Molecular basis for the rhino Yurlovo (hrrhY) phenotype: severe skin abnormalities and female reproductive defects associated with an insertion in the hairless gene

In 1989, mice bearing mutations at the hr (hairless) locus were first proposed as a model for the human hair growth disorder papular atrichia, since in both these mice and in corresponding patients, a complete hair loss develops due to disintegration of the normal follicle structure into dermal cysts and so-called utriculi. Recently, the human hairless gene was characterized, and pathogenetic mutations were found to be associated with a recessively inherited form atrichia with papular lesions; however, the functions of hr gene remain unclear. Allelic mutations in the murine hairless gene represent a potentially powerful tool to elucidate the role of the hairless gene protein product in hair follicle physiology. In 1980, several naked animals were discovered in a breeding colony of B10.R109/Y mice maintained in the Laboratory of Experimental Biological Models (L.E.B.M., Yurlovo, Moscow District, Russia). By cross breeding with hairles HRS/J hr/hr mice, this mutation was shown to be allelic with hairless. Here, we describe the molecular basis of the hr^rhY mutation in mice, which consists of a 13 bp insertion in exon 16 of the hr gene. Histological evaluation of Yurlovo mouse skin revealed some differences as compared to the hairless and rhino mutations, with the formation of dermal megacysts being the most specific peculiarity of the Yurlovo mutation. These results, together with previous studies of hr^rhY/hr^rhY mutant mice, suggest that the rhino Yurlovo (hr^rhY) mutation represents a third and potentially more severe variation of the hairless phenotype.     

SKHIN/Sprd, a new genetically defined inbred hairless mouse strain for UV-induced skin carcinogenesis studies

Strains of mice vary in their susceptibility to ultra-violet (UV) radiation-induced skin tumors. Some strains of hairless mice (homozygous for the spontaneous Hr(hr) mutation) are particularly susceptible to these tumors. The skin tumors that develop in hairless mice resemble, both at the morphologic and molecular levels, UV-induced squamous cell carcinomas (SCC) and their precursors in human. The most commonly employed hairless mice belong to the SKH1 stock. However, these mice are outbred and their genetic background is not characterized, which makes them a poor model for genetic studies. We have developed a new inbred strain from outbred SKH1 mice that we named SKHIN/Sprd (now at generation F31). In order to characterize the genetic background of this new strain, we genotyped a cohort of mice at F30 with 92 microsatellites and 140 single nucleotide polymorphisms (SNP) evenly distributed throughout the mouse genome. We also exposed SKHIN/Sprd mice to chronic UV irradiation and showed that they are as susceptible to UV-induced skin carcinogenesis as outbred SKH1 mice. In addition, we proved that, albeit with low efficiency, inbred SKHIN/Sprd mice are suitable for transgenic production by classical pronuclear microinjection. This new inbred strain will be useful for the development of transgenic and congenic strains on a hairless inbred background as well as the establishment of syngeneic tumor cell lines. These new tools can potentially help elucidate a number of features of the cutaneous response to UV irradiation in humans, including the effect of genetic background and modifier genes.     

Photosensitivity of murine skin greatly depends on the genetic background: clinically relevant dose as a new measure to replace minimal erythema dose in mouse studies

Artificial UV irradiation of murine skin is a frequently used method for testing photosensitivity, study carcinogenesis and photoprotective effects of different compounds. However, doses of UV radiation and mouse strains used in experiments vary greatly. The genetic background of mice may influence the photosensitivity as melanin content, pigmentation and hair cycle parameters are dissimilar. Doses of UV are often expressed in relation to the minimal erythema dose (MED) that was not necessarily determined for the given strain. We set out to standardize the method of measuring photosensitivity in three commonly used mouse strains, C57BL/6N, Balb/c and SKH‐1. We found that MED may not be determined for some strains as erythema development in mice with diverse genotypes differs greatly. We measured the oedema response in vivo and ex vivo by using OCT. Given the strain‐specific variability of erythema, we introduced Clinically Relevant Dose (CRD) as a new term to replace MED in experiments, to describe the lowest dose that triggers a perceptible skin reaction in mice. Not only the CRD but the proportion of erythema and oedema were different in strains examined. C57BL/6N mice display skin reactions at the lowest UVB dose, while SKH‐1 hairless mice show changes, mostly oedema, after higher doses of UVB. The cellular composition and skin thickness were examined by histopathology. IL‐1beta and IL‐6 levels in skin correlated with the increasing doses of UVB. Despite the variations in the degree of erythema and oedema, no major differences in cytokine expressions were seen among various strains of mice.     

