Medicine and Health Sciences Commons^™

A Comparative Analysis Of The Paris System And Institutional Reporting System For Urine Cytology In Upper Tract Urothelial Specimens, Kim Hookim, Md, James P. Casey, Md, Rossitza Draganova-Tacheva, Md, Marluce Bibbo, Md, Charalambos C. Solomides, Md

Department of Pathology, Anatomy, and Cell Biology Posters

The authors of this abstract have no conflicts of interest

Introduction

Cytology is integral in the assessment of urothelial cell carcinoma (UCC). However, upper urinary tract (UUT) specimens are cytologically challenging due to limited tissue and reactive atypia. At our institution UUT biopsies are processed as cell blocks (CB). We compared our institution’s reporting system (IRS) with the recently proposed Paris System for Reporting Urine Cytology (PRS) (Table 1) in UUT specimens and correlated the findings with CB and follow-up resections.

Calcium Uptake Hotspots In The Mitochondria Of Cardiac Muscle At The Interface With Dyadic Sr, Sergio De La Fuente, Celia Fernandez-Sanz, Caitlin Vail, Elorm J. Agra, Kira Holmstrom, Junhui Sun, Jyotsna Mishra, Toren Finkel, Elizabeth Murphy, Suresh K. Joseph, Shey-Shing Sheu, György Csordás

Department of Pathology, Anatomy, and Cell Biology Posters

Introduction

• Control of the mitochondrial ATP production by SR-derived Ca2+ signals includes local, nanodomain Ca2+ transfer from ryanodine receptors (RyR2) to the mitochondrial matrix (excitation-bioenergetics coupling).

• Ca2+ crosses the inner mitochondrial membrane (IMM) via the mtCU, a low-affinity Ca2+-activated Ca2+ channel complex.

• The surface area of cardiac IMM is extensively enhanced by cristae folding; however, mitoplast patch clamp studies showed mtCU current density the lowest amongst a range of tissues (Fieni 2012. Nat Commun).

Use Of Propensity Score Matching To Identify A Strong Association Between Strategic Concentration To Mitochondria-Sr Associations Of The Mitochondrial Ca2+ Uniporter: Ca2+ Uptake Hotspots In The Cardiac Mitochondria, Sergio De La Fuente, Caitlin Vail, Elorm J. Agra, Kira Holmstrom, Junhui Sun, Jyotsna Mishra, Toren Kinkel, Elizabeth Murphy, Suresh K. Joseph, Shey-Shing Shen, György Csordás

Department of Pathology, Anatomy, and Cell Biology Posters

Introduction:

• Control of the mitochondrial ATP production by SR-derived Ca²⁺ signals includes local, nanodomain Ca²⁺ transfer from ryanodine receptors (RyR2) to the mitochondrial matrix (excitation-bioenergetics coupling).
• Ca²⁺ crosses the inner mitochondrial membrane (IMM) via the mtCU, a low-affinity Ca²⁺-activated Ca²⁺ channel complex.
• The surface area of cardiac IMM is extensively enhanced by cristae folding; however, mitoplast patch clamp studies showed mtCU current density the lowest amongst a range of tissues (Fieni 2012. Nat Commun).

Gaining Competencies During Early Medical Training: Medical Students As Teaching Assistants In Dissection-Based Anatomy Course, Martin T. Brown, Bruce Fenderson, Guiyan Zhang

Department of Pathology, Anatomy, and Cell Biology Posters

Introduction and Objectives

• In 2002, ACGME identified six ACGME Core Competencies: patient care; medical knowledge; practice-based learning and improvement; interpersonal and communication skills; professionalism; and systems-based practice.
• AAMC recommended lists of similar competencies for the curricula of medical schools. Competency based curricula have been widely implemented in medical schools.
• Effective shifting in the graduate medical educational programs has been reported in various clinical specialties.
• There is a lack of reported efforts and development on competency training in early preclinical years of medical education.

