Abstract
The study of acoel morphologies has been recently stimulated by the knowledge that this group of animals represents an early offshoot of the Bilateria. Understanding how organ systems and tissues develop and the molecular underpinnings of the processes involved has become an area of new research. The microscopic anatomy of these organisms is best understood through the systematic use of immunochemistry and in situ hybridization procedures. These methods allow us to map, in precise detail, the expression patterns of genes and proteins, in space and time. With the additional use of genomic resources, they provide us with insights on how a group of “early” bilaterians have diversified over time. As these animals are new to the world of molecular studies, the protocols have involved a lot of new and specific adaptations to their specific anatomical-histological characteristics. Here we explain some of these protocols in detail, with the aim that should prove useful in our much-needed understanding of the origins of bilaterian animals. An anatomical sketch is provided at the beginning as a necessary guide for those not familiar with the Acoela.
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Cannon JT, Vellutini BC, Smith J, Ronquist F, Jondelius U, Hejnol A (2016) Xenacoelomorpha is the sister group to Nephrozoa. Nature 530:89–93. https://doi.org/10.1038/nature16520
Philippe H, Brinkmann H, Copley RR, Moroz LL, Nakano H, Poustka AJ, Wallberg A, Peterson KJ, Telford MJ (2011) Acoelomorph flatworms are deuterostomes related to Xenoturbella. Nature 470:255–260. https://doi.org/10.1038/nature09676
Baguñà J, Riutort M (2004) The dawn of bilaterian animals: the case of acoelomorph flatworms. BioEssays 26:1046–1057
Jondelius U, Wallberg A, Hooge M, Raikova OI (2011) How the worm got its pharynx: phylogeny, classification and bayesian assessment of character evolution in acoela. Syst Biol 60:845–871. https://doi.org/10.1093/sysbio/syr073
Achatz JG, Chiodin M, Salvenmoser W, Tyler S, Martinez P (2012) The Acoela: on their kind and kinships, especially with nemertodermatids and xenoturbellids (Bilateria incertae sedis). Org Divers Evol 13:267–286
Arroyo AS, López-Escardó D, de Vargas C, Ruiz-Trillo I (2016) Hidden diversity of Acoelomorpha revealed through metabarcoding. Biol Lett 12:20160674. https://doi.org/10.1098/rsbl.2016.0674
Smith J, Tyler S (1986) Frontal organs in the Acoelomorpha (Turbellaria): ultrastructure and phylogenetic significance. Hydrobiologia 132:71–78
Ehlers U (1991) Comparative morphology of the statocysts in the Plathelmithes and the Xenoturbellida. Hydrobiologia 227:263–271
Yamasu T (1991) Fine structure and function of ocelli and sagittocysts of acoel flatworms. Hydrobiologia 227:273–282. https://doi.org/10.1007/BF00027612
Rieger RM, Tyler S, Smith JPS, Rieger GE (1991) Platyhelminthes: Turbellaria. In: Harrsion FW, Bogitsch BJ (eds) Microscopic anatomy of invertebrates. Wiley, New York
Raikova OI, Reuter M, Kotikova EA, Gustafsson MKS (1998) A commissural brain! The pattern of 5-HT immunoreactivity in acoela (Plathelminthes). Zoomorphology 118:69–77. https://doi.org/10.1007/s004350050058
Reisinger E (1925) Ein landbewohnender Archiannelide. (Zugleich ein Beitrag zur Systematik der Archianneliden). Z Morphol Tiere 3:197–254
Martínez P, Hartenstein V, Sprecher SG (2017) Xenacoelomorpha nervous systems. In Oxford Research Encyclopedia of Neuroscience. Ed. S. Murray Sherman. New York: Oxford University Press
Jennings JB (1957) Studies on feeding, digestion, and food storage in free-living flatworms (Platyhelminthes: Turbellaria). Biol Bull 112:63–80
Achatz J, Gschwentner R, Rieger R (2005) Symsagittifera smaragdina n. spec., a new acoel (Acoela, Acoelomorpha) of the Mediterranean Sea. Zootaxa 1085:33–45
Pedersen KJ (1964) The cellular organization of Convoluta convoluta, an Acoel Turbellarian: a cytological, histochemical and fine structural study. Z Zellforsch 64:655–687
Hyman LH (1951) The invertebrates: Platyhelminthes and Rhynchocoela. The acoelomate bilateria vol II. McGraw-Hill Book Company, Inc, New York
Hooge M (2001) Evolution of body-wall musculature in the Platyhelminthes (Acoelomorpha, Catenulida, Rhabditophora). J Morphol 249:171–194
Hooge M, Tyler S (2006) Concordance of molecular and morphological data: The example of the Acoela. Integr Comp Biol 46:118–124
