A Bovine Lymphosarcoma Cell Line Infected with Theileria annulata Exhibits an Irreversible Reconfiguration of Host Cell Gene Expression

Theileria annulata, an intracellular parasite of bovine lymphoid cells, induces substantial phenotypic alterations to its host cell including continuous proliferation, cytoskeletal changes and resistance to apoptosis. While parasite induced modulation of host cell signal transduction pathways and NFκB activation are established, there remains considerable speculation on the complexities of the parasite directed control mechanisms that govern these radical changes to the host cell. Our objectives in this study were to provide a comprehensive analysis of the global changes to host cell gene expression with emphasis on those that result from direct intervention by the parasite. By using comparative microarray analysis of an uninfected bovine cell line and its Theileria infected counterpart, in conjunction with use of the specific parasitacidal agent, buparvaquone, we have identified a large number of host cell gene expression changes that result from parasite infection. Our results indicate that the viable parasite can irreversibly modify the transformed phenotype of a bovine cell line. Fifty percent of genes with altered expression failed to show a reversible response to parasite death, a possible contributing factor to initiation of host cell apoptosis. The genes that did show an early predicted response to loss of parasite viability highlighted a sub-group of genes that are likely to be under direct control by parasite infection. Network and pathway analysis demonstrated that this sub-group is significantly enriched for genes involved in regulation of chromatin modification and gene expression. The results provide evidence that the Theileria parasite has the regulatory capacity to generate widespread change to host cell gene expression in a complex and largely irreversible manner.     

2型猪链球菌Fbps基因敲除突变体的构建及毒力分析

目的:敲除2型猪链球菌(SS2)强毒株05ZYH33中的Fbps基因,研究该基因敲除对菌株生物活性及毒力的影响,为深入探讨猪链球菌致病机制提供实验基础。方法:从05ZYH33基因组中扩增Fbps基因上、下游同源臂,从pSET1质粒中扩增氯霉素抗性基因Cm,通过重叠PCR的方法将3个片段整合后连接到温敏自杀载体pSET4s上,电转入05ZYH33感受态细胞,通过改变培养温度实现双交换和质粒丢失,最后经抗性筛选获得敲除株05ZYH33ΔFBPS,分析敲除株的生物学性状,以CD1小鼠作为体外感染模型对突变株和野生株进行毒力比较。结果:PCR分析和测序结果均显示Fbps基因敲除成功,动物实验结果显示Fbps基因敲除后05ZYH33的毒力有所下降。结论:与野生株相比,突变株对小鼠的毒力有所降低。     

Microarray Chip Based Identification of a Mixed Infection of Bovine Herpesvirus 1 and Bovine Viral Diarrhea 2 From Indian Cattle

Bovine herpesvirus 1 (BHV1) and bovine viral diarrhea virus 2 (BVD2) are endemic in India although no mixed infection with these viruses has been reported from India. We report first mixed infection of these viruses in cattle during routine screening with a microarray chip. 62 of the 69 probes of BHV1 and 42 of the 57 BVD2 probes in the chip gave positive signals for the virus. The virus infections were subsequently confirmed by RT-PCR. We also discuss the implications of these findings.     

Characterization of Marek's Disease Virus Serotype 1 (MDV-1) Deletion Mutants That Lack UL46 to UL49 Genes: MDV-1 UL49, Encoding VP22, Is Indispensable for Virus Growth

Experiments were conducted to investigate the roles of Marek's disease virus serotype 1 (MDV-1) major tegument proteins VP11/12, VP13/14, VP16, and VP22 in viral growth in cultured cells. Based on a bacterial artificial chromosome clone of MDV-1 (BAC20), mutant viruses were constructed in which the MDV-1 homologs of UL46, UL47, UL48, or UL49 were deleted alone and in various combinations. It could be demonstrated that the UL46, UL47, and UL48 genes are dispensable for MDV-1 growth in chicken embryonic skin and quail muscle QM7 cells, although the generated virus mutants exhibited reduced plaque sizes in all cell types investigated. In contrast, a UL49-negative MDV-1 (20 Delta 49) and a UL48-UL49 (20 Delta 48-49) doubly negative mutant were not able to produce MDV-1-specific plaques on either cell type. It was confirmed that this growth restriction is dependent on the absence of VP22 expression, because growth of these mutant viruses could be partially restored on cells that were cotransfected with a UL49 expression plasmid. In addition, we were able to demonstrate that cell-to-cell spread of MDV-1 conferred by VP22 is dependent on the expression of amino acids 37 to 187 of MDV-1 VP22, because expression plasmids containing MDV-1 UL49 mutant genes with deletions of amino acids 1 to 37 or 188 to 250 were still able to restore partial growth of the 20 Delta 49 and 20 Delta 48-49 viruses. These results demonstrate for the first time that an alphaherpesvirus UL49-homologous gene is essential for virus growth in cell culture.     

