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Karalis V, Donovan KE, Sahin M. Primary Cilia Dysfunction in Neurodevelopmental Disorders beyond Ciliopathies. J Dev Biol 2022; 10:54. [PMID: 36547476 PMCID: PMC9782889 DOI: 10.3390/jdb10040054] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 12/04/2022] [Accepted: 12/09/2022] [Indexed: 12/15/2022] Open
Abstract
Primary cilia are specialized, microtubule-based structures projecting from the surface of most mammalian cells. These organelles are thought to primarily act as signaling hubs and sensors, receiving and integrating extracellular cues. Several important signaling pathways are regulated through the primary cilium including Sonic Hedgehog (Shh) and Wnt signaling. Therefore, it is no surprise that mutated genes encoding defective proteins that affect primary cilia function or structure are responsible for a group of disorders collectively termed ciliopathies. The severe neurologic abnormalities observed in several ciliopathies have prompted examination of primary cilia structure and function in other brain disorders. Recently, neuronal primary cilia defects were observed in monogenic neurodevelopmental disorders that were not traditionally considered ciliopathies. The molecular mechanisms of how these genetic mutations cause primary cilia defects and how these defects contribute to the neurologic manifestations of these disorders remain poorly understood. In this review we will discuss monogenic neurodevelopmental disorders that exhibit cilia deficits and summarize findings from studies exploring the role of primary cilia in the brain to shed light into how these deficits could contribute to neurologic abnormalities.
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Affiliation(s)
- Vasiliki Karalis
- The Rosamund Stone Zander Translational Neuroscience Center, Department of Neurology Boston Children’s Hospital, Harvard Medical School, Boston, MA 02115, USA
- FM Kirby Neurobiology Center, Boston Children’s Hospital, Boston, MA 02115, USA
| | - Kathleen E. Donovan
- The Rosamund Stone Zander Translational Neuroscience Center, Department of Neurology Boston Children’s Hospital, Harvard Medical School, Boston, MA 02115, USA
- FM Kirby Neurobiology Center, Boston Children’s Hospital, Boston, MA 02115, USA
| | - Mustafa Sahin
- The Rosamund Stone Zander Translational Neuroscience Center, Department of Neurology Boston Children’s Hospital, Harvard Medical School, Boston, MA 02115, USA
- FM Kirby Neurobiology Center, Boston Children’s Hospital, Boston, MA 02115, USA
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2
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Kanamaru T, Neuner A, Kurtulmus B, Pereira G. Balancing the length of the distal tip by septins is key for stability and signalling function of primary cilia. EMBO J 2022; 41:e108843. [PMID: 34981518 PMCID: PMC8724769 DOI: 10.15252/embj.2021108843] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Revised: 10/19/2021] [Accepted: 10/26/2021] [Indexed: 01/08/2023] Open
Abstract
Primary cilia are antenna-like organelles required for signalling transduction. How cilia structure is mechanistically maintained at steady-state to promote signalling is largely unknown. Here, we define that mammalian primary cilia axonemes are formed by proximal segment (PS) and distal segment (DS) delineated by tubulin polyglutamylation-rich and -poor regions, respectively. The analysis of proximal/distal segmentation indicated that perturbations leading to cilia over-elongation influenced PS or DS length with a different impact on cilia behaviour. We identified septins as novel repressors of DS growth. We show that septins control the localisation of MKS3 and CEP290 required for a functional transition zone (TZ), and the cilia tip accumulation of the microtubule-capping kinesin KIF7, a cilia-growth inhibitor. Live-cell imaging and analysis of sonic-hedgehog (SHH) signalling activation established that DS over-extension increased cilia ectocytosis events and decreased SHH activation. Our data underlines the importance of understanding cilia segmentation for length control and cilia-dependent signalling.
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Affiliation(s)
- Taishi Kanamaru
- Centre for Organismal Studies (COS)University of HeidelbergHeidelbergGermany
- German Cancer Research Centre (DKFZ)DKFZ‐ZMBH AllianceHeidelbergGermany
- Centre for Molecular Biology (ZMBH)University of HeidelbergHeidelbergGermany
| | - Annett Neuner
- Centre for Molecular Biology (ZMBH)University of HeidelbergHeidelbergGermany
| | - Bahtiyar Kurtulmus
- Centre for Organismal Studies (COS)University of HeidelbergHeidelbergGermany
- German Cancer Research Centre (DKFZ)DKFZ‐ZMBH AllianceHeidelbergGermany
- Centre for Molecular Biology (ZMBH)University of HeidelbergHeidelbergGermany
| | - Gislene Pereira
- Centre for Organismal Studies (COS)University of HeidelbergHeidelbergGermany
- German Cancer Research Centre (DKFZ)DKFZ‐ZMBH AllianceHeidelbergGermany
- Centre for Molecular Biology (ZMBH)University of HeidelbergHeidelbergGermany
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3
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Conkar D, Firat-Karalar EN. Microtubule-associated proteins and emerging links to primary cilium structure, assembly, maintenance, and disassembly. FEBS J 2020; 288:786-798. [PMID: 32627332 DOI: 10.1111/febs.15473] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 06/23/2020] [Accepted: 06/30/2020] [Indexed: 12/22/2022]
Abstract
The primary cilium is a microtubule-based structure that protrudes from the cell surface in diverse eukaryotic organisms. It functions as a key signaling center that decodes a variety of mechanical and chemical stimuli and plays fundamental roles in development and homeostasis. Accordingly, structural and functional defects of the primary cilium have profound effects on the physiology of multiple organ systems including kidney, retina, and central nervous system. At the core of the primary cilium is the microtubule-based axoneme, which supports the cilium shape and acts as the scaffold for bidirectional transport of cargoes into and out of cilium. Advances in imaging, proteomics, and structural biology have revealed new insights into the ultrastructural organization and composition of the primary cilium, the mechanisms that underlie its biogenesis and functions, and the pathologies that result from their deregulation termed ciliopathies. In this viewpoint, we first discuss the recent studies that identified the three-dimensional native architecture of the ciliary axoneme and revealed that it is considerably different from the well-known '9 + 0' paradigm. Moving forward, we explore emerging themes in the assembly and maintenance of the axoneme, with a focus on how microtubule-associated proteins regulate its structure, length, and stability. This far more complex picture of the primary cilium structure and composition, as well as the recent technological advances, open up new avenues for future research.
