Alterações em adrenais de cães relacionadas à morte súbita ou agônica: análise morfométrica, histopatológica, imunoistoquímica e correlação com os níveis de adrenalina e noradrenalina na medula adrenal

A necropsia é essencial para a identificação da causa de morte e dos processos que culminaram no óbito do animal. O presente estudo visou à pesquisa da real ocorrência de morte súbita e inesperada em cães submetidos à necropsia, e à determinação da discrepância entre as suspeitas dos proprietários em relação ao estado de saúde prévio e à causa de morte de seus cães, quando comparadas às conclusões necroscópicas. Este trabalho também focou nas alterações morfológicas e funcionais nas glândulas adrenais de cães necropsiados, a fim de se estudar a aplicação de possíveis marcadores da resposta adrenal ao estresse sofrido pelo animal na iminência do óbito. Foram utilizados os dados de 82 cães necropsiados na FMVZ-USP para análise da ocorrência real de morte súbita nestes animais. As alterações morfológicas nas adrenais de 46 cães necropsiados foram avaliadas através de análises morfométricas e histopatológicas. Também foram avaliados os índices de proliferação e apoptose nas células do córtex adrenal em relação à causa de morte do animal, através da marcação imunoistoquímica para o antígeno nuclear de proliferação celular (PCNA) e para BAX e Bcl-2, proteínas envolvidas na regulação da apoptose. A análise das alterações funcionais sofridas pelas adrenais focou na quantificação das concentrações das catecolaminas adrenalina e noradrenalina na medula adrenal dos cães por cromatografia líquida de alta eficiência com detecção eletroquímica (CLAE-DE). Dentre os resultados encontrados, a suspeita do proprietário de que seu cão sofreu uma morte súbita e inesperada é muito maior do que a real ocorrência deste tipo de morte em cães, sendo o óbito por decorrência de complicações de doenças muito mais frequente. As características morfométricas das adrenais dos cães apresentaram maior influência pelo peso corpóreo do animal e pela presença ou ausência de hiperplasia cortical do que pela associação com doenças crônicas ou condições agudas. Cães que vieram a óbito em decorrência de complicações de doenças crônicas exibiram fibrose em região corticomedular e focos de infiltrado inflamatório, ausentes nos animais com morte súbita ou doenças agudas, além de maior ocorrência de hiperplasia adrenocortical. Cães que sofriam de alterações cardíacas crônicas apresentaram alterações histopatológicas significativas mais marcantes em suas adrenais, como necrose, fibrose e depleção vacuolar cortical. Por outro lado, a congestão severa nas adrenais foi um achado mais frequente nos animais previamente saudáveis que sofreram morte súbita ou que vieram a óbito por doenças agudas. A avaliação dos índices de proliferação celular e apoptose no córtex das adrenais através da marcação imunoistoquímica para PCNA e BAX e Bcl-2, respectivamente, não apresentou potencial relevante para o estudo dos efeitos do estresse por doenças crônicas sobre as adrenais de cães. As concentrações de adrenalina e noradrenalina na medula adrenal se mostraram muito maiores em cães machos quando comparados às fêmeas. Os achados deste estudo podem auxiliar nas conclusões da necropsia, sendo especialmente relevantes em casos médico-legais, nos quais todos os achados possíveis devem ser relatados e analisados a fim de se prover um diagnóstico preciso, seguro e incontroverso

Otimização dos valores de referência da 17OH-progesterona neonatal de acordo com o peso ao nascimento no programa de triagem neonatal da APAE DE SÃO PAULO

