Growth Of Salivary Glands Research Articles

Description of Saliva Viscosity in Underweight Toddlers among 3-5 Years at Silo II Health Center Working Area Jember Regency

Background; Underweight is a health issue as one of the causes of infant mortality. UNICEF states that underweight contributes to more than one-third of the 9,2 million children under 5 years old, which succumb to death. Underweight toddlers have the potential to increase the risk of dental caries and disrupt the growth of salivary glands, leading to a decreased saliva flow rate. In underweight children, the lack of nutrition during the growth period can have a permanent impact on salivary glands and result in high saliva viscosity. Objective: This research was conducted in the working area of Silo II Community Health Center in Jember Regency, with the aim of examining the characteristics of saliva in underweight toddlers aged 3-5 years, especially about salivary viscosity. Material and Methods: A total of 161 toddlers were the subjects of the study, and saliva was collected using the unstimulated spitting method, followed by the measurement of saliva viscosity using an Ostwald viscometer. Results: The research findings indicate that underweight toddlers have high saliva viscosity with an average of 15,72 cP. Analysis based on age variables shows that 3-4-year-old toddlers have the highest average saliva viscosity (15,77 cP), while based on the severity of underweight, toddlers categorized as severely underweight have the highest average saliva viscosity (17,15 cP). Conclusions: In conclusion, the condition of saliva viscosity in underweight toddlers in the operational area of Puskesmas Silo II indicates high values, attributed to the insufficient intake of nutrients during the growth period..

Effects of liquid diet intake on nerve growth in salivary glands of growing rats.

The growth of parotid glands is inhibited by liquid diet intake during growing period, while that of submandibular glands is not affected. This study examined how liquid diet intake affects nerve growth in the parotid and submandibular glands of growing rats, because nerves are closely involved in the maintenance of salivary gland structure. Male Wistar rats were weaned at 21 days of age. Then, rats were fed a pellet diet and a liquid diet in the control group and experimental group, respectively. At 0, 2, 4, or 8 weeks, they were euthanised by isoflurane overdose, and parotid and submandibular glands were removed. The frozen sections were made and immuno-stained with anti-protein gene product 9.5 (PGP 9.5) antibody (general nerve marker), anti-tyrosine hydroxylase (TH) antibody (sympathetic nerve marker), or anti-neuronal nitric oxide synthase (nNOS) antibody (parasympathetic nerve marker). In control parotid glands, scattered punctate or short linear patterns of PGP 9.5-positive sites were observed at week 0. After 2 weeks, PGP 9.5-positive sites, some of which were arranged in long linear patterns, increased in number. There were some TH-positive sites at week 0. After 2 weeks, there were increasing numbers of TH-positive sites, often in long linear patterns. At week 0, there were very few nNOS-positive sites, and nNOS immunoreactivity increased over time. After week 4, they demonstrated linear patterns. In the experimental parotid glands, there were fewer PGP 9.5- and nNOS-positive sites than in control parotid glands at each time point, although TH immunoreactivity was similar between two groups at each time point. In control submandibular glands, few punctate exhibited PGP 9.5-positive site were observed at week 0. At week 4, PGP 9.5 immunoreaction increased and showed linear patterns. TH-positive sites demonstrated punctate or short linear patterns at week 0, and thereafter TH immunoreactivity increased and were arranged in long linear patterns. There were few nNOS-positive sites at week 0, and they gradually increased after week 4. The immunoreactivities of all antibodies in the experimental submandibular glands were similar to those in the control at each time point. Parasympathetic nerve growth in rat parotid glands was inhibited by liquid diet intake during the growth period, while liquid diet intake did not affect parasympathetic nerve growth nor sympathetic nerve growth in rat submandibular glands.

Feeding and Amines Stimulate the Growth of the Salivary Gland following Short-Term Starvation in the Black Field Cricket, Teleogryllus commodus.

