Understanding how epithelial progenitors within exocrine glands establish specific cell lineages and form complex functional secretory units is vital for organ regeneration. Here we identify the transcription factor Sox10 as essential for both the maintenance and differentiation of epithelial KIT+FGFR2b+ progenitors into secretory units, containing acinar, myoepithelial, and intercalated duct cells. The KIT/FGFR2b-Sox10 axis marks the earliest multi-potent and tissue-specific progenitors of exocrine glands. Genetic deletion of epithelial Sox10 leads to loss of secretory units, which reduces organ size and function, but the ductal tree is retained. Intriguingly, the remaining duct progenitors do not compensate for loss of Sox10 and lack plasticity to properly form secretory units. However, overexpression of Sox10 in these ductal progenitors enhances their plasticity toward KIT+ progenitors and induces differentiation into secretory units. Therefore, Sox10 controls plasticity and multi-potency of epithelial KIT+ cells in secretory organs, such as mammary, lacrimal, and salivary glands.

The secretory function of cells relies on the capacity of the endoplasmic reticulum (ER) to fold and modify nascent polypeptides and to synthesize phospholipids for the subsequent trafficking of secretory proteins through the ER-Golgi network. We have previously demonstrated that the transcription factor XBP-1 activates the expression of certain ER chaperone genes and initiates ER biogenesis. Here, we have rescued the embryonic lethality of XBP-1 deficient fetuses by targeting an XBP-1 transgene selectively to hepatocytes (XBP-1-/-;LivXBP1). XBP-1-/-;LivXBP1 mice displayed abnormalities exclusively in secretory organs such as exocrine pancreas and salivary gland that led to early postnatal lethality from impaired production of pancreatic digestive enzymes. The ER was poorly developed in pancreatic and salivary gland acinar cells, accompanied by decreased expression of ER chaperone genes. Marked apoptosis of pancreatic acinar cells was observed during embryogenesis. Thus, the absence of XBP-1 results in an imbalance between the cargo load on the ER and its capacity to handle it, leading to the activation of ER stress-mediated proapoptotic pathways. These data lead us to propose that XBP-1 is both necessary and sufficient for the full biogenesis of the secretory machinery in exocrine cells.

The glandular system is crucially involved in main aspects of ant social life. The function of glands has been primarily studied in the workers (the non-reproductive individuals in a colony). In contrast, little information is available on queens (the reproductive females in a colony) or males in spite of the obvious functional differences between these castes. Here we report a comparison of the general morphology of the mandibular, propharyngeal and postpharyngeal glands between the three castes of the black ant Lasius niger. The analysis clearly shows that all these cephalic glands differ in relative size between castes and suggests a link between gland structure and its behavioral role in queens, workers and males. In particular, males present a hypertrophied mandibular gland. This is consistent with the fact that these glands might be the source of the sex pheromone in this caste. By contrast, queens exhibited the most developed postpharyngeal glands. This is consistent with the production of particular cues by queens for workers to help them to distinguish between reproductive and non-reproductive females. Finally, the propharyngeal glands were most developed in the worker caste and of similar relative size in males and queens. Their function is still enigmatic.

Stick insects (Phasmatodea) use repellent chemical substances (allomones) for defence which are released from so-called defence glands in the prothorax. These glands differ in size between species, and are under neuronal control from the CNS. The detailed neural innervation and possible differences between species are not studied so far. Using axonal tracing, the neuronal innervation is investigated comparing four species. The aim is to document the complexity of defence gland innervation in peripheral nerves and central motoneurons in stick insects.

The nests of advanced eusocial ant species can be considered ecological islands with a diversity of ecological niches inhabited by not only the ants and their brood, but also a multitude of other organisms adapted to particular niches. In the current paper, we describe the myrmecophilous behavior and the exocrine glands that enable the staphylinid beetle Dinarda dentata to live closely with its host ants Formica sanguinea. We confirm previous anecdotal descriptions of the beetle's ability to snatch regurgitated food from ants that arrive with a full crop in the peripheral nest chambers, and describe how the beetle is able to appease its host ants and dull initial aggression in the ants.