Introdução: A Hiperplasia Adrenal Congênita por deficiência da 21-hidroxilase (HAC) é uma doença com mortalidade neonatal elevada sendo elegível para programas públicos de Triagem Neonatal (TN). A HAC é causada por mutações no gene CYP21A2, as quais acarretam diferentes comprometimentos da atividade enzimática e resultam em espectro amplo de manifestações clínicas. Apesar da eficiência da TN para diagnosticar os casos graves, a taxa elevada de resultados falso-positivos (RFP), principalmente relacionados à prematuridade, é um dos maiores problemas. Porém, resultados falso-negativos também podem ocorrer em coletas antes de 24 horas de vida. No Brasil, a coleta da amostra neonatal difere entre os municípios, podendo ser no terceiro dia de vida como após. Objetivo: Avaliar se os valores da 17OH-progesterona neonatal (N17OHP) das coletas no terceiro dia de vida diferem significativamente das coletas a partir do quarto dia. Determinar qual percentil (99,5 ou 99,8) pode ser utilizado como valor de corte para a N17OHP, de acordo com o peso ao nascimento e tempo de vida na coleta, a fim de que proporcione taxa menor de RFP. Métodos: Foi avaliada, retrospectivamente, a N17OHP de 271.810 recém-nascidos (Rns) de acordo com o tempo de vida na coleta (G1: 48 - = 72h) e peso ao nascimento (P1: <= 1.500g, P2: 1.501-2.000g, P3: 2.001-2.500g e P4: >= 2.500g), pelo método imunofluorimétrico. Testes com resultados alterados foram confirmados no soro por Espectrometria de Massas em Tandem - LC-MS/MS. Rns afetados e/ou assintomáticos e com valores persistentemente elevados de 17OHP sérica foram submetidos ao estudo molécular, sequenciamento do gene CYP21A2. Resultados: os valores da N17OHP no grupo G1 foram significativamente menores do que em G2 em todos os grupos de peso (p < 0.001). A taxa de RFP em G1 e G2 foi de 0,2% para o percentil 99,8 e de 0,5% para o percentil 99,5 em ambos os grupos. O percentil 99,8 da N17OHP foi o melhor valor de corte para distinguir os Rns não afetados dos afetados, cujos valores são: G1 (P1: 120; P2: 71; P3: 39 e P4: 20 ng /mL) e em G2 (P1: 173; P2: 90; P3: 66 e P4: 25 ng/mL). Vinte e seis Rns do grupo G1 apresentaram a forma perdedora de sal (PS) (13H e 13M), nestes a N17OHP variou de 31 a 524 ng/mL e vinte Rns no grupo G2 (8H e 12M), nestes a N17OHP variou de 53 a 736 ng/mL. Para ambos os grupos foram encontrados três Rns com a forma virilizante simples (1H e 2M) e os valores da N17OHP variaram de 36 a 51 ng/mL. Resultados falso-negativos não foram relatados. O valor preditivo positivo (VPP) no teste do papel filtro foi de 5,6% e 14,1% nos grupos G1 e G2, respectivamente, ao se utilizar o percentil 99,8, e de 2,3% e 7% nos grupos G1 e G2 ao se utilizar o percentil 99,5. Dentre os casos com TN alterada (RFP), 29 deles também apresentaram 17OHP sérica elevada quando dosada por LC-MS/MS. Os casos assintomáticos foram acompanhados até normalização da 17OHP sérica e/ou submetidos ao estudo molecular, que identificou dois Rns com genótipo que prediz a forma não clássica. Conclusão: a melhor estratégia para otimização do diagnóstico da HAC na triagem neonatal é se padronizar valores de corte da N17OHP em dois grupos de acordo com o tempo de vida na coleta (antes e depois de 72 horas), subdivididos em quatro grupos de peso. A utilização dos valores de corte do percentil 99,8 se mantém eficaz no diagnóstico da HAC-21OH na triagem neonatal, reduzindo de forma significativa a taxa de RFP, sem perda do diagnóstico da forma PS

Hiperaldosteronismo primário

Trabalho Final do Curso de Mestrado Integrado em Medicina, Faculdade de Medicina, Universidade de Lisboa, 2014

Adenocarcinoma da próstata incidental : um estudo retrospectivo

Trabalho Final do Curso de Mestrado Integrado em Medicina, Faculdade de Medicina, Universidade de Lisboa, 2014

Avaliação da perfusão esplénica em modelo de hemorragia de suíno, após reperfusão com duas soluções fisiológicas distintas

