Nematodes David Bird 515-6813 david_bird@ncsu.edu

1. NematodesDavid Bird515-6813david_bird@ncsu.edu • Lecture 1: Nematodes as plant parasites • Lecture 2: Model systems and the phylum Nematoda • Lecture 3: Nematode anatomy Nematology

2. C. elegans as reference http://www.wormatlas.org/handbook/contents.htm Compare details to plant-parasites in later lectures Nematology

3. C. elegans as reference • Complete cellular architecture of C. elegans known • Lineage and parts list • 558 cells at hatch (959 in adult hermaphrodite) Nematology

4. C. elegans as reference • Complete cellular architecture of C. elegans known • parts list • Tissues • epidermis/cuticle • growth and molting • musculature • nervous system (lecture 5) • Organs • pharynx • gut • excretory/secretory system • sex organs (lecture 4) • gonads • copulatory structures Nematology

5. Hypodermis torroidal valves Nematology

6. Cuticle Nematology

7. Molting Meloidogyne Nematology

8. Musculature • Two distinct muscle systems • Somatic muscle • Nematode mobility • Specialized muscles • Independent function • somatic muscle in “sedentary” plant-parasites becomes inactive; other muscles not affected • chemical nematicides (e.g., acetylcholinesterase inhibitors such as Aldicarb) may target one system (somatic) but not the other Nematology

9. Musculature • Somatic muscle • longitudinal rows of striated (multiple sarcomere) muscle between the epidermal nerve cords in apposing quadrants • composed of 95 cells in adult C. elegans; >50,000 in Ascaris adults (from 83 in the L2) • attached to cuticle via hemidesmosomes • composed of 3 parts: • cell body • nucleus, organelles • arm • reaches to the nerve cord • spindle • contractile proteins Nematology

10. Musculature • Non-striated, specialized muscles. In C. elegans: • feeding: 20 pharyngeal muscle cells • gut contraction: 2 intestinal muscle cells • defecation control: 1 anal sphincter; 1 anal depressor • sex-specific • 41 male-specific muscles for copulation • 8 vulval and 8 uterine muscles C. elegans vulva Nematology

11. Nervous system • Lecture 5 • 302 neurons at C. elegans hatch • overall organization: • dorsal/ventral nerve cords • circumpharyngeal nerve ring • many sensory neurons in head • 118 distinct functional classes: • sensory neuons • chemo receptors (amphids) • mechanoreceptors • thermo receptors • etc • interneurons • motor neurons • sex-specific neurons Nematology

12. C. elegans as reference • Complete cellular architecture of C. elegans known • parts list • Tissues • epidermis/cuticle • growth and molting • musculature • nervous tissue • Organs • pharynx • gut • excretory/secretory system • sex organs (lecture 4) • gonads • copulatory structures Nematology

13. Pharynx/buccal cavity • highly specialized for different life-styles • odontostyle of plant parasites • distinct developmental origin from gut • lined with cuticle • specialized feeding apparatus lost at molt Rhabdodemania minima (marine sp.) R. reniformis Nematology

14. C. elegans pharynx • a single, unified, epithelial organ with its own: • nervous system • muscle cells • gland cells • most features are organized radially. Nematology

15. Pharyngeal glands • Typically 3 (e.g. tylenchids) or 5 (e.g. C. elegans) • roles in digestion and host-parasite interactions • major source of protein secretions by parasites Nematology

16. Gut • 20 cells in C. elegans • Multiple functions: • secrete digestive enzymes • absorb nutrients (microvilli) • storage organ (lipoprotein granules) • synthesis of egg yolk proteins Nematology

17. Excretory/secretory system V adenophoreans L L • Adenophorean • simple, glandular • Secerentean • complex, glandular + “H”-shaped tubular Nematology

18. Excretory/secretory system • Secerentean tubes • many anatomical modifications • (e.g. tylenchids lack one side canal) • developmental regulation • C. elegans dauer • Meloidogyne pre-post penetration • Function • tubular part: • osmoregulation • C. elegans • excretion? • glandular part • secretion of the glycocalyx • Meloidogyne, Anguina,Toxocara • protease secretion (exocorporeal digestion?) • Nippostrongylus • Secretion of the egg matrix • (Tylenchulus only) • molting/exsheathment hormnes? • other specialized roles • tube-building? Nematology

19. Reproductive strategies • Most species are: • dioecious (two sexes) • gonochoristic (morphologically distinct males and females) • amphimictic (eggs and sperm form different individual parents) Nematology

20. Reproductive strategies • Most species are dioecious, gonochoristic and amphimictic, but: • C. elegans is a protandrous (sequential) hermaphrodite + true males • Strongyloides exhibits alternating free-living amphimixis and parasitic apomixis (parthenogenisis) C. elegans hermaphrodite Nematology

21. Reproductive strategies • Most species are dioecious, gonochoristic and amphimictic, but: • C. elegans is a protandrous (sequential) hermaphrodite + true males • Strongyloides exhibits alternating free-living amphimixis and parasitic apomixis (parthenogenisis) • Variation within a dioecious, gonochoristic genus: • Meloidogyne carolinensis: obligate amphimictic • M. hapla: facultative meiotic parthenogenisis • M. incognita: obligate mitotic parthenogenisis • role of males in such species? Nematology

22. C. elegans hermaphrodite • Didelphic gonad Nematology

23. Germ cell development:C. elegans ovary Nematology

24. Germ cell development:M. hapla ovary (V. Thomas and V. Williamson, UCD) Nematology

25. M. hapla meiosis The 16 bivalent chromosomes of an M. hapla oocyte. Each bivalent consists of 4 chromatids (2 per univalent) in close association , forming a tetrad. Tetrads indicate that meiosis is taking place. Nematology

26. 2n 2n M. hapla meiosis meiosis I Polar body 1 2n 2n meiosis II Polar body 2 n n Polar body 2 and egg nucleus fuse Sperm and egg nucleus fuse n 2n n n n 2n 2n Parthenogenesis Fertilization Nematology

27. C. elegans male • monodelphic testis • copulatory apparatus at tail Nematology

28. ATLAS OF C. elegans ANATOMYan illustrated handbook http://www.wormatlas.org/handbook/contents.htm Nematology

29. NematodesDavid Bird515-6813david_bird@ncsu.edu • Lecture 1: Nematodes as plant parasites • Lecture 2: Model systems and the phylum Nematoda • Lecture 3: Nematode anatomy • Lecture 4: Reproduction and development Nematology