Induction of bud formation of embryonic mouse tracheal epithelium by fibroblast growth factor plus transferrin in mesenchyme-free culture

Embryonic mouse tracheal epithelium, which branches in an epithelial-mesenchymal recombination culture with bronchial mesenchyme, was cultured under mesenchyme-free conditions. When embedded in a basement-membrane-like matrix and cultured in a serum-free medium supplemented with fibroblast growth factor 1 (FGF1), the tracheal epithelium did not branch, whereas the bronchial epithelium underwent branching morphogenesis. When the medium was enriched with transferrin (Tf), bud formation was induced in the tracheal epithelium and some buds branched secondarily. FGF7 and FGF10, in cooperation with Tf, induced tracheal bud formation to the same extent as FGF1, although the optimum concentrations differed. A bromodeoxyuridine-labeling study comparing cultures with and without Tf showed no Tf-specific amplification of cell proliferation. A whole-mount in situ hybridization study of the expression of Bmp4 and Shh genes in explants of mesenchyme-free culture revealed that both genes were ubiquitously expressed and that expression did not correlate with bud formation. This expression pattern was different from the distally localized expression pattern observed in normal lung rudiments and in extratracheal buds induced by the recombined bronchial mesenchyme. These results suggest that both bronchial and tracheal bud formations were initiated without localized exposure of the epithelium to FGFs and were not accompanied by localized expression of Bmp4 and Shh in the epithelium.

Telemedicine for evaluation of brain function by a metacomputer

A method of evaluating brain function using the metacomputer concept of the Globus system combined with a message-passing interface is described. The proposed method has the ability to exploit various geographically distributed resources and parallel computing linked to a high-technology medical instrumentation system, magnetoencephalography, to analyze the functional state of the brain. It is envisaged that the method will lead to the realization of an efficient telemedicine system for health care.

Metabolic pathways and pharmacokinetics of BOF-4272, a sulfoxide-containing drug, in the dog: in vivo and in vitro studies

BOF-4272, (+/-)-8-(3-methoxy-4- phenylsulfinylphenyl)pyrazolo[1,5-a]-1,3,5-triazine-4(1H)-one, is a new drug intended for the treatment of hyperuricemia. This report describes the detailed metabolic pathways of BOF-4272 in the dog. The metabolic pathways were investigated using the metabolites found in plasma, urine, and feces after intravenous or oral administration of BOF-4272, as well as the metabolites found in the liver S9 incubation mixture after the addition of BOF-4272 or BOF-4269. BOF-4269 (the sulfide metabolite of BOF-4272) was the only metabolite detected in plasma and feces after the intravenous or oral administration of BOF-4272. BOF-4269 was detected in dog plasma after a lag time following the oral administration of BOF-4272, and the Cmax and AUC0-t of BOF-4269 were higher in fed dogs than in fasted dogs after the oral administration of BOF-4272. A small amount of BOF-4269 was detected in dog plasma immediately after the intravenous administration of BOF-4272. Only BOF-4276 (the sulfone metabolite of BOF-4272) was detected in the S9 incubation mixture after the addition of BOF-4272. Mainly BOF-4272 was detected and small amounts of BOF-4276 and M-1 (the hydroxy metabolite of BOF-4269) were detected in the S9 incubation mixture after the addition of BOF-4269. These findings suggest that BOF-4272 is mainly metabolized to BOF-4269 by the intestinal flora in dogs, whereas little of this drug is metabolized to BOF-4269 in the dog liver. In conclusion, this work has allowed us to formulate the proposed metabolic pathways of BOF-4272 in the dog.

[Medical therapy in ulcerative colitis]

Salazosulfapyridine(SASP) and 5-aminosalicyclic acid(5-ASA) are useful in the therapy of mildly to moderately active ulcerative colitis. 5-ASA lacks sulfa moiety of SASP and is associated with a decreased incidence of side effects. In patients with moderate or severe ulcerative colitis, glucocorticoids which may be given in conjunction with SASP or 5-ASA are beneficial in producing remission. Proctitis or left-sided colitis is effectively treated with glucocorticoid enemas. If symptoms are refractory to outpatient management, the patient should be hospitalized and given initial therapy with glucocorticoids. Total colectomy(ileo-anal anastomosis; IAA et al) must be considered for acutely ill patients not responding to intensive medical therapy. Early surgical consultation is necessary in severely ill patients.

