The ultrastructure of the sternal gills forming a striking contrast with the coxal gills in a fresh-water amphipod (Crustacea)

Sternomoera yezoensis has specialized sterna with 21 sternal gills in addition to six pairs of coxal gills. Despite a common high permeability to chloride ions, the cpithelia of these two kinds of gills are diametrically opposed in the polarity of the cell membranemitochondria complex. The coxal gill epithelium (4-6 mum thick) is characterized by a welldeveloped AIS (apical infolding system) associated with a huge number of large mitochondria. The AIS exceeds two-thirds of the epithelial thickness and forms a highly sophisticated, subcuticular labyrinth. On the contrary, the sternal gill epithelium, an extension of the sternal epithelium proper, is extremely thick (10-15 mum) and is characterized by a very deep BIS (basolateral infolding system) associated with numerous slender mitochondria. The BIS reaches nine-tenths of the epithelial thickness and forms a giant, baso-lateral labyrinth. Shallower, less elaborate AIS and BIS without mitochondrial association originate from the opposite sides of these epithelia. Although AIS and BIS interpenetrate in the sternal gill epithelium, they never communicate. The results indicate that in addition to the coxal gills, the sterna with Ihe sternal gills function as transporting as well as respiratory organs, though the functional difference between these two kinds of gills remains to be elucidated.     

Two ultrastructurally distinct types of transporting tissues,the branchiostegal and the gill epithelia,in an estuarine tanaid,Sinelobus stanfordi (Crustacea,Peracarida)

Summary On each lateral side of the cephalothorax segments, the adult Sinelobus stanfordi has a branchial chamber which contains an elongated bag-shaped gill and is covered by a thick branchiostegite. The ultrastructural study revealed that the inner surface of the branchiostegite is composed of a transporting-type epithelium which is morphologically distinct from the gill epithelium. Both epithelia are covered by extremely thin (about 80 nm) cuticle layers, suggesting high permeability to gases, ions, and water. In contrast, the outer surface of the branchiostegite consists of ordinary epithelium covered by a very thick cuticle layer in common with the body surface. The inner branchiostegal epithelium (4–10 m thick) has a shallow (about 1 m deep) apical infolding system of the cell membrane (AIS) and an extensive three-dimensional tubular network (about 120 nm in diameter) which is formed by the invagination of the basolateral cell membrane (TNB). The TNB is associated with slender mitochondria and occupies the majority of the cytoplasmic area of the epithelial cell. The gill epithelium, on the other hand, is about 10 m thick and characterized by an abundance of oval mitochondria, well-developed (4–5 m deep) AIS, and a smooth basal cell membrane lacking any infoldings. These morphological features indicate that not only the gill epithelia, but also the inner branchiostegal epithelia, are involved in the ion-transporting processes. The ultrastructural differences between these two kinds of epithelia also suggest their different roles in the osmoregulation of this animal, since it inhabits estuaries which are subject to extreme changes in salinity.     

Identification of respiratory and ion-transporting epithelia in the phyllosoma larvae of the slipper lobster Scyllarus arctus

Phyllosoma larvae of the Palinura lack a branchial cavity and gills. In the phyllosoma, gas and ion exchanges that occur at the level of the gill in the adult must occur in other parts of the body or through the entire body. The objective of this study was to localize epithelia bordering the body of the phyllosoma larvae that had features comparable to those of the gill epithelia of adult decapods. The first phyllosoma instar of the small Mediterranean slipper lobster Scyllarus arctus was studied. First, we used a silver nitrate staining method to identify parts of the body with high ionic permeability. Confocal laser scanning microscopy with a fluorescent vital stain for mitochondria, dimethylaminostyrylmethylpyridiniumiodine (DASPMI), was then used to localize cells with a high density of mitochondria. Next, an ultrastructural study of selected epithelia was carried out. A thick (5 microns) mitochondria-rich epithelium covers the ventral side of the cephalic shield; its cells are characterized by the presence of well-developed apical infoldings adjacent to the cuticle. This part of the body has a high ionic permeability as indicated by a positive silver nitrate staining. The ventral mitochondria-rich epithelium might be involved in active ion transport. The rest of the body, particularly the dorsal side of the shield and the appendages, shows a lower ionic permeability (no positive silver nitrate staining) and is limited by a thin (1 micron) epithelium with low numbers of mitochondria. This epithelium exhibits features of a typical respiratory epithelium.     