Semmler H, Bailly X, Wanninger A (2008) Myogenesis in the basal bilaterian Symsagittifera roscoffensis (Acoela). Front Zool 5:1–15. https://doi.org/10.1186/1742-9994-5-14
Henry JQ, Martindale MQ, Boyer BC (2000) The unique developmental program of the acoel flatworm, Neochildia fusca. Dev Biol 220:285–295. https://doi.org/10.1006/dbio.2000.9628
Hejnol A (2015) Acoelomorpha and Xenoturbellida. In: Evolutionary developmental biology of invertebrates, vol 1. Springer Verlag, New York, pp 203–214
Raikova O, Reuter M, Gustafsson MKS, Maule AG, Halton DW, Jondelius U (2004) Evolution of the nervous system in Paraphanostoma (Acoela). Zool Scr:71–88
Semmler H, Chiodin M, Bailly X, Martinez P, Wanninger A (2010) Steps towards a centralized nervous system in basal bilaterians: Insights from neurogenesis of the acoel Symsagittifera roscoffensis. Develop Growth Differ 52:701–713. https://doi.org/10.1111/j.1440-169X.2010.01207.x
Achatz JG, Martinez P (2012) The nervous system of Isodiametra pulchra (Acoela) with a discussion on the neuroanatomy of the Xenacoelomorpha and its evolutionary implications. Front Zool 9:27
Raikova OI (2004) Neuroanatomy of basal bilaterians (Xenoturbellida, Nemertodermatida, Acoela) and its phylogenetic implications (PhD thesis). Åbo Akademi University
Perea-Atienza E, Gavilan B, Chiodin M, Abril JF, Hoff KJ, Poustka AJ, Martinez P (2015) The nervous system of Xenacoelomorpha: a genomic perspective. J Exp Biol 218:618–628. https://doi.org/10.1242/jeb.110379
Gavilán B, Perea-Atienza E, Martínez P (2016) Xenacoelomorpha: a case of independent nervous system centralization? Philos Trans R Soc B Biol Sci 371. https://doi.org/10.1098/rstb.2015.0039
De Mulder K, Kuales G, Pfister D, Willems M, Egger B, Salvenmoser W, Thaler M, Gorny AK, Hrouda M, Borgonie G, Ladurner P (2009) Characterization of the stem cell system of the acoel Isodiametra pulchra. BMC Dev Biol 9:1–17. https://doi.org/10.1186/1471-213X-9-69
Srivastava M, Mazza-Curll KL, Van Wolfswinkel JC, Reddien PW (2014) Whole-body acoel regeneration is controlled by Wnt and Bmp-Admp signaling. Curr Biol 24:1107–1113. https://doi.org/10.1016/j.cub.2014.03.042
Chiodin M, Børve A, Berezikov E, Ladurner P, Martinez P, Hejnol A (2013) Mesodermal gene expression in the acoel Isodiametra pulchra indicates a low number of mesodermal cell types and the endomesodermal origin of the gonads. PLoS One 8:e55499. https://doi.org/10.1371/journal.pone.0055499
Albuixech-Crespo B, López-Blanch L, Burguera D, Maeso I, Sánchez-Arrones L, Moreno-Bravo JA, Somorjai I, Pascual-Anaya J, Puelles E, Bovolenta P, Garcia-Fernàndez J, Puelles L, Irimia M, Ferran JL (2017) Molecular regionalization of the developing amphioxus neural tube challenges major partitions of the vertebrate brain. PLoS Biol 15. https://doi.org/10.1371/journal.pbio.2001573
Hejnol A, Martindale MQ (2008) Acoel development indicates the independent evolution of the bilaterian mouth and anus. Nature 456:382–386. https://doi.org/10.1038/nature07309
Perea-Atienza E, Sprecher SG, Martínez P (2018) Characterization of the bHLH family of transcriptional regulators in the acoel S. roscoffensis and their putative role in neurogenesis. EvoDevo 9:1–16. https://doi.org/10.1186/s13227-018-0097-y
Acknowledgments
The research in P. Martínez laboratory was carried out with the support of the Spanish Ministry of Science, Grants BFU2006-00898, BFU2009-07383, and BFU2012-32806. E. Perea-Atienza and B. Gavilán were supported by PhD fellowships from the Universitat de Barcelona (APIF). S.G. Sprecher acknowledges the Swiss National Science Foundation 31003A_169993. Elena Perea-Atienza and Brenda Gavilán contributed equally to the development of the described methodology. The authors would also like to thank Kathryn Apse and Prof. Seth Tyler (University of Maine) for letting us publish the acoel morphology diagrams in Fig. 1 of this chapter.
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Perea-Atienza, E., Gavilán, B., Sprecher, S.G., Martinez, P. (2020). Immunostaining and In Situ Hybridization of the Developing Acoel Nervous System. In: Sprecher, S. (eds) Brain Development. Methods in Molecular Biology, vol 2047. Humana, New York, NY. https://doi.org/10.1007/978-1-4939-9732-9_4
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DOI: https://doi.org/10.1007/978-1-4939-9732-9_4
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