EGF-dependent lobule formation and FGF7-dependent stalk elongation in branching morphogenesis of mouse salivary epithelium in vitro

When supplemented with appropriate growth factors, salivary gland epithelial explants isolated from mouse embryos undergo branching morphogenesis in vitro in the absence of mesenchyme. Epidermal growth factor (EGF) induces lobule formation, while fibroblast growth factor 7 (FGF7) promotes stalk elongation. A mixture of EGF and FGF7 produces an intermediate morphology, which resembles the branching pattern of salivary epithelium observed in vivo. To investigate how lobule formation and stalk elongation are related to the pattern of epithelial cell proliferation induced by EGF and FGF7, we performed a bromodeoxyuridine labeling study in whole-mount preparations. During the initial steps of lobule formation in EGF cultures, cleft and non-cleft regions had similar proliferative activity. However, once clefts had fully deepened, cells with low proliferative activity appeared at the bottom of the clefts. In contrast, during stalk elongation in FGF7 cultures, distal regions of the explants always showed higher proliferative activity than proximal regions. These results suggest that stalk elongation, but not cleft formation, may result from differential cell proliferation.

Significant role of laminin-1 in branching morphogenesis of mouse salivary epithelium cultured in basement membrane matrix

Mouse submandibular epithelium shows branching morphogenesis in mesenchyme-free conditions when covered with a basement membrane matrix (Matrigel) in medium supplemented with epidermal growth factor. In the present study, the role of laminin-1 (LN1), a major glycoprotein of Matrigel, in this culture system was defined. When the epithelium was cultured in a LN1-nidogen gel, the epithelium showed much branching, comparable to that observed with Matrigel. By electron microscopy, only a felt-like matrix was formed on the epithelial surface in the LN1-nidogen gel cultures, while an organized basal lamina structure was formed on the epithelial surface in direct or transfilter recombination cultures with mesenchyme. Next, the epithelium covered with Matrigel was cultured in medium containing either biologically active peptides from LN1, IKVAV-including peptide (2097-2108), AG10 (2183-2194), AG32 (2370-2381) or AG73 (2719-2730) from the alpha1 chain, or YIGSR-including peptide (926-933) from the beta1 chain. Only AG73 (RKRLQVQLSIRT from the alpha1 chain carboxyl-terminal globular domain) inhibited the epithelial branching in Matrigel. These results suggest that LN1-nidogen can support the branching morphogenesis of submandibular epithelium even if LN1-nidogen is not assembled into an intact basal lamina, and that the AG73 sequence is an important site on LN1, which interacts with submandibular epithelial cells.

Ontogeny of pulmonary neuroendocrine cells which express the alpha-subunit of guanine nucleotide-binding protein Go

In order to ascertain that alpha-subunit of guanine nucleotide-binding protein Go (Go alpha)-positive cells in the lung epithelia are pulmonary neuroendocrine cells (PNECs), we carried out an immunohistochemical study in young adult and fetal lungs of rodents and in cultured fetal lung explants. Serial sections showed that Go alpha-positive cells were immunostained for calcitonin gene-related peptide and serotonin in young adult mouse, rat, and hamster lungs and that these cells are, therefore, PNECs. In the fetal lungs of hamster and mouse, Go alpha-positive PNECs appeared in the epithelium of the lobar bronchus by gestational day 13 in hamster and by day 15.5 in mouse, and they increased with a proximal-to-distal wave during the late fetal period. Explants of immature lung from the fetal hamster on gestational day 11 were cultured. After 2 days of culture, Go alpha-positive PNEC clusters appeared in the main and lobar bronchi and many PNEC clusters were seen after 4 days of culture. To determine the functional significance of Go in the development of the fetal lung, pertussis toxin, a Go inhibitor, was added to the medium, and changes in branching morphogenesis and PNEC development were studied. Although branching morphogenesis was not disturbed by pertussis toxin, the toxin treatment induced large PNEC clusters in the cultured lung explant. In summary, we showed that Go alpha is a neuroendocrine marker for PNECs and that Go alpha-positive cells appear along with development of PNECs in fetal hamster lung in vivo and in vitro. The functional significance of Go in the development of fetal lung is obscure, but signals mediated through this GTP-binding protein could be related to some functions of PNECs.

