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A post-transcriptional switch that controls spatiotemporal and mutually exclusive expression of two alternative gene products from a single transcript is reported; these gene products—miR-198 and FSTL1—are found to have opposing functions on keratinocyte migration and wound healing. Pivotal point in wound healing Wound healing is a complicated process involving coordinated cell migration, cell proliferation and extracellular matrix remodelling in response to TGF-β and other growth factors. Prabha Sampath and colleagues report a post-transcriptional switch that controls spatiotemporal and mutually exclusive expression of two alternative gene products from a single transcript. The two have opposing effects: the secreted glycoprotein FSTL1 is necessary for wound healing and the microRNA miR-198 suppresses keratinocyte migration and is essential for epidermal homeostasis in healthy skin. In normal keratinocytes, miR-198 is predominantly expressed from the dual transcript and it in turn attenuates several keratinocyte migrating genes. After injury, TGF-β signalling switches off miR-198 expression by downregulating the RNA-binding protein KSRP, thereby promoting FSTL1 protein expression. The findings may be relevant to the pathology of chronic diabetic ulcers, in which expression of miR-198 persists. Post-transcriptional switches are flexible effectors of dynamic changes in gene expression 1 . Here we report a new post-transcriptional switch that dictates the spatiotemporal and mutually exclusive expression of two alternative gene products from a single transcript. Expression of primate-specific exonic microRNA-198 (miR-198) 2 , located in the 3′-untranslated region of follistatin-like 1 ( FSTL1 ) 3 messenger RNA, switches to expression of the linked open reading frame of FSTL1 upon wounding in a human ex vivo organ culture system. We show that binding of a KH-type splicing regulatory protein (KSRP, also known as KHSRP) to the primary transcript determines the fate of the transcript and is essential for the processing of miR-198: transforming growth factor-β signalling switches off miR-198 expression by downregulating KSRP, and promotes FSTL1 protein expression. We also show that FSTL1 expression promotes keratinocyte migration, whereas miR-198 expression has the opposite effect by targeting and inhibiting DIAPH1 , PLAU and LAMC2 . A clear inverse correlation between the expression pattern of FSTL1 (pro-migratory) and miR-198 (anti-migratory) highlights the importance of this regulatory switch in controlling context-specific gene expression to orchestrate wound re-epithelialization. The deleterious effect of failure of this switch is apparent in non-healing chronic diabetic ulcers, in which expression of miR-198 persists, FSTL1 is absent, and keratinocyte migration, re-epithelialization and wound healing all fail to occur.

Keratin 9 (K9) is a type I intermediate filament protein whose expression is confined to the suprabasal layers of the palmoplantar epidermis. Although mutations in the K9 gene are known to cause epidermolytic palmoplantar keratoderma, a rare dominant-negative skin disorder, its functional significance is poorly understood. To gain insight into the physical requirement and importance of K9, we generated K9-deficient (Krt9−/−) mice. Here, we report that adult Krt9−/−mice develop calluses marked by hyperpigmentation that are exclusively localized to the stress-bearing footpads. Histological, immunohistochemical, and immunoblot analyses of these regions revealed hyperproliferation, impaired terminal differentiation, and abnormal expression of keratins K5, K14, and K2. Furthermore, the absence of K9 induces the stress-activated keratins K6 and K16. Importantly, mice heterozygous for the K9-null allele (Krt9+/−) show neither an overt nor histological phenotype, demonstrating that one Krt9 allele is sufficient for the developing normal palmoplantar epidermis. Together, our data demonstrate that complete ablation of K9 is not tolerable in vivo and that K9 is required for terminal differentiation and maintaining the mechanical integrity of palmoplantar epidermis.