Dietary compound ellagic acid alleviates skin wrinkle and inflammation induced by UV‐B irradiation

Please cite this paper as: Dietary compound ellagic acid alleviates skin wrinkle and inflammation induced by UV‐B irradiation. Experimental Dermatology 2010; 19 : e182–e190. Abstract: Ellagic acid, a polyphenol compound present in berries and pomegranate, has received attention as an agent that may have potential bioactivities preventing chronic diseases. This study examined photoprotective effects of ellagic acid on collagen breakdown and inflammatory responses in UV (ultraviolet)‐B irradiated human skin cells and hairless mice. Ellagic acid attenuated the UV‐B‐induced toxicity of HaCaT keratinocytes and human dermal fibroblasts. Non‐toxic ellagic acid markedly prevented collagen degradation by blocking matrix metalloproteinase production in UV‐B‐exposed fibroblasts. Anti‐wrinkle activity of ellagic acid was further investigated in hairless mice exposed to UV‐B, in which it attenuated UV‐B‐triggered skin wrinkle formation and epidermal thickening. Topical application of 10 μmol/l ellagic acid diminished production of pro‐inflammatory cytokines IL‐1β and IL‐6, and blocked infiltration of inflammatory macrophages in the integuments of SKH‐1 hairless mice exposed to UV‐B for 8 weeks. In addition, this compound mitigated inflammatory intracellular cell adhesion molecule‐1 expression in UV‐B‐irradiated keratinocytes and photoaged mouse epidermis. These results demonstrate that ellagic acid prevented collagen destruction and inflammatory responses caused by UV‐B. Therefore, dietary and pharmacological interventions with berries rich in ellagic acid may be promising treatment strategies interrupting skin wrinkle and inflammation associated with chronic UV exposure leading to photoageing.     

R164C mutation in FOXQ1 H3 domain affects formation of the hair medulla

A number of single gene mutations in laboratory mice produce hair follicle defects resulting in deformed hair shafts. The radiation‐induced (SB/LeJ‐Foxq1^sa) satin mutant mice have a satin‐like sheen to their hair and dilute colouration. This sheen is due to failure of the hair shafts to develop normal medullas, while the pigment dilution is due to the unrelated beige (lysosomal trafficking regulator, Lyst^bg) mutation. A new allelic mutation, Foxq1^sa‐J, arose spontaneously on the albino (tyrosinase, Tyr^c) MRL/MpJ‐Fas^lpr background. The Foxq1^sa‐J allele has a C to T transition at position 490. By contrast, the Foxq1^sa mutant allele was confirmed to be a 67 base pair deletion followed by two base changes (GA to AT). Morphologic changes were similar to those seen in Hoxc13 transgenic and targeted mutant mice. This new allelic mutation provides yet another tool to investigate formation of the interior structures of hair shafts.     