O baço tem importantes funções hematopoiéticas e imunológicas, desempenhando um papel crucial na reposição da hipovolemia e de volume sanguíneo, em situações de hemorragia aguda. A administração de soluções fisiológicas tem grande importância na correção do volume circulante, evitando as complicações de hipovolemia. Este trabalho tem como objetivo avaliar as alterações provocadas no baço, após grave hemorragia dos suínos e reperfusão, utilizando duas soluções fisiológicas distintas, um cristaloide - solução de ringer lactato e um coloide - solução de hidroxietilamido. As lesões histopatológicas encontradas no baço foram congestão, hiperplasia da polpa branca, a notoriedade dos elipsoides e o infiltrado inflamatório, razão pela qual, se procedeu à sua avaliação semi-quantitativa. Relativamente à hiperplasia da polpa branca, foram encontradas diferenças estatisticamente significativas entre o grupo Ringer Lactato e o grupo Hidroxietilamido, verificando-se o aumento da hiperplasia da polpa branca no grupo Ringer Lactato. Quanto à área dos elipsoides, apenas um suíno em cada grupo registava grau 1. Houve uma preponderância do grau 2 no grupo de controlo (n = 5) e no grupo Ringer Lactato (n = 11), enquanto que no grupo Hidroxietilamido se registaram valores idênticos para os graus 2 e 3 (n = 5). A congestão ocorreu em todos os grupos, com predomínio do grau 2 (n = 7) nos grupos Ringer Lactato e Hidroxietilmido. Relativamente ao infiltrado inflamatório, no grupo de controlo predominou o grau 1 (n = 5) e registou-se a prevalência do grau 2 no grupo Ringer Lactato (n = 8) e no grupo Hidroxietilamido (n = 9). A área dos elipsoides variou nos diferentes grupos, não tendo revelado diferenças significativas entre os grupos. Foi observada congestão nos três grupos do estudo, não tendo sido, contudo, registadas diferenças significativas entre os grupos. Quanto ao infiltrado inflamatório, verificou-se que no grupo de controlo predominou o grau 1, enquanto que nos grupos Ringer Lactato e Hidroxietilamido prevaleceu o grau 2, o que se justifica pelo facto dos grupos Ringer Lactato e Hidroxietilamido terem sido submetidos a uma hemorragia. Foi assim possível concluir que a reperfusão volémica com Hidroxietilamido 130/0.4 pode reduzir a hiperreatividade esplénica, quando comparado com o Ringer Lactato, após hemorragia aguda. Verificamos que os elipsoides não sofrem qualquer afetação em situações de alterações hemodinâmicos. Atualizamos um sistema de classificação para avaliação de congestão esplénica, usando o modelo suíno. Aferimos que as situações causadoras de alterações hemodinâmicas ou da perfusão tecidual provocam aumento do infiltrado inflamatório.

Recent insights into the mucosal reactions associated with Giardia lamblia infections.

Giardia lamblia is an intestinal protozoan parasite infecting humans and various other mammalian hosts. The most important clinical signs of giardiasis are diarrhoea and malabsorption. Giardia lamblia is able to undergo continuous antigenic variation of its major surface antigen, named VSP (variant surface protein). While intestinal antibodies, and more specifically anti-VSP IgA antibodies, were proven to be involved in modulating antigenic variation of the parasite the participation of the local antibody response in control of the parasite infection is still controversial. Conversely, previous studies based on experimental infections in mice showed that cellular immune mechanisms are essential for elimination of the parasite from its intestinal habitat. Furthermore, recent data indicated that inflammatory mast cells have a potential to directly, or indirectly, interfere in duodenal growth of G. lamblia trophozoites. However, this finding was challenged by other reports, which did not find a correlation between intestinal inflammation and resistance to infection. Since intestinal infiltration of inflammatory cells and/or CD8+T-cells were demonstrated to coincide with villus-shortening and crypt hyperplasia immunological reactions were considered to be a potential factor of pathogenesis in giardiasis. The contribution of physiological factors to pathogenesis was essentially assessed in vitro by co-cultivation of G. lamblia trophozoites with epithelial cell lines. By using this in vitro model, molecular (through surface lectins) and mechanical (through ventral disk) adhesion of trophozoites to the epithelium was shown to be crucial for increased epithelial permeability. This phenomenon as well as other Giardia-induced intestinal abnormalities such as loss of intestinal brush border surface area, villus flattening, inhibition of disaccharidase activities, and eventually also overgrowth of the enteric bacterial flora seem to be involved in the pathophysiology of giardiasis. However, it remains to be elucidated whether at least part of these pathological effects are causatively linked to the clinical manifestation of the disease.

Assessment of foot health and animal welfare: clinical findings in 229 dairy Mediterranean Buffaloes (Bubalus bubalis) affected by foot disorders.

