of concentration, stage of mitosis, 

 and length of exposure. (Diagrams adapted from M. Gaulden and J. Carlson, Experi- 

 mental Cell Research 2:416-33, 1951) 