Photodynamic therapy with topical methyl‐ and hexylaminolevulinate for prophylaxis and treatment of UV‐induced SCC in hairless mice

Please cite this paper as: Photodynamic therapy with topical methyl‐ and hexylaminolevulinate for prophylaxis and treatment of UV‐induced SCC in hairless mice. Experimental Dermatology 2010; 19 : e166–e172. Abstract Background: Hexyl aminolevulinate (HAL) is a long‐chained 5‐aminolevulinic acid‐ester that has been proposed as a novel photosensitizing agent to methyl aminolevulinate (MAL) in topical photodynamic therapy (PDT). The more lipophilic HAL, may improve treatment outcome for non‐melanoma skin cancer. Objective: To compare the prophylactic and therapeutic effects of HAL‐ and MAL‐PDT for ultraviolet‐induced squamous cell carcinomas (SCCs) in hairless mice. Methods: Mice (n = 249) were irradiated with solar UV‐radiation (UVR) until SCC occurred. Before any skin changes developed, two prophylactic PDT treatments were given, using creams of HAL (2%, 6%, 20%) or MAL (20%) followed by illumination (632 nm, Aktilite, Photocure). Two therapeutic PDT‐treatments were given by randomization to the first developed SCC of 1 mm. Primary end‐points were time to first SCC of 1 mm and complete SCC clearance. Secondary end‐points were time to SCC‐recurrence, PpIX fluorescence and skin reactions to PDT. Results: The median time to first SCC was significantly longer for mice treated with prophylactic HAL‐PDT (2%, 6% and 20% HAL, 264 days) and MAL‐PDT (20% MAL, 269 days) than mice exposed to UVR (186 days) and UVR + placebo‐PDT (199 days) (P < 0.0001). The therapeutic efficacy of HAL‐ and MAL‐PDT showed cure rates of 23–61.5% (P = 0.11). Similar PpIX fluorescence intensity and severity of clinical reactions were seen for HAL‐ and MAL‐groups, although mice developed more intense hyper‐pigmentation when treated with 20% MAL‐PDT compared with 2% HAL‐PDT. Conclusions: PDT with HAL (2%, 6% and 20%) and MAL (20%) is equally effective to prevent and treat UV‐induced SCC in hairless mice.     

Glycyrrhizic acid prevents ultraviolet‐B‐induced photodamage: a role for mitogen‐activated protein kinases,nuclear factor kappa B and mitochondrial apoptotic pathway

Glycyrrhizic acid (GA), a natural triterpene, has received attention as an agent that has protective effects against chronic diseases including ultraviolet UV‐B‐induced skin photodamage. However, the mechanism of its protective effect remains elusive. Here, we used an immortalized human keratinocyte cell line (HaCaT) and a small animal model (BALB/c mice), to investigate the protective effects of GA against UV‐B‐induced oxidative damage, and additionally, delineated the molecular mechanisms involved in the UV‐B‐mediated inflammatory and apoptotic response. In the HaCaT cells, GA inhibited the UV‐B‐mediated increase in intracellular reactive oxygen species (ROS) and down‐regulated the release of pro‐inflammatory cytokines interleukin (IL)‐1α, ‐1β and ‐6, tumor necrosis factor (TNF)‐α and prostaglandin E2 (PGE2). GA inhibited UV‐B‐mediated activation of p38 and JNK MAP kinases, COX‐2 expression and nuclear translocation of NF‐κB. Furthermore, GA inhibited UV‐B‐mediated apoptosis by attenuating translocation of Bax from the cytosol to mitochondria, thus preserving mitochondrial integrity. GA‐treated HaCaT cells also exhibited elevated antiapoptotic Bcl‐2 protein, concomitant with reduced caspase‐3 cleavage and decreased PARP‐1 protein. In BALB/c mice, topical application of GA on dorsal skin exposed to UV‐B irradiation protected against epidermal hyperplasia, lymphocyte infiltration and expression of several inflammatory proteins, p38, JNK, COX‐2, NF‐κB and ICAM‐1. Based on the above findings, we conclude that GA protects against UV‐B‐mediated photodamage by inhibiting the signalling cascades triggered by oxidative stress, including MAPK/NF‐κB activation, as well as apoptosis. Thus, GA has strong potential to be used as a therapeutic/cosmeceutical agent against photodamage.     

