CHROMOSOMES LACKING KINETOCHORE PROTEINS - THEIR META-ANAPHASE LOCATION SUGGESTS POTENTIAL MALSEGREGATION

We have previously reported that a rare chromosome may not carry the k inetochore protein complex-the CENtromere Proteins or CENPs. These chr omosomes should not bind to spindle microtubules and, hence, should be found peripheral to the meta-anaphase arrangement exhibited by the ch romosomes which do carry CENPs. This communication shows that this act ually is the case. When 3T3 mouse cells were not treated with colcemid or hypotonic, the kinetochore-lacking (K-) as well as kinetochore-bea ring (K+) chromosomes were found off the spindle zone. When the spindl e is disrupted with mild hypotonic treatment or by colcemid, the frequ ency of K- chromosomes remains unchanged. However, even mild disruptio n of the spindle with hypotonic treatment increases the frequency of o ff-lying K+ chromosomes significantly. These data indicate that K- chr omosomes do not bind to the spindle and, hence, are a factor in the ge nesis of aneuploidy. A considerable proportion of K- chromosomes carry the putative centromere DNA indicating that these are not acentric fr agments. Since the CREST serum used recognizes all essential kinetocho re proteins, the K- centromeres must also lack all essential CENPs.