The Dentition and Feeding Mechanism in Adults of the Southern Hemisphere Lamprey Geotria australis Gray

Scanning electron micrographs of the teeth and sections and dissections of the head have been used to describe the functional interrelationships between the dentition and associated cartilages, muscles and ligaments in adults of the southern hemisphere lamprey Geotria australis. These studies, together with manipulation of the piston and oral disc in living specimens, elucidated the probable feeding mechanism in this species. The main cutting action appears to result from a scissoring movement brought about by the rapid interlocking of the three sharp and stout cusps of the transverse lingual lamina with large grooves on the rear face of the supraoral lamina. The movement of excised flesh back through the oral passage to the pharynx would be facilitated by the action of the pair of strongly cuspid longitudinal lingual laminae. The unique oral disc teeth of G. australis are apparently adapted to allow the disc to slide forward over the host and yet restrict any tendency to slip backwards.     

Smooth muscles in relation to the gill skeleton of Perca fluviatilis: organization and innervation

Summary Two laminae composed of smooth muscles, elastic tissue and collagen have been described in relation with the gill skeleton in Perca fluviatilis. A transverse smoothmuscle lamina joins the base of the cartilage rods of the two opposite hemibranchs. A longitudinal smooth-muscle lamina runs parallel to the afferent branchial artery and joins the cartilage rods from one filament to the other. In both laminae, the formaldehyde-induced fluorescence technique (Falck-Hillarp) reveals a network of nerve fibers displaying a green fluorescence characteristic of catecholamines. At the ultrastructural level, the presence of nerve endings containing clear and granular vesicles, and the degeneration of these endings after 6-hydroxydopamine treatment confirm the aminergic nature and the sympathetic origin of this innervation. Surgical denervation brings evidence that the innervation of both laminae is supplied by the metatrematic branches of the branchial nerves. The role of these smooth-muscle laminae remains speculative.     

Fate of the Molar Dental Lamina in the Monophyodont Mouse

The successional dental lamina (SDL) plays an essential role in the development of replacement teeth in diphyodont and polyphyodont animals. A morphologically similar structure, the rudimental successional dental lamina (RSDL), has been described in monophyodont (only one tooth generation) lizards on the lingual side of the developing functional tooth. This rudimentary lamina regresses, which has been proposed to play a role in preventing the formation of future generations of teeth. A similar rudimentary lingual structure has been reported associated with the first molar in the monophyodont mouse, and we show that this structure is common to all murine molars. Intriguingly, a lingual lamina is also observed on the non-replacing molars of other diphyodont mammals (pig and hedgehog), initially appearing very similar to the successional dental lamina on the replacing teeth. We have analyzed the morphological as well as ultrastructural changes that occur during the development and loss of this molar lamina in the mouse, from its initiation at late embryonic stages to its disappearance at postnatal stages. We show that loss appears to be driven by a reduction in cell proliferation, down-regulation of the progenitor marker Sox2, with only a small number of cells undergoing programmed cell death. The lingual lamina was associated with the dental stalk, a short epithelial connection between the tooth germ and the oral epithelium. The dental stalk remained in contact with the oral epithelium throughout tooth development up to eruption when connective tissue and numerous capillaries progressively invaded the dental stalk. The buccal side of the dental stalk underwent keratinisation and became part of the gingival epithelium, while most of the lingual cells underwent programmed cell death and the tissue directly above the erupting tooth was shed into the oral cavity.     

Stratification and synaptogenesis in the mushroom body of the honeybee,Apis mellifera

Stratification is a basic anatomical feature of central brain in both vertebrates and many invertebrates. The aim of this study was to investigate the relationship between stratification and synaptogenesis in the developing mushroom bodies of the honeybee. During metamorphosis, the vertical lobe of mushroom body shows progressive stratification with three thick primary strata and more secondary strata and laminae. Three primary strata are formed at the metamorphic stage P1, before the youngest generation of the mushroom body intrinsic neurons, Kenyon cells, is produced. Thus, the primary strata within the lobe are unlikely to represent three major subpopulations of the Kenyon cells sequentially produced in the mushroom bodies. Formation of laminae starts at the stage P2 and culminates at the end of metamorphosis. The laminae appear within the lobe rather than being added sequentially from the ingrowth stratum. Alternating dark and light lamina (lamina doublets) are formed in the vertical lobe in late metamorphosis (stages P6–P9), but they are not visible in adults. The pattern of stratification is not continuous along the vertical lobe at the same developmental stage, and resorting of axons of the Kenyon cells is likely to occur within dark laminae. In the developing vertical lobe, dark laminae show lower synaptic density and exhibit an ultra structure that is indicative for a delay in synaptogenesis relative to the primary strata. A local transient block of synaptogenesis within the dark laminae may provide correct targeting of Kenyon cells by extrinsic mushroom body neurons. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