Photocarcinogenesis and toxicity of benzoyl peroxide in hairless mice after simulated solar radiation

Please cite this paper as: Photocarcinogenesis and toxicity of benzoyl peroxide in hairless mice after simulated solar radiation. Experimental Dermatology 2009; Abstract: Topical benzoyl peroxide (BPO) gel has long been used to treat acne vulgaris and has recently been combined with clindamycin (BPO‐clin). No skin malignancies have been reported after clinical use of BPO, but there has been concern about the possible carcinogenicity of BPO alone and in combination with UV radiation. BPO can promote skin tumorigenesis in a mouse skin chemical carcinogenesis model. As acne vulgaris is frequently localized on sun‐exposed areas, we investigated whether BPO or BPO‐clin accelerates photocarcinogenesis in combination with simulated solar radiation (SSR) in 12 groups of 25 hairless female C3.Cg/TifBomTac‐immunocompetent mice. BPO or BPO‐clin was applied topically to the back five times each week, followed by SSR three times each week (2, 3, or 4 standard erythema doses) 3–4 h later, for 365 days or until death. Generally BPO and BPO‐clin did not accelerate the time to first, second or third tumor. Therefore, there is no evidence suggesting that BPO or BPO‐clin is photocarcinogenic. However, we found significantly higher mortality in the SSR exposed groups receiving BPO and BPO‐clin compared with groups receiving only BPO or BPO‐clin. Our results show that BPO and the combination of BPO and clindamycin do not accelerate photocarcinogenesis, but are toxic in hairless mice. Based on the current data, the cancer risk associated with the use of BPO and BPO‐clin in sun‐exposed areas is minimal. Thus, while the carcinogenic potential of BPO is not fully understood, at the present time, evidence suggests that this compound is safe to use.     

Transgenic rescue of desmoglein 3 null mice with desmoglein 1 to develop a syngeneic mouse model for pemphigus vulgaris

Background

An active disease mouse model of pemphigus vulgaris (PV) was developed using the adoptive transfer of splenocytes from Dsg3^−/− mice with a mixed C57BL/6J (B6) and 129/Sv genetic background into B6-Rag2^−/− mice. Further immunological investigation is needed to resolve the genetic mismatch between host and recipient mice. The B6-Dsg3^−/− mice did not grow old enough to provide splenocytes, probably due to severe oral erosions, with resulting inhibition of food intake.

Objective

To rescue the B6-Dsg3^−/− mice and to produce syngeneic PV model mice.

Methods

Transgenic expression of mouse Dsg1 was attempted to compensate for the genetic loss of Dsg3 using the keratin 5 promoter. We evaluated the compensatory ability of Dsg1 in vivo by comparing Dsg1^wt/wt, Dsg1^tg/wt, and Dsg1^tg/tg mice. We generated a PV model via the adoptive transfer of B6-Dsg1^tg/tgDsg3^−/− splenocytes to B6-Rag2^−/− mice.

Results

Dsg1^tg/tg and Dsg1^tg/wt mice expressed ectopic Dsg1 on keratinocyte cell surfaces in the lower layers of the epidermis, oral epithelium, and telogen hair follicles. Ectopic Dsg1 blocked the pathogenic effects of AK23 anti-Dsg3 mAb, and improved the body weight loss, telogen hair loss, and survival rate dose-dependently. While the B6-Dsg1^wt/wtDsg3^−/− mice died by week 2, over 80% of the B6-Dsg1^tg/tgDsg3^−/− mice survived at week 6. Furthermore, the syngeneic PV model mice showed the characteristic phenotype, including stable anti-Dsg3 antibody production and suprabasilar acantholysis on histology.

Conclusion

Transgenic expression of Dsg1 rescued the severe B6-Dsg3^−/− phenotype and provided a syngeneic mouse model of PV, which may be a valuable tool for clarifying immunological mechanisms in autoimmunity and tolerance of Dsg3.     

