P. Calvo

Ultrastructural and cytochemical study of the encystment in the Hypotrichous ciliate Histriculus similis

Summary Electron microscopic observations during the encystment of Histriculus similis confirmed that the cyst wall, composed of four layers, is derived from different kinds of precursors which are synthesized de novo. The ectocyst precursors are composed of stacked plates enclosed in a unit membrane. The mesocyst precursors are fibrous packets of variable shapes and sizes. The granular layer precursors are vesicles of different sizes and shapes surrounded by a unit membrane. A cytochemical and enzymatic study has been carried out to determine the cytochemical composition of the cyst wall precursors and their origin.

Ultrastructure, Encystment and Cyst Wall Composition of the Resting Cyst of the Peritrich Ciliate Opisthonecta henneguyi

Abstract The cyst wall of Opisthonecta henneguyi has been studied ultrastructurally and cytochemically by light and electron microscopy, as well as by chemical and electrophoretic analyses, to examine the structure of the cyst wall and its composition. The cyst wall consists of four morphologically distinct layers. The ectocyst is a thin dense layer. The mesocyst is the thickest layer and is composed of a compact material. The endocyst is a thin layer like the ectocyst, but less dense. The granular layer varies in thickness and is composed of a granular material. In the resting cyst, kinetosomes of both oral apparatus and trochal band as well as the myoneme system are maintained, and only cilia are resorbed. The sugars present in the cyst wall are predominantly N-acetylglucosamine (90%) and glucose (10%). The mesocyst is composed of chitin, and the endocyst includes glycoproteins and acid mucopolysaccharides. During secretion of the cyst wall, the endocyst and granular layer are secreted from precursors synthesized “de novo”. No cytoplasmic precursors of ectocyst and mesocyst have been detected.

Actin of Histriculus cavicola: Characteristics of the Highly Divergent Hypotrich Ciliate Actins

A macronuclear gene‐sized molecule carrying an actin gene from the hypotrich ciliate, Histriculus cavicola, was characterized. Southern blot analysis using a coding region probe suggested that actin in H. cavicola is encoded by a single gene. A comparison of the promoter regions indicated that the H. cavicola actin gene has a TATA box in the 51 flanking region in a position identical to those in other oxytrich ciliates. The coding sequence of this gene is not interrupted by any introns, and codes for a protein of 375 amino acid residues. This protein shares a high degree of similarity with other oxytrichid actins, and a relatively low similarity with actins from other eukaryotes. Comparative analyses of sequences indicated that most of the amino acid substitutions in hypotrich actins are found in surface loops, while the core structures are well‐conserved. The sites that interact with DNase I and several regions involved in actin‐actin contact have diverged considerably in hypotrich actins, while nucleotide‐binding sites are the best‐conserved interaction motif.

Study of Histriculus cavicola Cyst Wall Using Different Lectins

Summary Histriculus cavicola resting cyst walls have been examined with a variety of lectins binding specifically to certain sugar residues. Light and electron microscopic lectin histochemistry shows that the endocyst is the cyst wall layer with a greater and more varied saccharide residue content since it binds to the majority of lectins tested. The mesocyst contains some saccharide residues although these have not been detected in previous cytochemistry studies. The ectocyst is not stained with any of the lectins tested. None of the cyst wall layers were stained with MAA and UEA-I lectins, however we cannot rule out the possibility of the presence of sialic acid residues and/or fucose linked oligosaccharides from other linkages. Lectin blottings of isolated cyst wall proteins show the presence of several glycoproteins with molecular weights of 210-200, 190, 110-105, 95-85, 76, 73-68, 55, 50, 45, 40-36 kDa. The 190 kDa glycoprotein is located in the endocyst since this is the only band stained with PNA and DBA, lectins that bind strongly and only to the endocyst layer. This glycoprotein is the only one in which we have detected complex N and 0 linked glycans. The other glycoproteins present N linked glycans, although some of these may have 0 linked glycans, so far not detected by us.

Estimation of the Number of α-Tubulin Genes in Three Ciliated Protozoa

Summary: In an attempt to study the multitubulin family in ciliated protozoa, we have estimated the number of α-tubulin genes present in the genome of three “Spirotrich” ciliates by using an α-tubulin probe from the ciliate Stylonychia lemnae . Southern hybridization analyses of single or double-digested DNA from ciliates Histriculus cavicola, Euplotes eurystomus and Stentor coeruleus revealed banding patterns consistent with the presence of three, two and at least nine α-tubulin genes in each species, respectively. Comparison of the hybridizing patterns of Histriculus and Euplotes digested DNAs showed a great similarity between both species. The existence of common restriction fragments is an evidence of a sequence homology at the genomic level and might attribute much weight to a close relation between both ciliates. The controversial relationships among “Spirotrich” ciliates are discussed.