From Embryo to Adult: The Complete Development and Unusual Replacement of the Dentition of the Tammar Wallaby (Macropus eugenii)

Unlike their reptile-like ancestors with continuous tooth replacement, mammals have evolved to replace each tooth either only once, or not at all. In previous large-scale comparative studies, it has been suggested that this tooth replacement only occurs from a successional dental lamina produced lingually to the primary tooth. This study aims to document the complete tooth development and replacement pattern of the tammar wallaby (Macropus eugenii). The tammar wallaby is a diprotodont marsupial, a group defined by their two procumbent lower incisors. To provide a comprehensive documentation of the spatio-temporal pattern of tooth development, we used Lugol’s Iodine staining and microCT scanning (diceCT) of embryos and pouch young into adulthood, resulting in high resolution 3D models for both soft and mineralised stages of development for all tooth positions. Our results reveal that the eponymous lower incisors are the successional generation at the third incisor locus, where the primary dentition initiates but never erupts. Furthermore, we track the development of the only replacement tooth, the permanent third premolar (P3), from initiation to eruption, and found it develops from the primary dental lamina, mesial to the dP3. This is contrary to the conventional view of lingual replacement from successional lamina in mammals. Our findings indicate that no functional tooth replacement occurs in the tammar wallaby, and expands the diversity of tooth replacement patterns found in mammals. We also conclude that since almost all marsupial and placental mammals produce replacement teeth from the distalmost deciduous premolar, this tooth should be considered homologous in these two groups.

     

Interpretation of the toothplates of chimaeroid fishes

It has been argued that the toothplates of chimaeroid fishes exhibit a mode of growth that is fundamentally different from that of other chondrichthyans. Chimaeroid toothplates are supposed to be statodont, growing from the basal surface, whereas other chondrichthyan dentitions are lyodont, growing from the lingual towards the labial surface of the jaw. That idea is shown to be mistaken, because chimaeroid toothplates grow from the lingual surface, like other chondrichthyan dentitions. The mistake resulted from confusion about the nomenclature of toothplate surfaces, and on the choice of Chimaera as a Recent model. Callorhynchus is a more appropriate model, since it is shown to exhibit a primitive toothplate conformation, with the labial and symphysial margins of the occlusal surface bounded by a descending lamina which is applied to the margin of the jaw cartilage and grows basally throughout life. The descending lamina is well developed in toothplates of the extinct chimaeroid genera Ischyodus, Pachymylus and Brachymylus, but is much reduced in all Recent genera other than Callorhynchus. A basally-growing descending lamina also bounds the labial and symphysial margins of the principal toothplates in the Mesozoic myriacanthoids and Squaloraja. The toothplates of the Palaeozoic ‘cochliodonts' are reviewed; amongst them, the chondrenchelyids are the only forms with a basally growing descending lamina. So far as the dentition and its mode of growth arc concerned, the closest Palaeozoic relatives of chimaeroids seem to be the chondrenchelyids. The only statodont (basally growing) toothplates found in the course of this work are those of ptyctodont placoderms, which are therefore unlikely to be related to any chondrichthyans. Statodonty in its original sense (failure to shed teeth) is shown to be widespread and possibly primitive in chondrichthyans. Cochliodont and chimaeroid toothplates grow in a logarithmic spiral. Toothplates of primitive chimaeroid type, with basally growing marginal descending laminae, can develop only when the constant angle of the spiral is small (less than about 35°), and when the oral surface of the jaw grows to the same logarithmic spiral.     

