Ref ID : 7580
Maria Jerka-Dziadosz; Ultrastructural Study on Development of the Hypotrich Ciliate Paraurostyla weissei II. Formation of the Adoral Zone of Membranelles and its Bearing on Problems of Ciliate Morphogenesis. Protistologica XVII(1):67-81, 1981
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The assembly and patterning of primordia of the adoral zone of membranelles (AZM) in a hypotrich ciliate Paraurostyla weissei were studied using light and transmission electorn microscopy. The primordium of the AZM originates by rapid multiplication of basal bodies within the primordial region, whose boundaries are specified relationally in respect of the cell size. The kinetosomes then align into pairs. In each pair one kinetosome bears the postciliary microtubular ribbon (Pc), the other the transverse microtubular ribbon (T). The kinetosomes in a pair are connected by fibrous links; on the right side of the posterior kinetosome (the one with Pc) there is a lateral fibril running perpendicularly to the axis of a pair. Pairs in the anarchic field show random orientation in respect of cell boundaries. When membranelles assemble the pairs line up with homogenous orientation with all Pc directed posteriorly and T anteriorly. The second round of kinetosome proliferation producing the third and fourth rows of kinetosomes in each membranelle occurs at the induction site: at the anterior-right margin of promembranelle. The analysis of the spatio-temporal aspect of patterning of the oral primordium revealed that membranelles differentiate in sequential order down the body axis and each subsequent membranelle goes through the same developmental steps. It is suggested that developmental changes occuring in the oral primordium are visible manifestation of a determination wave which passes the undetermined OP region in antero-posterior direction and causes a segmentation of an unpatterned field into serially repeating units.