SF-Assemblin genes in Paramecium: phylogeny and phenotypes of RNAi silencing on the ciliary-striated rootlets and surface organization

Background Cilia emanate from basal bodies just underneath the cell membrane. Basal bodies must withstand torque from the ciliary beat and be appropriately spaced for cilia to beat in metachronal waves. Basal body rootlets provide stability for motile cilia. Paramecium has three. Our focus is on the largest one, the striated rootlet (SR). Paramecium basal bodies align in straight rows. Previously we found a potential role for the SR in this alignment. Here we present a phylogeny of the Paramecium homologs of the SF-Assemblin gene of the SR of Chlamydomonas, and the organization of these genes. We describe the phenotypes from RNA interference (RNAi) silencing of genes and gene groups. Methods Phenotypes of the RNAi depletions were characterized by immunofluorescence (IF), electron microscopy, and mass spectrometry. Results We found 30 genes for Paramecium SF-Assemblin homologs (SFA) organized into 13 Paralog Groups (further categorized in five Structural Groups). Representatives of Paralog Groups were found in the SRs. Silencing the transcripts of any of the Structural Groups correlates with misaligned rows of basal bodies, SRs, and cortical units. The silencing of Structural Groups was key and gave us the ability to systematically disrupt SR structures and cell surface organization. Conclusions Silencing of SFA genes and Paralog Groups shows no effects on the SR or the cell surface organization. Silencing of the larger Structural Groups has an enormous impact on rows of basal bodies, SRs and cortical units, and SR striations, and length. Misaligned basal bodies have cilia causing the cells to swim in abnormal paths.

Primordial germ cells and oocytes of Branchiostoma virginiae (Cephalochordata, Acrania) are flagellated epithelial cells: relationship between epithelial and primary egg polarity

SummaryPrimordial germ cells (PGCs) are described from the gonad of c. 2 cm juvenile Branchiostoma virginiae; early oocytes (c. 10 μm) and enlarging, previtellogenic oocytes (c. 35 μm) are described from the ovary of c. 5 cm adults. The germinal epithelium of the juvenile gonad and adult ovary is composed of both germinal and somatic cells. In the juvenile, somatic cells retain contact with the basal lamina of the germinal epithelium though their perikarya may be displaced towards the lumen; the germinal epithelium is, therefore, a simple but pseudostratified epithelium. In the adult ovary, somatic cells may lose contact with the basal lamina and the epithelium appears to become stratified. PGCs and oocytes are identified as germ cells by the presence of nuage. PGCs and oocytes are polarised epithelial cells. They rest on a basal lamina, extend apically towards a lumen, form adhering junctions with neighbouring cells, and exhibit apical-basal polarity. PGCs and early oocytes have an apical flagellum with an associated basal body, accessory centriole, and one or more striated rootlet fibres. The flagellum is surrounded by a collar of microvilli. Once oocytes begin to enlarge and bulge basally into the connective tissue layer, the flagellum is lost, but the basal bodies and ciliary rootlets are present at the apex of 35 μm oocytes. Similarities of the oogenic pattern in cephalochordates and echinoderms indicate that the establishment of egg polarity in deuterostomes is influenced by the polarity of the germinal epithelium.

Ultrastructure of the basal body apparatus in epidermal cells of a sponge larva (Aplysilla SP: Demospongiae)

The basal body and its associated rootlet are the organelles responsible for anchoring the flagellum or cilium in the cytoplasm. Structurally, the common denominators of the basal apparatus are the basal body, a basal foot from which microtubules or microfilaments emanate, and a striated rootlet. A study of the basal apparatus from cells of the epidermis of a sponge larva was initiated to provide a comparison with similar data on adult sponges.Sexually mature colonies of Aplysillasp were collected from Keehi Lagoon Marina, Honolulu, Hawaii. Larvae were fixed in 2.5% glutaraldehyde and 0.14 M NaCl in 0.2 M Millonig’s phosphate buffer (pH 7.4). Specimens were postfixed in 1% OsO4 in 1.25% sodium bicarbonate (pH 7.2) and embedded in epoxy resin. The larva ofAplysilla sp was previously described (as Dendrilla cactus) based on live observations and SEM by Woollacott and Hadfield.

Biologie et étude ultrastructurale des spermatozoïdes du cnidaire Clytia hemispherica (Leptomedusae): mise en évidence d'un processus acrosomal

Mature sperm of Clytia hemispherica were studied by electron microscopy in the gonads, at their exit from the gonads, and at fertilization. The presence of an acrosomal complex at their anterior pole, which has long been a subject of controversy in cnidarians, was demonstrated. A chemoattractant and an inductor of the acrosomal reaction, both released at the animal pole of the eggs, were responsible for the accumulation of spermatozoons and the formation of the acrosomal process. A striated rootlet extending from the pericentriolar region to the plasma membrane was described, and its possible relationship to positive chemotaxis discussed. Ultrastructural modifications of the testes induced by light, a factor controlling spermiation, were investigated.

Ultrastructure of the zoospore of Blastocladia ramosa (Blastocladiales)

Species of Blastocladia, unlike other members of the order Blastocladiales, have an obligately fermentative metabolism. The ultrastructure of the zoospores of Blastocladia ramosa is described and compared with that of zoospores of aerobic members of the Blastocladiales. Zoospores of Blastocladia ramosa are structurally similar to other blastocladialean zoospores in that they have (i) a nuclear cap composed of aggregated ribosomes delimited by an envelope of endoplasmic reticulum; (ii) a posteriorly located nucleus; (iii) nine sets of microtubules that surround the nucleus and nuclear cap; and (iv) a striated rootlet associated with the kinetosome. Zoospores of Blastocladia ramosa differ by having mitochondria with unusual fine structure and by lacking microbodies and microbody – lipid globule complexes. As shown by enzymatic digestion and staining, glycogen appears to be the primary storage material in the zoospore. Structures which resemble water expulsion vacuoles are present. The morphological differences between zoospores of Blastocladia ramosa and other zoospores of the Blastocladiales appear to be related to physiological differences.