BACKGROUND Lameness represents the third most important health-related cause of economic loss in the dairy industry after fertility and mastitis. Although, dairy Mediterranean Buffaloes (MB) and dairy cows share similar breeding systems predisposing to similar herd problems, published studies exploring its relevance and role in these ruminants are still rare and incomplete. The aims of this study were to describe the clinical findings of foot disorders (FDs) in dairy MB and their influence on animal welfare, determined by assessment of locomotion score (LS), body condition score (BCS) and cleanliness score (CS). RESULTS Of 1297 multiparous MB submitted to routine trimming procedures, 229 buffaloes showed at least one FD. The prevalence of buffaloes affected by FDs was 17.7 %, while motility and lameness indexes were 84.1 % (1091/1297) and 15.9 % (206/1297), respectively. Overgrowth was present in 17.0 % (220/1297), corkscrew claw in 15.8 % (205/1297), interdigital phlegmon in 0.9 % (12/1297), white line abscess in 0.8 % (11/1297), digital dermatitis in 0.1 % (1/1297) and interdigital hyperplasia in 0.1 % (1/1297). Simultaneous presence of FDs was recorded in 17.0 % of MB (221/1297): overgrowth and corkscrew claw occurred together in 15.8 % of cases (205/1297), overgrowth and interdigital phlegmon in 0.3 % (4/1297), overgrowth and white line abscess in 0.8 % (11/1297), digital dermatitis and interdigital hyperplasia in 0.1 % (1/1297). The presence of FDs was always associated with lameness (LS > 2), except from 23 MB with simultaneous overgrowth and interdigital phlegmon occurrence. The majority of MB within the under-conditioned group (95.5 %, 43/45) and all those with CS > 2 (122/122) had a locomotion score above the threshold of normality (LS > 2). Furthermore, foot diseases such as interdigital hyperplasia, white line abscess and digital dermatitis or interdigital hyperplasia seemed to occur more frequently associated with decreased BCS and increased CS scores. CONCLUSIONS This study describes for the first time the involvement of white line disease, interdigital phlegmona, digital dermatitis and interdigital hyperplasia in foot disorders of dairy Mediterranean buffalo and shows their association with an impairment of animal welfare.

The renin-angiotensin system and male reproduction: new functions for old hormones

The blood-borne renin-angiotensin system (RAS) is known best for its role in the maintenance of blood pressure and electrolyte and fluid homeostasis. However, numerous tissues show intrinsic angiotensin-generating systems that cater for specific local needs through actions that add to, or differ from, the circulating RAS. The male reproductive system has several sites of intrinsic RAS activity. Recent focus on the epididymis, by our laboratories and by others, has contributed important details about the local RAS in this tissue. The RAS components have been localized morphologically and topographically; they have been shown to be responsive to androgens and to hypoxia; and angiotensin has been shown to influence tubular, and consequently, fluid secretion. Components of the RAS have also been found in the testis, vas deferens, prostate and semen. Angiotensin II receptors, type 1 and, to a lesser extent, type 2 are widespread, and angiotensin IV receptors have been localized in the prostate. The roles of the RAS in local processes at these sites are still uncertain and have yet to be fully elucidated, although there is evidence for involvement in tubular contractility, spermatogenesis, sperm maturation, capacitation, acrosomal exocytosis and fertilization. Notwithstanding this evidence for the involvement of the RAS in various important aspects of male reproduction, there has so far been a lack of clinical evidence, demonstrable by changes in fertility, for a crucial role of the RAS in male reproduction. However, it is clear that there are several potential targets for manipulating the activity of the male reproductive system by interfering with the locally generated angiotensin systems.

Histological analysis of gallbladder diseases in relation to opisthorchiasis in endemic areas of Thailand

Chronic gallbladder disease frequently accompanies infection with the liver fluke, Opisthorchis viverrini, in Northeast Thailand. However, the pathology and pathogenesis of the gallbladder disease have not been described. Accordingly, gallbladder specimens from 187 consecutive patients who had undergone cholecystectomy at a referral hospital in an endemic area in Thailand were histologically characterized in relation to O. viverrini infection. The infection was assessed by the presence of parasite eggs in the bile and/or antibody response to the liver fluke. The average level of parasite-specific IgG was significantly higher in patients with Opisthorchis eggs in the bile than those without (P < 0.001). The main histopathologic features of the gallbladder included inflammation, mucosal atrophy/or hyperplasia, goblet cell metaplasia, mucous gland hyperplasia, Rokitansky-Aschoff sinus formation, dysplasia and fibrosis. The fibrosis was strongly associated with elevated levels of Opisthorchis-specific antibody (P < 0.001) but not with the presence of parasite eggs. Other pathologic features did not vary in frequency or severity with parasitological status. Our results show that severe fibrosis of the gallbladder is a more common histologic feature of cholecystitis among those with O. viverrini infection compared to those without infection. The close relationship between parasite-specific IgG and severe fibrosis suggests that specific immune response to the parasite play an important role in the pathogenesis of the fibrotic change. (C) 2003 Elsevier B.V. All rights reserved.