Birgitte Lane and colleagues show that Ferguson-Smith disease, an autosomal dominant skin cancer condition characterized by the development of multiple self-healing tumors, is caused by a disease-specific spectrum of mutations in TGFBR1 . Multiple self-healing squamous epithelioma (MSSE), also known as Ferguson-Smith disease (FSD), is an autosomal-dominant skin cancer condition characterized by multiple squamous-carcinoma–like locally invasive skin tumors that grow rapidly for a few weeks before spontaneously regressing, leaving scars 1 , 2 . High-throughput genomic sequencing of a conservative estimate (24.2 Mb) of the disease locus on chromosome 9 using exon array capture identified independent mutations in TGFBR1 in three unrelated families. Subsequent dideoxy sequencing of TGFBR1 identified 11 distinct monoallelic mutations in 18 affected families, firmly establishing TGFBR1 as the causative gene. The nature of the sequence variants, which include mutations in the extracellular ligand-binding domain and a series of truncating mutations in the kinase domain, indicates a clear genotype-phenotype correlation between loss-of-function TGFBR1 mutations and MSSE. This distinguishes MSSE from the Marfan syndrome–related disorders in which missense mutations in TGFBR1 lead to developmental defects with vascular involvement but no reported predisposition to cancer.

Keratin 7 (K7) is a Type II member of the keratin superfamily and despite its widespread expression in different types of simple and transitional epithelia, its functional role in vivo remains elusive, in part due to the lack of any appropriate mouse models or any human diseases that are associated with KRT7 gene mutations. Using conventional gene targeting in mouse embryonic stem cells, we report here the generation and characterisation of the first K7 knockout mouse. Loss of K7 led to increased proliferation of the bladder urothelium although this was not associated with hyperplasia. K18, a presumptive type I assembly partner for K7, showed reduced expression in the bladder whereas K20, a marker of the terminally differentiated superficial urothelial cells was transcriptionally up-regulated. No other epithelia were seen to be adversely affected by the loss of K7 and western blot and immunofluorescence microscopy analysis revealed that the expression of K8, K18, K19 and K20 were not altered in the absence of K7, with the exception of the kidney where there was reduced K18 expression.

Pachyonychia congenita (PC) is a rare genodermatosis affecting the nails, skin, oral mucosae, larynx, hair, and teeth. Pathogenic mutations in keratins K6a or K16 are associated with the PC-1 phenotype whereas K6b and K17 mutations are associated with the PC-2 phenotype. Analysis of clinical, pathological, and genetic data from the literature and two research registries reveal that >97% of PC cases exhibit fingernail and toenail thickening, and painful plantar keratoderma. Prospective evaluation of 57 PC patients from 41 families revealed variable clinical findings: hyperhidrosis (79%), oral leukokeratosis (75%), follicular keratosis (65%), palmar keratoderma (60%), cutaneous cysts (35%), hoarseness or laryngeal involvement (16%), coarse or twisted hair (26%), early primary tooth loss (14%), and presence of natal or prenatal teeth (2%). Stratification of these data by keratin mutation confirmed the increased incidence of cyst formation and natal teeth among PC-2 patients, although cysts were more commonly seen in PC-1 than previously reported (25%–33%). Previously unreported clinical features of PC include development of painful oral and nipple lesions during breastfeeding, copious production of waxy material in ears, and inability to walk without an ambulatory aid (50%). Possible pathogenic mechanisms are discussed with respect to the clinicopathologic and genetic correlations observed.

Defolliculated (Dfl) is a spontaneous mouse mutant with a hair-loss phenotype that includes altered sebaceous gland differentiation, short hair shafts, aberrant catagen stage of the hair cycle, and eventual loss of the hair follicle. Recently a similar mutant, finnegan (Fgn), with an identical phenotype was discovered during a phenotypic screen for mutations induced by chemical mutagenesis. The gene underlying the phenotype of both finnegan and defolliculated has been mapped to chromosome 11 and here we show that both mice harbor mutations in gasdermin 3 (Gsdm3), a gene of unknown function. Gsdm3Dfl is a B2 insertion near the 3′ splice site of exon 7 and Gsdm3Fgn is a point mutation T278P. To investigate the role of the gasdermin gene family an antiserum was raised to a peptide highly homologous to all three mouse gasdermins and human gasdermin. Immunohistochemical analysis revealed that gasdermins are expressed specifically in cells at advanced stages of differentiation in the upper epidermis, the differentiating inner root sheath and hair shaft and in the most mature sebocytes of the sebaceous gland and preputial, meibomium, ceruminous gland, and anal glands. This expression pattern suggests a role for gasdermins in differentiation of the epidermis and its appendages.