Objectives:

• To explore methods for strengthening medical students’ competency training during preclinical undergraduate medical education.
• To measure …

In-Silico Identification Of Prognostically Inversely Correlated Mirnas And Mrnas (Pic’S) In Multiple Cancers, Chirayu Pankaj Goswami, Zi-Xuan Wang

Department of Pathology, Anatomy, and Cell Biology Posters

Despite numerous methods available to identify potential mRNA targets for miRNAs, prognostic relationship of these molecules in diseases like cancers where deregulation of gene expression is a major pathogenic factor, has not yet been emphasized. We performed in-silico identification of prognostically inversely correlated miRNA - mRNA pairs (PIC’s) in multiple cancers using expression data from The Cancer Genome Atlas. Partners in a PIC show inverse correlation of expression and opposite hazard implication. Using a three step approach, we identified a total of 1,253,443 PIC’s from 23 cancer types, several of which have previously been shown to have a predicted or …

Succinate Dehydrogenase Deficiency In Sporadic Pituitary Adenomas: A Potential Mechanism For Tumorigenesis, Edward Andrews, Md, Stacey K. Mardekian, Md, Markku Miettinen, Mark T. Curtis, Md

Department of Pathology, Anatomy, and Cell Biology Resident's Posters

In order to determine whether succinate dehydrogenase (SDH) deficiency plays a role in spor-adic, non-familial pituitary adenomas, we analyzed 80 pituitary adenomas for SDH deficiency from patients without familial tumor syndromes or without known SDH deficiency-associated neoplasms. SDH deficiency was determined by immunohistochemical (IHC) stains for SDHB since the loss of any of the four SDH subunits results in the loss of SDHB expression. Three pituitary adenomas showed complete loss of SDHB staining, and of these two also showed loss of SDHA staining. We further characterized these adenomas by looking at Ki67, IGF1R, and 5-hmC levels via IHC. SDHx …

Comparison Of Two Quantitative Image Analysis Systems For Breast Cancer Immunohistochemistry, Reid H. Phillips, Bs, Sue Direnzo, Bs, Charalambos C. Solomides, Md

Department of Pathology Honors Program Student Research Symposium

Automated image analysis systems for breast cancer immunohistochemistry promise efficiency and reliability in the quantification of therapy targets such as the estrogen receptor (ER) or human epidermal growth factor receptor (Her2). Thomas Jefferson University Hospital owns two such systems, the Aperio ScanScope AT (Leica Biosystems) and Ventana iScan Coreo (Roche). A comparison study was performed to determine if choice of system affects target quantification and subsequent clinical tumor classification. Tumor expressions of ER, progesterone receptor (PR), proliferation marker Ki67, and Her2 were quantified with both systems for tissue samples from twenty breast cancer patients. Positive tumor classification was based on …

Evaluating The Utility Of Thyroglobulin Wash Testing In The Management Of Well-Differentiated Thyroid Carcinoma, Katelyn M. Seither, Rossitza Draganova-Tacheva, Md

Department of Pathology Honors Program Student Research Symposium

Introduction

• Thyroid cancer is the most common endocrine neoplasm worldwide, representing 1.7% of new cancer diagnoses and 0.5% of cancer deaths each year (Baldini et al.)
• The majority of thyroid cancers are primary (originating within the gland itself), are well-differentiated, and are derived from follicular epithelial cells
• Papillary thyroid cancer is the most common subtype

70-80% of all thyroid cancers

Peak incidence in women of child-bearing age

Generally indolent behavior, excellent prognosis with total thyroidectomy

30-90% of patients exhibit recurrent or persistent metastasis to the cervical lymph nodes (Torres et al.) and 20% of cases present with occult cancer that …

The Intersection Between Hpv And Hiv Infections: Is There An Increased Susceptibility To Hiv Acquisition In Hpv-Infected Women?, Montida Fleming, Ba, Fred Gorstein, Md

Department of Pathology Honors Program Student Research Symposium

It has been well documented that HIV infection is associated with HPV infection and the progression to cervical carcinoma. Since the spread of HIV/AIDS epidemic, HPV-related cervical carcinoma had such a high prevalence in HIV-infected individuals that it became established as an AIDS-defining illness. Cervical cancer is the most common AIDS-related malignancy, and the sixth most common presenting AIDS-defining illness in women.¹ Additionally, HIV infection leads to a 5-fold increase in multiple new HPV infections within 6 weeks of seroconversion.² Not only does HIV impact acquisition of HPV at molecular and cellular levels, HIV and HPV viruses interact …

20 Year-Old Male With Destructive Lesion Of Orbital Roof, Paris A. Barkan, Bs, Lawrence C. Kenyon, Md, Phd

Department of Pathology Honors Program Student Research Symposium

Patient History

Mr. G.R. is a 20-year-old man with no significant past medical history. He presented in July of 2013 with two months of worsening pain over the right orbit. Periorbital edema was also present. Initial treatment with eye drops, antibiotics (erythromycin followed by cephalexin), and steroids (prednisone) failed to control his symptoms.