Transgenic rabbits carrying mammary gland specific gene constructs are extensively used for excreting recombinant proteins into the milk. Here, we report refined phenotyping of previously generated Venus transposon-carrying transgenic rabbits with particular emphasis on the secretion of the reporter protein by exocrine glands, such as mammary, salivary, tear and seminal glands. The Sleeping Beauty (SB) transposon transgenic construct contains the Venus fluorophore cDNA, but without a signal peptide for the secretory pathway, driven by the ubiquitous CAGGS (CAG) promoter. Despite the absence of a signal peptide, the fluorophore protein was readily detected in milk, tear, saliva and seminal fluids. The expression pattern was verified by Western blot analysis. Mammary gland epithelial cells of SB-CAG-Venus transgenic lactating does also showed Venus-specific expression by tissue histology and fluorescence microscopy. In summary, the SB-CAG-Venus transgenic rabbits secrete the recombinant protein by different glands. This finding has relevance not only for the understanding of the biological function of exocrine glands, but also for the design of constructs for expression of recombinant proteins in dairy animals.

Although several autoimmune diseases are known to develop in postmenopausal women, the mechanisms by which estrogen deficiency influences autoimmunity remain unclear. Recently, we found that retinoblastoma-associated protein 48 (RbAp48) induces tissue-specific apoptosis in the exocrine glands depending on the level of estrogen deficiency. In this study, we report that transgenic (Tg) expression of RbAp48 resulted in the development of autoimmune exocrinopathy resembling Sjögren's syndrome. CD4(+) T cell-mediated autoimmune lesions were aggravated with age, in association with autoantibody productions. Surprisingly, we obtained evidence that salivary and lacrimal epithelial cells can produce interferon-gamma (IFN-gamma) in addition to interleukin-18, which activates IFN regulatory factor-1 and class II transactivator. Indeed, autoimmune lesions in Rag2(-/-) mice were induced by the adoptive transfer of lymph node T cells from RbAp48-Tg mice. These results indicate a novel immunocompetent role of epithelial cells that can produce IFN-gamma, resulting in loss of local tolerance before developing gender-based autoimmunity.

The honeybee (Apis mellifera L.) uses various chemical signals produced by the worker exocrine glands to maintain the functioning of its colony. The roles of worker postcerebral glands (PcGs), thoracic glands (TGs), and mandibular glands (MGs) and the functional changes they undergo according to the division of labor from nursing to foraging are not as well studied. To comprehensively characterize the molecular roles of these glands in workers and their changes according to the division of labor of workers, we analyzed the proteomes of PcGs, TGs, and MGs from nurse bees and foragers using shotgun proteomics technology. We identified approximately 2000 proteins from each of the nurse bee or forager glands and highlighted the features of these glands at the molecular level by semiquantitative enrichment analyses of frequently detected, gland-selective, and labor-selective proteins. First, we found the high potential to produce lipids in PcGs and MGs, suggesting their relation to pheromone production. Second, we also found the proton pumps abundant in TGs and propose some transporters possibly related to the saliva production. Finally, our data unveiled candidate enzymes involved in labor-dependent acid production in MGs.

This study has used multiple-labelling immunohistochemistry and quantitative analysis to examine the projections of subpopulations of parasympathetic and sympathetic neurons to different vascular and secretory structures in five cranial exocrine glands of guinea-pigs. Multiple subpopulations of parasympathetic axons, identified by immunoreactivity (IR) for various combinations of peptides, innervated arteries, arterioles, ducts and acini in sublingual, submandibular, parotid, lacrimal and zygomatic glands, although axons were absent from ducts in the parotid gland. Most parasympathetic axons contained IR for vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), with or without enkephalin (Enk). The proportion of parasympathetic axons that contained Enk-IR varied greatly between target tissues and glands: Enk-IR was more common in axons supplying secretory ducts, acini and arterioles than in axons innervating more proximal arteries; Enk-IR was less common in axons supplying the lacrimal gland than axons supplying the submandibular, lacrimal and zygomatic glands. Sympathetic axons with IR for tyrosine hydroxylase (TH) innervated arterial vessels in all glands, but innervated secretory structures only in the salivary glands. Sympathetic axons supplying proximal arterial segments often contained NPY-IR and sometimes also contained IR for dynorphin. Dynorphin-IR was more common in axons in the parotid, lacrimal and zygomatic glands than in the sublingual and submandibular glands. In contrast, axons supplying arterioles, ducts and acini lacked peptide IR. These results indicate that neuronal pathways regulating proximal arteries in cranial exocrine glands are different from the neuronal pathways regulating arterioles and acini, and may be different from neurons projecting to proximal secretory ducts. Furthermore, the peptides enkephalin, NPY and dynorphin are likely to make variable contributions to autonomic neurotransmission in different arterial segments and in different cranial exocrine glands.