Pharmacokinetics of BOF-4272, a xanthine oxidase inhibitor, after single intravenous or oral administration to male mice and rats

BOF-4272, (+/-)-8-(3-methoxy-4-phenylsulphinylphenyl) pyrazolo [1,5-a]-1,3,5-triazine-4 (1H)-one), is a new drug intended for the treatment of hyperuricaemia. This report describes the detailed pharmacokinetics of BOF-4272 in mice and rats after intravenous or oral administration. Plasma concentrations of BOF-4272 at 2-8h after intravenous administration were significantly higher in mice than in rats. Plasma concentrations of BOF-4272 after oral administration were significantly higher in fed mice than in fasted mice, but were similar in fasted and fed rats. The elimination half-life of the distribution phase (t1/2(alpha)) was similar in mice (0.158 h) and rats (0.210 h). The elimination half-life of the terminal elimination phase (t1/2(beta)) in mice was 1.936 h, while that in rats was 0.742 h. The volume of the central compartment (V1) was almost the same in mice (415 mL kg(-1)) and rats (440 mL kg(-1)). However, the volume of the peripheral compartment (V2) in mice was 1068 mL kg(-1), while that in rats was 92 mL kg(-1). The steady-state volume of distribution (Vss) was 2.8 times larger in mice than in rats. The area under the plasma concentration-time curve (AUC) in mice was 5332 ng h mL(-1), while that in rats was 3806 ng h mL(-1). The AUC0-24 h after oral administration was 2.5 times greater in fed mice than in fasted mice, and was 1.4 times greater in fasted rats than in fed rats. The correlation coefficients of Cmax and AUC0-24 h in both mice and rats after oral administration were greater than 0.997 in the dose range 1 - 125 mg kg(-1), indicating that the linear range of absorption or elimination (or both) of BOF-4272 is very wide. The results of the present study demonstrate that the mouse is a suitable animal species for evaluating the clinical pharmacokinetics of BOF-4272.

Bud formation precedes the appearance of differential cell proliferation during branching morphogenesis of mouse lung epithelium in vitro

Cell proliferation is an essential requirement for epithelial expansion and tubular branching; however, little is known of how these events are coupled during morphogenesis. We have previously shown that, in the absence of mesenchyme, fibroblast growth factor 1 (FGF-1) elicits budding of the mouse lung epithelium cultured in a basement membrane matrix. Although bud formation seems to be the manifestation of a localized response of lung epithelial cells to FGF-1, it is unclear whether budding results from induction of differential rates of cell proliferation within the epithelium. We performed continuous labeling and pulse-chase experiments in FGF-1-treated mesenchyme-free lung epithelial cultures at distinct stages of bud induction using bromodeoxyuridine (BrdU), to determine when and to what extent cell proliferation contributes to bud formation. When explants were incubated with BrdU either before bud induction (0-18 hr in culture) or at the onset of budding (24-30 hr), labeled nuclei were found distributed throughout the entire explant. In contrast, BrdU incubation after the onset of budding (30-48 hr) resulted in labeling concentrated in the budding areas, and a decrease of labeling toward the proximal region of the explant, between buds. These results demonstrate that differential rates of cell proliferation between bud and nonbud areas do not appear until when buds are almost completely formed. Thus, in the developing lung epithelium in vitro, bud outgrowth is not triggered by induction of localized cell proliferation.

