Pré-visualização25 páginas
of some oligohymenophoreans may also contain phosphatases (Lobo da Cunha & Azevedo, 1990). As in other ciliates, the alveoli are underlain by an epiplasmic layer (Allen, 1967, 1971). The epi- plasm of hymenostomes includes some of the same proteins as found in other protists \u2013 the multigene families of articulins and epiplasmins (Huttenlauch & Stick, 2003; Huttenlauch, Peck, & Stick, 1998; Pomel et al., 2006). Differential extraction tech- niques demonstrated that this layer, isolated as a ghost cell, provides a cortical scaffold for the cell (Collins, Baker, Wilhelm, & Olmsted, 1980; Keryer et al., 1990). On one hand, the varieties of cortical proteins in related Tetrahymena species are vastly different, and yet the form of these cells is very similar (Williams, 1984). On the other hand, the microstome and macrostome phenotypes of T. vorax , which are morphologically dramatically different, show very similar profiles of cortical pro- teins (Buhse & Williams, 1982). Nevertheless, Keryer et al. (1990) demonstrated the over-abundance of a particular band in one cortical mutant of Paramecium . Thus, a molecular change in a sin- gle component can have dramatic morphological effects. This has now been confirmed also for Tetrahymena : knockout constructs of the cortical protein Epc1p have altered cell shape (Williams, 2004). How these very different molecules can assemble similarly- or differently-shaped cells remains to be explained. In peritrichs , the epiplasm is often quite thick on the non-ciliated body surface, and it is penetrated by pores that are presumably homologues of the parasomal sacs of other oligohymenophoreans (Lom, 1994). In scuticociliates and hymenostomes , there are one to many supraepiplasmic micro- tubules , called longitudinal microtubules , which extend the length of the cell (Allen, 1967; Antipa, 1972; Peck, 1977a). Presumed homologues of these microtubules appear transiently during division of peniculines (Sundararaman & Hanson, 1976). The most prominent features of the ciliate cor- tex, the cilia associated with the somatic kinetids , have been extensively studied in Tetrahymena and Paramecium . Freeze-fracture analyses dem- onstrated that the somatic cilia have few randomly distributed particles over most of their length. However, at the base, distal to the ciliary neck- lace , were nine plaques of three longitudinal rows of particles at the ciliary base (Plattner, 1975; Sattler & Staehelin, 1974). These plaques are associated with Ca 2+ \u2212binding sites and are linked via an internal plaque complex to the peripheral doublets of the ciliary axoneme (Dute & Kung, 1978; Plattner). Ca 2+ and cyclic nucleotides affect ciliary movement, and so influence the behavioral responses of oligohymenophoreans (Machemer & Sugino, 1989; Noguchi, Kurahashi, Kamachi, & Inoue, 2004). Parasomal sacs are associated with the base of the cilium. These sacs are regions of pinocytosis as cationized ferritin is internalized by them (Nilsson & Van Deurs, 1983). Moreover, there is suggestive evidence that they may also be a route for the exocytosis of certain enzymes (Allen & Fok, 2000; Nielsen & Villadsen, 1985). The somatic kinetid of oligohymenophoreans has been characterized as a monokinetid as follows: a divergent, well-developed postciliary ribbon that extends usually to the next kinetid in the kinety but not to overlap its postciliary ribbon; a well- developed, anteriorly-directed kinetodesmal fibril that originates near triplets 5\u20137 and tapers as it overlaps fibrils from other kinetids; a reduced to well-developed, radially-oriented transverse rib- bon that extends typically from triplet 4 laterally towards the adjacent kinety; and, in some cases, a transverse fibre that originates near triplet 3 and extends laterally in association with the trans- verse ribbon (Figs. 15.6\u201315.9) (Lynn, 1981, 1991). Dikinetids, often in the anterior part of the cell, have similar fibrillar associates to the monoki- netid, but the anterior kinetosome usually bears a tangential transverse ribbon (Figs 15.6\u201315.8) (Lynn, 1981). While the monokinetid description applies very well to the kinetids of scuticociliates , hymenostomes , apostomes , and some astomes , the kinetids of peniculines , predominantly dikinetids, differ in that both sets of transverse ribbons are tangential to the perimeter of the kinetosome (Fig. 15.6) (Lynn, 1981, 1991). Somatic kinetids of peri- trichs are so highly modified that there are really no obvious similarities ( see below ). Extending the length of the kineties, near the base of the kinetosomes, are several basal microtubules that may supply additional structural support to the cortex (Allen, 1967; Antipa, 1972). In peniculines , somatic kinetids can be connected by filamentous bands at mid-kinetosome level while their bases are surrounded by a complex network of filaments, called the infraciliary lattice (Allen, 1971). This lattice does have contractile properties and demon- strates cross-reaction to antibodies that recognize the filamentous layer of the litostomes (Garreau de Loubresse, Keryer, Viguès, & Beisson, 1988). Antipa (1972) carefully described structural dif- ferentiation of somatic kinetids in the cortex of the scuticociliate Conchophthirius : the kinetids in the thigmotactic region of the cortex of this ciliate were modified compared to those of the locomo- tory cortex. Since the reviews of Lynn (1981, 1991) and Grain (1984), there have been relatively few reports of the ultrastructure of oligohymenophorean kinetids. Those that have appeared have confirmed these basic patterns. Some selected older and recent references are: for peniculines \u2013 Paramecium (Allen, 1971); Frontonia , Urocentrum (Didier, 1971); for the scu- ticociliates \u2013 Cinetochilum (de Puytorac, Didier, Detcheva, & Grolière, 1974a), Conchophthirus (Antipa, 1972); Dexiotricha (Peck, 1977a); Myxophthirus (Da Silva Neto, 1992), Paranophrys (Didier & Wilbert, 1976), Proboveria (de Puytorac, Grain, Grolière, & Lopez-Ochoterena, 1978); for hymenostomes \u2013 Colpidium (Lynn & Didier, 15.3 Somatic Structures 303 304 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA 1978), Glaucoma (Peck, 1978), Ichthyophthirius (Chapman & Kern, 1983), Turaniella (Iftode et al., 1984); for apostomes \u2013 Hyalophysa (Bradbury, 1966b), Collinia (de Puytorac & Grain, 1975); for astomes \u2013 Coelophrya , Dicoelophyra (Grain & de Puytorac, 1974). Undoubtedly the most unusual oligohymenophorean somatic kinetid is that of the scuticociliate Schizocaryum , whose somatic cortex is covered by cirrus-like polykinetids \u201corganized\u201d adjacent to a typical oligohymenophorean monoki- netid (Fig. 15.9) (Lynn & Frombach, 1987). The vast majority of sessiline peritrich species only display somatic ciliature at the time of cell division or when stimulated to leave their stalk by adverse environmental circumstances (Barlow & Finley, 1976; Rose & Finley, 1976). At this time, the daughter zooid or telotroch differentiates a band of cilia, called the trochal band , at the pole opposite the oral region, composed of from one row in Lagenophrys up to eight rows in Ophrydium (Fig. 15.3) (Lom, 1994). The trochal band of ses- siline peritrichs , such as Opisthonecta , which are permanently motile, can be a complex arrangement of ciliated kinetosomes. The fibrillar associates and arrangement provide no evidence of homol- ogy with the somatic kinetids of other oligohy- menophoreans (Bradbury, 1965). The trochal band surrounds the scopula , a structure at the extreme aboral pole, which includes kinetosomes with modified and reduced cilia, microtubular rootlets extending into the cytoplasm, and secretory gran- ules (Fauré-Fremiet, 1984; Lom & Corliss, 1968; Willey