Ultrastructure of the foregut and associated glands of Calicotyle kröyeri (Monogenea: Monopisthocotylea)

The mouth, pharynx and oesophagus of Calicotyle are lined by syncytial epithelia, and there are numerous unicellular glands associated with the oesophagus. An infolding of unmodified external tegument lines the mouth cavity and is connected by discrete cytoplasmic processes to subjacent perikarya. It contains two types of secretory body and its luminal surface is invested with a finely filamentous coating. The pharynx and oesophagus are lined by irregularly-folded epithelia that are interconnected by a septate desmosome. Membranous inclusions distinguish the pharynx epithelium and there is a well developed basal lamina for insertion of the pharyngeal muscles. The oesophagus epithelium is perforated by the openings of the oesophageal glands. These lie in the surrounding parenchyma and produce a dense, membrane-bound secretion which is conveyed by duct-like extensions of the glands to the oesophagus lumen. The ducts are supported in places by microtubules and are anchored to the oesophageal epithelium by septate desmosomes. A septate desmosome also marks the junction between the epithelium and the gut caeca.     

The colon of Leucophaea maderae: fine structure and physiological features

The colon of L. maderae consists of a single columnar epithelium covered with a cuticle and of a musculo-connective sheath. The apical plasma membranes form a system of leaflets with numerous mitochondria inserted in association with microfilaments. Lateral plasma membranes are linked together by junctional complexes consisting of a zonula adherens and a long convoluted septate junction of the pleated type. In the basal region of the cell, numerous membrane infolds and scattered scalariform junctions with associated mitochondria are present. These cell specializations are typical of arthropod transporting organs, being distinctive features of ion and fluid transporting epithelia. The isolated colon exhibited a transepithelial electrical potential difference (PD) of about 100 mV, lumen side positive with respect to the haemolymph side. The PD was almost abolished by metabolic inhibitors, it was reduced by acetazolamide and SITS, and it was unaffected by ouabain. These effects suggest that HCO3- and Cl- are involved in the genesis of the PD, whereas Na+ is not directly responsible of the PD. Measurements of Na+ and Cl- fluxes across the colon wall confirm that Na+ moves following the PD across the tissue, while Cl- movement occurs against an electrochemical potential difference. The electrical profile of the epithelial cells is of the well type and it suggests that the primary or secondary active step for Cl- transport across the epithelium should be located at the mucosal border of the cell.     

Immunolocalization of Na+,K+-ATPase in the organs of the branchial cavity of the European lobster Homarus gammarus (Crustacea, Decapoda)

The localization of Na+,K(+)-ATPase in epithelia of the organs of the branchial cavity of Homarus gammarus exposed to seawater and dilute seawater was examined by immunofluorescence microscopy and immunogold electron microscopy with a monoclonal antibody IgG alpha 5 raised against the avian alpha-subunit of the Na-,K(+)-ATPase. In juveniles held in seawater, fluorescent staining was observed only in the epithelial cells of epipodites. In juveniles held in dilute seawater, heavier immunoreactivity was observed in the epithelial cells of epipodites, and positive immunostaining was also observed along the inner-side epithelial layer of the branchiostegites. No fluorescent staining was observed in the gill epithelia. At the ultrastructural level, the Na+,K(+)-ATPase was localized in the basolateral infolding systems of the epipodite and inner-side branchiostegite epithelia of juveniles held in dilute seawater, mostly along the basal lamina. The expression of Na+,K(+)-ATPase therefore differs within tissues of the branchial cavity and according to the external salinity. These and previous ultrastructural observations suggest that the epipodites, and to a lesser extent the inner-side epithelium of the branchiostegites, are involved in the slight hyper-regulation displayed by lobsters at low salinity. Enhanced Na+,K(+)-ATPase activity and de novo synthesis of Na+,K(+)-ATPase within the epipodite and branchiostegite epithelia may be key points enabling lobsters to adapt to low salinity environments.     

Fine structure of the axial complex of Sphaerechinus granularis (Lam.) (Echinodermata: Echinoidea)

Summary Three regions of the axial complex in Sphaerechinus granularis can be distinguished: 1) The axial organ which protrudes from one side of the axial sinus; the sinus septum which separates the sinus from the body cavity and encloses the stone canal; the pulsating vessel which runs along the inside of the axial organ. 2) The blindly-ending terminal sinus in which the pulsating vessel broadens out to the contractile terminal process. 3) The ampulla of the stone canal which connects the axocoel and water vascular system and which opens out through the madreporite.A single-layered, monociliated coelomic epithelium surrounds all regions of the axial complex. This epithelium contains smooth muscle cells at the contractile areas. Canaliculi, surrounded by basal lamina, are formed through infolding of epithelia; they end blindly in the fluid and connective tissue -matrix of the inner structures.The lacunae of the dorso-ventral mesentery connect the periesophageal and the perianal haemal ring with the axial organ. The axial organ contains many coelomocytes rich in pigment and granules. These coelomocytes are separated into compartments by elastic fibres. Phagocytosis of whole cells and transformational stages of coelomocytes suggest storage and degradation functions. An excretory function via the water vascular system is also suggested.     