Bleomycin‐induced fibrosis in MC1 signalling‐deficient C57BL/6J‐Mc1re/e mice further supports a modulating role for melanocortins in collagen synthesis of the skin

The melanocortin‐1 receptor (MC₁) binds α‐melanocyte‐stimulating hormone (α‐MSH) with high affinity and has a physiological role in cutaneous melanin pigmentation. Previously, we reported that human dermal fibroblasts also express functional MC₁. α‐MSH suppressed transforming growth factor‐β₁‐ and bleomycin (BLM)‐induced collagen synthesis in vitro and in vivo. Using MC₁ signalling‐deficient C57BL/6J‐Mc1r^e/e mice, we tested as to whether MC₁ has a regulatory role on dermal collagen synthesis in the BLM model of scleroderma. Notably, mice with a C57BL/6J genetic background were previously shown to be BLM‐non‐susceptible. Interestingly, treatment of C57BL/6J‐Mc1r^e/e but not of C57BL/6J‐wild‐type mice with BLM increased cutaneous collagen type I content at RNA and protein level along with development of skin fibrosis. Cutaneous levels of connective tissue growth factor and monocyte chemotactic protein‐1 were also increased in BLM‐treated C57BL/6J‐Mc1r^e/e mice. Primary dermal fibroblasts from C57BL/6J‐wt mice further expressed MC₁, suggesting that these cells are directly targeted by melanocortins to affect collagen production of the skin. Our findings support the concept that MC₁ has an endogenous regulatory function in collagen synthesis and controls the extent of fibrotic stress responses of the skin.     

Topical hydrocortisone,clobetasol propionate,and calcipotriol do not increase photocarcinogenesis induced by simulated solar irradiation in hairless mice

Please cite this paper as: Topical hydrocortisone, clobetasol propionate, and calcipotriol do not increase photocarcinogenesis induced by simulated solar irradiation in hairless mice. Experimental Dermatology 2010; 19 : 973–979. Abstract: Topical corticosteroids such as hydrocortisone‐17‐butyrate (HCB) and clobetasol‐17‐propionate (CP) and vitamin D₃ derivatives such as calcipotriol (CAL) are widely used to treat psoriasis. The immunosuppressive effects of corticosteroids make their topical use a concern for skin carcinogenicity. Few studies have assessed the effect of topical corticosteroids and topical vitamin D₃ derivatives on photocarcinogenesis induced by ultraviolet radiation. We investigated whether HCB, CP, or CAL can accelerate photocarcinogenesis using simulated solar radiation (SSR). HCB, CP, or CAL was applied topically to the backs of hairless, female, C3.Cg/TifBomTac‐immunocompetent mice in 16 groups of 25 mice each. The drugs were applied three times weekly followed by 0, 2, 4, or 6 standard erythema doses (SED) of SSR for 365 days or until death. No change was observed in the time required for tumor development in mice treated with HCB and 2 SED (HCB‐2SED) and HCB‐6SED. However, the time required for tumor development increased with HCB‐4SED treatment. Treatment with CP‐2SED did not change the time to onset of the first and second tumor, but all other CP treatments in combination with SSR increased the time. CAL‐2SED decreased the time to onset of the first tumor but not of the second and third tumor. CAL‐4SED and CAL‐6 SED did not change or increased the time to tumor development. Our data indicated that topical administration of HCB and CAL did not alter the photocarcinogenesis of SSR and that topical CP administration had a photoprotective effect. Thus, HCB, CP, and CAL do not increase photocarcinogenesis induced by SSR.     

Molecular events associated with apoptosis and proliferation induced by ultraviolet-B radiation in the skin of hairless mice