Conditional inactivation of the Men1 gene leads to pancreatic and pituitary tumorigenesis but does not affect normal development of these tissues

Mutations of the MEN1 gene, encoding the tumor suppressor menin, predispose individuals to the cancer syndrome multiple endocrine neoplasia type 1, characterized by the development of tumors of the endocrine pancreas and anterior pituitary and parathyroid glands. We have targeted the murine Men1 gene by using Cre recombinase-loxP technology to develop both total and tissue-specific knockouts of the gene. Conditional homozygous inactivation of the Men1 gene in the pituitary gland and endocrine pancreas bypasses the embryonic lethality associated with a constitutional Men1(-/-) genotype and leads to beta-cell hyperplasia in less than 4 months and insulinomas and prolactinomas starting at 9 months. The pituitary gland and pancreas develop normally in the conditional absence of menin, but loss of this transcriptional cofactor is sufficient to cause beta-cell hyperplasia in some islets; however, such loss is not sufficient to initiate pituitary gland tumorigenesis, suggesting that additional genetic events are necessary for the latter.

Emerging roles of urotensin-II in cardiovascular disease

Urotensin-II (UII) is a highly potent endogenous peptide within the cardiovascular system. Through stimulation of Galphaq-coupled UT receptors, UII mediates contraction of vascular smooth muscle and endothelial-dependent vasorelaxation, and positive inotropy in human right atrium and ventricle. A pathogenic role of the UT receptor system is emerging in cardiovascular disease states, with evidence for upregulation of the UT receptor system in patients with congestive heart failure (CHF), pulmonary hypertension, cirrhosis and portal hypertension, and chronic renal failure. In vitro and in vivo studies show that under pathophysiological conditions, UII might contribute to cardiomyocyte hypertrophy, extracellular matrix production, enhanced vasoconstriction, vascular smooth muscle cell hyperplasia, and endothelial cell hyper-permeability. Single nucleotide polymorphisms of the UII gene may also impart a genetic predisposition of patients to diabetes. Therefore, the UT receptor system is a potential therapeutic target in the treatment of cardiac, pulmonary, and renal diseases. UT receptor antagonists are currently being developed to prevent and/or reverse the effects of over-activated UT receptors by the endogenous ligand. This review describes UII peptide and converting enzymes, and UT receptors in the cardiovascular system, focusing on pathophysiological roles of UII in the heart and blood vessels. (C) 2004 Elsevier Inc. All rights reserved,

Primary aldosteronism - careful investigation is essential and rewarding

Once considered rare, primary aldosteronism (PAL) is now regarded as the commonest potentially curable and specifically treatable form of hypertension. At Greenslopes Hospital Hypertension Unit (GHHU), the decision in 1991 to screen all (and not just hypokalemic or resistant) hypertensives by aldosterone/renin ratio (ARR) testing led to a 10-fold increase in detection rate of PAL and four-fold increase in removal rate of aldosterone-producing adenomas (APAs). The GHHU/Princess Alexandra Hospital Hypertension Unit PAL series stands at 977 patients and 250 APAs removed with hypertension cured in 50-60% (remainder improved). Reliable detection requires that interfering medications are withdrawn (or their effects considered) before ARR measurement, and reliable methods (such as fludrocortisone suppression testing) to confirm PAL. Adrenal venous sampling is the only dependable way to differentiate APA from bilateral adrenal hyperplasia. Genetic testing has facilitated detection of alucocorticoid-remediable, familial PAL. Identification of mutations causing the more common familial variety described by GHHU in 1991 should further aid in detection of PAL. (C) 2003 Elsevier Ireland Ltd. All rights reserved.

