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The endostyle is an organ found in invertebrate chordate species of tunicates, lancelets, and in the larval stage of vertebrate lampreys. It assists in filter-feeding.[1] It has evolved into the thyroid in vertebrate chordates.
Since the endostyle is found in all three chordate lineages, it is presumed to have arisen in the common ancestor of these taxa, along with a shift to internal feeding for extracting suspended food particles from the water.[2] When feeding, food particles suspended in the water adhere to the mucus the endostyle produces.[3] The filtered water is then expelled through the gill slits, while the food and mucus are swept into the esophagus by movements of the cilia that coat the endostyle.[3][4]
The endostyle in larval lampreys (ammocoetes) metamorphoses into the thyroid gland in adults, and is regarded as being homologous to the thyroid in all other vertebrates due to its iodine-concentrating activity.[5]
Early beliefs of the endostyle included the idea by Muller in 1873 stating that the endostyle that reside in the ammocoete has extremely similar functions as the protochordate hypobranchial groove. Thus, numerous investigations into the endostyle ensued, only for the theory to be denied by future researchers. However, during this research, it was found that ammocoete endostyles include the capability and functionality to accumulate radioactive iodine isotopes. This once again made the endostyle a very pertinent topic of research by a multitude of scientists. Already in 1963, research had concluded that cephalochordate and tunicate endostyles have the ability to capture iodine, thus further perpetuating new research.[4] A half century later, the homology between the tyroid in vertebrae and the endostyle in amphioxi and in ascidian larvae was further supported by showing that their development involved fairly homologous transcription factors.[6] Similar genetic studies on a hemichordate[7] tentatively indicate that the endostyle also might share origin with the stomochord.[8]
- ^ "Endostyle - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2021-01-05.
- ^ Dumont, Jacques; Opitz, R.; Christophe, D.; Vassart, Gilbert; Roger, P.P.; Maenhaut, C. (30 November 2011). "Ontogeny, Anatomy, Metabolism and Physiology of the Thyroid". Endotext [Internet]. PMID 25905409.
- ^ a b L., Jordan, E. (1967). Chordate Zoology. Delhi: S. Chanda & Co. ISBN 81-219-1639-9. OCLC 712010960.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ a b Olsson, Ragnar (September 1963). "Endostyles and endostylar secretions: A comparative histochemical study". Acta Zoologica. 44 (3): 299–328. doi:10.1111/j.1463-6395.1963.tb00411.x.
- ^ Ogasawara, Michio; Di Lauro, Roberto; Satoh, Nori (1 June 1999). "Ascidian Homologs of Mammalian Thyroid Transcription Factor-1 Gene Are Expressed in the Endostyle". Zoological Science. 16 (3): 559–565. doi:10.2108/zsj.16.559. hdl:2433/57227. ISSN 0289-0003. S2CID 27892843.
- ^ Jin Hiruta; Francoise Mazet; Kinya Yasui; Peijun Zhang; Michiya Ogasawara (2005). "Comparative expression analysis of transcription factor genes in the endostyle of invertebrate chordates". Developmental Dynamics. 233 (3): 1031–1037. Retrieved March 2, 2025.
- ^ Jens H. Fritzenwanker; John Gerhart; Robert M. Freeman Jr.; Christopher J. Lowe (2014). "The Fox/Forkhead transcription factor family of the hemichordate Saccoglossus kowalevskii". EvoDevo. 5 (1). Retrieved March 2, 2025.
- ^ Christopher J. Lowe (2021). "Molecular insights into deuterostome evolution from hemichordate developmental biology". Current Topics in Developmental Biology. 141: 75–117. Retrieved March 2, 2025.
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