Bolshakov F.V.1, Melnikov N.P.1,2, Skorentseva K.V.3, Koroleva A.S.2, Borisenko I.E.4, Ereskovsky A.V.3,5, Lavrov A.I.1* 2026. Structure, transcriptional signature, and regeneration of oscular rim in calcareous sponge Leucosolenia corallorrhiza // Invert. Zool. Vol.23. No.3: 367–392 [in English].
1 Pertsov White Sea Biological Station, Biological Faculty, Lomonosov Moscow State University, Leninskie gory 1-12, Moscow 119991 Russia.
2 Department of Invertebrate Zoology, Biological Faculty, Lomonosov Moscow State University, Leninskie gory 1-12, Moscow 119991 Russia.
3 Koltzov Institute of Developmental Biology of Russian Academy of Sciences, Vavilova 26, Moscow 119334 Russia.
4 Department of Embryology, Biological Faculty, Saint Petersburg State University, Universitetskaya emb. 7/9, Saint Petersburg 199034 Russia.
5 Aix Marseille University, Institut Méditerranéen de Biodiversité et d’Ecologie (IMBE), CNRS, IRD, Avignon University, Marseille, France.
* Corresponding author
Fyodor Bolshakov: fedbolsh@mail.ru ORCID https://orcid.org/0000-0001-7543-2826
Nikolai Melnikov: melnikov.nikolay.2016@post.bio.msu.ru, ORCID https://orcid.org/0000-0002-1154-2556
Kseniia Skorentseva: skorentseva.ksenya.2016@post.bio.msu.ru, ORCID https://orcid.org/0000-0002-4222-0517
Anna Koroleva: anyakor99@gmail.com, ORCID https://orcid.org/0000-0002-2410-0554
Ilya Borisenko: i.borisenko@spbu.ru, ORCID https://orcid.org/0000-0002-5575-7639
Alexander Ereskovsky: alexander.ereskovsky@imbe.fr, ORCID https://orcid.org/0000-0003-1079-7204
Andrey Lavrov: lavrovai@my.msu.ru, ORCID https://orcid.org/0000-0002-0788-9039
doi: 10.15298/invertzool.23.3.02
ABSTRACT: The osculum is a structure through which filtered water leaves the aquiferous system of the sponge. The osculum is, however, not a mere opening, as it appears to participate in the water flow sensing and regulation. Additionally, the osculum is a central element of the axial patterning system of the sponge. Here we report data on the structure, gene expression profile, and regeneration of the osculum in the asconoid calcareous sponge Leucosolenia corallorrhiza (Haeckel, 1872). In this species, osculum openings are located on large, erect oscular tubes. The most distal part of the oscular tube, the oscular rim, differs structurally from the rest of the sponge body: here, the choanoderm is substituted by the endopinacoderm. The endopinacoderm forms a perpendicular two-layer fold called the oscular diaphragm. The diaphragm can regulate the effective size of the osculum opening, likely through the contractile activity of the supracellular actomyosin cable running along the inner edge of the diaphragm. The oscular rim also shows a unique transcriptional signature; when compared to other body regions, it shows the highest number of unique differentially expressed transcripts. Transcriptional profile of the oscular rim includes numerous components of the Wnt and TGF-β signaling pathways. Finally, the regeneration of the oscular tube represents a rapid epithelial morphogenesis occurring through morphallactic rearrangements of pre-existing tissues. The functional osculum is restored in 3 to 5 days after the amputation. During this process, the regenerative membrane transforms directly into the oscular diaphragm. The endopinacocyte lining of the oscular rim arises through transdifferentiation of the choanocytes near the wound. The preliminary experiments suggest that the course of the regeneration could depend on the amputation site.
KEY WORDS: osculum, differential expression, Porifera, Wnt signaling pathway, TGF-beta signaling pathway.
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