BACKGROUND: It is recognized that UV radiation produced apoptotic cells (sun burn cells) in the epidermis of mice. However, the relationship between apoptosis and cell proliferation after UV exposure in the skin of hairless mice are still unclear. OBJECTIVE: To investigate the effects of ultraviolet (UV) radiation on molecular events associated with apoptosis and proliferation in SKH1-hr mouse skin. METHODS: Mice were irradiated with daily UVB exposure of 0.1 or 0.25 J/cm(2) for 14 days. The skin tissues were analyzed at 2 and 24 h after the end irradiation for the presence of apoptotic cells and Bromodeoxyuridine (BrdU)-positive cells. We measured the expression of p53, p21, bcl-2, bax and E2F-1. RESULTS: The results indicated that UVB irradiation caused to increase apoptotic cells in the epidermis of mice. The expression of p53 and p21 was increased at 2 and 24 h after irradiation compared with the control. UV radiation induced high levels of bax at 2 and 24 h after irradiation with a concomitant decrease in bcl-2 expression. The expression of E2F-1 in the skin was also increased at 2 and 24 h after irradiation. Coinciding with these changes, BrdU positive cells increased at 2 and 24 h after UVB exposure at the epidermis of hairless mice, which observed the apoptotic expression. CONCLUSION: These results suggest that UVB irradiation of mouse skin induces apoptosis and is mediated by the p53/p21/E2F-1/bax pathway and that the dead cells are replaced by hyperproliferative cells, leading to epidermal hyperplasia.     

A novel xenograft model of cutaneous T‐cell lymphoma

Please cite this paper as: A novel xenograft model of cutaneous T‐cell lymphoma. Experimental Dermatology 2010; 19 : 1096–1102. Abstract: Cutaneous T‐cell lymphomas (CTCLs) are characterized by accumulation of malignant T cells in the skin. Early disease resembles benign skin disorders but during disease progression cutaneous tumors develop, and eventually the malignant T cells can spread to lymph nodes and internal organs. However, because of the lack of suitable animal models, little is known about the mechanisms driving CTCL development and progression in vivo. Here, we describe a novel xenograft model of tumor stage CTCL, where malignant T cells (MyLa2059) are transplanted to NOD/SCID‐B2m^?/? (NOD.Cg‐Prkdc^scid B2m^tm1Unc/J) mice. Subcutaneous transplantation of the malignant T cells led to rapid tumor formation in 43 of 48 transplantations, whereas transplantation of non‐malignant T cells isolated from the same donor did not result in tumor development. Importantly, the tumor growth was significantly suppressed in mice treated with vorinostat when compared to mice treated with vehicle. Furthermore, in most mice the tumors displayed subcutaneous and/or lymphatic dissemination. Histological, immunohistochemical and flow cytometric analyses confirmed that both tumors at the inoculation site, as well as distant subcutaneous and lymphatic tumors, originated from the transplanted malignant T cells. In conclusion, we describe a novel mouse model of tumor stage CTCL for future studies of disease dissemination and preclinical evaluations of new therapeutic strategies.     

UVA tanning devices interact with solar-simulated UV radiation in skin tumor development in hairless mice

Summary The carcinogenic effect of three UVA tanning sources was studied in lightly pigmented hairless mice. The three tanning sources (Bellarium-S SA-1-12, Philips TL 09R and Philips TL 10R) have different emission spectra, and emit different amounts of UVB. Radiation from the tanning sources was administered for 20 min/day, 5 day/week in daily doses equivalent to those used in suntan salons. The radiation was given alone or after 12 weeks of exposure to solar-simulated UV radiation (SOLAR UV) (10min/day, 4 day/week; daily dose, 19.5 kJ/m² UVA and 3.9 kJ/m² UVB). Irradiation with Bellarium-S SA-1-12 for 47 weeks and Philips TL 09R for 74 weeks induced skin tumours in 20/20 and 13/20 of the animals, respectively. When irradiation with Bellarium-S SA-1-12 and Philips TL 09R was administered after 12 weeks of SOLAR-UV exposure, a strong enhancement of SOLAR-UV-induced photocarcinogenesis was observed (p<0.001). Irradiation with Philips TL 10R was only slightly carcinogenic, and during 85 weeks of irradiation only one skin tumor appeared in a group of 20 mice. However, when irradiation with Philips TL 10R was administered after 12 weeks of exposure to SOLAR UV, an enhancement of SOLAR-UV-induced carcinogenesis was observed (p<0.001). Our results suggest that the hazards of exposure to commercial tanning devices are increased when they are used after a period of natural sun exposure. Even tanning sources with a low carcinogenic potential are able to increase SOLAR-UV-induced carcinogenesis significantly.     