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Affiliation(s)
- Deniz Conkar
- Department of Molecular Biology and Genetics, Koc University, Istanbul, Turkey
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4
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Abstract
We report a complete 3D structural model of typical epithelial primary cilia based on structural maps of full-length primary cilia obtained by serial section electron tomography. Our data demonstrate the architecture of primary cilia differs extensively from the commonly acknowledged 9+0 paradigm. The axoneme structure is relatively stable but gradually evolves from base to tip with a decreasing number of microtubule complexes (MtCs) and a reducing diameter. The axonemal MtCs are cross-linked by previously unrecognized fibrous protein networks. Such an architecture explains why primary cilia can elastically withstand liquid flow for mechanosensing. The nine axonemal MtCs in a cilium are found to differ significantly in length indicating intraflagellar transport processes in primary cilia may be more complicated than that reported for motile cilia. The 3D maps of microtubule doublet-singlet transitions generally display longitudinal gaps at the inner junction between the A- and B-tubules, which indicates the inner junction protein is a major player in doublet-singlet transitions. In addition, vesicles releasing from kidney primary cilia were observed in the structural maps, supporting that ciliary vesicles budding may serve as ectosomes for cell-cell communication.
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5
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Fernández-Santos JM, Utrilla JC, Vázquez-Román V, Villar-Rodríguez JL, Gutiérrez-Avilés L, Martín-Lacave I. Primary Cilium in the Human Thyrocyte: Changes in Frequency and Length in Relation to the Functional Pathology of the Thyroid Gland. Thyroid 2019; 29:595-606. [PMID: 30767621 DOI: 10.1089/thy.2018.0401] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
BACKGROUND Primary cilia (PC) are conserved structures in the adult thyroid gland of different mammals. It was recently described that in humans, PC are usually present as a single copy per follicular cell emerging from the follicular cell apex into the follicular lumen. METHODS To understand the role developed by PC in thyroid hormonogenesis better, their changes in different human functional thyroid diseases (diffuse toxic hyperplasia/Graves' disease [GD] and nodular hyperplasia [NH]/nodular goiter), in comparison to normal thyroid tissue, were investigated using immunofluorescence, morphometry, and electron microscopy analyses. RESULTS Significantly decreased ciliary frequencies were found in both NH (51.16 ± 11.69%) and GD (44.43 ± 23.70%) compared to normal thyroid tissue (76.09 ± 7.31%). Similarly, PC lengths were also significantly decreased in both NH (2.02 ± 0.35 μm) and GD (2.4 ± 0.48 μm) compared to normal glands (3.93 ± 0.90 μm). Moreover, in GD patients, hyperactive-follicle foci always showed diminished ciliary frequency and length compared to any other thyroid follicle pattern, independent of their thyroid status. Finally, in GD, the percentage of thyrocytes exhibiting PC in the "normal-appearance areas" was significantly lower in correspondence with the subsistence of signs of thyroid biosynthetic hyperactivity after long-term antithyroid drug treatment. CONCLUSIONS The results suggest a direct relationship between ciliogenesis and both follicle activity and tissue heterogeneity in the functional pathology of the thyroid gland.
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Affiliation(s)
- José María Fernández-Santos
- 1 School of Medicine, Department of Normal and Pathological Cytology and Histology, University of Seville, Seville, Spain
| | - José Carmelo Utrilla
- 1 School of Medicine, Department of Normal and Pathological Cytology and Histology, University of Seville, Seville, Spain
| | - Victoria Vázquez-Román
- 1 School of Medicine, Department of Normal and Pathological Cytology and Histology, University of Seville, Seville, Spain
| | | | - Lorenzo Gutiérrez-Avilés
- 1 School of Medicine, Department of Normal and Pathological Cytology and Histology, University of Seville, Seville, Spain
| | - Inés Martín-Lacave
- 1 School of Medicine, Department of Normal and Pathological Cytology and Histology, University of Seville, Seville, Spain
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6
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Utrilla JC, Gordillo-Martínez F, Gómez-Pascual A, Fernández-Santos JM, Garnacho C, Vázquez-Román V, Morillo-Bernal J, García-Marín R, Jiménez-García A, Martín-Lacave I. Comparative study of the primary cilia in thyrocytes of adult mammals. J Anat 2015; 227:550-60. [PMID: 26228270 DOI: 10.1111/joa.12360] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/15/2015] [Indexed: 11/29/2022] Open
Abstract
Since their discovery in different human tissues by Zimmermann in 1898, primary cilia have been found in the vast majority of cell types in vertebrates. Primary cilia are considered to be cellular antennae that occupy an ideal cellular location for the interpretation of information both from the environment and from other cells. To date, in mammalian thyroid gland, primary cilia have been found in the thyrocytes of humans and dogs (fetuses and adults) and in rat embryos. The present study investigated whether the existence of this organelle in follicular cells is a general event in the postnatal thyroid gland of different mammals, using both immunolabeling by immunofluorescence and electron microscopy. Furthermore, we aimed to analyse the presence of primary cilia in various thyroid cell lines. According to our results, primary cilia are present in the adult thyroid gland of most mammal species we studied (human, pig, guinea pig and rabbit), usually as a single copy per follicular cell. Strikingly, they were not found in rat or mouse thyroid tissues. Similarly, cilia were also observed in all human thyroid cell lines tested, both normal and neoplastic follicular cells, but not in cultured thyrocytes of rat origin. We hypothesize that primary cilia could be involved in the regulation of normal thyroid function through specific signaling pathways. Nevertheless, further studies are needed to shed light on the permanence of these organelles in the thyroid gland of most species during postnatal life.
