The distal sperm flagellum: its potential for motility after separation from the basal structures

The distal region of the sperm flagellum of Gallus domesticus has been separated and purified. It consists of a 9+2 axoneme, without basal or accessory structures. Such distal segments have been demembranated and then reactivated, either by adding ATP or by releasing ATP photolytically from caged ATP: we find that they are capable of a period of independent motility. Bends form repetitively and travel towards the tip, though it is an abnormal, irregular pattern of beating. It is argued that this motility is not dependent on damage to the flagellum at the fracture site. Evidence is presented that the potential for such motility depends upon the existence of bends on the axoneme before the reactivation. The reactivated motility is short-lived: 50 % of the distal flagellar segments, placed in the reactivating solution, become quiescent and straight within 60 s. However, vigorous beating can be induced in such quiescent segments of axoneme by compressing one end with a glass microneedle. We record, provisionally, that the site of compression does not determine the direction in which bends move along the flagellar segment. The effect of compression in re-initiating motility suggests that a mechanical resistance is necessary, somewhere along the axoneme, for normal, sustained motility; it is proposed that the specialized basal structures, collectively, provide such a resistance in the intact flagellum.