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The Morphogenetic Cycle in Euplotes eurystomus and Its Bearing on Problems of Ciliate Morphogenesis *
Author(s) -
WISE BENJAMIN N.
Publication year - 1965
Publication title -
the journal of protozoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 0022-3921
DOI - 10.1111/j.1550-7408.1965.tb03266.x
Subject(s) - morphogenesis , cilium , biology , ciliate , primordium , basal body , microbiology and biotechnology , organelle , anatomy , cell division , ciliata , cell , genetics , protozoa , flagellum , gene
SYNOPSIS. The normal cycle of asexual reproduction in Euplotes eurystomus was subjected to a detailed morphological study using whole‐mounted and sectioned material prepared by the method of silver impregnation. The cycle was arbitrarily divided into 7 stages (numbered 0–6) characterized by nuclear and cortical events. Particular attention was focused on the development of the oral primordium (OP), and the production of new kinetal cilia (or “dorsal bristles”). The OP is interpreted as originating from an invagination or infolding of the parental cortex, followed by considerable in situ growth and differentiation beneath the cell surface. It is suggested that differentiation beneath the parental cell surface may in some way facilitate morphogenesis of other cortical structures without necessitating dedifferentiation of the parent's buccal apparatus. During stage 6, the division constriction plays an important morphogenetic role in shaping the opisthe's buccal apparatus. During stage 4, a zone of ciliary increase (ZCI) appears in the central portion of each kinety. New kinetal cilia arise as semi‐circular clusters of 1 to 9 kinetosomes flanking each old basal structure; the latter persist until the new organelles are well established. An analysis of total kinetal cilia in animals during stages 0 to 3 indicates that, while ciliary number varies according to animal size, there is no increase in cilia prior to formation of the ZCI. Several aspects of the asexual cycle in Euplotes seem to bear importantly on the more general problem of ciliate morphogenesis. The pattern or gradient concept might be useful in the analysis of factors determining primordial sites, although later development of the primordium into a specific organelle or organelle system is probably controlled by autonomous epigenetic processes that are somewhat independent of the parental cortical pattern. The hypothesis of kinetosome continuity cannot account for the origin of primordial fields in cortical regions remote from pre‐existing kinetosomes, as observed in Euplotes. The initiation of morphogenetic activity on the cortex is closely correlated with, and may be causally related to, the appearance of replication bands in the macronucleus. The known metabolic significance of these bands, particularly the release of nuclear RNA, lends support to this suggestion.