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Affiliation(s)
- J C Utrilla
- Department of Normal and Pathological Cytology and Histology, University of Seville, School of Medicine, Seville, Spain
| | - F Gordillo-Martínez
- Department of Normal and Pathological Cytology and Histology, University of Seville, School of Medicine, Seville, Spain
| | - A Gómez-Pascual
- Department of Normal and Pathological Cytology and Histology, University of Seville, School of Medicine, Seville, Spain
| | - J M Fernández-Santos
- Department of Normal and Pathological Cytology and Histology, University of Seville, School of Medicine, Seville, Spain
| | - C Garnacho
- Department of Normal and Pathological Cytology and Histology, University of Seville, School of Medicine, Seville, Spain
| | - V Vázquez-Román
- Department of Normal and Pathological Cytology and Histology, University of Seville, School of Medicine, Seville, Spain
| | - J Morillo-Bernal
- Department of Normal and Pathological Cytology and Histology, University of Seville, School of Medicine, Seville, Spain
| | - R García-Marín
- Department of Normal and Pathological Cytology and Histology, University of Seville, School of Medicine, Seville, Spain
| | - A Jiménez-García
- Endocrine Surgery Unit of 'Virgen Macarena' University Hospital, Seville, Spain
| | - I Martín-Lacave
- Department of Normal and Pathological Cytology and Histology, University of Seville, School of Medicine, Seville, Spain
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Fisch C, Dupuis-Williams P. [The rebirth of the ultrastructure of cilia and flagella]. Biol Aujourdhui 2012; 205:245-67. [PMID: 22251859 DOI: 10.1051/jbio/2011023] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2011] [Indexed: 11/14/2022]
Abstract
The sensory and motility functions of eukaryotic cilia and flagella are essential for cell survival in protozoans and for cell differentiation and homoeostasis in metazoans. Ciliary biology has benefited early on from the input of electron microscopy. Over the last decade, the visualization of cellular structures has greatly progressed, thus it becomes timely to review the ultrastructure of cilia and flagella. Briefly touching upon the typical features of a 9+2 axoneme, we dwell extensively on the transition zone, the singlet zone, the ciliary necklace, cap and crown. The relation of the singlet zone to sensory and/or motile function, the link of the ciliary cap to microtubule dynamics and to ciliary beat, the involvement of the ciliary crown in ovocyte and mucosal propulsion, and the role of the transition zone/the ciliary necklace in axonemal stabilization, autotomy and as a diffusion barrier will all be discussed.
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Affiliation(s)
- Cathy Fisch
- ATIGE Centriole et Pathologies Associées, INSERM/UEVE U829, 91000 Évry, France.
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8
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Abstract
Eukaryotic cilia and flagella perform motility and sensory functions which are essential for cell survival in protozoans, and to organism development and homoeostasis in metazoans. Their ultrastructure has been studied from the early beginnings of electron microscopy, and these studies continue to contribute to much of our understanding about ciliary biology. In the light of the progress made in the visualization of cellular structures over the last decade, we revisit the ultrastructure of cilia and flagella. We briefly describe the typical features of a 9+2 axoneme before focusing extensively on the transition zone, the ciliary necklace, the singlet zone, the ciliary cap and the ciliary crown. We discuss how the singlet zone is linked to sensory and/or motile function, the contribution of the ciliary crown to ovocyte and mucosal propulsion, and the relationship between the ciliary cap and microtubule growth and shortening, and its relation to ciliary beat. We further examine the involvement of the transition zone/the ciliary necklace in axonemal stabilization, autotomy and as a diffusion barrier.
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Mokrzan EM, Lewis JS, Mykytyn K. Differences in renal tubule primary cilia length in a mouse model of Bardet-Biedl syndrome. Nephron Clin Pract 2007; 106:e88-96. [PMID: 17519557 DOI: 10.1159/000103021] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2006] [Accepted: 01/29/2007] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND Bardet-Biedl syndrome (BBS) is a heterogeneous genetic disorder that comprises numerous features, including renal cystic disease. Twelve BBS genes have been identified (BBS1-12). Although the exact functions of the BBS proteins are unknown, evidence suggests that they are involved in cilia assembly, maintenance and/or function. Renal primary cilia dysfunction can lead to cystic kidney disease. To test whether lacking Bbs4 affects cilia assembly and structure, we analyzed primary cilia in Bbs4-null (Bbs4(-/-)) mice. METHODS Renal tubule cultures from wild-type (Bbs4(+/+)) and Bbs4(-/-) mice were examined by immunocytochemistry and scanning and transmission electron microscopy. RESULTS Our culture conditions generated ciliated epithelial cells that were mostly of collecting duct origin. The microtubule ultrastructure of cilia and basal bodies did not appear disrupted in Bbs4(-/-) cells. In control cells, cilia length was maximal at 7 days in culture. In cells cultured from Bbs4(-/-) mice, cilia were shorter initially, but surpassed the length of control cilia by 10 days. Renal primary cilia were also longer in Bbs4(-/-) kidneys. CONCLUSIONS Lacking Bbs4 does not lead to aberrant cilia or basal body structure. However, the dynamics of cilia assembly is altered in Bbs4(-/-) cells, suggesting a role for Bbs4 in the regulation of ciliary assembly.
