{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nThe PF20 orthologues in mammals, commonly known as SPAG16, are critical components of the axonemal central apparatus that regulate the mechanical function of ciliary and flagellar motility. Investigations in mouse models and Chlamydomonas have shown that the larger isoform, SPAG16L, localizes to the central pair region of the axoneme and is essential for proper flagellar movement, as its absence results in sperm motility defects and reduced fertility despite normal-appearing microtubule structures."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nMoreover, SPAG16L engages in key protein–protein interactions that modulate its function. It interacts with other central apparatus proteins such as SPAG6 and associates with testis-specific kinases like TSSK2, which phosphorylate SPAG16L and likely influence dynein motor activity essential for microtubule sliding and flagellar bending. In addition, a smaller isoform, SPAG16S, predominantly found in the nucleus of male germ cells, is implicated in the transcriptional upregulation of SPAG16L, linking axonemal structural integrity with gene regulatory mechanisms in spermatogenesis."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "3", "end_ref": "5"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nIn addition to their well‐defined roles in motile cilia and flagella, these proteins are also expressed in non‐ciliated tissues. This broader distribution suggests additional functions, such as stabilizing cytoplasmic microtubules, which may contribute to maintaining cellular architecture beyond the confines of ciliary structures."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "6"}]}, {"type": "t", "text": ""}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Zhibing Zhang, Rossana Sapiro, David Kapfhamer, et al. "}, {"type": "b", "children": [{"type": "t", "text": "A sperm-associated WD repeat protein orthologous to Chlamydomonas PF20 associates with Spag6, the mammalian orthologue of Chlamydomonas PF16."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Mol Cell Biol (2002)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1128/MCB.22.22.7993-8004.2002"}], "href": "https://doi.org/10.1128/MCB.22.22.7993-8004.2002"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "12391165"}], "href": "https://pubmed.ncbi.nlm.nih.gov/12391165"}]}, {"type": "r", "ref": 2, "children": [{"type": "t", "text": "Zhibing Zhang, Igor Kostetskii, Waixing Tang, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Deficiency of SPAG16L causes male infertility associated with impaired sperm motility."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biol Reprod (2006)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1095/biolreprod.105.049254"}], "href": "https://doi.org/10.1095/biolreprod.105.049254"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "16382026"}], "href": "https://pubmed.ncbi.nlm.nih.gov/16382026"}]}, {"type": "r", "ref": 3, "children": [{"type": "t", "text": "Zhibing Zhang, Xuening Shen, Brian H Jones, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Phosphorylation of mouse sperm axoneme central apparatus protein SPAG16L by a testis-specific kinase, TSSK2."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biol Reprod (2008)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1095/biolreprod.107.066308"}], "href": "https://doi.org/10.1095/biolreprod.107.066308"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "18367677"}], "href": "https://pubmed.ncbi.nlm.nih.gov/18367677"}]}, {"type": "r", "ref": 4, "children": [{"type": "t", "text": "David R Nagarkatti-Gude, Ruth Jaimez, Scott C Henderson, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Spag16, an axonemal central apparatus gene, encodes a male germ cell nuclear speckle protein that regulates SPAG16 mRNA expression."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "PLoS One (2011)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1371/journal.pone.0020625"}], "href": "https://doi.org/10.1371/journal.pone.0020625"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "21655194"}], "href": "https://pubmed.ncbi.nlm.nih.gov/21655194"}]}, {"type": "r", "ref": 5, "children": [{"type": "t", "text": "Kathleen A Lesich, Zhibing Zhang, Courtney B Kelsch, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Functional deficiencies and a reduced response to calcium in the flagellum of mouse sperm lacking SPAG16L."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biol Reprod (2010)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1095/biolreprod.109.080143"}], "href": "https://doi.org/10.1095/biolreprod.109.080143"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "20042536"}], "href": "https://pubmed.ncbi.nlm.nih.gov/20042536"}]}, {"type": "r", "ref": 6, "children": [{"type": "t", "text": "Jimena Alciaturi, Gabriel Anesetti, Florencia Irigoin, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Distribution of sperm antigen 6 (SPAG6) and 16 (SPAG16) in mouse ciliated and non-ciliated tissues."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Mol Histol (2019)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1007/s10735-019-09817-z"}], "href": "https://doi.org/10.1007/s10735-019-09817-z"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "30911868"}], "href": "https://pubmed.ncbi.nlm.nih.gov/30911868"}]}]}]}