Although many of the genes that regulate development of the endocrine pancreas have been identified, comparatively little is known about how the exocrine pancreas forms. Previous studies have shown that exocrine pancreas development may be modeled in zebrafish. However, the timing and mechanism of acinar and ductal differentiation and morphogenesis have not been described. Here, we characterize zebrafish exocrine pancreas development in wild type and mutant larvae using histological, immunohistochemical and ultrastructural analyses. These data allow us to identify two stages of zebrafish exocrine development. During the first stage, the exocrine anlage forms from rostral endodermal cells. During the second stage, proto-differentiated progenitor cells undergo terminal differentiation followed by acinar gland and duct morphogenesis. Immunohistochemical analyses support a model in which the intrapancreatic ductal system develops from progenitors that join to form a contiguous network rather than by branching morphogenesis of the pancreatic epithelium, as described for mammals. Contemporaneous appearance of acinar glands and ducts in developing larvae and their disruption in pancreatic mutants suggest that common molecular pathways may regulate gland and duct morphogenesis and differentiation of their constituent cells. By contrast, analyses of mind bomb mutants and jagged morpholino-injected larvae suggest that Notch signaling principally regulates ductal differentiation of bipotential exocrine progenitors.

Cdc42 is a small GTPase essential for the cell cycle, morphogenesis, and cell adhesion, and it is involved in the polarity of epithelial cells. However, the functional roles of Cdc42 in exocrine glands, such as the maintenance of acini and water secretion, are not yet well understood. In this study, we generated acinar-cell-specific Cdc42 conditional knockout (Cdc42cKO) mice to assess their maintenance of acinar cells and physiological functions in the salivary glands (SGs) and lacrimal glands (LGs). Our data revealed that the loss of Cdc42 altered the luminal structures to bulging structures and induced acinar cell apoptosis in both the parotid glands (PGs) and LGs of Cdc42cKO mice. Interestingly, saliva secretion in response to pilocarpine stimulation was decreased in the Cdc42cKO group, whereas tear secretion was increased. Consistent with the water secretion results, protein expression of the water channel AQP5 in acinar cells was also decreased in the PGs but conversely increased in the LGs. Moreover, the changes that increased AQP5 expression in LGs occurred in the acinar cells rather than the duct cells. The present study demonstrates that Cdc42 is involved in the structural and survival maintenance of acinar cells in SGs and LGs. On the other hand, depletion of Cdc42 caused the opposite physiological phenomena between PGs and LGs.

Several ion channels and transporters regulate fluid secretion in salivary and lacrimal glands. In salivary glands, the major anion channel involved in fluid secretion is the calcium-activated chloride channel anoctamin 1 (ANO1). Several members of the transient receptor potential (TRP) channel superfamily regulate ANO1 activity. Here, we report a functional interaction between thermosensitive TRP vanilloid (TRPV)4 and ANO1 in acinar cells isolated from mouse salivary and lacrimal glands. TRPV4 activation induced chloride currents and shrinkage of acinar cells by increasing intracellular calcium concentrations. The chloride currents evoked by a TRPV4-specific activator (GSK1016790A) were identified as ANO1-mediated currents. Moreover, TRPV4 activation by an inositol 1,4,5-trisphosphate (IP3)-dependent mechanism was found to contribute to the muscarinic pathway of fluid secretion. Muscarinic stimulation of saliva and tear secretion was down-regulated in both TRPV4-deficient mice and in acinar cells treated with a TRPV4-specific antagonist (HC-067047). Furthermore, the temperature dependence of muscarinic salivation was shown to depend mainly on TRPV4. Our results suggest that TRPV4 interacts with IP3 receptors and ANO1 to regulate the muscarinic pathway that mediates salivation and lacrimation.-Derouiche, S., Takayama, Y., Murakami, M., Tominaga, M. TRPV4 heats up ANO1-dependent exocrine gland fluid secretion.

