An analysis of the formation of ciliary primordia in the hypotrichous ciliate Urostyla weissei. II. Results from ultraviolet microbeam irradiation

Pattern formation in ciliary organelle systems of ciliated protozoa

Genetic, morphometric, and microsurgical investigations of the pattern of ciliary organells in ciliate protozoa support the view that ther are two types of developmental process responsible for the positioning of these organelles. The first is exemplified by the propagation of ciliary rows through localized addition of new ciliary units along the axis of the row, a process which is responsible for the maintenance of the pre-existing number of rows in clonal lineages over a large number of fissions. The second is illustrated by two examples: (1) Ciliary units are distributed among ciliary rows of Euplotes minuta according to an invariant geometrical pattern that is independent both of the total number of units and of the number of rows. (2) Microsurgical alteration of the topographical contours of a related ciliate, Paraurostyla weissei, brings about a shift in the sites of formation of certain specific ciliary rudiments to new positions that are determined in relation to the newly constructed form. The two modes of pattern formation in ciliates are discussed from both genetic and developmental viewpoints. The localized positional mechanisms within the ciliary rows allow for a 'configurational heredity' shich is, however, subject to constraints of nuclear genic control both of the stable range of number of rows and of the positioning mechanism itself. The large-scale systems of pattern determination are probably more closely related to the field properties of developing multicellular organisms. In ciliates such systems are almost certainly located in the cell membrane or in the relatively fixed cytoplasmic layer just beneath the membrane.

An overview of techniques for immobilizing and viewing living cells

Microscopists making observations on living cells are often faced with the challenge of getting those cells to hold still for extended observation times. This paper presents an overview/summary of a range of techniques for non-destructive immobilization of living cells (with an emphasis on protozoa), permitting microscopic observations and photography. A variety of chemical and physical immobilization techniques are discussed, but particular attention is paid to a comparative discussion of the mechanical devices (rotocompressors or microcompressors) used for reversible trapping of living cells.

Formation and positioning of surface-related structures in protozoa

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Laser microbeam induction of incomplete doublets of Oxytricha fallax

Destruction by laser microbeam of oral and ventral cirral primordia for the future opisthe of 1/2 of a pre-fission doublet results in the permanent loss of ability to form oral and ventral cirral primordia on the irradiated half. This observation provides further evidence for the postulated ‘determinative region’ present on each ventral surface of these organisms. The opisthe of the irradiated doublet retains both original rows of marginal cirri, which are located mid-dorsally with respect to the remaining ventral surface. These two rows of marginal cirri are reproduced faithfully in all future opisthes, but are lost in most proter lines. The pattern of loss in proters involves migration of the extra rows of marginal cirri to the cell's right margin followed by aberrant morphogenesis and subsequent resorption. These results show that the reproduction of marginal cirri is at least partially dependent upon the presence of marginal cirri and their inherent structural characteristics as well as upon their position on the cell surface.