The salivary gland of the black field cricket, Teleogryllus commodus Walker changed size between being starved and fed. Crickets without access to food for 72 h showed a reduction in both wet and dry mass of the glands compared with the glands from continuously fed animals at 72 h. Glands returned to size following ingestion within 10 min. Salivary glands of starved crickets (72 h) were incubated in saline containing either serotonin (5-HT) or dopamine (DA). Glands increased to pre-starvation size after 1 h incubation in situ with either 10-4 moles L-1 5-HT or 10-4 moles L-1 DA, although lower concentrations (10-5 moles L-1) did not affect gland size. From immunohistochemistry, amines appeared to shift from zymogen cells during starvation to parietal cells following feeding. High-performance liquid chromatography showed that serotonin concentration is higher than dopamine in the salivary gland removed from starved and fed crickets, but the quantity of these compounds was not dependent upon feeding state; the amine quantities increased as gland size increased. Further work is necessary to determine what might be the stimulus for gland growth and if dopamine and serotonin play a role in the stimulation of salivary gland growth after a period of starvation.

Juvenile recurrent parotitis: Soft foods contribute to the delayed development of salivary glands.

Juvenile recurrent parotitis (JRP) is the second-most common childhood disease of the salivary glands after mumps. Since popularisation of mumps vaccination, children suffered from JRP more often, and the aetiology remains unclear. Chinese children had the habit of soft foods due to the special dietary habit of Asia. To clarify whether mastication was related to the pathogenesis of JRP and whether the growth of salivary glands was influenced by soft diet. Investigation of dietary habit and masticatory efficiency from 2015 to 2018 of children diagnosed with JRP compared with the normal children by the dentition. Mice had been fed a soft diet beginning in their development phase. The gland weight, amount of saliva, salivary amylase, histological and ultrastructural observation and the expression levels of EGF, FGFr2 and Wnt3a had been tested. The JRP children preferred soft foods and had a significantly lower masticatory efficiency than do normal children. When normalised by body weight, the gland weight, amount of saliva and amount of salivary amylase in the experimental group were significantly lower. The ultrastructural results showed that the acinar cells in the experimental groups were smaller and contained fewer electron-dense secretory granules than those in the control groups. The expression levels of EGF, FGFr2 and Wnt3a in the salivary glands of mice in the experimental groups were significantly lower than those of mice in the control groups. The soft diet indeed influenced the salivary gland through insufficient mastication, which could be one of the primary factors inducing JRP.

Engineering innervated secretory epithelial organoids by magnetic three-dimensional bioprinting for stimulating epithelial growth in salivary glands

Current saliva-based stimulation therapies for radiotherapy-induced xerostomia are not fully effective due to the presence of damaged secretory epithelia and nerves in the salivary gland (SG). Hence, three-dimensional bio-engineered organoids are essential to regenerate the damaged SG.Herein, a recently validated three-dimensional (3D) biofabrication system, the magnetic 3D bioprinting (M3DB), is tested to generate innervated secretory epithelial organoids from a neural crest-derived mesenchymal stem cell, the human dental pulp stem cell (hDPSC). Cells are tagged with magnetic nanoparticles (MNP) and spatially arranged with magnet dots to generate 3D spheroids. Next, a SG epithelial differentiation stage was completed with fibroblast growth factor 10 (4–400 ng/ml) to recapitulate SG epithelial morphogenesis and neurogenesis. The SG organoids were then transplanted into ex vivo model to evaluate their epithelial growth and innervation.M3DB-formed spheroids exhibited both high cell viability rate (>90%) and stable ATP intracellular activity compared to MNP-free spheroids. After differentiation, spheroids expressed SG epithelial compartments including secretory epithelial, ductal, myoepithelial, and neuronal. Fabricated organoids also produced salivary α-amylase upon FGF10 stimulation, and intracellular calcium mobilization and trans-epithelial resistance was elicited upon neurostimulation with different neurotransmitters. After transplantation, the SG-like organoids significantly stimulated epithelial and neuronal growth in damaged SG.It is the first time bio-functional innervated SG-like organoids are bioprinted. Thus, this is an important step towards SG regeneration and the treatment of radiotherapy-induced xerostomia.

Pharmacological activation of the EDA/EDAR signaling pathway restores salivary gland function following radiation-induced damage.