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Affiliation(s)
- Elaine M Mokrzan
- Department of Pharmacology, Division of Human Genetics, Ohio State University, Columbus, Ohio 43210, USA
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10
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Hagiwara H, Ohwada N, Takata K. Cell Biology of Normal and Abnormal Ciliogenesis in the Ciliated Epithelium. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 234:101-41. [PMID: 15066374 DOI: 10.1016/s0074-7696(04)34003-9] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/08/2022]
Abstract
Ciliogenesis is divided into four stages: (1) generation of centrioles, (2) migration of duplicated centrioles, (3) formation of the basal body-associated structures, and (4) elongation of cilia. The ultrastructural profile of ciliogenesis is fundamentally the same among various kinds of animal species. In acentriolar centriologenesis, centrioles are generated around deuterosomes by the use of fibrous granules. Components of the centriolar precursor structures, and genes that regulate the differentiation of ciliated cells, have been revealed. Ciliary abnormalities are classified into two categories: specific congenital defects of ciliary structure and acquired nonspecific anomalies of the ciliary apparatus. When ciliogenesis is disturbed, various nonspecific ciliary abnormalities develop in the cell. Inhibition of centriole migration results in the development of intracytoplasmic axonemes, cilia within periciliary sheaths, and intracellular ciliated vacuoles. Swollen cilia and the bulging type of compound cilia are formed during ciliary budding and elongation. Primary cilia can also develop from one of a pair of centrioles. They lack dynein arms and are immobile, but work as a mechanosensor and play a role during morphogenesis of the kidney. Abnormal function or structure of primary cilia results in the development of polycystic kidney disease. The axonemes of primary cilia or monocilia in the embryonic node cells are associated with dynein arms and move vortically. They have a role in determining the left-right (L-R) asymmetry of the fetus. This review also discusses the ciliogenesis of a primary cilium in the cell.
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Affiliation(s)
- Haruo Hagiwara
- Department of Anatomy and Cell Biology, Gunma University Graduate School of Medicine, Maebashi, Gunma 371-8511, Japan
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11
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Guay-Woodford LM. Murine models of polycystic kidney disease: molecular and therapeutic insights. Am J Physiol Renal Physiol 2003; 285:F1034-49. [PMID: 14600027 DOI: 10.1152/ajprenal.00195.2003] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Numerous murine (mouse and rat) models of polycystic kidney disease (PKD) have been described in which the mutant phenotype results from a spontaneous mutation or engineering via chemical mutagenesis, transgenic technologies, or gene-specific targeting in mouse orthologs of human PKD genes. These murine phenotypes closely resemble human PKD, with common abnormalities observed in tubular epithelia, the interstitial compartment, and the extracellular matrix of cystic kidneys. In both human and murine PKD, genetic background appears to modulate the renal cystic phenotype. In murine models, these putative modifying effects have been dissected into discrete factors called quantitative trait loci and genetically mapped. Several lines of experimental evidence support the hypothesis that PKD genes and their modifiers may define pathways involved in cystogenesis and PKD progression. Among the various pathway abnormalities described in murine PKD, recent provocative data indicate that structural and/or functional defects in the primary apical cilia of tubular epithelia may play a key role in PKD pathogenesis. This review describes the most widely studied murine models; highlights the data regarding specific gene defects and genetic modifiers; summarizes the data from these models that have advanced our understanding of PKD pathogenesis; and examines the effect of various therapeutic interventions in murine PKD.
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Affiliation(s)
- Lisa M Guay-Woodford
- Division of Genetic and Translational Medicine, Department of Medicine, University of Alabama at Birmingham, Kaul 740, 1530 3rd Ave. South 19th St., Birmingham, AL 35294, USA.
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12
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Yoder BK, Tousson A, Millican L, Wu JH, Bugg CE, Schafer JA, Balkovetz DF. Polaris, a protein disrupted in orpk mutant mice, is required for assembly of renal cilium. Am J Physiol Renal Physiol 2002; 282:F541-52. [PMID: 11832437 DOI: 10.1152/ajprenal.00273.2001] [Citation(s) in RCA: 178] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Cilia are organelles that play diverse roles, from fluid movement to sensory reception. Polaris, a protein associated with cystic kidney disease in Tg737(o)(rpk) mice, functions in a ciliogenic pathway. Here, we explore the role of polaris in primary cilia on Madin-Darby canine kidney cells. The results indicate that polaris localization and solubility change dramatically during cilia formation. These changes correlate with the formation of basal bodies and large protein rafts at the apical surface of the epithelia. A cortical collecting duct cell line has been derived from mice with a mutation in the Tg737 gene. These cells do not develop normal cilia, which can be corrected by reexpression of the wild-type Tg737 gene. These data suggest that the primary cilia are important for normal renal function and/or development and that the ciliary defect may be a contributing factor to the cystic disease in Tg737(o)(rpk) mice. Further characterization of these cells will be important in elucidating the physiological role of renal cilia and in determining their relationship to cystic disease.
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Affiliation(s)
- Bradley K Yoder
- Department of Cell Biology, University of Alabama at Birmingham, 35294, USA.