In October of 2013, CT and MRI scans revealed a permeative destructive lesion centered in the right orbital roof with extension into the superior orbit and the floor of the anterior cranial fossa. There was no abnormal enhancement in the visualized brain parenchyma.

The radiologic appearance of …

Mechanisms That Modify Immune Response In Neonatal Alloimmune Thrombocytopenia, Robert Cooper, Jay H. Herman

Department of Pathology Honors Program Student Research Symposium

What is NAIT?

Neonatal alloimmune thrombocytopenia (NAIT) is a form of fetal and neonatal thrombocytopenia caused by maternal-fetal platelet antigen incompatibility that results in placental transfer of maternal IgG alloantibodies against the platelet antigen. Currently, there are 28 human platelet antigen systems (HPA) that are polymorphisms of various membrane glycoprotein (GP) integrins. The first HPA and most immunogenic was discovered in the 1960’s and is now termed HPA-1, a diallelic system with HPA-1a and HPA-1b on the GPβ3 subunit of the fibrinogen receptor (Murphy). Approximate HPA-1 phenotype frequencies are: homozygous 1a,1a (~70%); heterozygous 1a,1b (~28%); homozygous 1b,1b (~2%).

Typically an …

Lead Toxicity: What Is It And How Is It Happening?, Kimberly A. Parada, Ba, Jay S. Schneider, Phd

Department of Pathology Honors Program Student Research Symposium

EPIDEMIOLOGY

Lead poisoning accounts for 0.6% of the global burden of disease.

In Pennsylvania in 2010, 148,751 children under 72 months of age were tested for blood lead levels. Of those children, 19,176 had blood lead levels greater than 5 μg/dl.

• A lower socioeconomic status increases the chances for lead exposure.
• Lead toxicity is an under-appreciated problem that is entirely preventable.

Hiv Associated Neurocognitive Disorders In An Antiretroviral Therapy Era, Molly Halloran, David S. Strayer, Md, Phd

Department of Pathology Honors Program Student Research Symposium

HIV emerged as a major threat to world health over 30 years ago, and while its effects on the immune system are widely known, HIV also has broad and devastating effects on the nervous system. Despite our potent antiretroviral therapies (ART), these HIV-associated neurocognitive disorders (HAND) continue to afflict HIV infected individuals. With over 33 million people infected worldwide and evidence that neurological damage can accrue in virologically well controlled individuals, HAND is a pressing challenge. Nevertheless, many questions remain unanswered about this spectrum of disorders.

Her-2 Heterogeneity In Breast Cancer: A Case Study, Kinnari Patel, Theodore Parsons

Department of Pathology Honors Program Student Research Symposium

CASE

The patient is a 75 year-old female with a history of stage 1 invasive ductal carcinoma of the left breast measuring 1.2 cm. Core biopsy of the mass demonstrated Nottingham grade 3 invasive ductal carcinoma; ER negative, PR negative, HER-2 negative (1+). The patient underwent mastectomy in April 2013. Mastectomy confirmed Nottingham grade 3 invasive ductal carcinoma pT1c/pN0/pMX with peritumoral lymphovascular invasion and invasive tumor less than 1 mm from the superoanterior margin. Due to comorbidities the patient was not considered a candidate for adjuvant chemotherapy.

In January 2014 the patient presented with a mastectomy site recurrence. Needle core …

Plasmapheresis And Hiv-Associated Thrombotic Microangiopathy: An Institutional Review, Megan Fisher, Ms2, Nancy Edger Hall, Rn, Mba, Jennifer Webb, Md, Julie Karp, Md

Department of Pathology Honors Program Student Research Symposium

Thrombotic thrombocytopenic purpura (TTP) is a systemic disorder that classically results from a deficiency in the von Willebrand factor-cleaving enzyme, ADAMTS13. The human immunodeficiency virus (HIV) is a secondary cause of TTP. It has been recognized that some patients with HIV-associated TTP do not have a deficiency in ADAMTS13 activity. The role of plasmapheresis (PLEX) in these patients is unclear. This study reviewed 8 cases of HIV-associated TTP at Thomas Jefferson University Hospital. All patients responded to treatment; however, we were unable to make any conclusions regarding the use of PLEX in patients with normal ADAMTS13 activity. HAART initiation is …