Radiotherapy of head and neck cancers often results in collateral damage to adjacent salivary glands associated with clinically significant hyposalivation and xerostomia. Due to the reduced capacity of salivary glands to regenerate, hyposalivation is treated by substitution with artificial saliva, rather than through functional restoration of the glands. During embryogenesis, the ectodysplasin/ectodysplasin receptor (EDA/EDAR) signaling pathway is a critical element in the development and growth of salivary glands. We have assessed the effects of pharmacological activation of this pathway in a mouse model of radiation-induced salivary gland dysfunction. We report that post-irradiation administration of an EDAR-agonist monoclonal antibody (mAbEDAR1) normalizes function of radiation damaged adult salivary glands as determined by stimulated salivary flow rates. In addition, salivary gland structure and homeostasis is restored to pre-irradiation levels. These results suggest that transient activation of pathways involved in salivary gland development could facilitate regeneration and restoration of function following damage.

Effects of glucocorticoid on postnatal development of rat sublingual glands

Hormones have been reported to be involved in salivary gland's growth and development, but few studies have investigated the effects of glucocorticoids on the morphology of the sublingual glands around the weaning period. The objective of this study was to ascertain the effects of glucocorticoid administration on rat sublingual glands around the weaning period. Male Wistar rats were administered triamcinolone, a glucocorticoid, once every other day from 8 days after birth (experimental group). A control group was given vehicle only. The sublingual glands were then extracted at 15, 20, 25, and 30 days after birth. Samples thus obtained were subjected to Alcian blue and periodic acid-Schiff staining, lectin staining, and immunohistochemical staining to assess cellular proliferative potential. And acinar cell circumferences were measured. We found that glucocorticoid had no effect on the production of acid or neutral mucopolysaccharides by acinar cells around the weaning period. Glucocorticoid administration resulted in hypertrophy of acinar cells between 15 and 30 days after birth. Early appearance of changes in α-mannose, α-glucosamine, and N-acetylglucosamine in secretory granules suggested that glucocorticoid may have acted to promote cell differentiation. The glucocorticoid had no effect on the proliferative potential of sublingual gland acinar cells around the weaning period.

Cellular signals underlying β-adrenergic receptor mediated salivary gland enlargement

We examined the cellular signaling pathways involved in parotid gland enlargement induced by repeated isoproterenol administration in rats. Immunoblot analysis revealed early (1 h) activation of the mitogen activated protein kinase (MAPK) ERK1/2, and progressive activation of epidermal growth factor receptor (EGFR), p38MAPK and p70S6 kinase (p70S6K) during 72 h of isoproterenol treatment. Expression of β-adrenergic receptors (ARs) of the β2, but not β1, subtype increased over time in parallel with increases in the proliferation marker PCNA and parotid gland weight. Levels of β2-AR mRNA, assessed by quantitative RT-PCR and Northern blot analysis, were upregulated in parotid glands of isoproterenol treated rats. cAMP response element binding protein (CREB), a positive regulator of β2-AR transcription, was activated at 1 h after isoproterenol administration, as evidenced by increased nuclear translocation and DNA binding using immunohistochemical staining and electrophoretic mobility shift assay. ELISA of NF-κB, also a β2-AR transcriptional regulator, revealed an increase in p65 and p50 subunits in nuclear protein extracts from parotid glands of isoproterenol treated rats. Together, these results demonstrate that β-adrenergic stimulation activates diverse cell survival and progrowth signaling pathways, including cAMP and EGFR linked activation of ERK1/2, p38MAPK, and p70S6K, and also induction of β2-ARs, possibly mediated by CREB and NF-κB, resulting in salivary gland enlargement. We propose that during isoproterenol treatment activation of the β1-AR, the predominant β-AR subtype in unstimulated salivary glands, initiates proliferative signaling cascades, and that upregulation of the β2-AR plays an essential role in later stages of salivary gland growth.

Virus Progeny of Murine Cytomegalovirus Bacterial Artificial Chromosome pSM3fr Show Reduced Growth in Salivary Glands due to a Fixed Mutation of MCK-2

Murine cytomegalovirus (MCMV) Smith strain has been cloned as a bacterial artificial chromosome (BAC) named pSM3fr and used for analysis of virus gene functions in vitro and in vivo. When sequencing the complete BAC genome, we identified a frameshift mutation within the open reading frame (ORF) encoding MCMV chemokine homologue MCK-2. This mutation would result in a truncated MCK-2 protein. When mice were infected with pSM3fr-derived virus, we observed reduced virus production in salivary glands, which could be reverted by repair of the frameshift mutation. When looking for the source of the mutation, we consistently found that virus stocks of cell culture-passaged MCMV Smith strain are mixtures of viruses with or without the MCK-2 mutation. We conclude that the MCK-2 mutation in the pSM3fr BAC is the result of clonal selection during the BAC cloning procedure.