Biology of the leech Actinobdella inequiannulata Moore, 1901 (Annelida: Hirudinea: Rhynchobdellida: Glossiphoniidae), parasitic on the white sucker, Catostomus commersoni Lacepede, 1803, and the longnose sucker, Catostomus catostomus Forster, 1773, in Algonquin Provincial Park, Ontario, Canada

Actinobdella inequiannulata was found on the white sucker. Catostomus commersoni, and less frequently on the longnose sucker, Catostomus catostomus, in Algonquin Provincial Park, Ontario, Canada. Catostomus commersoni parasitized with Act. inequiannulata was collected from July to October 1973 and May to October 1974. In May and October, less than 3% of the fish carried leeches. In July, 80% of the fish were parasitized with an average of 1.5 leeches/fish. Observations on leech weight suggest that young leeches attach to fish from May to September, some mature in July, and a second generation of leeches reparasitize the fish in August and September. The mean size of leeches on suckers increased from May until July, after which the size remained relatively constant. Leeches produced characteristic lesions on the opercula of suckers. Fully developed lesions on fish opercula produced by aggregated leeches had varying amounts of central erosion, extravasation, dermal and epidermal hyperplasia, and necrosis.

Targeted delivery of heparin and LMWH using a fibrin antibody prevents restenosis

This study investigates a stent-less local delivery system for anti-restenotic agents utilizing antibodies to cross-linked fibrin (XLF). Heparin and low molecular weight heparin (LMWH) were conjugated to an antibody to cross-linked fibrin D-dinner (1D2). Rabbit right carotid arteries were injured with a balloon catheter, then the animals were given a bolus injection of 40 mug/k,g 1D2-heparin (26-70 mug/kg heparin) or 1D2-LMWH (29-80 mug/kg LMWH) conjugates or controls of saline (0.5 ml/kg), heparin (150 U/kg), LMWH (2 mg), or 1D2 (40 mug/kg), with or without a heparin bolus and sacrificed after 2 weeks (8 groups, n = 6/group). The injured artery of rabbits given 1D2-heparin or 1D2-LMWH conjugates had reduced neointimal development, with decreased luminal narrowing and positive remodelling compared with animals given control drugs. Animals given 1D2-heparin conjugate (with a heparin bolus) had three to five times more endothelial cells than the rabbits given saline or unconjugated heparin, while rabbits given 1D2-LMWH conjugate had up to 59% fewer neointimal cells than those given unconjugated drugs. There was little difference in extracellular matrix organization or composition. Thus cross-linked fibrin-antibodies can site-deliver anti-restenotic agents to injured areas of the artery wall where they influence wall remodelling and endothelial and neointimal cell number, reducing neointimal formation without systemic complications. Local delivery of anti-restenotic agents should minimise systemic effects, bleeding complications and potentially the cost of treatment due to a single, lower dose. (C) 2004 Elsevier Ireland Ltd. All rights reserved.

An in vivo comparative study of sonic, desert and Indian hedgehog reveals that hedgehog pathway activity regulates epidermal stem cell homeostasis

Despite the well-characterised role of sonic hedgehog (Shh) in promoting interfollicular basal cell proliferation and hair follicle downgrowth, the role of hedgehog signalling during epidermal stem cell fate remains largely uncharacterised. In order to determine whether the three vertebrate hedgehog molecules play a role in regulating epidermal renewal we overexpressed sonic (Shh), desert (Dhh) and Indian (Ihh) hedgehog in the basal cells of mouse skin under the control of the human keratin 14 promoter. We observed no overt epidermal morphogenesis phenotype in response to Ihh overexpression, however Dhh overexpression resulted in a range of embryonic and adult skin manifestations indistinguishable from Shh overexpression. Two distinct novel phenotypes were observed amongst Shh and Dhh transgenics, one exhibiting epidermal progenitor cell hyperplasia with the other displaying a complete loss of epidermal tissue renewal indicating deregulation of stem cell activity. These data suggest that correct temporal regulation of hedgehog activity is a key factor in ensuring epidermal stem cell maintenance. In addition, we observed Shh and Dhh transgenic skin from both phenotypes developed lesions reminiscent of human basal cell carcinoma (BCC), indicating that BCCs can be generated despite the loss of much of the proliferative (basal) compartment. These data suggest the intriguing possibility that BCC can arise outside the stem cell population. Thus the elucidation of Shh (and Dhh) target gene activation in the skin will likely identify those genes responsible for increasing the proliferative potential of epidermal basal cells and the mechanisms involved in regulating epidermal stem cell fate.