Involvement Of Several Signaling Pathways Research Articles

Recent Insights into Hippocampal Dysfunction and Neuroplasticity in Sleep Disorders: An Update from Preclinical Studies.

Sleep disorders are prevalent neurological conditions linked to neurocognitive impairments. Understanding the neuroplasticity changes in the hippocampus, which plays a central role in regulating neurocognitive function, is crucial in the context of sleep disorders. However, research on neurodegenerative disorders and the influence of sleep disorders on hippocampal neuroplasticity remains largely unclear. Therefore, this review aims to highlight the latest advancements regarding hippocampal neuroplasticity and functional changes during sleep disorders, drawing insights from clinical and preclinical research involving sleep-deprived animal models. These articles were gathered through comprehensive literature searches across databases, including Google Scholar, PubMed, Web of Science, and Scopus. Maternal sleep deprivation has been observed to cause neurocognitive impairment in offspring, along with changes in protein expression levels associated with neuroplasticity. Similarly, sleep deprivation in adult mice has been shown to affect several cognitive functions and fear extinction without influencing the acquisition of fear conditioning. While mechanistic research on neurocognitive dysfunction induced by maternal and adult sleep deprivation is limited, it suggests the involvement of several signaling pathways, including neurotrophic factors, synaptic proteins, and inflammatory molecules, which are triggered by sleep deprivation. Further studies are needed to clarify the mechanistic pathways underlying hippocampal dysfunction and synaptic alterations associated with sleep disturbances.

Role of Vacha as Neurological and Metabolic Disorders: Evidence from Ethnopharmacology, Phytochemistry, Pharmacology and Preclinical Study

Vacha (Acorus calamus Linn (Acoraceae)) is a traditional Indian medicinal herb, which is practiced to treat a wide range of health ailments, including neurological, gastrointestinal, respiratory, metabolic, kidney, and liver disorders. The purpose of this paper is to provide a comprehensive up-to-date report on its ethnomedicinal use, phytochemistry, and pharmacotherapeutic potential, while identifying potential areas for further research. To date, 145 constituents have been isolated from this herb and identified, including phenylpropanoids, sesquiterpenoids, and monoterpenes. Compelling evidence is suggestive of the biopotential of its various extracts and active constituents in several metabolic and neurological disorders, such as anticonvulsant, antidepressant, antihypertensive, anti-inflammatory, immunomodulatory, neuroprotective, cardioprotective, and anti-obesity effects. The present extensive study is expected to provide insights into the involvement of several signaling pathways and oxidative mechanisms that can mitigate oxidative stress, and other indirect mechanisms modulated by active biomolecules of A. calamus to improve neurological and metabolic disorders.
 Keywords: Acorus calamus, Acoraceae, Phytochemistry, Pharmacotherapeutic potential

FGF-mediated establishment of left-right asymmetry requires Rab7 function in the dorsal mesoderm in Xenopus.

Gastrulation denotes a very important developmental process, which includes significant structural tissue rearrangements and patterning events that shape the emerging vertebrate organism. At the end of gastrulation, the three body axes are spatially defined while the left-right axis still lacks any molecular or morphological polarity. In most vertebrates, this is established during neurulation by a symmetry breaking LR organizer. However, this mesoderm-derived structure depends on proper induction and specification of the mesoderm, which in turn requires involvement of several signaling pathways. Endocytosis and the endosomal machinery offer manifold platforms for intracellular pathway regulation, especially late endosomes claim increasing attention. The late endosomal regulator Rab7 has been linked to mesoderm specification during gastrulation. Distinct axial defects due to compromised dorsal mesoderm development in rab7-deficient Xenopus embryos suggested a requirement of Rab7 for FGF-dependent mesoderm patterning and LR asymmetry. Here we specifically addressed such a role of Rab7, demonstrating a functional requirement for LR organizer development and symmetry breakage. Using different FGF/MAPK pathway components we show that Rab7 participates in dorsal mesoderm patterning. We suggest a hierarchical classification of Rab7 upstream of MAPK-dependent mesoderm specification, most probably at the level of the small GTPase Ras. Thus, this study affords an insight on how the Rab7-regulated endosomal machinery could participate in signal transduction to enable correct mesoderm specification and left-right asymmetry.