Equilibrium mechanics of monolayered epithelium

In order to fully understand the epithelial mechanics it is essential to integrate different levels of epithelial organization. In this work, we propose a theoretical approach for connecting the macroscopic mechanical properties of a monolayered epithelium to the mechanical properties at the cellular level. The analysis is based on the established mechanical models—at the macroscopic scale the epithelium is described within the mechanics of thin layers, while the cellular level is modeled in terms of the cellular surface (cortical) tension and the intercellular adhesion. The macroscopic elastic energy of the epithelium is linked to the energy of an average epithelial cell. The epithelial equilibrium state is determined by energy minimization and the macroscopic elastic moduli are calculated from deformations around the equilibrium. The results indicate that the epithelial equilibrium state is defined by the ratio between the adhesion strength and the cellular surface tension. The lower and the upper bounds for this ratio are estimated. If the ratio is small, the epithelium is cuboidal, if it is large, the epithelium becomes columnar. Importantly, it is found that the cellular cortical tension and the intercellular adhesion alone cannot produce the flattened squamous epithelium. Any difference in the surface tension between the apical and basal cellular sides bends the epithelium towards the side with the larger surface tension. Interestingly, the analysis shows that the epithelial area expansivity modulus and the shear modulus depend only on the cellular surface tension and not on the intercellular adhesion. The results are presented in a general analytical form, and are thus applicable to a variety of monolayered epithelia, without relying on the specifics of numerical finite-element methods. In addition, by using the standard theoretical tools for multi-laminar systems, the results can be applied to epithelia consisting of layers with different mechanical properties.     

The adoral sense organ in protobranch bivalves (Mollusca): comparative fine structure with special reference to Nucula nucleus

Abstract. The adoral sense organ in bivalve molluscs is a paired ridge of specialized epithelium positioned laterally at the base of the labial palps near the mouth opening, clearly distinguishable from the surrounding epithelia. Six species of the protobranch order Nuculoida, and one species of Solemyoida, were investigated by light microscopy concerning presence, gross anatomy, and innervation of the adoral sense organ. The organ was described in detail for Nucula nucleus and N. nitidosa by transmission electron microscopy; in these two species, the organ was characterized as a pseudostratified epithelial thickening with specialized cells bearing a specialized microvillar border and a basal matrix with a lamellar layer. Three types of bipolar primary receptor cells were recognized and these were reconstructed for N. nucleus. Most of the receptor cells had 2 cilia orientated parallel to the cell surface; in addition, there were 2 types of supporting cells and 1 type of basal cell. The surrounding epithelial cells were narrow with short microvilli and lacked cilia. The homology of the organ within protobranch bivalves was suggested by a character-complex of (1) position, (2) dimension of the epithelium, (3) innervation, (4) pseudostratified construction, (5) dimension of the specialized microvillar border, (6) thickening of the basal matrix, and (7) presence of specialized cell types such as receptor cells. Despite the estimated high number of protobranch species there is only scant information available on the adoral sense organ from 24 species of 8 genera. Structures and receptor types that are similar to those found in the adoral sense organ are widespread in molluscs and other invertebrate groups; this may indicate a plesiomorphy of these characters rather than an apomorphy for the protobranch clade. Therefore, the adoral sense organ may be of minor phylogenetic value above the level of protobranch orders.     

