Centrosomenfreie Spindelpole in Tipuliden-Spermatocyten

Abstract

In spermatocytes I of the crane-fly Pales crocata under experimental conditions the normal relation between spindle poles and centrosomes can be disturbed. Bipolar spindles can be formed without participation of one or both centrosomes. Multipolar spindles often arise by formation of acentric (centrosomeless) poles in addition to the two centric ones. The effect of centric and acentric poles on chromosome movement is identical. Co-oriented bivalents which (in contrast to univalents and trivalents) exhibit stable orientation in normal spindles, are able to re-orient in multipolar figures. Size and shape of monocentric, bipolar spindles often do not differ from normal bicentric spindles and chromosome movement in them also is normal. Sometimes the spindles are not pointed at the acentric pole and occasionally fan-shaped monocentric, monopolar spindles are formed. Centrosomes which remain unconnected with the spindle keep more or less their diacinetic appearance. These and other results demonstrate that in tipuline spermatocytes the spindle is—at least mainly—organized by the chromosomes, the centrosomes having at best a subsidiary function in focussing the spindle poles.