Differential Expression of Long Noncoding RNAs in Murine Myoblasts After Short Hairpin RNA-Mediated Dysferlin Silencing In Vitro: Microarray Profiling

Background Long noncoding RNAs (lncRNAs) are noncoding RNA transcripts greater than 200 nucleotides in length and are known to play a role in regulating the transcription of genes involved in vital cellular functions. We hypothesized the disease process in dysferlinopathy is linked to an aberrant expression of lncRNAs and messenger RNAs (mRNAs). Objective In this study, we compared the lncRNA and mRNA expression profiles between wild-type and dysferlin-deficient murine myoblasts (C2C12 cells). Methods LncRNA and mRNA expression profiling were performed using a microarray. Several lncRNAs with differential expression were validated using quantitative real-time polymerase chain reaction. Gene Ontology (GO) analysis was performed to understand the functional role of the differentially expressed mRNAs. Further bioinformatics analysis was used to explore the potential function, lncRNA-mRNA correlation, and potential targets of the differentially expressed lncRNAs. Results We found 3195 lncRNAs and 1966 mRNAs that were differentially expressed. The chromosomal distribution of the differentially expressed lncRNAs and mRNAs was unequal, with chromosome 2 having the highest number of lncRNAs and chromosome 7 having the highest number of mRNAs that were differentially expressed. Pathway analysis of the differentially expressed genes indicated the involvement of several signaling pathways including PI3K-Akt, Hippo, and pathways regulating the pluripotency of stem cells. The differentially expressed genes were also enriched for the GO terms, developmental process and muscle system process. Network analysis identified 8 statistically significant (P<.05) network objects from the upregulated lncRNAs and 3 statistically significant network objects from the downregulated lncRNAs. Conclusions Our results thus far imply that dysferlinopathy is associated with an aberrant expression of multiple lncRNAs, many of which may have a specific function in the disease process. GO terms and network analysis suggest a muscle-specific role for these lncRNAs. To elucidate the specific roles of these abnormally expressed noncoding RNAs, further studies engineering their expression are required.

Abstract 13301: Microarray Reveals Differentially Expressed Long Non-coding Ribonucleic Acids In Dysferlinopathy

Introduction: Dysferlinopathy is a type of muscular dystrophy, a group of inherited degenerative muscle disorders characterized by progressive muscle weakness. It is caused by the deficiency of dysferlin, a type II transmembrane protein highly expressed in the skeletal muscle and the heart. Dysferlin interacts with several proteins and plays a crucial role in calcium dependent membrane repair in skeletal muscles. Long non-coding RNAs (lncRNAs) are non-coding RNA transcripts greater than 200 nucleotides that participate in regulating gene expression through multiple mechanisms. Hypothesis: We hypothesized the disease process in dysferlinopathy is linked to an aberrant expression of lncRNAs. Methods: LncRNA and mRNA expression profiling between the normal and dysferlin deficient murine myoblasts (C2C12 cells) were performed using a microarray (n=3). Several differentially expressed lncRNAs were validated using qRT-PCR. Tissue expression analysis was performed for selected lncRNAs across ten mice tissues. Further bioinformatics analysis was used to explore the potential function, lncRNA-mRNA correlation and potential targets of the differentially expressed lncRNAs. Results: We found 3470 lncRNAs and 2335 mRNAs that are differentially expressed by more than two fold. A set of 13 lncRNAs were selected based on their fold change, and were validated using qRT-PCR. Six out of the 13 lncRNAs tested were predominantly expressed in either myoblasts or skeletal muscle tissue. Pathway analysis of the differentially expressed genes indicated the involvement of several signaling pathways including PI3K-Akt, FoxO, Wnt, cAMP and Hippo. The differentially expressed genes were also enriched for the GO terms, developmental process and muscle system process. Conclusion: The results thus far imply that dysferlinopathy is associated with an aberrant expression of multiple lncRNAs many of which may have a specific function in the disease process. Identification of lncRNAs that are predominantly expressed in the skeletal muscle lineage suggests a muscle specific role for these lncRNAs. We are currently working on overexpressing selected lncRNAs in the normal and dysferlin deficient cells to understand their role in regulating key cellular functions.

Cholesterol-Lowering Drugs on Akt Signaling for Prevention of Tumorigenesis.