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13
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Pazour GJ, Dickert BL, Vucica Y, Seeley ES, Rosenbaum JL, Witman GB, Cole DG. Chlamydomonas IFT88 and its mouse homologue, polycystic kidney disease gene tg737, are required for assembly of cilia and flagella. J Cell Biol 2000; 151:709-18. [PMID: 11062270 PMCID: PMC2185580 DOI: 10.1083/jcb.151.3.709] [Citation(s) in RCA: 855] [Impact Index Per Article: 35.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2000] [Accepted: 09/07/2000] [Indexed: 11/22/2022] Open
Abstract
Intraflagellar transport (IFT) is a rapid movement of multi-subunit protein particles along flagellar microtubules and is required for assembly and maintenance of eukaryotic flagella. We cloned and sequenced a Chlamydomonas cDNA encoding the IFT88 subunit of the IFT particle and identified a Chlamydomonas insertional mutant that is missing this gene. The phenotype of this mutant is normal except for the complete absence of flagella. IFT88 is homologous to mouse and human genes called Tg737. Mice with defects in Tg737 die shortly after birth from polycystic kidney disease. We show that the primary cilia in the kidney of Tg737 mutant mice are shorter than normal. This indicates that IFT is important for primary cilia assembly in mammals. It is likely that primary cilia have an important function in the kidney and that defects in their assembly can lead to polycystic kidney disease.
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MESH Headings
- Amino Acid Sequence
- Animals
- Chlamydomonas/cytology
- Chlamydomonas/genetics
- Cilia/genetics
- Cilia/metabolism
- Cilia/pathology
- Cilia/ultrastructure
- Cloning, Molecular
- Conserved Sequence
- Flagella/genetics
- Flagella/metabolism
- Flagella/pathology
- Flagella/ultrastructure
- Humans
- Kidney/metabolism
- Kidney/pathology
- Meiosis
- Mice
- Mice, Knockout
- Microscopy, Electron, Scanning
- Molecular Motor Proteins/genetics
- Molecular Motor Proteins/metabolism
- Molecular Motor Proteins/pathology
- Molecular Motor Proteins/ultrastructure
- Molecular Sequence Data
- Mutation/genetics
- Phenotype
- Plant Proteins
- Polycystic Kidney, Autosomal Recessive/genetics
- Polycystic Kidney, Autosomal Recessive/pathology
- Polycystic Kidney, Autosomal Recessive/physiopathology
- Protein Binding
- Protein Subunits
- Proteins/chemistry
- Proteins/genetics
- Protozoan Proteins/chemistry
- Protozoan Proteins/genetics
- Protozoan Proteins/metabolism
- Repetitive Sequences, Amino Acid/genetics
- Repetitive Sequences, Amino Acid/physiology
- Sequence Alignment
- Sequence Homology, Amino Acid
- Tumor Suppressor Proteins
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Affiliation(s)
- G J Pazour
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA
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14
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Masuda M, Yamazaki K, Kanzaki J, Hosoda Y. Ultrastructure of melanocytes in the dark cell area of human vestibular organs: functional implications of gap junctions, isolated cilia, and annulate lamellae. Anat Rec (Hoboken) 1994; 240:481-91. [PMID: 7879900 DOI: 10.1002/ar.1092400406] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
BACKGROUND It is known that melanocytes exist in almost all parts of the inner ear, such as the cochlear duct, stria vascularis, Reissner's membrane, modiolus, vestibular organs in the region surrounding the cristae and maculae, semicircular canals, and pars rugosa of the endolymphatic sac. But there have been few studies using human materials, because of the difficulty of obtaining materials. We attempted to investigate the detailed ultrastructure of melanocytes in the vestibular organs of human inner ear. METHODS Eight surgical specimens obtained from patients with vestibular schwannoma were studied by light microscopy and electron microscopy. RESULTS Melanocytes were found in the subepithelial layer of the dark cell area. Melanocytes had round or spindle-shaped nuclei and clear cytoplasm with brown pigment granules. Besides melanocytes, there were melanophages, fibroblasts, and small blood vessels. Through electron microscopy we found melanocytes with round-shaped melanosomes in various stages of pigmentation, well-developed Golgi apparatus and endoplasmic reticulum in the cytoplasm, and many cytoplasmic processes. Gap junctions were occasionally found between the cytoplasmic processes. And there were pinocytotic vesicles just under the limiting membrane of melanocytes, and intermediate filaments were abundant in the cytoplasm. Isolated cilia of melanocytes, annulate lamellae, and fusiform banded structures in the connective tissue area around melanocytes were found. CONCLUSIONS Melanocytes in human vestibular organs actively synthesize melanosomes. Frequent findings of isolated cilia and fusiform banded structures and the incidental existence of annulate lamellae may be an indicator of this metabolically activated state of melanocytes. Moreover, monitoring environmental changes by isolated cilia, melanocytes in the human inner ear could act not only as one cell but also as a group to achieve their physiological functions by means of information transmission through gap junctions.
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Affiliation(s)
- M Masuda
- Department of Otorhinolaryngology, Keio University, School of Medicine, Tokyo, Japan
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15
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Prescott AR, Webb SF, Rawlins D, Shaw PJ, Warn RM. Microtubules rich in post-translationally modified alpha-tubulin form distinct arrays in frog lens epithelial cells. Exp Eye Res 1991; 52:743-53. [PMID: 1855548 DOI: 10.1016/0014-4835(91)90026-b] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Isolated frog lens epithelia were stained with antibodies against tyrosinated, detyrosinated or acetylated alpha-tubulin and observed by several means including a scanning confocal microscope. The most prominent feature of Rana pipiens lens cells was a primary cilium close to the apical surface of the cells above the centrosome. This structure was associated with microtubules rich in modified alpha-tubulin. The cilium was less pronounced but still discernible in the cells of another species R. ridibunda. In both species, the modified (acetylated or detyrosinated) microtubules formed arrays spatially distinct from the unmodified (tyrosinated) microtubules. The modified microtubules formed a basket of microtubules with a curly distribution around the nucleus while the tyrosinated array consisted predominantly of rather straighter microtubules running from the apical centrosome to the cell periphery, down the lateral sides of the cells and across the basal surface adjacent to the lens capsule and basement membrane. It is concluded that the organization of modified microtubules previously described for several types of cultured cells may represent a remnant of the three-dimensional perinuclear array of such microtubules described here for the cells of an intact epithelium.