Infection and replication sites of Spiroplasma kunkelii (Class: Mollicutes) in midgut and Malpighian tubules of the leafhopper Dalbulus maidis

Spiroplasma kunkelii distribution and infection mechanisms in the intestines and Malpighian tubules of Dalbulus maidis were investigated by transmission electron microscopy. Spiroplasmas were found between microvilli and in endocytic vesicles of the midgut epithelium. At the basal part, cytoplasmic vesicles contained multiple spiroplasmas with tube-like extensions and spiroplasmas accumulated between the laminae rara and densa of the basal lamina. Tip structures of flask-shaped spiroplasmas pierced the lamina densa that was discontinuous in close proximity to spiroplasmas. Spiroplasmas were found in hemolymph, crossed the basal lamina of Malpighian tubule epithelium and accumulated at high numbers in muscle cells that had cytopathogenic changes. S. kunkelii had perithrochous approximately 8nm diameter structures determined to be fimbriae protruding from the cell surface, and similar structures were adhering to the basal lamina of midgut epithelium and to external lamina of muscle cells. Further, spiroplasmas had pili-like appendages at one or both cell poles and appeared to conjugate. This is the first time that fimbriae and pili have been observed in a mollicutes.     

Light microscopy and scanning electron microscopy studies on the reduction of the tongue microstructures in the white stork (Ciconia ciconia,Aves)

The structure of the tongue in the white stork (Ciconia ciconia) is observed macroscopically and under light and scanning electron microscopy. Our observations of the tongue reveal a rare terminal reduction of the size of the tongue and microstructures of the lingual mucosa among the investigations of birds published so far. The short, triangular tongue with a pointed tip is approximately 2.5 cm long in the adult and is situated in the caudal part of the oral cavity close to the laryngeal prominence. On the dorsal surface of the tongue, no typical mucosa microstructures like lingual papillae, median groove or lingual prominence are observed. The main structure of the tongue is composed of rostral part of hyoid apparatus, that is, entoglossal cartilage connects with basihyoid. Very thin mucosa is composed of fibrous connective tissue covered with orthokeratinized epithelium. No lingual glands and muscles are observed in the lamina propria of mucosa. Even though the triangular shape of the tongue in the white stork is typical for birds, the inner structure of the reduced organ is composed only of flat cartilagineous entoglossum of hyoid apparatus. During feeding behaviour of the white stork, the food transportation in oral cavity called cranio‐inertial transport is undoubtedly affected by structural reduction of the tongue.     

Electron microscopy of extracellular materials during the development of a sea star,Patiria miniata (Echinodermata: Asteroidea)

The fine structure of conspicuous extracellular materials during the life history of a sea star (Patiria miniata) is described. The outer surface of the developing sea star is covered by two morphologically different cuticles that appear sequentially during ontogeny. The primary cuticle, which is about 120 nm thick and two-layered, is present from mid-blastula through the end of the larval stage. The secondary cuticle, which is about 1 micron thick and three-layered, first appears on the epidermis of the rudiment region of the larva and, after metamorphosis, covers the entire epidermis of the juvenile and adult stages. During ontogeny, there are only two conspicuous gut cuticles: the first lines the newly invaginated archenteron at the start of the gastrula stage, and the second lines the esophagus during the larval stage. A blastocoelic basal lamina first appears at mid-blastula and persists as subectodermal and subendodermal basal laminae. Ruthenium red-positive granules are detectable between the lateral surfaces of adjacent ectodermal cells during part of the gastrula stage; this transient intercellular material may possibly aid in lateral adhesion between cells.     

Immunohistochemical analysis of the distribution of type VI collagen in the lingual mucosa of rats during the morphogenesis of filiform papillae

Iwasaki, S., Yoshizawa, H. and Aoyagi, H. 2012. Immunohistochemical analysis of the distribution of type VI collagen in the lingual mucosa of rats during the morphogenesis of filiform papillae. —Acta Zoologica (Stockholm) 93 : 80–87. We examined the distribution after immunostaining of immunofluorescence of type VI collagen, differential interference contrast (DIC) images, and images obtained using confocal laser‐scanning microscopy in transmission mode, after toluidine blue staining, during morphogenesis of the filiform papillae, keratinization of the lingual epithelium and myogenesis in the rat tongue on semi‐ultrathin sections of epoxy resin‐embedded samples. Immunoreactivity specific for type VI collagen was dispersed over a relatively wide range of connective tissue in the mesenchyme of fetuses on day 15 after conception (E15), at which time the lingual epithelium was composed of one or two layers of cuboidal cells and the lingual muscle was barely recognizable. Slight immunoreactivity specific for type VI collagen was scattered within the lamina propria in fetuses on E17 and on E19, and immunoreactivity was relatively distinct on the connective tissue around the lingual muscle during myogenesis. In fetuses on E19, the epithelium was already stratified squamous. At postnatal stages from P0 to P14, keratinization of the lingual epithelium advanced gradually as morphogenesis of the filiform papillae proceeded during postnatal development. In newborns on P0, myogenesis of the tongue was almost completed. The intensity of immunoreactivity specific for type VI collagen at postnatal stages was mainly restricted on the endomysium and perimysium around the lingual muscle, while scant immunoreactivity was evident in the connective tissue in the lamina propria. Immunoreactivity around the fully mature lingual muscle on P7 and P14 was weaker than that on E19 and P0. Thus, type VI collagen appeared in the connective tissue that surrounded the lingual muscles such as the endomysium and perimysium, in parallel with changes in extracellular components during myogenesis of the tongue.     