Chlamydiae and polymorphonuclear leukocytes: unlikely allies in the spread of chlamydial infection

While much is known about the attachment of the chlamydiae to the host cell and intracellular events during the developmental cycle, little is known about the mechanism(s) by which elementary bodies exit the cell. In this report, we use the guinea-pig conjunctival model of Chlamydia caviae infection to present in vivo ultrastructural evidence supporting two mechanisms for release of chlamydiae from the mucosal epithelia. Four days after infection, histopathologic observation shows an intense infiltration of polymorphonuclear leukocytes (PMN) in the conjunctival epithelium. Using transmission electron microscopy, a gradient-directed PMN response to chlamydiae-infected epithelial cells was observed. As PMN infiltration intensifies, epithelial hemidesmosome/integrin/focal adhesion adherence with the basal lamina is disconnected and PMNs literally lift off and release infected superficial epithelia from the mucosa. Many of these infected cells appear to be healthy with intact microvilli, nuclei, and mitochondria. While lysis of some infected cells occurs with release of chlamydiae into the extracellular surface milieu, the majority of infected cells are pushed off the epithelium. We propose that PMNs play an active role in detaching infected cells from the epithelium and that these infected cells eventually die releasing organisms but, in the process, move to new tissue sites via fluid dynamics.     

The ultrastructural investigation of the midgut in the quill mite Syringophilopsis fringilla (Acari,Trombidiformes: Syringophilidae)

The midgut of the females of Syringophilopsis fringilla (Fritsch) composed of anterior midgut and excretory organ (=posterior midgut) was investigated by means of light and transmission electron microscopy. The anterior midgut includes the ventriculus and two pairs of midgut caeca. These organs are lined by a similar epithelium except for the region adjacent to the coxal glands. Four cell subtypes were distinguished in the epithelium of the anterior midgut. All of them evidently represent physiological states of a single cell type. The digestive cells are most abundant. These cells are rich in rough endoplasmic reticulum and participate both in secretion and intracellular digestion. They form macropinocytotic vesicles in the apical region and a lot of secondary lysosomes in the central cytoplasm. After accumulating various residual bodies and spherites, the digestive cells transform into the excretory cells. The latter can be either extruded into the gut lumen or bud off their apical region and enter a new digestive cycle. The secretory cells were not found in all specimens examined. They are characterized by the presence of dense membrane-bounded granules, 2–4 μm in diameter, as well as by an extensive rough endoplasmic reticulum and Golgi bodies. The ventricular wall adjacent to the coxal glands demonstrates features of transporting epithelia. The cells are characterized by irregularly branched apical processes and a high concentration of mitochondria. The main function of the excretory organ (posterior midgut) is the elimination of nitrogenous waste. Formation of guanine-containing granules in the cytoplasm of the epithelial cells was shown to be associated with Golgi activity. The excretory granules are released into the gut lumen by means of eccrine or apocrine secretion. Evacuation of the fecal masses occurs periodically. Mitotic figures have been observed occasionally in the epithelial cells of the anterior midgut.     

Differential transmission of HIV traversing fetal oral/intestinal epithelia and adult oral epithelia

While human immunodeficiency virus (HIV) transmission through the adult oral route is rare, mother-to-child transmission (MTCT) through the neonatal/infant oral and/or gastrointestinal route is common. To study the mechanisms of cell-free and cell-associated HIV transmission across adult oral and neonatal/infant oral/intestinal epithelia, we established ex vivo organ tissue model systems of adult and fetal origin. Given the similarity of neonatal and fetal oral epithelia with respect to epithelial stratification and density of HIV-susceptible immune cells, we used fetal oral the epithelium as a model for neonatal/infant oral epithelium. We found that cell-free HIV traversed fetal oral and intestinal epithelia and infected HIV-susceptible CD4(+) T lymphocytes, Langerhans/dendritic cells, and macrophages. To study the penetration of cell-associated virus into fetal oral and intestinal epithelia, HIV-infected macrophages and lymphocytes were added to the surfaces of fetal oral and intestinal epithelia. HIV-infected macrophages, but not lymphocytes, transmigrated across fetal oral epithelia. HIV-infected macrophages and, to a lesser extent, lymphocytes transmigrated across fetal intestinal epithelia. In contrast to the fetal oral/intestinal epithelia, cell-free HIV transmigration through adult oral epithelia was inefficient and virions did not infect intraepithelial and subepithelial HIV-susceptible cells. In addition, HIV-infected macrophages and lymphocytes did not transmigrate through intact adult oral epithelia. Transmigration of cell-free and cell-associated HIV across the fetal oral/intestinal mucosal epithelium may serve as an initial mechanism for HIV MTCT.     