Apocrine secretion is a recently discovered widespread non-canonical and non-vesicular secretory mechanism whose regulation and purpose is only partly defined. Here, we demonstrate that apocrine secretion in the prepupal salivary glands (SGs) of Drosophila provides the sole source of immune-competent and defense-response proteins to the exuvial fluid that lies between the metamorphosing pupae and its pupal case. Genetic ablation of its delivery from the prepupal SGs to the exuvial fluid decreases the survival of pupae to microbial challenges, and the isolated apocrine secretion has strong antimicrobial effects in "agar-plate" tests. Thus, apocrine secretion provides an essential first line of defense against exogenously born infection and represents a highly specialized cellular mechanism for delivering components of innate immunity at the interface between an organism and its external environment.

The basitarsus of the mid- and/or hindlegs of several Amblyoponinae ants shows a deep longitudinal groove or sulcus on its anterior face in workers and queens. Histological examination reveals this sulcus is associated with a conspicuous novel epithelial gland, which brings the number of exocrine glands in the legs of ants to 25. The ultrastructural characteristics of the gland show the presence of a well-developed smooth endoplasmic reticulum. This is indicative for the elaboration of a non-proteinaceous and thus possibly pheromonal secretion. Behavioural observations show that this secretion is collected by the tarsomeres and spread onto the brood and nest, suggesting a role in nestmate recognition. A similar basitarsal sulcus gland was also found in Nothomyrmecia, Paraponera and Tetraponera, which represents both a wide phylogenetic and ecological distribution, as it includes arboreal, ground-dwelling as well as subterranean taxa.

Interleukin (IL)-6 is a multi-functional cytokine that can either promote or suppress tissue inflammation depending on the specific disease context. IL-6 is elevated in the exocrine glands and serum of patients with Sjögren's syndrome (SS), but the specific role of IL-6 in the pathogenesis of this disease has not been defined. In this study, we showed that IL-6 expression levels were increased with age in C56BL/6.NOD-Aec1Aec2 mice, a primary SS model, and higher than the control C57BL/6 mice. To assess the role of IL-6 during the immunological phase of SS development, a neutralizing anti-IL-6 antibody was administered into 16 week-old female C56BL/6.NOD-Aec1Aec2 mice, 3 times weekly for a consecutive 8 weeks. Neutralization of endogenous IL-6 throughout the immunological phase of SS development led to increased apoptosis, caspase-3 activation, leukocytic infiltration, and IFN-γ- and TNF-α production in the salivary gland. To further determine the effect of IL-6 on the apoptosis of exocrine gland cells, recombinant human IL-6 or the neutralizing anti-IL-6 antibody was injected into female C57BL/6 mice that received concurrent injection of anti-CD3 antibody to induce the apoptosis of exocrine gland tissues. Neutralization of IL-6 enhanced, whereas administration of IL-6 inhibited apoptosis and caspase-3 activation in salivary and lacrimal glands in this model. The apoptosis-suppressing effect of IL-6 was associated with up-regulation of Bcl-xL and Mcl-1 in both glands. Moreover, IL-6 treatment induced activation of STAT3 and up-regulated Bcl-xL and Mcl-1 gene expression in a human salivary gland epithelial cell line. In conclusion, IL-6 inhibits the apoptosis of exocrine gland tissues and exerts a tissue-protective effect under inflammatory conditions including SS. These findings suggest the possibility of using this property of IL-6 to preserve exocrine gland tissue integrity and function under autoimmune and inflammatory conditions.

Exocrine secretion commonly employs micron-scale vesicles that fuse to a limited apical surface, presenting an extreme challenge for maintaining membrane homeostasis. Using Drosophila melanogaster larval salivary glands, we show that the membranes of fused vesicles undergo actomyosin-mediated folding and retention, which prevents them from incorporating into the apical surface. In addition, the diffusion of proteins and lipids between the fused vesicle and the apical surface is limited. Actomyosin contraction and membrane crumpling are essential for recruiting clathrin-mediated endocytosis to clear the retained vesicular membrane. Finally, we also observe membrane crumpling in secretory vesicles of the mouse exocrine pancreas. We conclude that membrane sequestration by crumpling followed by targeted endocytosis of the vesicular membrane, represents a general mechanism of exocytosis that maintains membrane homeostasis in exocrine tissues that employ large secretory vesicles.

