Comparative spermatology of selected polyclad flatworms (platyhelminthes)

Heterotrimeric Kinesin II is required for flagellar assembly and elongation of nuclear morphology during spermiogenesis in Schmidtea mediterranea

Development of sperm requires microtubule-based movements that drive assembly of a compact head and flagellated tails. Much is known about how flagella are built given their shared molecular core with motile cilia, but less is known about the mechanisms that shape the sperm head. The Kinesin Superfamily Protein 3A (KIF3A) pairs off with a second motor protein (KIF3B) and the Kinesin Associated Protein 3 (KAP3) to form Heterotrimeric Kinesin II. This complex drives intraflagellar transport (IFT) along microtubules during ciliary assembly. We show that KIF3A and KAP3 orthologs in Schmidtea mediterranea are required for axonemal assembly and nuclear elongation during spermiogenesis. Expression of Smed-KAP3 is enriched during planarian spermatogenesis with transcript abundance peaking in spermatocyte and spermatid cells. Disruption of Smed-kif3A or Smed-KAP3 expression by RNA-interference results in loss of spermatozoa and accumulation of unelongated spermatids. Confocal microscopy of planarian testis lobes stained with alpha-tubulin antibodies revealed that spermatids with disrupted Kinesin II function fail to assemble flagella, and visualization with 4',6-diamidino-2-phenylindole (DAPI) revealed reduced nuclear elongation. Disruption of Smed-kif3A or Smed-KAP3 expression also resulted in edema, reduced locomotion, and loss of epidermal cilia, which corroborates with somatic phenotypes previously reported for Smed-kif3B. These findings demonstrate that heterotrimeric Kinesin II drives assembly of cilia and flagella, as well as rearrangements of nuclear morphology in developing sperm. Prolonged activity of heterotrimeric Kinesin II in manchette-like structures with extended presence during spermiogenesis is hypothesized to result in the exaggerated nuclear elongation observed in sperm of turbellarians and other lophotrochozoans.

Systematic congruence in Polycladida (Platyhelminthes, Rhabditophora): are DNA and morphology telling the same story?

Using 28S ribosomal DNA sequences, we inferred the internal relationships of the order Polycladida. We identified morphological characters for clade support when possible. Monophyletic Acotylea and Cotylea were consistently recovered. In Acotylea, the superfamilies Stylochoidea, Cryptoceloidea and Leptoplanoidea were supported, with Stylochoidea representing the most basal acotylean lineage. In Leptoplanoidea, we united genera lacking a penis armature into the new family Notocomplanidae. Gnesiocerotidae was recovered as the most basal leptoplanoid lineage, and Stylochoplanidae and Notoplanidae were paraphyletic. Among cotyleans, Cestoplanidae, Diposthus popeae + Pericelis spp., Boniniidae, Pseudocerotidae and Prosthiostomidae formed clades. Genera in Euryleptidae were monophyletic, but the family itself was recovered with low support only. The established superfamilies Pseudocerotoidea, Euryleptoidea, Periceloidea and Chromoplanoidea are not supported. Pericelis has been moved to Diposthidae and Pericelidae has been abolished. A clade of Boniniidae + Theama spp. + Chromyella sp. was supported. In Pseudocerotidae, the number of male reproductive structures unites Pseudobiceros and Thysanozoon. Tytthosoceros has been abolished, with all currently described species now placed in Phrikoceros. Our results support several additional synonymies and taxonomic corrections. This new phylogeny provides an increased understanding of relationships in the order and offers a framework for future testing of hypotheses of character evolution and life-history strategies.

Investigation of the ultrastructure of Dendrocoelum constrictum (Platyhelminthes, Tricladida) spermatogenesis and mature spermatozoa

To add to our understanding of dendrocoelid spermatozoa and to describe additional phylogenetic characters, the ultrastructure of the testis was investigated in the subterranean freshwater planarian Dendrocoelum constrictum. This is the first study investigating spermatogenesis and spermatozoon ultrastructure in a subterranean freshwater planarian species. We found that the basic structure of spermatozoa in D. constrictum is similar to that of other Tricladida that have been studied previously. In fact, D. constrictum spermatozoa possess an elongated nucleus, one giant mitochondrion, and two subterminal flagella with a 9+'1' pattern. The flagella emerge together from one side of the spermatozoon. However, D. constrictum has some characteristics that have not yet been described for other freshwater planarians. In fact, the number of cortical microtubules reaches the maximum number in the anterior and middle part of region I, and then decrease until they disappear towards the posterior extremity of the spermatozoon. The extreme tip of the anterior region of the spermatozoon exhibits a specific external ornamentation of the plasma membrane.

Ontogeny of the complex sperm in the macrostomid flatworm Macrostomum lignano (Macrostomorpha, Rhabditophora)

Spermiogenesis in Macrostomum lignano (Macrostomorpha, Rhabditophora) is described using light- and electron microscopy of the successive stages in sperm development. Ovoid spermatids develop to highly complex, elongated sperm possessing an undulating distal (anterior) process (or "feeler"), bristles, and a proximal (posterior) brush. In particular, we present a detailed account of the morphology and ontogeny of the bristles, describing for the first time the formation of a highly specialized bristle complex consisting of several parts. This complex is ultimately reduced when sperm are mature. The implications of the development of this bristle complex on both sperm maturation and the evolution and function of the bristles are discussed. The assumed homology between bristles and flagellae questioned.