Cholesterol has been reported to be accumulated in cancer cells. The metabolic dysregulation of the cholesterol is associated with tumor development and progression. The cholesterol-lowering drugs have been found to be involved in the prevention and treatment of various cancers. Akt, a serine/threonine kinase, can modulate the role of several downstream proteins involved in cell proliferation, migration, invasion, metabolism, and apoptosis. Since its involvement in several signaling pathways, its dysregulation is commonly reported in several cancers. Thus, targeting Akt could be an effective approach for cancer prevention and therapy. Cholesterol-lowering drugs have been found to affect the expression of Akt, and its activation in the cancer cells and thus have shown anticancer activity in different type of cancers. These drugs act on various signaling pathways such as PTEN/Akt, PI3k/Akt, Akt/NF-κB, Akt/FOXO1, Akt/mTOR, etc., which will be discussed in this article. This review article will discuss the significance of cholesterol in cancer cells, cholesterol-lowering drugs, the role of Akt in cancer cells, and the effects of cholesterol-lowering drugs on Akt in the prevention of therapy resistance and metastasis.

Targeting TJP1 attenuates cell-cell aggregation and modulates chemosensitivity against doxorubicin in leiomyosarcoma.

Tight junction protein 1 (TJP1) is a membrane-associated cytosolic protein important for cell-cell communication in intercellular barriers in epithelial and non-epithelial cells. Here, we explored the functional involvement of TJP1 in non-epithelial tumors such as soft tissue sarcoma, especially in leiomyosarcoma (LMS). TJP1 expression in soft tissue sarcoma was analyzed in normal and tumor tissues as well as from public datasets such as the TCGA provisional dataset, in which TJP1 expression was compared with other subtypes such as undifferentiated sarcomas, and myxofibrosarcomas. SK-LMS-1 cell lines with reduced TJP1 expression showed attenuated anchorage-independent colony formation as well as reduced intercellular aggregation on non-coated culture plates compared with control as well as parental SK-LMS-1 cells. Transcriptome profiling following TJP1 knockdown in SK-LMS-1 cells suggested the involvement of several signaling pathways, including NF-κB pathway and growth factor receptor signaling. In addition, TJP1 downregulation induced enhanced response against anti-cancer agents, doxorubicin and gefitinib. Taken together, these results suggest that TJP1 contributes to sarcoma genesis and might be useful therapeutic target. KEY MESSAGES: • TJP1 expression at RNA level higher in tumor than in normal tissues of sarcoma. • Targeting TJP1 attenuates cell-cell aggregation and anchorage-independent growth. • Targeting TJP1 is beneficial in anti-cancer therapy in LMS.

Role of Vacha (Acorus calamus Linn.) in Neurological and Metabolic Disorders: Evidence from Ethnopharmacology, Phytochemistry, Pharmacology and Clinical Study.

Vacha (Acorus calamus Linn. (Acoraceae)) is a traditional Indian medicinal herb, which is practiced to treat a wide range of health ailments, including neurological, gastrointestinal, respiratory, metabolic, kidney, and liver disorders. The purpose of this paper is to provide a comprehensive up-to-date report on its ethnomedicinal use, phytochemistry, and pharmacotherapeutic potential, while identifying potential areas for further research. To date, 145 constituents have been isolated from this herb and identified, including phenylpropanoids, sesquiterpenoids, and monoterpenes. Compelling evidence is suggestive of the biopotential of its various extracts and active constituents in several metabolic and neurological disorders, such as anticonvulsant, antidepressant, antihypertensive, anti-inflammatory, immunomodulatory, neuroprotective, cardioprotective, and anti-obesity effects. The present extensive literature survey is expected to provide insights into the involvement of several signaling pathways and oxidative mechanisms that can mitigate oxidative stress, and other indirect mechanisms modulated by active biomolecules of A. calamus to improve neurological and metabolic disorders.

Inhibition of PARP activity does not affect the differentiation processes caused by retinoic acid in SH-SY5Y cells

Differentiation is a complex process by which cells become specialized in their physiological functions. As this process is followed by a decrease in proliferation ability, the induction of differentiation could be an ideal cancer treatment. We analyzed the effects of a common differentiation agent, retinoic acid, on neuroblastoma SH-SY5Y cells under the conditions of poly(ADP-ribose) polymerase (PARP) inhibition. Namely, PARP1 can be indirectly involved in processes of chromatin remodelling, so the aim was to investigate whether its inhibition can influence the process of differentiation. Cells differentiated after retinoic acid treatment into neural cells, with neurite outgrowth, proliferation arrest and induction of tissue plasminogen activator. PARP inhibition did not influence the process of differentiation. Analysis of gene expression revealed the involvement of several signaling pathways in RA-dependent differentiation. Beside TGFβ and Notch pathways, master transcription factors directing epithelial-mesenchymal transition were shown to also take part in the differentiation process.