Development of pulmonary neuroendocrine cells of fetal hamster in explant culture

Fetal hamster lung explant was cultured in serum-free medium on gestational Day 11-2 days before the appearance of pulmonary neuroendocrine cells (PNEC)--and the development and differentiation of PNEC from immature fetal lung epithelium was examined through immunostaining for neural cell adhesion molecule (NCAM) to establish an in vitro system to study the mechanisms involved. PNEC were present in the main bronchus after 2 days of culture. Thereafter, NCAM-positive clusters of PNEC increased and were distributed from the large bronchus to the terminal bronchiole with a proximal-to-distal wave. To elucidate the role of NCAM in the fetal development of PNEC, whole fetal lung was cultured on gestational Day 11 with an anti-NCAM antibody. This antibody slightly inhibited the growth and branching morphogenesis of the lung and disturbed the formation of PNEC clusters. NCAM may function to form clusters of PNEC known as neuroepithelial bodies. We cultured fetal lung epithelial explant at gestational Day 11 after removing mesenchyme, including nerve tissue, with dispase digestion. Immunohistochemical staining for NCAM revealed that PNEC were induced in cultured fetal epithelium without mesenchymal tissue, but basement membrane Matrigel was necessary to maintain cultured epithelium. In conclusion, PNEC derive from immature airway epithelial cells. This organ culture system, therefore, is a useful experimental model and should facilitate further investigations of the development and differentiation of PNEC. Mesenchymal and neural tissues are not always necessary for the development of PNEC, but matrix substance and/or growth factors may be required to induce or maintain PNEC.

FGF-1 and FGF-7 induce distinct patterns of growth and differentiation in embryonic lung epithelium

Fibroblast growth factors (FGFs) and receptors (FGFRs) are expressed in the developing lung and appear to be major regulators of lung growth and differentiation. By using mesenchyme-free lung epithelial cultures we show that FGF-1 (aFGF) and FGF-7 (KGF) produce different effects in the developing lung. FGF-1 stimulates epithelial proliferation that results in bud formation (branching), while FGF-7 promotes epithelial proliferation that leads to formation of cyst-like structures. In addition, FGF-7 stimulates epithelial differentiation, stimulating expression of SP-A and SP-B mRNA throughout the explant, and inducing formation of focal areas of highly differentiated cells. The FGF-1 effects on differentiation are limited to induction of surfactant protein SP-B mRNA at the tips of the explant. The FGF-induced patterns of growth appear to correlate with the distribution of epithelial FGFRs mRNAs; FGFR-2 IIIb (KGFR) is diffusely expressed in the day 11 lung epithelium, while FGFR-4 appears in distal but not in proximal sites. We propose that cyst-like structures may result from FGF-7 binding to the uniformly distributed FGFR-2-IIIb. Lung bud formation may be regulated by FGF-1 and/or other ligands binding to FGFR-2 and a distally located FGFR, such as FGFR-4, leading to an increasing binding and activation of FGFRs at the tips of the explant. Thus, in the embryonic lung epithelium, growth effects of FGFs appear to be dependent on location of FGFRs, while effects on differentiation are ligand-dependent.

Branching morphogenesis of embryonic mouse lung epithelium in mesenchyme-free culture

Embryonic mouse lung epithelium was separated from its mesenchyme and cultured under mesenchyme-free conditions. When covered with Matrigel, the cultured epithelium underwent branching morphogenesis in medium containing acidic fibroblast growth factor (aFGF), in which the epithelial cells constructed a simple columnar cell layer forming a lumen, as seen in normal development. The epithelial growth and branching morphogenesis induced by aFGF was completely inhibited by an antibody against aFGF. Heparin caused extra epithelial growth in cooperation with aFGF, but its use resulted in luminal expansion instead of enhanced branching. Basic FGF induced abnormal morphogenesis of the epithelium, though the lumen formed was lined by a simple columnar cell layer. Epidermal growth factor could not maintain epithelial cell growth, and the epithelium became a smaller and smoother ball than that at the start of cultivation. When covered with a collagen gel instead of Matrigel, the epithelium remained in its initial form, neither newly branching nor becoming a smooth ball, in the presence of aFGF. These results show that the epithelium of lung rudiments was able to branch under mesenchyme-free culture conditions in which a basement membrane matrix and aFGF were substitutes for the mesenchyme.

