title: High-pressure freezing and freeze-substitution fixation reveal the ultrastructure of immature and mature spermatozoa of the plant-parasitic nematode Trichodorus similis (Nematoda; Triplonchida; Trichodoridae).
abstract: The spermatozoa from testis and spermatheca of the plant-parasitic nematode Trichodorus similis Seinhorst, 1963 (Nematoda; Triplonchida; Trichodoridae) were studied with transmission electron microscopy (TEM), being the first study on spermatogenesis of a representative of the order Triplonchida and important to unravel nematode sperm evolution. Comprehensive results could only be obtained using high-pressure freezing (HPF) and freeze-substitution instead of chemical fixation, demonstrating the importance of cryo-fixation for nematode ultrastructural research. The spermatozoa from the testis (immature spermatozoa) are unpolarized cells covered by numerous filopodia. They contain a centrally-located nucleus without a nuclear envelope, surrounded by mitochondria. Specific fibrous bodies (FB) as long parallel bundles of filaments occupy the peripheral cytoplasm. No structures resembling membranous organelles (MO), as found in the sperm of many other nematodes, were observed in immature spermatozoa of T. similis. The spermatozoa from the uterus (mature or activated spermatozoa) are bipolar cells with an anterior pseudopod and posterior main cell body (MCB), which include a nucleus, mitochondria and MO appearing as large vesicles with finger-like invaginations of the outer cell membrane, or as large vesicles connected to the inner cell membrane. The peripheral MO open to the exterior via pores. In the mature sperm, neither FBs nor filopodia were observed. An important feature of T. similis spermatozoa is the late formation of MO; they first appear in mature spermatozoa. This pattern of MO formation is known for several other orders of the nematode class Enoplea: Enoplida, Mermithida, Dioctophymatida, Trichinellida but has never been observed in the class Chromadorea.
authors.affiliation: Nematology Research Unit, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, 9000 Ghent, Belgium.
authors.forename: Behnam
authors.initials: B
authors.lastname: Lak
authors.affiliation: A.V. Zhirmunsky Institute of Marine Biology, FEB RAS, Vladivostok 690041, Russia; Far East Federal University, Vladivostok, Russia.
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Yushin
authors.affiliation: Nematology Research Unit, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, 9000 Ghent, Belgium.
authors.forename: Dieter
authors.initials: D
authors.lastname: Slos
authors.affiliation: Nematology Research Unit, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, 9000 Ghent, Belgium.
authors.forename: Myriam
authors.initials: M
authors.lastname: Claeys
authors.affiliation: Nematology Research Unit, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, 9000 Ghent, Belgium; Royal Belgian Institute of Natural Sciences, Department of Invertebrates, Vautierstraat 29, 1000 Brussels, Belgium.
authors.forename: Wilfrida
authors.initials: W
authors.lastname: Decraemer
authors.affiliation: Nematology Research Unit, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, 9000 Ghent, Belgium. Electronic address: wim.bert@UGent.be.
authors.forename: Wim
authors.initials: W
authors.lastname: Bert
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000648:ultrastructure; D017110:Freeze Substitution; D005615:Freezing; D008297:Male; D046529:Microscopy, Electron, Transmission; D009348:Nematoda / Q000648:ultrastructure*; D009685:Nuclear Envelope / Q000648:ultrastructure; D010944:Plants / Q000469:parasitology; D011554:Pseudopodia / Q000648:ultrastructure; D013079:Sperm Maturation; D013091:Spermatogenesis; D013094:Spermatozoa / Q000648:ultrastructure*
keywords: Cryo-fixation; Fibrous bodies; Filopodia; Membranous organelles; Nuclear envelope; Pseudopod