Ultrastructural changes in the gill epithelium of the green crab Carcinus maenas in relation to the external salinity

Observation of semi-thin and ultrathin sections performed in the gills of green crabs (Carcinus maenas) kept in 100% and in dilute 30% sea water respectively reveals marked differences between the six anterior and the three posterior pairs of gills. The anterior gill lamellae are almost entirely lined by a thin pavement epithelium (0.9 to 3 mum thick) which does not undergo any noticeable change when crabs are acclimated from full to dilute sea water. This supports the view it is chiefly involved in the respiratory function. In addition to the pavement epithelium, the posterior gills exhibit small areas corresponding to a thick prismatic epithelium (10 mum) the ultrastructure of which is similar to that of most of the so-called 'salt transporting epithelia'. When submitted to reduced external salinity, this epithelium undergoes structural changes consisting of elaboration of an extensive apical plasma membrane infolding system, enlargement of the subcuticular compartment and close association of mitochondria with basolateral membrane infoldings. Pilaster cells exhibit ultrastructural features of either thin (respiratory) or thick (salt transporting) epithelial differentiation according to their localization within the gill. Their peculiar organization suggests they ensure, in addition, mechanical reinforcement of the gill lamellae against blood hydrostatic pressure. The fact that salt-transporting epithelium areas do not exceed, at most, 30% of the total lamellar surface is probably related to the weak osmoregulatory capabilities of the shore crab.     

Ultrastructure of the anterior alimentary tract of a monogenean, Diclidophora merlangi

The anterior alimentary tract of Diclidophora merlangi is composed of a complex series of morphologically distinct epithelia interconnected by septate desmosomes and penetrated by the openings of numerous unicellular glands. The mouth and buccal cavity are lined by an infolding of modified body tegument, distinguished by uniciliate sense receptors, buccal gland openings, and in the buccal region by a dense, spiny appearance. The prepharynx is covered by an irregularly folded epithelium and, for part of its length, by the luminal cytoplasm of the prepharyngeal gland cells. The epithelium is syncytial and pleiomorphic, and regional variation in structure is common. A separate epithelium invests the lips of the pharynx and its free surface is greatly amplified by numerous, dense lamellae of varying dimensions. The lip epithelium is continuous with cytoplasmic processes of cells located external to the pharynx. A further, distinct epithelium borders the pharynx lumen and is composed of discrete cytoplasmic units connected by short septate desmosomes. The oesophagus is lined by a modified caecal epithelium, lacking haematin cells, and, in places, is perforated by the openings of oesophageal gland cells; it is continuous with the syncytial connecting tissue of the gut caeca.     

Ultrastructure of the supporting cells in the paratympanic organ of chicken,Gallus gallus domesticus

The paratympanic organ is a specialized sensory organ of birds located in the medial wall of the tympanic cavity. It possesses a sensory epithelium formed by type II hair cells and supporting cells. The supporting cells are tall, narrow units that extend from the basement membrane to the free epithelial surface. They show a fine structure characterized by numerous mitochondria, a conspicuous Golgi complex and a well-developed RER. Moreover, some uncommon structures, probably formed by heaped RER cisternae, are frequently present in the cytoplasm. Adjacent supporting cells are connected by numerous and extensive gap junctions; moreover, small gap junctions between hair cell and supporting cells are to be found. The possible mechanical and metabolical functions of the paratympanic organ supporting cells are discussed. J. Morphol. 236:65–73, 1998. © 1998 Wiley-Liss, Inc.     

Conserved form and function of the germinal epithelium through 500 million years of vertebrate evolution

The germinal epithelium, i.e., the site of germ cell production in males and females, has maintained a constant form and function throughout 500 million years of vertebrate evolution. The distinguishing characteristic of germinal epithelia among all vertebrates, males, and females, is the presence of germ cells among somatic epithelial cells. The somatic epithelial cells, Sertoli cells in males or follicle (granulosa) cells in females, encompass and isolate germ cells. Morphology of all vertebrate germinal epithelia conforms to the standard definition of an epithelium: epithelial cells are interconnected, border a body surface or lumen, are avascular and are supported by a basement membrane. Variation in morphology of gonads, which develop from the germinal epithelium, is correlated with the evolution of reproductive modes. In hagfishes, lampreys, and elasmobranchs, the germinal epithelia of males produce spermatocysts. A major rearrangement of testis morphology diagnoses osteichthyans: the spermatocysts are arranged in tubules or lobules. In protogynous (female to male) sex reversal in teleost fishes, female germinal epithelial cells (prefollicle cells) and oogonia transform into the first male somatic cells (Sertoli cells) and spermatogonia in the developing testis lobules. This common origin of cell types from the germinal epithelium in fishes with protogynous sex reversal supports the homology of Sertoli cells and follicle cells. Spermatogenesis in amphibians develops within spermatocysts in testis lobules. In amniotes vertebrates, the testis is composed of seminiferous tubules wherein spermatogenesis occurs radially. Emerging research indicates that some mammals do not have lifetime determinate fecundity. The fact emerged that germinal epithelia occur in the gonads of all vertebrates examined herein of both sexes and has the same form and function across all vertebrate taxa. Continued study of the form and function of the germinal epithelium in vertebrates will increasingly clarify our understanding of vertebrate reproduction. J. Morphol. 277:1014–1044, 2016. © 2016 Wiley Periodicals, Inc.     