Enzyme immunoassay of sulfamethoxazole in chicken tissues: interlaboratory study

Three laboratories participated in the interlaboratory study of an enzyme immunoassay (EIA) method for determination of sulfamethoxazole (SMX) using samples of the same muscle, liver and plasma from chickens administered with SMX. Interlaboratory variation in the determined values were similar to those of other studies determined by gas chromatography and liquid chromatography. It was suggested that the interlaboratory difference in determined SMX residues from chicken tissues did not become problems of using EIA method, in spite of the differences of equipments and operators.

Substitution for mesenchyme by basement-membrane-like substratum and epidermal growth factor in inducing branching morphogenesis of mouse salivary epithelium

Mouse salivary epithelium cannot undergo branching morphogenesis in the absence of the surrounding mesenchyme. To clarify the nature of the mesenchymal influence on the epithelium, we have investigated the culture conditions in which the epithelium could normally branch in the absence of mesenchymal cells. Combination of basement-membrane-like substratum (Matrigel) and epidermal growth factor (EGF) could substitute for the mesenchyme, the epithelium showing typical branching morphogenesis. Transforming growth factor alpha had the same effect as EGF. Matrigel plus basic fibroblast growth factor or transforming growth factor beta 1 and collagen gel plus EGF were not sufficient to support the branching of the epithelium. These results clearly reveal that the role of mesenchyme in salivary morphogenesis is both to provide the epithelium with an appropriate substratum and to accelerate growth of the epithelium.

Branching morphogenesis of mouse salivary epithelium in basement membrane-like substratum separated from mesenchyme by the membrane filter

Branching morphogenesis of mouse salivary gland has been studied with organ-culture system. We developed a novel transfilter culture system for analyzing branching morphogenesis of the salivary epithelium. The submandibular salivary epithelium from early 13-day mouse fetus, clotted with Matrigel and separated from the mesenchyme by membrane filter, showed extensive growth and branching morphogenesis, morphological differentiation of lobules and stalks, and a typical cleft shape. The epithelium showed little growth and no branching without Matrigel clot or without the mesenchyme. This branching morphogenesis was induced even when the pore size of the filter was reduced to 0.05 microns. Use of type I collagen gel instead of Matrigel mostly induced incomplete morphogenesis with various histological abnormalities. These results suggest that the salivary epithelium can undergo branching morphogenesis in the absence of the mechanical action of mesenchymal cells although it needs an appropriate extracellular matrix and some mesenchymal factors transmitted through the filter.

Accumulation of collagen III at the cleft points of developing mouse submandibular epithelium

The distribution of collagens I, III, IV and V was studied by immunoperoxidase staining of early developing mouse submandibular glands. Collagen I was always present in the extracellular matrices of the mesenchyme and at the epithelial-mesenchymal interfaces of the 12-day gland with no clefts and of the 13-day gland with a few definite clefts. Collagen III was found in a similar fashion to that of collagen I in the mesenchyme, but the distribution at the epithelial-mesenchymal interfaces was very different. In the mid 12-day gland with a round lobule, collagen III was distributed at every slightly indented site of basal epithelial surfaces. At the late 12-day stage, a few initial signs of cleft appeared on the surface, at which accumulation of collagen III became evident. Intense immunoreaction of collagen III in the early 13-day gland was seen at the bottom of every narrow cleft. No specific accumulation of collagens IV and V was observed in clefts of the late 12-day and early 13-day glands. Staining of collagen III in the 12-day gland cultured for 10 h in the presence of bovine dental pulp collagenase inhibitor, which has been shown to stimulate cleft initiation, was very prominent at the bottom of every narrow cleft. These observations suggest that collagen III works as a key substance for either in vitro or in vivo cleft initiation of the mouse embryonic submandibular epithelium.