Branching Takes Nerve

Innervation is required to maintain epithelial progenitor cells that support salivary gland growth and development.

Mitogen-activated protein kinase up-regulation and activation during rat parotid gland atrophy and regeneration: role of epidermal growth factor and β2-adrenergic receptors

The rat secretory ductal obstruction model has been widely used to assess salivary gland injury, growth, and differentiation. In this study, a novel ductal obstruction and release procedure was used to explore the signaling pathways leading to salivary gland regeneration. Rats underwent bilateral parotid ductal obstruction in which the duct was occluded against a plastic disk subcutaneously and released by external ligature removal. This ductal obstruction/release procedure was validated to produce glandular atrophy and regeneration with histological analysis and periodic acid-Schiff staining. Immunoblot analysis indicated that during ductal obstruction and the early post-release period (day 7), expression of immunoreactive proliferating cell nuclear antigen and vimentin was increased in the parotid glands compared with sham-operated animals. Immunohistochemical staining and immunoblots revealed up-regulation of the mitogen-activated protein kinases (MAPKs), extracellular signal-regulated receptor kinase (ERK)1/2, and p38 during the atrophic and regeneration phases of ductal obstruction/release. Similarly, increases in activated, i.e., phosphorylated, ERK1/2 (pERK1/2) and p38 (phospho-p38) were demonstrable in both ductal and recovering acinar cells, with pERKs expressed predominantly in the nuclei and phospho-p38 distributed throughout the cells. Furthermore, levels of epidermal growth factor (EGF) receptor and β2-adrenergic receptor (β2-AR) were elevated in the ligated glands and at day 7 post-release; β1-AR levels did not change over the same time period. These results support the view that cell proliferation is involved in duct ligation-induced atrophy of the rat parotid gland and gland recovery upon ligature removal. Up-regulation of ERKs and p38, and the activation of these MAPKs by up-regulated EGF and β2-ARs, may be important signaling components underlying glandular atrophy and subsequent regeneration.

Multifunctional roles of growth factors or biologically active peptides in salivary glands and saliva

Salivary glands secrete saliva which contains mucins, antimicrobial substances and growth factors. Since epidermal growth factor (EGF) and nerve growth factor (NGF) were demonstrated in murine submandibular glands (SMGs), several growth factors and biologically-active peptides have been studied in the human or other mammalian salivary glands and saliva. These growth factors may have a functional role in cell migration, proliferation and maturation within not only salivary glands but also other organs. In the SMGs of mice and rats, EGF, NGF and other known growth factors are usually synthesized in granular convoluted tubule cells (GCT). However, human SMGs are devoid of GCT cells, and growth factors in human salivary glands are usually produced in striated ducts. These findings suggest an evolutionary trace of ductal cells in mammals. The present review describes expression patterns of the following salivary gland growth factors: nerve growth factor (NGF); transforming growth factor α and β (TGF-α/β) bone morphogenetic protein (BMP); insulin-like growth factor (IGF); fibroblastic growth factor (FGF); and somatostatin, as well as their receptors. This review also discusses their cell biological roles in pathophysiological conditions.

Differential distribution and expression of leptin and the functional leptin receptor in major salivary glands of humans.

Leptin plays a central role in the regulation of food intake and energy expenditure in rodents. However, it has become clear that this hormone has more than only a satiety-inducing function, and that there are other sources of leptin, such as the central nervous system, placenta and the gastrointestinal tract in addition to adipose tIssue. Knowing about the important role of the salivary glands in food intake and digestion, it was the objective of the present study to investigate how leptin and its receptor are expressed and distributed in the major salivary glands of humans. We found leptin distributed throughout the major salivary glands with obvious intracellular concentrations in granula. In contrast, immunostaining for the leptin receptor was found exclusively in the membranes of the glandular cells. A high density of the leptin receptor was localised in the epithelia of the duct lumen. PCR analysis proved the autonomous expression of leptin by the salivary glands independently from adipocytes. Accordingly the long receptor isoform was expressed by any examined tIssue. In the light of recent findings of leptin influencing the growth of rodent salivary glands, the presence and distribution of leptin and its receptor suggests an autocrine role of salivary leptin within the glands.