Effect of genetically determined immunodeficiency on epidermal dendritic cell populations in C57BL/6J mice

Summary Mice homozygous for three different recessive mutations known to cause pleiotropic defects in the immune system and in the skin were used to evaluate the relationship between the classical immune system and dendritic epidermal cell populations. Numbers of Langerhans cells (LCs) and Thy-1⁺ dendritic cells (Thy-1⁺DEC) were determined using indirect immunofluorescence microscopy of epidermal whole mounts taken from viable motheaten (me ^v ), nude (nu), and rhino (rh ^hr ) mice. All mutants were maintained on the C57BL/6J strain background and were compared with their respective littermate normal controls. Viable motheaten mice had normal numbers of LCs at 1 month of age. However, by 8 weeks of age, LC density had decreased threefold. Nude and rhino mice had normal numbers of LCs at all ages tested. There was no significant effect of the viable motheaten mutation on numbers of Thy-1⁺DEC. Although nude mice showed normal numbers of Thy-1⁺ DEC at 1 month of age, these athymic mice had a threefold decrease in numbers of such cells by 6 months. In contrast to the reduced numbers of Thy-1⁺DEC seen in nude mice, rhino mice showed a four- to fivefold increase in the numbers of these epidermal cells at all ages tested. These findings suggest new mouse models for investigating the development, regulation, and biological properties of epidermal dendritic cell populations.This work was supported in part by grants from the US-Israel Binational Foundation for Science, the United States-Israel Bi-national Agricultural Research and Development Fund (BARD), the Foundation for the Study of Cell Biology and Molecular Virology, Phoenix, Arizona and United States Public Health Service grant CA-20408. E. S. is a fellow of the Foulkes Foundation, London, UK     

IL‐17A/F in Leishmania major‐resistant C57BL/6 mice

Proinflammatory IL‐17 plays an important role in various diseases and defence against extracellular microorganisms. Healing of leishmaniasis is promoted by Th1/Tc1 cells, whereas Th2/Treg are associated with worsened disease outcome. In addition, high expression of IL‐17A in Leishmania‐susceptible BALB/c and artificial overexpression of IL‐17A in T cells in resistant C57BL/6 mice worsened disease outcome. Since C57BL/6 mice lacking only IL‐17A exhibited no phenotype, and IL‐17A and IL‐17F share similar receptors, but differentially regulate chemokine secretion, we studied mice lacking both IL‐17A and IL‐17F (IL‐17A/F^?/?) in infections with Leishmania major. Interestingly, lesion volumes and parasite burdens were comparable to controls, IL‐17A/F^?/? mice developed a Th1/Tc1 phenotype, and exhibited normal lesion resolution. Thus, in C57BL/6 mice, secretion of IL‐17A and IL‐17F does not influence disease progression. It appears that—depending on the genetic background—cytokines of the IL‐17 family might be responsible for disease progression primarily in susceptible mice.     

RNA‐seq analysis of Lgr6+ stem cells and identification of an Lgr6 isoform

We studied Lgr6⁺ stem cells in experimental UV carcinogenesis in hairless mice. For further characterization through RNA‐seq, these stem cells were isolated by FACS from transgenic hairless mice bearing an EGFP‐Ires‐CreERT2 reporter cassette inserted into exon 1 of the Lgr6 gene (purity confirmed by human ERT2 expression). Between Lgr6/EGFP⁺ and Lgr6/EGFP^? basal cells (Tg/wt), 682 RNAs were differentially expressed, indicating stemness and expression of cancer‐related pathways in Lgr6/EGFP⁺ cells. We discovered that suspected “Lgr6 null” mice (Tg/Tg) expressed RNA of an Lgr6 isoform (delta‐Lgr6, lacking 74 N‐terminal aa) which could be functional and explain the lack of a phenotype.