The role of interstitial collagens in cleft formation of mouse embryonic submandibular gland during initial branching

An interstitial collagenase was purified from the explant medium of bovine dental pulp and was shown to degrade collagens I and III but not IV and V. The enzyme halted cleft initiation in the epithelium of 12-day mouse embryonic submandibular glands in vitro, indicating the active involvement of interstitial collagens in the branching morphogenesis. Transmission electron microscopic observation of the intact 12-day gland without any clefts showed the scattered localization of a few collagen fibrils at the epithelial-mesenchymal interface of the bulb and also revealed the presence of numerous microfibrils around the stalk. Collagen bundles were regularly seen close to the wavy basal lamina at the bottom of clefts of the intact 13-day gland and 12-day gland cultured for 17 h under normal conditions. Mesenchymal cells were found in the clefts together with the frequent localization of peripheral nerve fibres and capillary endothelial cells. The collagen bundles were more often observed in the 12-day gland cultured in the presence of bovine dental pulp collagenase inhibitor, which had been shown to enhance cleft formation. In contrast, collagen fibrils were rarely found at the epithelial-mesenchymal interface of the 12-day gland cultured in the presence of Clostridial or bovine dental pulp collagenase. The findings indicated that the formation of interstitial collagen bundles is essential to form clefts in the epithelium both in vivo and in vitro.

Mechanical aspects of the mesenchymal influence on epithelial branching morphogenesis of mouse salivary gland

Three activities of mesenchymes from mouse embryonic submandibular gland, lung, stomach, mandible and skin were comparatively studied. The first ability was the induction of branching of submandibular epithelial lobes. Epithelial lobes branched well in recombination with submandibular or lung mesenchyme, less well with stomach mesenchyme, but never with mandibular or dermal mesenchyme. The second behavioural aspect studied was the contraction of collagen gels. When respective mesenchymal cells were dispersed at 2á0×105cellsml-1 in collagen gels (1á5mgml-1) and incubated, dermal mesenchymal cells had the highest gel-contracting activity. The gel-contracting activity of submandibular or lung mesenchymal cells was two thirds as high as that of dermal cells and that of stomach or mandibular mesenchymal cells was much lower. The last activity was to separate three plastic beads that were recombined with mesenchymes in place of epithelial lobes. Salivary or lung mesenchyme effected a large separation of the beads, whereas dermal mesenchyme left beads contacting one another. There was a positive correlation between the branch- inducing activity and the beads-separating activity within the five kinds of mesenchymes. In time-lapse cinematography of recombinates, cells of submandibular and lung mesenchyme were observed moving (or flowing) around, and their property was different from that of dermal mesenchyme. In the presence of cytochalasins, both the contraction of collagen gels and separation of plastic beads by submandibular mesenchymal cells were completely inhibited. These results suggest the importance of mechanical influences of the mesenchyme in salivary branching morphogenesis.

Cell proliferation is not required for the initiation of early cleft formation in mouse embryonic submandibular epithelium in vitro

An X-ray irradiation method was employed to analyse the role of cell proliferation in vitro in the cleft formation of mouse embryonic submandibular epithelium at early stages. When the mid 12-day gland was exposed to 200 rad of X-rays, the growth was severely retarded. In contrast, late 12-day and early 13-day glands grew apparently in a normal fashion, as did the control gland, for up to 40 h. In either case, they formed shallow clefts within 10 h of culture. With 1000 rad irradiation, the mid 12-day gland did not grow at all, but formed clefts within 20 h of culture followed by a rapid degeneration. Under the same conditions, the growth of the late 12-day gland, which was at the stage just before branching, was retarded until 10 h of culture, followed by a slight increase in epithelial size, but cleft formation was also observed within 6–10 h, as in the control gland. When exposed to a dose of 1000 rad of X-rays, the early 13-day and the late 12-day glands exhibited similar radiosensitivity; the initial narrow clefts in the epithelium deepened and new clefts began to form within 6–10 h of culture. [3H]thymidine incorporation studies revealed that a dose of 1000 rad reduced DNA synthesis of mid and late 12-day glands by 72 and 65%, respectively. Histological examination of X-irradiated late 12-day gland showed that mitotic figures were rarely seen in the epithelium at 6 h of culture. Aphidicolin, a specific inhibitor of DNA synthesis, could not halt the cleft formation of the late 12-day gland. In this experiment 89% of DNA synthesis was inhibited. Treatment of an X-ray irradiated late 12-day gland with aphidicolin blocked 92% of the DNA synthesis, but did not prevent cleft formation taking place. These results indicate that neither cell division nor DNA synthesis, is required for the initiation process of the cleft formation of the mouse embryonic submandibular epithelium at early morphogenetic stages in vitro.