Identification of major soluble salivary gland proteins in teneral Glossina morsitans morsitans

Salivary glands of tsetse flies (Diptera: Glossinidiae) contain molecules that are involved in preventing blood clotting during feeding as well as molecules thought to be intimately associated with trypanosome development and maturation. Here we present a protein microchemical analysis of the major soluble proteins of the salivary glands of Glossina morsitans morsitans, an important vector of African trypanosomes. Differential solubilization of salivary proteins was followed by reverse-phase, high-performance liquid chromatography (HPLC) and analysis of fractions by 1-D gel electrophoresis to reveal four major proteins. Each protein was subjected to amino acid microanalysis and N-terminal microsequencing. A protein chemical approach using high-resolution 2-D gel electrophoresis and mass spectrometry was also used to identify the salivary proteins. Matrix-assisted, laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry and quadrupole time-of-flight (Q-TOF) tandem mass spectrometry methods were used for peptide mass mapping and sequencing, respectively. Sequence information and peptide mass maps queried against the NCBI non-redundant database confirmed the identity of the first protein as tsetse salivary gland growth factor-1 (TSGF-1). Two proteins with no known function were identified as tsetse salivary gland protein 1 (Tsal 1) and tsetse salivary gland protein 2 (Tsal 2). The fourth protein was identified as Tsetse antigen-5 (TAg-5), which is a member of a large family of anti-haemostatic proteins. The results show that these four proteins are the most abundant soluble gene products present in salivary glands of teneral G. m. morsitans. We discuss the possible functions of these major proteins in cyclical transmission of African trypanosomes.

Acinar Cell Hypertrophy, Proliferation and Cell Death in Rat Submandibular Glands Induced by Long-Term Isoproterenol Administration.

The purpose of this study was to elucidate the relationship between cell proliferation and cell death of submandibular gland (SMG) acinar cells in rats treated with the β-adrenergic secretagogue isoproterenol (IPR) which elicits massive growth of salivary glands. We analyzed this process using computerized imaging analysis, 5-bromo-2'-deoxyuridine (BrdU) immunohistochemical staining, the terminal deoxyribonucleotidyl transferase (TdT)-mediated-deoxyuridine triphosphate (dUTP)-biotin nick end labeling (TUNEL) method and ultrastructural observations for 10 days of IPR treatment and for 3 weeks thereafter. Proliferation of acinar cells occurred at days 2 and 3 of IPR administration, and acinar cell hypertrophy continued during the entire 10-day treatment period. Numerous TUNEL-positive cells and vesicular structures were found in the acinar area by day 3 post-IPR administration. Ultrastructurally, vacuolated structures that resembled degenerating apoptotic bodies were located in and between the acinar cells. A different type of cell death, which was associated with an electron-lucent and edematous cytoplasm but not with mitochondrial lysis or cell membrane destruction, was also recognized in the acinus. It is suggested that this other type of cell death may correspond to secondary necrosis.

Sympathetic and parasympathetic regulation of cystatin S gene expression

The autonomic nervous system plays a regulatory role in the differentiation and growth of salivary glands, and in the expression of salivary specific genes. Cystatin S, a member of the evolutionarily conserved family 2 of the cysteine proteinase inhibitor superfamily, expressed in submandibular and parotid glands of rats during development, can be induced in adults by the β-adrenergic agonist isopreterenol (IPR). It was shown previously that unilateral sympathectomy or bilateral parasympathectomy reduces IPR-induced cystatin S expression. The present experiments demonstrate that IPR-induced cystatin S gene expression in submandibular glands is reduced as early as 3 days post bilateral denervation of both branches of the autonomic nervous system. The reduction is nearly equal to that of either sympathectomy or parasympathectomy alone, suggesting that factor(s) in both sympathetic and parasympathetic fibers are simultaneously required for IPR-induced cystatin S gene expression.

