4 Sponges.pptx
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Sponges are the simplest multicellular animals and lack tissues and organs. They have a basic body plan and five main cell types. While they lack complexity, sponges exhibit some characteristics of more complex animals like metazoans including cellular differentiation, complex sexual reproduction, and the ability to distinguish self from non-self. Placozoans may represent the simplest animal phylum and have only four cell types but cellular junctions that are similar to more complex animals. Debate remains around whether sponges and placozoans are the earliest branching animals or were secondarily simplified from more complex ancestors.
4 Sponges.pptx
- 1. Phylum Porifera -- 5000 -10000 sp. -- mostly marine some none terrestrial -- 3 classes, most important distinction are skeletal characteristics
- 2. I. General Ecological Characteristics II. Body Plan III. Metazoan Characteristics A. Cell types B. Allorecognition C. Reproduction and Embryology D. Other metazoan homologies. IV. Sponge Phylogeny Phylum Porifera
- 3. I. General Ecological Characteristics Sponges are: Sessile, benthic Filter feeders Competitors for space Fed upon by specialist predators Grow in many forms, solitary, colonial, branching, as thin sheets over substrates From few cm to over 1 m in size Estimated in some cases to be several hundred years old
- 4. The classification of sponges is based on skeletal morphology II. General Characteristics of the Porifera Body Plan
- 6. 3 major types of body construction Asconoid Syconoid Leuconoid (this has little to do with the classification of sponges, which is based on skeletal morphology) II. General Characteristics of the Poriferan Body Plan
- 7. Asconoid Sponge Syconoid Sponge
- 8. Leuconoid Arrangement Osculum Ostia These are the largest, and most sponges have this type of construction
- 11. Carnivorous sponges from deep water and shallow caves Evolution of macrophagy from a microphagous, filter feeding life style
- 12. II. Other Characteristics of the Poriferan Body Plan No true muscular system Lacking sensory organs, nervous system Often amorphous and asymmetrical, no anterior, posterior, oral surfaces No true tissues All physiological functions carried out at the cellular level Begs the question: Colony of protista or a simple metazoan (i.e. an integrated animal ?)
- 13. spongocoel Archeocyte Choanocyte Porocyte Pinacocyte Osculum Sclerocytes III. Metazoan-like Characteristics of Sponges A. 5 different principal cell types (20 total) http://www.biology.ualberta.ca/facilities/multimedia/uploads/zoology/Porifera
- 14. Stem cells have the capacity of self-replication and to give rise to more than one type of mature daughter cells Image courtesy of BioMEDIA ASSOCIATES Archeocytes in sponge embryos are considered totipotent stem cells that can give rise to an entire organism - in adults they produce a few cell types (sclerocytes, germ cells, etc.) but not an entire organism; they are considered pluripotent Muller (2006) Seminars in Cell and Developmental Biology #17:481-491
- 15. III. Metazoan-like Characteristics of Sponges B. Complex reproduction
- 16. Sexual reproduction involves fertilization, release of a planktonic larva, and its eventual settlement and metamorphosis on the bottom. III. Metazoan-like Characteristics of Sponges Parenchymula or Amphiblastula Carried in the plankton Settlement & metamorphosis Adult Juvenile Egg sperm Unique but complex embryonic development, with a hollow blastula stage but does not form a gastrula
- 17. III. Metazoan-like Characteristics of Sponges C. Other sponge metazoan homologies: Epithelium -- pinacoderm: epithelial-like layer homologous to animal epithelia with collagenous sublayer ( ...but basal lamina only in Homoscleromorphs) -- septate junctions (desmosomes) albeit primitive and small (only Calcarea has full animal-like desmosomes) -- extracellular matrix -- spongin is collagen-like molecule -- ubiquitin protein similarity (tag other proteins for proteolysis)