CVD and Oxidative Stress.

Nowadays, it is known that oxidative stress plays at least two roles within the cell, the generation of cellular damage and the involvement in several signaling pathways in its balanced normal state. So far, a substantial amount of time and effort has been expended in the search for a clear link between cardiovascular disease (CVD) and the effects of oxidative stress. Here, we present an overview of the different sources and types of reactive oxygen species in CVD, highlight the relationship between CVD and oxidative stress and discuss the most prominent molecules that play an important role in CVD pathophysiology. Details are given regarding common pharmacological treatments used for cardiovascular distress and how some of them are acting upon ROS-related pathways and molecules. Novel therapies, recently proposed ROS biomarkers, as well as future challenges in the field are addressed. It is apparent that the search for a better understanding of how ROS are contributing to the pathophysiology of CVD is far from over, and new approaches and more suitable biomarkers are needed for the latter to be accomplished.

Application of resveratrol in diabetes: rationale, strategies and challenges.

The increasing prevalence, involvement of several signaling pathways, variable pathogenesis, progressive natural history and complications of type 2 diabetes emphasize an urgent need for a molecule with multiple actions. Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a polyphenolic antioxidant present in red wine gaining a worldwide interest because of its multi-target effect against diabetes and other life-threatening diseases. Improving insulin sensitivity, enhancing GLUT4 translocation, reducing oxidative stress, regulating carbohydrate metabolizing enzymes, activating SIRT1 and AMPK, and decreasing adipogenic genes are some promising mechanisms established until now for resveratrol. Apart from these, resveratrol attenuates the end organ damage and reduced diabetic complications. Resveratrol exerts its beneficial antidiabetic action as evidenced from the in vitro, preclinical and clinical studies. Considering all the benefits of resveratrol in diabetes, resveratrol based different nutraceutical products have been developed commercially to use in humans. However, this compound is still under investigation because of some limitations. Resveratrol can be taken in to account in the treatment of diabetes after overcoming all hurdles and difficulties. This article examines the basic scientific evidences, animal experiments, and human/clinical data supporting the antidiabetic action of resveratrol and describes the strategies and challenges to recommend resveratrol from preclinical to clinical use.

Modulation of urokinase plasminogen activator system by poly(ADP-ribose)polymerase-1 inhibition.

The urokinase plasminogen activator (uPA) system is a complex regulator of extracellular proteolysis which is involved in various physiological and pathological processes. The major components of this system are the serine protease uPA, two inhibitors PAI-1 and PAI-2, and the receptor uPAR. It has been previously shown by several groups that the uPA system has an important role in cancer progression and therefore its possible prognostic and therapeutic value has been evaluated. The aim of this study is to tackle the role of poly(ADP-ribosyl)ation in the induction of uPA activity in a glioblastoma cell line, A1235. This cell line is sensitive to alkylation damage and is a model for drug treatment. The components of the uPA system and the level of DNA damage were analyzed after alkylation agent treatment in combination with poly(ADP-ribose)polymerase-1 (PARP-1) inhibition. Here we show that the increase in uPA activity results from the net balance change between uPA and its inhibitor at mRNA level. Further, PARP-1 inhibition exerts its influence on uPA activity through DNA damage increase. Involvement of several signaling pathways, as well as cell specific regulation influencing the uPA system are discussed.

SOCS3 Deletion Promotes Optic Nerve Regeneration In Vivo

Axon regeneration failure accounts for permanent functional deficits following CNS injury in adult mammals. However, the underlying mechanisms remain elusive. In analyzing axon regeneration in different mutant mouse lines, we discovered that deletion of suppressor of cytokine signaling 3 (SOCS3) in adult retinal ganglion cells (RGCs) promotes robust regeneration of injured optic nerve axons. This regeneration-promoting effect is efficiently blocked in SOCS3-gp130 double-knockout mice, suggesting that SOCS3 deletion promotes axon regeneration via a gp130-dependent pathway. Consistently, a transient upregulation of ciliary neurotrophic factor (CNTF) was observed within the retina following optic nerve injury. Intravitreal application of CNTF further enhances axon regeneration from SOCS3-deleted RGCs. Together, our results suggest that compromised responsiveness to injury-induced growth factors in mature neurons contributes significantly to regeneration failure. Thus, developing strategies to modulate negative signaling regulators may be an efficient strategy of promoting axon regeneration after CNS injury.