Molecular Profiling Of Patients With Non Small Cell Lung Cancer At Jefferson University Hospital, Erin Bange, Renu Bajaj, Ms, Phd, Cg (Ascp), Cm, Facmg

Department of Pathology Honors Program Student Research Symposium

Companion diagnostics is the use of specific tests whose results are linked to a particular drug. It allows clinicians the ability to better target the mechanism of pathology in the patient and follow it up with a therapy specifically designed to treat the disease process at hand. This approach to medicine has particularly been championed in the field of oncology with the development of such drugs as Zelboraf for the treatment of metastatic melanoma with the BRAFV600 mutation or Xalkori for late stage lung cancer expressing an abnormal ALK protein. In the case of non-small cell lung cancer (NSCLC) Jefferson …

Personalized Immune Therapy For Cancer A Potential Game-Changing Treatment, Emily Evron, Emanual Rubin, Md

Department of Pathology Honors Program Student Research Symposium

T-CELL RECEPTOR, NORMALLY

T-cell receptors reside on the surface of T-cells, and recognize a specific antigen presented by an MHC molecule

Next, the T-cells become either CD4 or CD8 cells

Co-stimulation is a key step in activating the T-cell; B7 proteins on the surface of antigen-presenting cells interact with CD28/CTLA-4 receptors on the T-cell.

Peripheral T-Cell Lymphoma Arising From Age-Related Ebv-Associated Lymphoproliferative Disorder (Ar-Ebvlpd), Alaina Chodoff, Msii, Guldeep Uppal, Md, Jerald Z. Gong, Md

Department of Pathology Honors Program Student Research Symposium

In the setting of underlying immune suppression, Epstein Barr Virus (EBV) is a well-recognized oncogenic agent that induces the malignant proliferation of B-cells. EBV-lymphoproliferative disorders (LPDs) have recently been linked to immunosenescence. We present a unique case of Age-Related EBV-Lymphoproliferative Disorder (AR-EBVLPD) in a 70 year old female that deviates from the characteristic progression of this disease. Over the course of 18 months, the patient’s clinical condition worsened without a definitive diagnosis to explain the severe, atypical widespread chronic inflammation spanning her gastrointestinal tract, from esophagus to small bowel. The diagnosis of AR-EBVLPD, polymorphic extranodal subtype, was delayed until the …

Giant Cell Tumor Of Soft Tissue: A Case Study, Rachel Schneider, Brian J. O'Hara

Department of Pathology Honors Program Student Research Symposium

BACKGROUND

Giant cell tumors of soft tissue are relatively uncommon tumors. They are considered to be the soft tissue counterpart to giant cell tumors of bone. Both tumors consist of multi-nucleated giant cells evenly distributed throughout a background of epithelioid mononuclear cells, and are usually benign, but can be locally invasive. Giant cell tumors of soft tissue typically occur in patients over age 40, and show no gender or racial predilection. They present as firm, well demarcated masses, which are not connected to the underlying muscle, tendon, or bone. Giant cell tumors of soft tissue are generally small, and tend …

Small Cell Carcinoma Of The Breast, Victor Carlson, Paolo Cotzia, Md, Juan P. Palazzo, Md

Department of Pathology Honors Program Student Research Symposium

INTRODUCTION

Small cell carcinoma of the breast (SCCB) is a rare, highly aggressive neoplasm first reported in 1983. With striking histologic similarity to small cell carcinoma of the lung, it is comprised of small cells with relatively large, hyperchromatic nuclei and scanty cytoplasm. While capable of hormone secretion, this is a rare occurrence in this variant of small cell carcinoma. Patients typically present with a suspicious breast mass confirmed on imaging, with variable lymph node invasion.