- 18. Integrative and Comparative Biology Advance Access published online on June 22, 2009 Integrative and Comparative Biology, doi:10.1093/icb/icp038 Epithelia and integration in sponges Sally P. Leys1,*, Scott A. Nichols{dagger} and Emily D. M. Adams* *Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9; {dagger}Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA Correspondence: 1E-mail: sleys@ualberta.ca An epithelium is important for integrity, homeostasis, communication and co-ordination, and its development must have been a fundamental step in the evolution of modern metazoan body plans. Sponges are metazoans that are often said to lack a true epithelium. We assess the properties of epithelia, and review the history of studies on sponge epithelia, focusing on their homology to bilaterian epithelia, their ultrastructure, and on their ability to seal. Electron micrographs show that adherens-type junctions are present in sponges but they can appear much slighter than equivalent junctions in other metazoans. Fine septae are seen in junctions of all sponge groups, but distinct septate junctions are only known from Calcarea. Similarly, all sponges can have collagenous sheets underlying their epithelia, but only homoscleromorphs are established to have a distinct basal lamina. The presence of most, but not all, gene families known to be involved in epithelial development and function also suggests that sponge epithelia function like, and are homologous to, bilaterian epithelia. However, physiological evidence that sponge epithelia regulate their internal environment is so far lacking. Given that up to six differentiated epithelia can be recognized in sponges, distinct physiological roles are expected. Recognition that sponges have epithelia challenges the perception that sponges are only loose associations of cells, and helps to relate the biology and physiology of the body plan of the adult sponge to the biology of other metazoans.
- 19. III. Metazoan-like Characteristics of Sponges C. Other sponge metazoan homologies: Regulation of Development -- True Hox genes are not found, but many homologous developmental transcription factors are conserved -- Most of the developmental signaling pathways (Wnt, Notch) and they are expressed along the same embryonic axis in sponges (and Cnidaria). Many of these signaling pathways and transcription factors have not been found in Protists. From Adamaska et al., 2011
- 20. Some sponges form new individuals hours after their cells are separated from one another. If species are combined, the cells segregate with their own III. Metazoan-like Characteristics of Sponges Allorecognition D. Non-self recognition
- 21. Metazoan-like Characteristics of Sponges Allorecognition Histoincompatability Immune response: antagonism toward foreign substances antagonism must be specific toward that substance future responses should be altered by the first response The sponge immune response is mediated by molecules which have been found to control histo-recognition in deuterostomes including Immunoglobulin-like domains and citokines
- 22. Summary -- Sponges lack complexity, but their body plan is ecologically and evolutionarily successful --They should be considered metazoans since they have fundamental characteristics of multicellular animals; --They are derived from flagellated protists but may be a early and now distant branch of the metazoa; animals are monophyletic
- 23. Phylum Placozoa -- 2-3 mm, 25 um- thick, resembling a large ameba -- Lacks anterior posterior polarity -- Asexual reproduction is prevalent --The most primitive animal? Trichoplax adhaerens
- 24. Phylum Placozoa Dorsal Fiber synctium cilium epithelium-like layer thick glandular layer Flagellated cells -- Feed ventrally by absorption of digested material -- Lack organs but tissue-like outer walls (no basement membrane) -- A bit more than 2000 cells -- Only 4 different cell types (20 in sponges; > 220 in mammals) -- Smallest genome of all animals Intercellular junctions
- 25. Three competing Scenarios A. Earliest view of them as the basal metazoan B. Special cellular junctions consisting of two opposing dense plaques (desmosomes) not found in most sponges C. 16S rRNA datamaybe secondarily simplified from more complex ancestors?
- 26. Mitochondrial genome of Trichoplax adhaerens supports Placozoa as the basal lower metazoan phylum Dellaporta, Stephen L. et al. (2006) Proc. Natl. Acad. Sci. USA 103, 8751-8756 Largest known mt genome 46 kbp, 2x that of most metazoa with introns and other intrageneic spacers and large protein coding regions that are usually lacking in other animals Blue: known mt proteins Gray: ribosomal genes Green: unknown open reading frames Red lines: introns