Deep partial-thickness burns damage most of the dermis and can cause severe pain, scarring, and mortality if left untreated. This study serves to evaluate the effectiveness of crosslinked keratin–alginate composite sponges as dermal substitutes for deep partial-thickness burns. Crosslinked keratin–alginate sponges were tested for the ability to support human dermal fibroblasts in vitro and to support the closure and healing of partial-thickness burn wounds in Sus scrofa pigs. Keratin–alginate composite sponges supported the enhanced proliferation of human dermal fibroblasts compared to alginate-only sponges and exhibited decreased contraction in vitro when compared to keratin only sponges. As dermal substitutes in vivo, the sponges supported the expression of keratin 14, alpha-smooth muscle actin, and collagen IV within wound sites, comparable to collagen sponges. Keratin–alginate composite sponges supported the regeneration of basement membranes in the wounds more than in collagen-treated wounds and non-grafted controls, suggesting the subsequent development of pathological scar tissues may be minimized. Results from this study indicate that crosslinked keratin–alginate sponges are suitable alternative dermal substitutes for clinical applications in wound healing and skin regeneration.

Keratins are intermediate filament proteins whose expression in epithelial tissues is closely linked to their differentiated state. The greatest complexity of this expression is seen in the epidermis and associated structures. The critical basal (proliferative) cell layer expresses the major keratin pair, K5 and K14, but it also expresses an additional type I keratin, K15, about which far less is known. We have compared the expression of K15 with K14 in normal, pathological, and tissue culture contexts; distinct differences in their expression patterns have been observed that imply different regulation and function for these two genes. K15 appears to be preferentially expressed in stable or slowly turning over basal cells. In steady-state epidermis, K15 is present in higher amounts in basal cells of thin skin but in lower amounts in the rapidly turning over thick plantar skin. Although remaining high in basal cell carcinomas (noninvasive) it is suppressed in squamous cell carcinomas (which frequently metastasize). Wounding-stimulated epidermis loses K15 expression, whereas K14 is unchanged. In cultured keratinocytes, K15 levels are suppressed until the culture stratifies, whereas K14 is constitutively expressed throughout. Therefore, unlike K14, which appears to be a fundamental component of all keratinocytes, K15 expression appears to be more tightly coupled to a mature basal keratinocyte phenotype.

Defolliculated is a novel spontaneous mouse mutation that maps to chromosome 11 close to the type I keratin locus. Histology shows abnormal differentiation of the sebaceous gland, with the sebocytes producing little or no sebum and undergoing abnormal cornification. The hair follicles fail to regress during catagen leading to abnormally long follicles. In contrast the hair shafts are shorter than normal, suggesting altered differentiation or proliferation of matrix cells during anagen. The shafts emerge from the follicle with cornified material still attached. The dermis contains increased numbers of immune cells, including T cells (CD4-positive), macrophages, and mast cells, at all time points examined. Complete elimination of all pelage and tail follicles occurs after two to three hair cycles, apparently by necrosis. Defolliculated may be a useful model for determining further functions of the sebaceous gland, and for understanding the regulation of catagen and hair follicle immunology.

The development of gustatory papillae in mammalian embryos requires the coordination of a series of morphological events, such as proliferation, differentiation and innervation. In mice, the circumvallate papilla (CVP) is a specialized structure that develops in a characteristic spatial and temporal pattern in the posterior region of the tongue dorsal surface. The distinct expression patterns of Shh and Ptc, which play important roles in the development of other epithelial appendages, have been localized in the trench wall that gives rise to von Ebner's gland (VEG). To define the cellular mechanisms responsible for morphogenesis and differentiation during early development of CVP and VEG, the localization patterns of keratins (cytokeratins) K7, K8, K18, K19, K14 and connexin-43, which are dependent on Shh expression in other developmental systems, have been examined in detail. The distinct localization of keratins K7, K8, K18, K19, K14 and connexin-43 in the epithelium giving rise to the CVP and VEG suggests that cytodifferentiation is established prior to morphological changes. Interestingly, the localization of proliferating cell nuclear antigen, a marker for cell proliferation, is similar to that of Shh. An understanding of the regulatory roles of cell-cell interactions and signalling molecules in orchestrating a mutual network will bring us nearer to defining the molecular and cellular mechanisms underlying morphogenesis in mammalian taste bud development.