We previously reported that mice deficient in UDP-GlcNAc:lysosomal enzyme GlcNAc-1-phosphotransferase (mucolipidosis type II or Gnptab -/- mice), the enzyme that initiates the addition of the mannose 6-phosphate lysosomal sorting signal on acid hydrolases, exhibited extensive vacuolization of their exocrine gland cells, while the liver, brain, and muscle appeared grossly unaffected. Similar pathological findings were observed in several exocrine glands of patients with mucolipidosis II. To understand the basis for this cell type-specific abnormality, we analyzed these tissues in Gnptab -/- mice using a combined immunoelectron microscopy and biochemical approach. We demonstrate that the vacuoles in the exocrine glands are enlarged autolysosomes containing undigested cytoplasmic material that accumulate secondary to deficient lysosomal function. Surprisingly, the acid hydrolase levels in these tissues ranged from normal to modestly decreased, in contrast to skin fibroblasts, which accumulate enlarged lysosomes and/or autolysosomes also but exhibit very low levels of acid hydrolases. We propose that the lysosomal defect in the exocrine cells is caused by the combination of increased secretion of the acid hydrolases via the constitutive pathway along with their entrapment in secretory granules. Taken together, our results provide new insights into the mechanisms of the tissue-specific abnormalities seen in mucolipidosis type II.

Exocytosis is a fundamental cellular process by which cells secrete cargos from their apical membrane into the extracellular lumen. Cargo release proceeds in sequential steps that depend on coordinated assembly and organization of an actin cytoskeletal network. Here, we identified the conserved actin-crosslinking protein Swip-1 as a novel regulator controlling exocytosis of glue granules in the Drosophila salivary gland. Real-time imaging revealed that Swip-1 is simultaneously recruited with F-actin onto secreting granules in proximity to the apical membrane. We observed that Swip-1 is rapidly cleared at the point of secretory vesicle fusion and colocalizes with actomyosin network around the fused vesicles. Loss of Swip-1 function impairs secretory cargo expulsion, resulting in strongly delayed secretion. Thus, our results uncover a novel role of Swip-1 in secretory vesicle compression and expulsion of cargo during regulated exocytosis. Remarkably, this function neither requires Ca2+ binding nor dimerization of Swip-1. Our data rather suggest that Swip-1 regulates actomyosin activity upstream of Rho-GTPase signaling to drive proper vesicle membrane crumpling and expulsion of cargo.

Unraveling cell fate plasticity during tissue homeostasis and repair can reveal actionable insights for stem cell biology and regenerative medicine. In the pancreas, it remains controversial whether lineage transdifferentiation among the exocrine cells occur under pathophysiological conditions. Here, to address this question, we used a dual recombinase-mediated genetic system that enables simultaneous tracing of pancreatic acinar and ductal cells using two distinct genetic reporters, avoiding the "ectopic" labeling by Cre-loxP recombination system. We found that acinar-to-ductal transdifferentiation occurs after pancreatic duct ligation or during caerulein-induced pancreatitis, but not during homeostasis or after partial pancreatectomy. On the other hand, pancreatic ductal cells contribute to new acinar cells after significant acinar cell loss. By genetic tracing of cell proliferation, we also quantify the cell proliferation dynamics and deduce the turnover rate of pancreatic exocrine lineages during homeostasis. Together, these results suggest that the lineage transdifferentiation happens between acinar cells and ductal cells in the pancreatic exocrine glands under specific conditions.

Exocrine glands share a common morphology consisting of ductal, acinar, and basal/myoepithelial cells, but their functions and mechanisms of homeostasis differ among tissues. Salivary glands are an example of exocrine glands, and they have been reported to contain multipotent stem cells that differentiate into other tissues. In this study, we purified the salivary gland stem/progenitor cells of adult mouse salivary glands using the cell surface marker CD133 by flow cytometry. CD133+ cells possessed stem cell capacity, and the transplantation of CD133+ cells into the submandibular gland reconstituted gland structures, including functional acinar. CD133+ cells were sparsely distributed in the intercalated and exocrine ducts and expressed Sox9 at higher levels than CD133- cells. Moreover, we demonstrated that Sox9 was required for the stem cell properties CD133+ cells, including colony and sphere formation. Thus, the Sox9-related signaling may control the regeneration salivary glands.