Clinical examination of the crystalline lens by retrocorneal specular microscopy

Normal crystalline lenses and a variety of primary and secondary cataracts were photographed with a contact clinical specular microscope having a new W10X long working distance objective. In the normal lens, the anterior and posterior cell pattern and the lens fiber pattern could be seen. In patients with developing cataracts, a variety of abnormal structures was observed; in some cases the detailed morphologic structure of the light scattering objects could be appreciated. In pseudophakic patients, precipitates, leukocytes, and debris were observed on the surface of IOL implants. The methods described enable cellular and morphologic changes occurring with time in the lens and capsule to be studied. The results obtained show the potential usefulness of specular microscopy for evaluation and documentation of retrocorneal pathologic structures at high magnification.

Determination of the curvature of epithelial cell mass by mesenchyme in branching morphogenesis of mouse salivary gland

Mouse submaxillary epithelium undergoes branching morphogenesis with increase in the curvature of its surface in vivo. Recombination experiments in vitro of the epithelium and mesenchyme between 13- and 14-day rudiments showed (1) that the 14-day mesenchyme more actively induced the epithelium to branch than the 13-day mesenchyme, (2) that the 14-day mesenchyme could produce clefts on smaller epithelial lobes than the 13-day mesenchyme, (3) that the 14-day mesenchyme produced lobes with similar diameter to lobes of the 14-day intact rudiment, and (4) that the lobular morphology of assembled 14-day lobes became obscure in recombinants with the 13-day mesenchyme while it was well maintained in recombinants with the 14-day mesenchyme. From these results it is concluded that the mesenchyme determines the curvature of epithelial surface, and that clefts are formed on the epithelial surface as a result of increase in the epithelial curvature.

Mesenchymal control over elongating and branching morphogenesis in salivary gland development

Recombination of the epithelium and mesenchyme between quail anterior submaxillary gland (elongating type) and quail anterior lingual or mouse submaxillary gland (branching type) was effected in vitro to clarify whether the elongating morphogenesis was directed by the epithelial or the mesenchymal component. Quail anterior submaxillary epithelium recombined with quail anterior lingual or mouse submaxillary mesenchyme came to branch. Conversely, quail anterior lingual or 12-day mouse submaxillary epithelium recombined with quail anterior submaxillary mesenchyme came to elongate, though the mesenchyme was less effective with 13-day mouse submaxillary epithelium. These results suggest that the elongating or branching morphogenesis of quail salivary glands is controlled by the mesenchyme.

Analysis of elongating morphogenesis of quail anterior submaxillary gland: absence of localized cell proliferation

Quail anterior submaxillary glands elongated extensively without branching (more than sevenfold) from 8 to 10 incubation days. Investigation of mitotic activity of the rudiments in vivo showed no localized cell proliferation throughout the rudiments, and recombination experiments in vitro to examine regional differences in mitogenic activity of the surrounding mesenchyme also showed that no mesenchymal region specifically stimulates the epithelial cell proliferation. Histological observation of the rudiments showed that epithelial cells did not lengthen in a parallel direction to the long axis of the rudiment, and that mesenchymal cells encircled the epithelial cord perpendicularly to its axis. The basement membrane was obscure in the distal end of the rudiments, while it was easily detected in the other part of the rudiments. These results suggest that the elongating morphogenesis of the anterior submaxillary rudiments is not achieved by localized cell proliferation but by almost uniformly distributed cell proliferation, and mesenchymal cells surrounding the rudiment or the basement membrane may be involved in the controlling mechanisms of the elongating morphogenesis.