Plate-like permanent dental laminae of upper jaw dentition in adult gobiid fish, Sicyopterus japonicus

Sicyopterus japonicus (Teleostei, Gobiidae) possesses a unique upper jaw dentition different from that known for any other teleosts. In the adults, many (up to 30) replacement teeth, from initiation to attachment, are arranged orderly in a semicircular-like strand within a capsule of connective tissue on the labial side of each premaxillary bone. We have applied histological, ultrastructural, and three-dimensional imaging from serial sections to obtain insights into the distribution and morphological features of the dental lamina in the upper jaw dentition of adult S. japonicus. The adult fish has numerous permanent dental laminae, each of which is an infolding of the oral epithelium at the labial side of the functional tooth and forms a thin plate-like structure with a wavy contour. All replacement teeth of a semicircular-like strand are connected to the plate-like dental lamina by the outer dental epithelium and form a tooth family; neighboring tooth families are completely separated from each other. The new tooth germ directly buds off from the ventro-labial margin of the dental lamina, whereas no distinct free end of the dental lamina is present, even adjacent to this region. Cell proliferation concentrated at the ventro-labial margin of the dental lamina suggests that this region is the site for repeated tooth initiation. During tooth development, the replacement tooth migrates along a semicircular-like strand and eventually erupts through the dental lamina into the oral epithelium at the labial side of the functional tooth. This unique thin plate-like permanent dental lamina and the semicircular-like strand of replacement teeth in the upper jaw dentition of adult S. japonicus probably evolved as a dental adaptation related to the rapid replacement of teeth dictated by the specialized feeding habit of this algae-scraping fish.     

A network of Wnt, hedgehog and BMP signaling pathways regulates tooth replacement in snakes

Most dentate vertebrates, from fish to humans, replace their teeth and yet the molecular basis of tooth replacement is poorly understood. Canonical Wnt signaling regulates tooth number in mice and humans, but it is unclear what role it plays in tooth replacement as it naturally occurs. To clarify this, we characterized Wnt signaling activity in the dental tissues of the ball python Python regius. This species replaces teeth throughout life (polyphyodonty) and in the same manner as in humans, i.e., sequential budding of teeth from the tip of the dental lamina. From initiation stage onwards, canonical Wnt read-out genes (Lef1 and Axin2) are persistently expressed by cells in the dental lamina tip and surrounding mesenchyme. This implies that molecular signaling at work during dental initiation carries over to tooth replacement. We show that canonical Wnt signaling promotes cell proliferation in python dental tissues and that by confining Wnt activity in the dental lamina the structure extends instead of thickens. Presumably, lamina extension creates space between successive tooth buds, ensuring that tooth replacement occurs in an ordered manner. We suggest that hedgehog signaling confines Wnt activity in the dental epithelium by direct planar repression and, during tooth replacement stages, by negatively regulating BMP levels in the dental mesenchyme. Finally, we propose that Wnt-active cells at the extending tip of the python dental lamina represent the immediate descendents of putative stem cells housed in the lingual face of the lamina, similar to what we have recently described for another polyphyodont squamate species.     