Haploidentical Hematopoietic Stem Cell Transplantation: Rationale, Development, And Jefferson’S Method, Susan Mcilvaine, Dolores Grosso, Rn, Crnp, Dnp, Beth Colombe

Department of Pathology Honors Program Student Research Symposium

INTRODUCTION

There are many indications for hematopoietic stem cell transplantation. In addition to hematologic malignancies, transplants are performed in certain non-hematologic malignancies, for marrow disorders such as Sickle Cell Anemia, and for various inherited disorders such as SCID. Traditionally, transplants have been performed between donors and recipients that are a complete HLA match (typically matched siblings). That is, patients have identical HLA alleles on both copies of chromosome 6. HLA alleles code for major histocompatibility complex molecules, which are the proteins that cause transplant rejection when a mismatch between donor and recipient is present. Thus, matched transplants have been historically …

Small Cell Carcinoma Of The Bladder: A Rare Entity, Andrew H. Matthews, Ruth Birbe, Md

Department of Pathology Honors Program Student Research Symposium

BACKGROUND

Primary small cell carcinoma of the urinary bladder is a rare tumor, accounting for less than 1% of the annual 70,000 cases of urinary bladder cancer.¹ Accordingly, little data is available beyond case series to guide diagnosis or treatment. Overall prognosis remains poor with five year survival often markedly below 50%. Current staging and treatment remains largely based on extrapolation from small cell carcinoma of the lung. We review two recent cases of bladder small cell carcinoma with a focus on comparing and contrasting with lung small carcinoma.

Bcl2 Expression And Bcl2/Myc Dual Expression Predicts Inferior Survival In Primary Central Nervous System Lymphoma, Guldeep Uppal, Md, Zi-Xuan (Zoe) Wang, Phd, Renu Bajaj, Phd, Mark T. Curtis, Md, Phd, Charalambos C. Solomides, Md, Jon Glass, Md, Peter M. Banks, Stephen C. Peiper, Md, Jerald Z. Gong, Md

Department of Pathology, Anatomy, and Cell Biology Resident's Posters

Background

Primary CNS lymphoma (PCNSL) is a rare type of diffuse large B-cell lymphoma (DLBCL) arising from and usually confined to CNS. Understating of the pathogenesis and prognostic markers is a challenge due to rarity of this neoplasm and paucity of the material available to study. Recent studies have shown that dual expression of MYC and BCL2 in DLBCL contributes to inferior overall survival. The prognostic value of MYC and BCL2 in PCNSL is not well studied.

Chronic Arsenic Exposure And Angiogenesis In Human Bronchial Epithelial Cells Via The Ros/Mir-199a-5p/Hif-1Α/Cox-2 Pathway., Jun He, Min Wang, Yue Jiang, Qiudan Chen, Shaohua Xu, Qing Xu, Bing-Hua Jiang, Ling-Zhi Liu

Department of Pathology, Anatomy, and Cell Biology Faculty Papers

Background: Environmental and occupational exposure to arsenic is a major public health concern. Although it has been identified as a human carcinogen, the molecular mechanism underlying the arsenic-induced carcinogenesis is not well understood.Objectives: We aimed to determine the role and mechanisms of miRNAs in arsenic-induced tumor angiogenesis and tumor growth.Methods: We utilized an in vitro model in which human lung epithelial BEAS-2B cells were transformed through long-term exposure to arsenic. A human xenograft tumor model was established to assess tumor angiogenesis and tumor growth in vivo. Tube formation assay and chorioallantoic membranes assay were used to assess tumor angiogenesis.Results: We …

Different Mechanisms Of Inflammation Induced In Virus And Autoimmune-Mediated Models Of Multiple Sclerosis In C57bl6 Mice., Abhinoy Kishore, Anurag Kanaujia, Soma Nag, A M Rostami, Lawrence C. Kenyon, Kenneth S Shindler, Jayasri Das Sarma

Department of Pathology, Anatomy, and Cell Biology Faculty Papers

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the human central nervous system (CNS). Neurotropic demyelinating strain of MHV (MHV-A59 or its isogenic recombinant strain RSA59) induces MS-like disease in mice mediated by microglia, along with a small population of T cells. The mechanism of demyelination is at least in part due to microglia-mediated myelin stripping, with some direct axonal injury. Immunization with myelin oligodendrocyte glycoprotein (MOG) induces experimental autoimmune encephalomyelitis (EAE), a mainly CD4(+) T-cell-mediated disease, although CD8(+) T cells may play a significant role in demyelination. It is possible that both autoimmune and nonimmune mechanisms such as …

Proline-Rich Tyrosine Kinase 2 (Pyk2) Regulates Igf-I-Induced Cell Motility And Invasion Of Urothelial Carcinoma Cells, Marco Genua, Shi-Qiong Xu, Simone Buraschi, Stephen C. Peiper, Leonard G. Gomella, Antonio Belfiore, Renato V. Iozzo, Andrea Morrione