Potential Involvement of Several Signaling Pathways in Initiation of the Chicken Acrosome Reaction1

Avian sperm biology has demonstrated specific features in preparation for fertilization. For example, capacitationlike processes and motility hyperactivation do not exist in the form described in mammals. The present study investigated the potential involvement of several signaling pathways, including protein kinase A (PKA), phosphatidylinositol 3 kinase (PIK3), mitogen-activated protein kinase 3/1 (MAPK3/1), and MAPK14 in the chicken acrosome reaction (AR). The presence in chicken spermatozoa of key proteins involved in these signaling pathways (i.e., cAMP-responsive element-binding protein [CREB], AKT, MAPK1, and MAPK14 and their respective phosphorylated forms) was detected using immunoblotting and localized by immunocytochemistry, mainly in the heads. The potential involvement of these pathways in the AR induced by inner perivitelline layer (IPVL) and Ca(2+) was then examined using specific inhibitors and phosphorylation status measurements. The effects of the specific inhibitors on motility were also measured. Phosphorylations of AKT, CREB, and MAPK1, but not MAPK14, were increased at the time of AR. Phosphorylation of AKT was increased in the presence of IPVL alone, whereas both IPVL and Ca(2+) were needed to increase CREB and MAPK1 phosphorylations. Inhibition of the three corresponding pathways blocked the increase in phosphorylation and significantly decreased AR. Inhibitions of the PKA and MAPK1 pathways also significantly decreased motility, whereas MAPK14 and PIK3 inhibition had no effect on motility. Our results suggest that the AR could be mediated by activation of the PKA, PIK3, and MAPK1 pathways through a sequential action involving, successively, PIK3 and then PKA and MAPK1 activations.

Stressing out the ER: a role of the unfolded protein response in prion-related disorders.

Transmissible Spongiform Encephalopathies are fatal and infectious neurodegenerative diseases characterized by extensive neuronal apoptosis and the accumulation of an abnormally folded form of the cellular prion protein (PrP), denoted PrP(SC). Compelling evidence suggests the involvement of several signaling pathways in prion pathogenesis, including proteasome dysfunction, alterations in the protein maturation pathways and the unfolded protein response. Recent reports indicate that endoplasmic reticulum stress due to the PrP misfolding may be a critical factor mediating neuronal dysfunction in prion diseases. These findings have applications for developing novel strategies for treatment and early diagnosis of transmissible spongiform encephalopathies and other neurodegenerative diseases.

IDENTIFICATION OF GENES DIFFERENTIALLY EXPRESSED IN A NOVEL MODEL OF ACUTE SEVERE NECROTIZING PANCREATITIS IN MICE

The outcome in necrotizing pancreatitis is depending on the development and intensity of the systemic inflammatory response syndrome (SIRS). The mechanisms involved in the occurrence of SIRS are only understood in part. Our aim was to identify differentially expressed genes by microarray analysis in organs affected from SIRS induced by acute pancreatitis and map these genes to known pathways. In 8 animals, severe necrotizing pancreatitis was induced by retrograde infusion of 5% sodium taurocholate into the common bile duct in mice leading to 60% lethality from acute pancreatitis within 24 hours. 5 animals were sham operated controls receiving saline infusion in the common bile duct. 8 hours after induction of acute pancreatitis the animals were sacrificed and total RNA was isolated from liver, spleen, lungs and intestine. RNAs were pooled and Cy3 as wells as Cy5 labeled cDNA was prepared from 40 μg of pooled total RNA. Hybridization of PIQOR immunology mouse sense microarrays was performed overnight. Online pathway analysis was performed by pathway explorer utilizing Biocarta and KEGG pathways. The number of differentially expressed genes in liver (400; 37.38%) and spleen (408; 38.13%) was higher than observed in small intestine (163; 15.24%) and lung (154; 14.39%), thus indicating the involvement of these organs in the systemic changes induced by acute pancreatitis. Expression of 11 (1.02%) identical genes were altered in all 4 tissues, 44 (4.11%) in 3 and 291 (27.20%) in 2 tissues. In liver and spleen, altered genes mapped significantly to 14 and 8 pathways respectively (p < 0.05) including TNFR signaling pathway and oxidative stress induced gene expression pathway. Pathway analysis of intestine and lung only revealed 3 and 4 pathways with significant alterations. Our data provides first evidence of the involvement of several signaling pathways related to severe necrotizing pancreatitis in mice and builds the foundation for several hypotheses for immunologic alterations induced by necrotizing pancreatitis.