Metamorphosis of the mountain brook lamprey Ichthyomyzon greeleyi

Synopsis Metamorphosis of the nonparasitic mountain brook lamprey, I. greeleyi, is described within 7 phases based on external morphological changes. The commencement of metamorphosis in early August is consistent with the pattern for northern hemisphere lampreys which display an inverse relationship with latitude. The sequence of external changes including the development of eyes, oral disc, teeth, tongue, oral fimbriae and lateral line its consistent among individuals of I. greeleyi and lampreys in general. Some of the changes realized during metamorphosis of I. greeleyi are important to the adult period while others reflect their presumed parasitic ancestry. Energy reserves by nonfeeding I. greeleyi during the 104–140 days required to complete metamorphosis are replaced by water so that total length and body weight do not change significantly during this time.     

Ultrastructure of the basal lamina of bovine ovarian follicles and its relationship to the membrana granulosa

Different morphological phenotypes of follicular basal lamina and of membrana granulosa have been observed. Ten preantral follicles (< 0. 1 mm), and 17 healthy and six atretic antral follicles (0.5-12 mm in diameter) were processed for light and electron microscopy to investigate the relationship the between follicular basal lamina and membrana granulosa. Within each antral follicle, the shape of the basal cells of the membrana granulosa was uniform, and either rounded or columnar. There were equal proportions of follicles 相似文献   

牙鲆变态过程中的细胞凋亡

利用整体的原位TUNEL方法检测了牙鲆(Paralichthysolivaceus)变态过程中身体各器官细胞凋亡的分布及变化情况。结果如下:(1)与眼睛移动相关的脑颅骨骼的细胞凋亡右侧眼睛移动开始之后,在额骨、中筛软骨和犁骨软骨中出现细胞凋亡,并保持到眼睛移动结束;(2)中枢神经和感觉器官的细胞凋亡在眼睛移动开始之前,脊髓和脊髓鞘出现细胞凋亡,在眼睛移动开始之后,脊髓和脊髓鞘细胞凋亡停止,而在脑、眼睛和内耳出现细胞凋亡,并一直持续到眼睛移动结束;(3)与游泳、捕食和消化等功能相关的器官的细胞凋亡在眼睛移动开始后,冠状幼鳍的基部出现凋亡;在变态中后期,尾鳍基部出现细胞凋亡;下颌骨、鳃弓以及肝脏在眼睛移动开始之后,出现细胞凋亡,也一直持续到眼睛移动结束。细胞凋亡通过有序地去除多余的细胞来参与器官形态建立和重组,本研究的结果表明,在牙鲆器官功能变化过程中,细胞凋亡在与其相适应的的器官形态重塑中起着重要作用[动物学报52(2):355-361,2006]。     

Spatial, temporal, and hormonal regulation of epidermal keratin expression during development of the frog, Xenopus laevis.

To study the mechanism of hormone-induced keratin expression in the epidermis during Xenopus metamorphosis, a monospecific antibody was raised against a unique carboxy-terminal peptide of the 63-kDa keratin. Immunohistological analysis demonstrated that the onset of 63-kDa keratin expression showed distinct regional and temporal differences. The expression started at stage 54 in the hindlimb epidermis, at stage 57 in the head, and over 1 month later at stage 63 in the tail. The amount of 63-kDa keratin was further regulated during epidermal stratification and differentiation. The 63-kDa keratin was expressed first in basal epidermal cells before stratification began. The outer layer of the larval epidermis (periderm) did not express the 63-kDa keratin. As the cells moved out of basal layer, they stained more intensely with the anti-keratin antibody indicating that 63-kDa keratin synthesis is up-regulated during differentiation. Similar results were obtained with cultures of purified epidermal cells grown in high calcium conditions. Since we have shown that thyroid hormone (T3) induces 63-kDa keratin gene expression and hydrocortisone (HC) modulates T3 action we examined the effects of T3 and HC at the single cell level with the anti-keratin antibody. Immunostaining demonstrated that T3 alone and T3 plus HC increased the number of 63-kDa keratin-positive cells as well as the amount of 63-kDa keratin per cell. Unexpectedly these hormones had the same effects on head and tail epidermal cells even though the latter cells degenerate during metamorphosis. The major difference between tail and head cells was that the percentage 63-kDa keratin-producing cells was much greater in the head than in the tail.     