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Affiliation(s)
- A R Prescott
- Cell Biology Group, School of Biological Sciences, University of East Anglia, Norwich, U.K
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16
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Harrisson F. Primary cilia associated with striated rootlets in granulated and folliculo-stellate cells of the avian adenohypophysis. ANATOMY AND EMBRYOLOGY 1989; 180:543-7. [PMID: 2610386 DOI: 10.1007/bf00300551] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
During observation of the ultrastructure of adenohypophyses of normal and experimentally-manipulated quails, primary cilia were found in secretory cells as well as in non-granulated, folliculo-stellate cells of both cephalic and caudal lobes of the gland. These solitary cilia shared morphological characteristics with those observed in other cell types and species, i.e. they arose from a basal body, which basically had a centriolar structure and 9 doublets of microtubules and no central tubules in their axoneme. A 8 + 1 arrangement of microtubules was exceptionally observed. A 9 + 2 pattern, which is commonly described in motile cilia, was never found. The cilia extended in extracellular spaces between secretory cells, but not in the follicular cavities nor in the blood vessels. In addition to the basal body, a single centriole was frequently present in its vicinity. The basal body was often associated with a basal foot or satellite from which microtubules radiated, and with ladderlike structures corresponding to the classical description of striated rootlets. The presumptive roles of primary cilia in general, and of their morphological features in particular, are discussed in view of our results and compared to the several observations reported in mammalian adenohypophyses. As the evidence gained in favour of a given function of primary cilia has, so far, always been circumstantial, extreme caution in interpretation must be exercise.
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Affiliation(s)
- F Harrisson
- Department of Anatomy and Embryology, State University Centre of Antwerp, Belgium
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Warfvinge K, Elofsson R. Single modified cilia displayed by cells of human internal stratified epithelia (oral cavity, vagina). Cell Tissue Res 1988; 251:237-41. [PMID: 3345540 DOI: 10.1007/bf00215830] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Serial sections of human vaginal and keratinized oral-gingival epithelia were investigated for ciliary structures. Most melanocytes of the gingival epithelium lacked cilia, whereas almost all basal keratinocytes of the deeper portion of the epithelial ridges possessed one cilium each. In the suprabasal layers of the ridges only a few keratinocytes exhibited a single cilium. In the basal layer, at the top of the connective tissue papillae, approximately every second keratinocyte displayed a single cilium. In the suprabasal layers above the ridges no ciliated keratinocytes were observed. The basal cells of the vaginal epithelium were endowed with cilia, while cilia were absent from the suprabasal cells. In the human forearm epidermis most melanocytes and keratinocytes are supplied with a single cilium; it has been suggested that they may play a role in light reception. However, the widespread occurrence of 9 + 0 cilia in epithelial cells of internal epithelia and their coincidence with the sites of renewal of keratinocytes suggests that a relationship may exist between solitary cilia and mitotic activity.
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Affiliation(s)
- K Warfvinge
- Department of Medical Cell Research, University of Lund, Sweden
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Fujiwara K, Watanabe T. Mucous-producing cells and ciliated epithelial cells in mandibular radicular cyst: an electron microscopic study. J Oral Maxillofac Surg 1988; 46:149-51. [PMID: 3422281 DOI: 10.1016/0278-2391(88)90269-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- K Fujiwara
- Department of Pathology, Saga Medical School, Japan
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Kawamata S, Kubota Y, Sawataishi M, Takaya K. The fine structure of atypical ciliated cells in the human gastric epithelium. VIRCHOWS ARCHIV. B, CELL PATHOLOGY INCLUDING MOLECULAR PATHOLOGY 1986; 51:363-74. [PMID: 2876543 DOI: 10.1007/bf02899045] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Gastric mucosa obtained from the body and pyloric portions of the human stomach were observed by light and transmission electron microscopy. Ciliated cells were found in two of 18 subjects examined, one patient with gastric ulcer and the other one with gastric adenocarcinoma. The ciliated cells were found in epithelia at sites away from the main lesions. The tissues containing ciliated cells showed intestinal metaplasia combined with mild chronic gastritis in both cases. The epithelial layer facing the gastric lumen was composed of columnar cells with numerous uniform microvilli and goblet cells. This epithelium extended to the superficial parts of the tubules surrounded by the lamina propria. The deeper portions of the tubules were composed of mucous secretory, endocrine, and rarely ciliated cells. These ciliated cells were provided with numerous cilia the numbers of which varied considerably from cell to cell. This was in contrast to the primary cilium which is usually single. The central part of the apical cell membrane was sometimes concave in the area from where cilia tended to arise. It was also observed that numerous basal bodies as well as mucus-like granules were contained in the same cell. The axonemal pattern was different from that of ordinary cilia and showed 9 + 0 and 8 + 1 patterns. In longitudinal sections it was found that one peripheral doublet was displaced to the center of the axoneme as it left the basal body.