Department of Pathology, Anatomy, and Cell Biology Faculty Papers

The insulin-like growth factor receptor I (IGF-IR) plays an essential role in transformation by promoting cell growth and protecting cancer cells from apoptosis. We have recently demonstrated that the IGF-IR is overexpressed in invasive bladder cancer tissues and promotes motility and invasion of urothelial carcinoma cells. These effects require IGF-I-induced Akt- and MAPK-dependent activation of paxillin. The latter co-localizes with focal adhesion kinases (FAK) at dynamic focal adhesions and is critical for promoting motility of urothelial cancer cells. FAK and its homolog Proline-rich tyrosine kinase 2 (Pyk2) modulate paxillin activation; however, their role in regulating IGF-IR-dependent signaling and motility in …

A Compact Guide To The Diagnosis And Management Of Neurofibromatosis Type 1, Timothy Beer, David Strayer, Md, Phd

Timothy C Beer

Brief Introduction Neurofibromatosis type 1 (NF-1) is a multisystem neurocutaneous disorder resulting from mutations in the NF-1 gene on chromosome 17 (q11.2). Mutations in NF-1 result in deficient activity of the tumor suppresor protein neurofibromin, allowing for uncontrolled constitutive activity of the proliferative Raspathway in several neural cell types, including neurons, oligodendrocytes, astrocytes and Schawnn cells. Half of NF-1 cases are inherited in autosomal dominant fashion, while half develop sporadically. The syndrome has 100% penetrance but highly variable expressivity. The prevalence of this syndrome is 1/3,000, making it common enough to warrant YOU, the physician, taking a moment to learn …

Uterine Dysfunction In Biglycan And Decorin Deficient Mice Leads To Dystocia During Parturition., Zhiping Wu, Abraham W Aron, Elyse E Macksoud, Renato V Iozzo, Chi-Ming Hai, Beatrice E Lechner

Department of Pathology, Anatomy, and Cell Biology Faculty Papers

Cesarean birth rates are rising. Uterine dysfunction, the exact mechanism of which is unknown, is a common indication for Cesarean delivery. Biglycan and decorin are two small leucine-rich proteoglycans expressed in the extracellular matrix of reproductive tissues and muscle. Mice deficient in biglycan display a mild muscular dystrophy, and, along with mice deficient in decorin, are models of Ehlers-Danlos Syndrome, a connective tissue anomaly associated with uterine rupture. As a variant of Ehlers-Danlos Syndrome is caused by a genetic mutation resulting in abnormal biglycan and decorin secretion, we hypothesized that biglycan and decorin play a role in uterine function. Thus, …

Mutant Tdp-43 In Motor Neurons Promotes The Onset And Progression Of Als In Rats, Cao Huang, Jianbin Tong, Fangfang Bi, Hongxia Zhou, Xu-Gang Xia

Department of Pathology, Anatomy, and Cell Biology Faculty Papers

Amyotrophic lateral sclerosis (ALS) is characterized by progressive motor neuron degeneration, which ultimately leads to paralysis and death. Mutation of TAR DNA binding protein 43 (TDP-43) has been linked to the development of an inherited form of ALS. Existing TDP-43 transgenic animals develop a limited loss of motor neurons and therefore do not faithfully reproduce the core phenotype of ALS. Here, we report the creation of multiple lines of transgenic rats in which expression of ALS-associated mutant human TDP-43 is restricted to either motor neurons or other types of neurons and skeletal muscle and can be switched on and off. …

Switches, Excitable Responses And Oscillations In The Ring1b/Bmi1 Ubiquitination System., Lan K Nguyen, Javier Muñoz-García, Helene Maccario, Aaron Ciechanover, Walter Kolch, Boris N Kholodenko

Department of Pathology, Anatomy, and Cell Biology Faculty Papers

In an active, self-ubiquitinated state, the Ring1B ligase monoubiquitinates histone H2A playing a critical role in Polycomb-mediated gene silencing. Following ubiquitination by external ligases, Ring1B is targeted for proteosomal degradation. Using biochemical data and computational modeling, we show that the Ring1B ligase can exhibit abrupt switches, overshoot transitions and self-perpetuating oscillations between its distinct ubiquitination and activity states. These different Ring1B states display canonical or multiply branched, atypical polyubiquitin chains and involve association with the Polycomb-group protein Bmi1. Bistable switches and oscillations may lead to all-or-none histone H2A monoubiquitination rates and result in discrete periods of gene (in)activity. Switches, overshoots …