Distribution of E-cadherin and Ep-CAM in the human lung during development and after injury

Paraffin sections were obtained of human fetal, adult, and pathological lung (pulmonary fibrosis after radiotherapy or chemotherapy). The localization of epithelial adhesion molecules E-cadherin and Ep-CAM (former epithelial surface 40 kDa glycoprotein) was investigated by immunoperoxidase and/or immunofluorescence techniques with monoclonal antibodies. During development, the epithelia of the primary pulmonary primordium, the secondary bronchi and the adult bronchial epithelium retained immunoreactivity for E-cadherin and Ep-CAM with lateral immunostaining of cell membranes. In normal adult lungs, Ep-CAM was detected in type I and II alveolar epithelial cells, whereas E-cadherin was confined to the basolateral domain of type II cells. In pulmonary fibrosis, Ep-CAM could be further detected on the cell surface of epithelial remnants. In contrast, E-cadherin expression was characterized by a change of the membrane localization to a spotty, cytoplasmic pattern in the alveolar epithelium, possibly indicating functional inactivation of the protein during fibrogenesis.     

Mesenchymal control of branching pattern in the fetal mouse lung

The effect of mesenchyme on specialization of respiratory epithelium in the fetal mouse was tested in organ cultures. Heterologous combinations were made between respiratory and non-respiratory lung epithelia and the corresponding mesenchymes. Isolated terminal respiratory buds of fetal mouse lungs were recombined with mesenchyme from chick lung parabronchi, mouse trachea or from the avascular, non-respiratory air sacs of chick lungs. Isolated non-branching chick air sacs were combined with mouse terminal bud mesenchyme or mesenchyme from the respiratory branches of chick lungs. Air sac epithelia branched in a pattern characteristic of the chick lung when combined with chick respiratory mesenchyme and in a pattern characteristic of mouse lung when combined with mouse terminal bud mesenchyme. Mouse terminal bud epithelia did not branch with either mouse tracheal mesenchyme or chick air sac mesenchyme but branched in a chick pattern with chick parabronchial mesenchyme. Electron microscopic examination of the cultures showed that all chick air sac epithelial cultures failed to produce surfactant (lamellar bodies) even when they branched. Control cultures of mouse terminal buds contained large numbers of lamellar bodies; mesenchyme which suppressed branching reduced the number of lamellar bodies to only a few in a small proportion of the cells. Culture medium supplemented with growth factors and hormones increased the number of lamellar bodies in heterologous mouse combinations but did not bring the number to control levels. Supplemented medium had no effect on lamellar body production by chick air sac epithelium. The results indicate that branching pattern is determined by the mesenchyme surrounding the epithelial primordium. However, the capacity to synthesize surfactant is determined by the source of the epithelium; mesenchyme may control the degree of expression but not the absolute presence or absence of the differentiated condition.     

Origin and shaping of the laterality organ in zebrafish

Handedness of the vertebrate body plan critically depends on transient embryonic structures/organs that generate cilia-dependent leftward fluid flow within constrained extracellular environments. Although the function of ciliated organs in laterality determination has been extensively studied, how they are formed during embryogenesis is still poorly understood. Here we show that Kupffer's vesicle (KV), the zebrafish organ of laterality, arises from a surface epithelium previously thought to adopt exclusively extra-embryonic fates. Live multi-photon confocal imaging reveals that surface epithelial cells undergo Nodal/TGFbeta signalling-dependent ingression at the dorsal germ ring margin prior to gastrulation, to give rise to dorsal forerunner cells (DFCs), the precursors of KV. DFCs then migrate attached to the overlying surface epithelium and rearrange into rosette-like epithelial structures at the end of gastrulation. During early somitogenesis, these epithelial rosettes coalesce into a single rosette that differentiates into the KV with a ciliated lumen at its apical centre. Our results provide novel insights into the morphogenetic transformations that shape the laterality organ in zebrafish and suggest a conserved progenitor role of the surface epithelium during laterality organ formation in vertebrates.