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Odor DL, Blandau RJ. Observations on the solitary cilium of rabbit oviductal epithelium: its motility and ultrastructure. THE AMERICAN JOURNAL OF ANATOMY 1985; 174:437-53. [PMID: 3909797 DOI: 10.1002/aja.1001740407] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Solitary cilia have been observed on rabbit oviductal epithelial cells. In tissue cultures of fimbrial epithelium of 3- and 4-day-old animals observed by phase microscopy, most of these single cilia exhibited a vortical or funnel-type movement while others had the usual to-and-fro motility. Primary cilia are usually considered immotile. Transmission electron microscopy of specifically identified single cilia revealed differences between the ciliary shafts and basal bodies of the single cilia as compared to those of mature oviductal ciliated cells. The basal body of the solitary cilium often had at least two triangular, striated, basal foot processes, lacked electron-dense satellite material around its basal end, and occasionally had striated rootlets. In contrast, the cilia of mature ciliated cells had only one basal foot, exhibited much electron-dense satellite material, and lacked rootlets. Cross sections of the single cilia showed patterns of microtubules different from the usual 9 + 2 axonemal complexes of normal cilia and included 9 + 0, 10 + 2 singlets, 7 + 2 doublets, and 8 + 1 doublet and 2 singlets; one did have the usual 9 + 2 arrangement. We postulate that the presence of more than one basal foot process may be responsible for the vortical motility observed. The primary cilia are shorter than normal cilia; the longest one measured was 1.86 micron in length, 0.28 micron in width at its base, and 0.14 micron at its tip. Based on the light-microscopic, scanning-electron-microscopic and transmission-electron-microscopic observations, such solitary cilia were observed more frequently in the oviductal tissues of the 3- to 4-day postnatal rabbits grown in tissue culture and in ovariectomized and ovariectomized/progesterone-treated adult animals than in estrous, ovulatory, or ovariectomized/estradiol-treated rabbits.
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Elofsson R, Andersson A, Falck B, Sjöborg S. The ciliated human keratinocyte. JOURNAL OF ULTRASTRUCTURE RESEARCH 1984; 87:212-20. [PMID: 6085808 DOI: 10.1016/s0022-5320(84)80061-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Human keratinocytes were investigated for the presence of single cilia. Almost all basal keratinocytes were found to carry a single cilium in normal, occluded, and psoriatic skin. The ciliary structure was progressively reduced in keratinocytes approaching the surface. No remnants of the ciliary apparatus were found in the granular layer. In one case of nickel-allergic dermatitis (patch test), the keratinocytes had lost their cilia; the significance of this surprising finding remains to be elucidated.
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22
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Tachi S. Electron microscopic analysis of the effect of progesterone upon the hormone-sensitive solitary cilia and centriolar complexes in the luminal epithelial cells of the uterus of the ovariectomized-adrenalectomized rat. THE AMERICAN JOURNAL OF ANATOMY 1984; 169:45-58. [PMID: 6720610 DOI: 10.1002/aja.1001690104] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The time course of the hormonally controlled deciliation cycles of the centriolar complexes in the cells of the luminal epithelium of the uterus of the ovariectomized and adrenalectomized rat was analyzed at ultrastructural levels. The results were expressed quantitatively. The half-life of the solitary cilia after progesterone administration in the cell population was 14.6 hr, longer approximately by 1 hr than that previously reported for the estrogen-induced deciliation of the same cells. The time course of the progesterone-induced loss of solitary cilia strongly suggested that the phenomenon is biphasic. After the initial loss of 50%, the process progressed slowly. Twenty-four hours after the injection of the hormone, 35% of the cilia remained; after 60 hours, 4% were still present. This is in striking contrast to the effect of estrogen, which causes almost complete deciliation within 24 hr after the injection of the hormone. Prolonged exposure of the deciliated luminal epithelial cells to progesterone leads to disarrangement of the diplosome relationship. The phenomenon might be causally correlated with the block of estrogen-induced mitoses by this hormone; this view, however, needs further experimental corroboration.
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Lungarella G, de Santi MM, Tosi P. Ultrastructural study of the ciliated cells from renal tubular epithelium in acute progressive glomerulonephritis. Ultrastruct Pathol 1984; 6:1-7. [PMID: 6730021 DOI: 10.3109/01913128409016659] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Light microscopic examination of the renal tubular epithelium of a female with a rapid progressive glomerulonephritis revealed in several areas the presence of cells bearing ciliumlike structures. At transmission electron microscopy, normal tubular cells appeared to be partially replaced by epithelial cells showing numerous 9 X 2 cilia and a normally developed basal apparatus. The cilia showed several ultrastructural details (i.e., outer dynein arms, spokes) such as observed in kinocilia of the respiratory epithelium. In addition, a number of poorly differentiated cells showing cilia with a 9 + 0 pattern and at the same time cilia with a 9 + 2 pattern of microtubular arrangement were also seen. The possible biologic significance of these cilia is discussed.
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Abstract
Utilizing transmission electron microscopy we have found multiple cilia with a 9 + 2 microtubular pattern (the same type found in the bronchial tree) in the renal tubules of four adults with the nephrotic syndrome. Each patient had a different pathologic diagnosis: amyloidosis, lipoid nephrosis, membranoproliferative glomerulonephritis, and focal segmental glomerulosclerosis. Previously, multiple renal tubular cilia with 9 + 2 architecture had been reported in patients with Burnett's syndrome, systemic lupus erythematosus, and congenital nephrotic syndrome. Additionally, we found multiple cilia in the metanephric tubules of 4 of 4 human fetuses. Pathologists should be aware that cilia with various microtubular patterns occur in human adult kidneys.