The Drosophila Cyclin D-Cdk4 complex promotes cellular growth

Mammalian cyclin D-Cdk4 complexes have been characterized as growth factor-responsive cell cycle regulators. Their levels rise upon growth factor stimulation, and they can phosphorylate and thus neutralize Retinoblastoma (Rb) family proteins to promote an E2F-dependent transcriptional program and S-phase entry. Here we characterize the in vivo function of Drosophila Cyclin D (CycD). We find that Drosophila CycD-Cdk4 does not act as a direct G(1)/S-phase regulator, but instead promotes cellular growth (accumulation of mass). The cellular response to CycD-Cdk4-driven growth varied according to cell type. In undifferentiated proliferating wing imaginal cells, CycD-Cdk4 caused accelerated cell division (hyperplasia) without affecting cell cycle phasing or cell size. In endoreplicating salivary gland cells, CycD-Cdk4 caused excessive DNA replication and cell enlargement (hypertrophy). In differentiating eyes, CycD-Cdk4 caused cell enlargement (hypertrophy) in post-mitotic cells. Interaction tests with a Drosophila Rb homolog, RBF, indicate that CycD-Cdk4 can counteract the cell cycle suppressive effects of RBF, but that its growth promoting activity is mediated at least in part via other targets.

Autonomic regulation of cystatin S gene expression in rat submandibular glands

Innervation of rat submandibular and parotid glands by the autonomic nervous system regulates saliva volume, its rate of secretion and its composition. The autonomic nervous system also plays a regulatory role in the differentiation and growth of salivary glands, and in the expression of specific sets of genes. Rat cystatin S, a member of family 2 of the cysteine proteinase inhibitor superfamily, is expressed in submandibular and parotid glands of human and rat. In the rat, cystatin S gene expression is tissue- and cell type-specific, is temporally regulated during postnatal development, and not observed in adult animals. The β-adrenergic agonist isoproterenol (IPR) induces hypertrophic and hyperplastic enlargements of rat salivary glands and the expression of a number of genes including cystatin S. Sympathectomy reduces, but does not completely block, IPR-induced expression of the cystatin S gene in submandibular glands of adult female rats, indicating the participation of sympathetic factor(s) in its regulation. Bilateral parasympathectomy also reduces IPR-induced cystatin S gene expression, suggesting a role of the parasympathetic nervous system in its regulation. Experiments described in this paper suggest that similar factor(s) arising from both the sympathetic and parasympathetic branches of the autonomic nervous system simultaneously participate in IPR-induced cystatin S gene expression in submandibular glands.

Evidence of a role for nerve growth factor in the effect of sialoadenectomy on body temperature of parasite-infected mice

Mice infected with Schistosoma mansoni were used to investigate the role of the submaxillary salivary gland and nerve growth factor (NGF) in temperature response. The results showed that the infection increased (36.5 ± 0.3vs35.7 ± 0.2), while sialoadenectomy decreased (34.4 ± 0.2vs35.7 ± 0.2) body temperature. These temperature changes were associated with high or low circulating NGF levels, respectively. It was also found that infection altered the distribution of oxytocin-positive neurones in the hypothalamus and that administration of 20 μg of purified NGF in normal mice raised (36.1 ± 0.2vs35.1 ± 0.2) and of NGF antibodies decreased (34.0 ± 0.2vs35.1 ± 0.2) body temperature. Taken together, these observations suggest that salivary NGF influences the temperature set-point in adult rodents, but the mechanism regulating these events remains to be elucidated.

TGF-β1 Inhibits Growth and Branching Morphogenesis In Embryonic Mouse Submandibular and Sublingual Glands in Vitro: (Salivary glands/extracellular matrix/epithelium/mesenchyme/organ culture).

Members of the TGF-β superfamily of polypeptides are key regulators in developmental processes. Several studies have shown that expression of TGF-β mRNA and protein are developmentally regulated and that both are prominently expressed in tissues undergoing epithelial-mesenchymal interactions such as branching morphogenesis. It has been shown that TGF-β1 protein is present in E 14 mouse submandibular glands at a time when branching is already establihsed. Here we demonstrate by RT-PCR and immunofluorescence that both TGF-β1 mRNA and protein are present in E 13 submandibular and sublingual glands at a time when branching is being initiated. Addition of TGF-β1 to E 13 rudiments resulted in reductions in organ size and inhibition of branching. Sensitivity to TGF-β1 depended on the developmental stage of the rudiments (early or late E 13) and the dose of growth factor used. TGF-β1 Also caused epithelial abnormalities, notably treated organs had elongated ducts. The effects were most pronounced in the sublingual gland. Taken together these results suggest a regulatory role for endogenous TGF-β1 in the growth and morphogenesis of mouse salivary glands.