The biology of a prostate cancer metastasis suppressor protein: Raf kinase inhibitor protein

Raf kinase inhibitor protein (RKIP) was originally identified as a protein that bound membrane phospholipids and was named phosphatidylethanolamine binding protein-2 (PEBP-2). RKIP was than identified as a protein that bound Raf and blocked its ability to phosphorylate MEK, thus earning its new name of RKIP. Subsequent to identification of its role in the Raf:MEK pathway, RKIP has been demonstrated to regulate several other signaling pathways including G-protein signaling and NF-kappaB signaling. Its involvement in several signaling pathways has engendered RKIP to contribute to several physiological processes including membrane biosynthesis, spermatogenesis, neural development, and apoptosis. RKIP is expressed in many tissues including brain, lung, and liver and thus, dysregulation of RKIP expression or function has potential to contribute to pathophysiology in these tissues. Loss of RKIP expression in prostate cancer cells confers a metastatic phenotype on them. Additionally, restoration of RKIP expression in a metastatic prostate cancer cell line does not effect primary tumor growth, but it does inhibit prostate cancer metastasis. These parameters identify RKIP as a metastasis suppressor gene. In this review, the biology and pathophysiology of RKIP is described.

The Global Transcriptional Response to Transient Cell Wall Damage in Saccharomyces cerevisiae and Its Regulation by the Cell Integrity Signaling Pathway

In the yeast Saccharomyces cerevisiae, environmental stress conditions that damage the cell wall lead to activation of the so-called "compensatory mechanism," aimed at preserving cell integrity through a remodeling of this extracellular matrix. Here we used DNA microarrays to investigate the molecular basis of this response to two agents that induce transient cell wall damage; namely Congo Red and Zymolyase. Treatment of the cells with these two agents elicited the up-regulation of 132 and 101 genes respectively, the main functional groups among them being involved in cell wall construction and metabolism. The main response does not occur until hours after exposure to the cell wall-perturbing agent. In some cases, this response was transient, but more sustained in others, especially in the case of the genes involved in cell wall remodeling. Clustering of these data together with those from the response to constitutive cell wall damage, revealed the existence of a cluster of co-regulated genes that was strongly induced under all conditions assayed. Those genes induced by cell wall damage showed an enrichment in DNA binding motifs for Rlm1p, Crz1p, SBF (Swi4p/Swi6p), Msn2p/Msn4p, Ste12p, and Tec1p transcription factors, suggesting a complex regulation of this response together with the possible involvement of several signaling pathways. With the exception of PHO89 and FKS2, none of the genes induced by Congo Red was up-regulated in a slt2 strain. Moreover, characterization of the transcriptional response to Congo Red in a rlm1 mutant strain revealed that only a few genes (i.e. PHO89, FKS2, YLR042C, and CHA1) were induced at least partially independently of the transcription factor Rlm1p, the rest being totally dependent on this transcription factor for their activation. Our findings consistently demonstrate that the cell integrity signaling pathway regulates the cell wall damage compensatory response, mainly through transcriptional activation mediated by Rlm1p.

Genetic pathways required for epidermal morphogenesis

The epidermis is composed of keratinocytes which undergo a highly reproducible terminal differentiation program resulting in the formation of a protective barrier, which is established during embryogenesis. Significant progress has recently been made in understanding the genetic pathways associated with the earliest event characteristic of epidermal morphogenesis, commitment to stratification. This process depends on the expression of p63, a transcription factor which is transcribed into isoforms that contain (TA) or lack (AN) a transactivation domain. In the absence of p63 expression, epithelia remain single-layered, while ectopic TAp63alpha expression in single-layered epithelia initiates stratification. Later events during epidermal morphogenesis require withdrawal from the cell cycle and commitment to terminal differentiation. Some of the genetic pathways underlying these events are beginning to be elucidated, however, the exact molecular events remain to be determined. In this review, we summarize the involvement of several signaling pathways in different stages of epidermal morphogenesis.