Localization of type II collagen in the lingual mucosa of rats during the morphogenesis of circumvallate papillae

Iwasaki, S., Aoyagi, H. and Yoshizawa, H. 2011. Localization of type II collagen in the lingual mucosa of rats during the morphogenesis of circumvallate papillae. —Acta Zoologica (Stockholm) 92 : 67–74. Immunoreactivity specific for type II collagen was recognized first in the mesenchymal connective tissue just beneath the circumvallate papilla placode in fetuses on E13. At this stage, most of the lingual epithelium was pseudostratified epithelium composed of one or two layers of cuboidal cells. However, the epithelium of the circumvallate papilla placode was composed of several layers of cuboidal cells. Immunoreactivity specific for type II collagen was detected mainly on the lamina propria just beneath the lingual epithelium of the rudiment of the circumvallate papilla in fetuses on E15 and on E17, and slight immunostaining was detected on the lamina propria around the rudiment. In fetuses on E19, immunoreactivity specific for type II collagen was widely and densely distributed on the connective tissue around the developing circumvallate papillae and on the connective tissue that surrounded the lingual muscle. Immunoreactivity specific for type II collagen was sparsely distributed on the lamina propria of central bulge. After birth, morphogenesis of the circumvallate papillae advanced gradually with the increase in size of the tongue. Immunoreactivity specific for type II collagen was distinctively distributed in the lamina propria around circumvallate papilla, in the central bulge, and in the connective tissue that surrounded the lingual muscle.     

CP27 localization in the dental lamina basement membrane and in the stellate reticulum of developing teeth.

cp27 is a novel gene involved in early vertebrate development that features a distinct protein localization pattern in developing tooth organs. During initial tooth development, CP27 was detected at the epithelial-mesenchymal interface of dental lamina stage tooth organs. At later stages of tooth development, CP27 was localized in the stellate reticulum, the oral mucosa mesenchyme, and alveolar bone. The significant changes in the highly restricted distribution pattern suggest that CP27 might be involved at several different levels during tooth development.     

Ontogeny of the partial secondary wall of the otoccipital region of the endocranium in prehatching Alligator mississippiensis (Archosauria, Crocodylia)

The ontogeny of the posterior otic and anterior occipital portions of the neural endocranium of prehatching Alligator mississippiensis was investigated by reconstruction from sectioned material. In Stage 6 of this species, in which the endochondral ossification of the otoccipital region of the neural endocranium is only in its very early stage, two bony outgrowths-laminae-are present at the external wall of the posterior portion of the neural endocranium. The anterior lamina arises from the external surface of the basal plate at the level of the posterior margin of the subcapsular process; the posterior lamina arises from the external surface of that portion of the pila occipitalis that forms the posteroventral wall of the metotic fissure. During ontogeny, both laminae lying in the anteroposterior sequence ossify in membrane, fuse together, grow laterodorsally, and fuse with the lateral wall of the lateral semicircular canal and the crista parotica. This lamina forms a new, secondary wall enclosing the posterior section of the otic capsule and contains the large external jugular foramen (or foramen vagi) in its basal portion. The laminae, designated lamina juxtaotica anterior and posterior (lamina juxtaotica when fused together), have not been recorded previously in crocodylians and are absent in all other Recent reptiles. From the functional point of view, the juxtaotic lamina 1) forms the margins of the external jugular foramen, and 2) forms the floor of the posterior section of the Eustachian tube. In birds, the structure called the metotic cartilage, which arises in ontogeny as an independent element, has a similar position as the juxtaotic lamina. However, the two structures differ in their developmental origins and their relation to the Eustachian tube and the ramus hyomandibularis of the facialis nerve. Moreover, there is no external jugular foramen in birds.     

Regional ultrastructural and cytochemical comparisons of the epithelial-mesenchymal interface during rat incisor development

A major theme in understanding epithelial-mesenchymal interactions during development focuses upon regional mesenchyme specification of epithelial differentiation. One particularly useful epidermal organ system for studying this issue is the rodent continuously growing and erupting incisor tooth organ. One advantage of this particular system resides in the regional features of the rodent incisor tooth organ. Along the labial surface, inner dental epithelial cells differentiate into ameloblasts that produce enamel extracellular matrix, whereas the epithelia along the lingual surface do not become ameloblasts and do not produce enamel matrix. This study has been designed to compare ultrastructural features of labial versus lingual surfaces, with particular emphasis upon mesenchymal cell shape, the orientation of extracellular matrix collagen, the basal lamina, and the distribution of sulfated glycoconjugates. Critical analyses of the data indicated that different microenvironments exist between epithelia and mesenchyme in the labial versus the lingual surfaces of the developing rodent incisor tooth organ.