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Bryan JH. Abnormal cilia in a male-sterile mutant mouse. VIRCHOWS ARCHIV. A, PATHOLOGICAL ANATOMY AND HISTOPATHOLOGY 1983; 400:77-86. [PMID: 6407195 DOI: 10.1007/bf00627011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
In mice homozygous for the mutation hydrocephalic-polydactyl (hpy) ciliary axonemes from tracheal, oviducal, and ependymal lining cells showed a variety of abnormalities. Defects included: a deficiency of inner dynein arms, extra central tubules, a displacement of one outer doublet and/or the central tubules, and double axonemes. More than one kind of defect was seen in some axonemes. None of the types of defects observed in mutants were encountered in equivalent samples from non-mutant littermates. Except for the most common defect, the deficiency in dynein arms, which occurred to about the same extent (approximately 34%) in all three tissues, there were marked variations in frequency among the tissue types with respect to the other defects. In general, defects such as central tubule anomalies, displaced tubules, and double axonemes occurred with the highest frequencies in axonemes from tracheal epithelial cells and with the lowest frequencies in samples of oviducal epithelium. Fused cilia were seen only in ependymal cell samples. Some of the defects encountered were common to sperm flagella axonemes while others appeared restricted to somatic tissues, suggesting, perhaps, each tissue type may exert its own modulating influence on the expression of the mutant gene.
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26
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Tucker RW. Role of microtubules and centrioles in growth regulation of mammalian cells. CELL AND MUSCLE MOTILITY 1983; 3:259-95. [PMID: 6200201 DOI: 10.1007/978-1-4615-9296-9_8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Dørup J, Maunsbach AB. The ultrastructural development of distal nephron segments in the human fetal kidney. ANATOMY AND EMBRYOLOGY 1982; 164:19-41. [PMID: 7114486 DOI: 10.1007/bf00301876] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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28
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Dalen H. An ultrastructural study of primary cilia, abnormal cilia and ciliary knobs from the ciliated cells of the guinea-pig trachea. Cell Tissue Res 1981; 220:685-97. [PMID: 7296649 DOI: 10.1007/bf00210455] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Single primary cilia are found in developing as well as mature ciliated cells of guinea-pig tracheal epithelium. A few biciliated cells were observed, and in a rare case one cell had developed four such processes. Primary cilia are characterized by a 9 + 0 microtubular arrangement near the base, while a transition to an 8 + 1 pattern occurs at a slightly more distal position. Spokes are lacking, and dynein arms are absent or incompletely developed. The function, if any, of primary cilia remains unknown. In the population of the motile 9 + 2 cilia atypical forms are very rare, i.e. less than 0.1%. Of the various abnormalities cilia with supernumary microtubules are most common. Only one atypical basal body was observed. Although some of the aberrant forms undoubtedly are non-motile, their very low number suggests that they have no practical influence on the muco-ciliary clearance. Local extrusions of the ciliary membrane, here named ciliary knobs, are believed to be fixation artefacts. It is suggested that they represent circumscribed regions of the ciliary membrane which are sensitive to changes in the environmental osmotic pressure.
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Abstract
A primary cilium is a normal component of every rabbit corneal endothelial cell, rather than being a rare or sporadic organelle, as previously believed. In common with other cilia of this type it possesses an axonemal organization of 9 +0 which converts distally to 8 + 1; it occurs only one per cell; and the basal body is accompanied by a proximal centriole. Additional structures associated with the basal body are nine transitional fibers, four striated satellite arms, and several rootlets. Ladderlike structures extend between the two centrioles to form the wall of a barrel. Reexamination of primary cilia from other tissues indicates that the ultrastructure of endothelial cilia may be characteristic of primary cilia in general.
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Lafarga M, Hervás JP, Crespo D, Villegas J. Ciliated neurons in supraoptic nucleus of rat hypothalamus during neonatal period. ANATOMY AND EMBRYOLOGY 1980; 160:29-38. [PMID: 7469034 DOI: 10.1007/bf00315647] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Cilia 9+0 have been found in differentiating neurosecretory neurons of the hypothalamic supraoptic nuclei of Wistar rats. These ciliated neurosecretory cells were always observed during the neonatal period of the rat and no more than one cilium per cell has been encountered. Single cilia arising from typical basal bodies were usually located in deep invaginations of the neuronal perikaryon, but can also be seen in superficial positions. Their basal bodies were commonly found in the vicinity of Golgi complexes, and associated structures such as striated rootlets and alar sheets were also present. In addition, single centrioles frequently appeared in these neurons, occurring close to basal bodies but also in centrosomatic areas. The respective roles of these morphological features are suggested and their possible ontogenetic significance is briefly discussed.
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31
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Breucker H, Zeiske E, Melinkat R. Development of the olfactory organ in the rainbow fish Nematocentris maccullochi (Atheriniformes, Melanotaeniidae). Cell Tissue Res 1979; 200:53-68. [PMID: 498254 DOI: 10.1007/bf00236887] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The development of the olfactory organ in the rainbow fish, Nematocentris maccullochi, was studied using scanning and transmission electron microscopy; it was compared with the developmental process in other teleosts, especially in the closely related atherinids and cyprinodonts. The formation of the nares parallels that in atherinids, salmonids, cyprinids and heterosomats, but differs from that found in cyprinodonts. Another ontogenetic feature in which the olfactory organs of the rainbow fish and also of atherinids differ from those of cyprinodonts, is the occurrence of transitory kinociliary cells which disappear during the postlarval period. The divergent evolutionary pathways are discussed with reference to experimental investigations. During development, ciliated and microvillous receptor cell types occur. At the primary larval stage ciliated receptor neurons are exclusively present. At a later stage the microvillous type develops and becomes equal in frequency. Thus, the microvillous receptor represents a separate type of olfactory neuron and is not a progenitor of the ciliated receptor cell.
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