Impact of ETIF Deletion on Safety and Immunogenicity of Equine Herpesvirus Type 1-Vectored Vaccines

Heterologous gene transfer by viral vector systems is often limited by factors such as preexisting immunity, toxicity, low packaging capacity, or weak immunogenic potential. A novel viral vector system derived from equine herpesvirus type 1 (EHV-1) not only overcomes some of these obstacles but also promotes the robust expression of a delivered transgene and the induction of antigen-specific immune responses. Regarding an enhanced safety profile, we assessed the impact of the gene encoding the sole essential tegument protein, ETIF, on the replication and immunogenicity of recombinant EHVs. The deletion of ETIF severely attenuates replication in permissive RK13 cells and a human lung epithelial cell line but without influencing transgene expression. Whereas the intranasal administration of a recombinant luciferase EHV in BALB/c mice resulted in transgene expression in nasal cavities and lungs for 5 to 6 days, the ETIF deletion limited expression to 2 days and resulted in 30-fold-less luminescence. Attenuated replication was accompanied by a decreased capacity to induce CD8⁺ T cells against a delivered HIV Gag transgene in BALB/c mice following repeated intranasal application. However, a single subcutaneous immunization with a gag DNA vaccine primed specific T cells for substantial expansion by two subsequent intranasal booster immunizations with either the gag recombinant ETIF mutant or the parental virus. In addition to inducing Gag-specific serum antibodies, this prime-boost strategy clearly outperformed three sequential immunizations with the parental or EHV-ΔETIF virus or repeated DNA vaccination by inducing substantial specific secretory IgA (sIgA) titers.Viruses are evolutionarily predestined to transfer genetic material into eukaryotic cells and use the cellular machinery to express virally harbored genes. Hence, intensive research has focused on the potential of various viruses to deliver heterologous genes (for a review, see references 8 and 44). Depending on the type of viral vector system used, it is possible to induce efficient transgene-specific T- and B-cell immune responses (15, 34, 36, 43) as well as mucosal immune responses (16, 51), which can be enhanced by applying homologous or heterologous prime-boost strategies (4, 25, 56).Unfortunately, the use of common viral vector systems for heterologous gene transfer is often limited by factors such as neurovirulence (e.g., rabies virus) (12, 28), weak immunogenic potential (e.g., avian poxviruses) (44), or low packaging capacity (e.g., adeno-associated viruses and first- and second-generation adenoviral vectors) (21, 44). However, the most important obstacle in vector development is preexisting immunity. Due to high infection rates (e.g., adenoviruses, adeno-associated viruses, and human herpesviruses) and systematic vaccination programs (e.g., poxviruses and measles virus) (14, 45), a large percentage of the human population has already acquired strong immune responses to currently used vector systems. Although it has been assumed that preexisting immunity to the administered recombinant virus would simply weaken the induction of transgene-specific immune responses, a recent clinical anti-HIV vaccination study revealed that the risk of infection with HIV might even be increased with inept vector systems used as delivery vehicles. Male subjects who had received a recombinant adenoviral vaccine harboring the HIV-1 Gag, Pol, and Nef genes showed an increased risk of HIV infection compared to a relevant control group (30). Thus, the further development of existing vector systems as well as the establishment of novel ones are necessary for successful heterologous gene delivery.We previously showed that equine herpesvirus type 1 (EHV-1) strain RacH is a promising candidate as a novel viral vector system. The virus has been attenuated by 256 passages on porcine embryonic kidney cells (37) and lacks both copies of the IR6 gene, previously described as one of the main virulence factors of EHV-1 (41). The expression of all viral genes depends on one single immediate-early gene (20) that is trans-activated by the essential equine trans-inducing factor (ETIF), the EHV-1 homologue of HSV-1 VP16, also known as α-trans-inducing factor (α-TIF) (32, 42). ETIF is a major tegument protein encoded in the unique long region and is expressed at late times during viral replication. Besides transactivation of the immediate-early gene, it is also involved in the secondary envelopment of virions (33, 53).All currently available data indicate that EHV-1 strain RacH is apathogenic in humans, with severely impaired replication in human cells. Nevertheless, the virus effectively infects a broad spectrum of different mammalian cells and can be grown to high titers in vitro. In addition, due to the absence of the virus in humans, it can be assumed that the problem of preexisting immunity should be of minor importance. Furthermore, it is known that neutralizing antibodies directed against human herpesviruses show no cross-reactivity to EHV-1. We could also show that recombinant EHV-1 is able to elicit considerable transgene-specific cellular immune responses in BALB/c mice via various routes of application (50). This is most likely due to the virus''s natural tropism for peripheral blood mononuclear cells (PBMCs), which play an important role in inducing innate and adapted immune responses (3, 54). Above all, due to the virus''s ability to infect epithelial cells, EHV-1 is characterized by inducing strong mucosal immune responses (9). Considering that distinct mucosal immune responses have been defined as one of the correlates of protective immunity against HIV (10, 29), this represents an important feature for a vector system, not only for a potential HIV vaccine but also for diseases transmitted by the mucosal route in general.Therefore, we aimed to extend previous findings and characterize transgene expression and viral replication of a recombinant EHV-1 with the ETIF open reading frame (ORF) (UL48) deleted for purposes of attenuation. In addition, we studied the immunogenic potential of ETIF-deleted EHV-1. More specifically, we examined the quality and magnitude of transgene-specific immune responses upon the application of homologous or heterologous prime-boost strategies, including recombinant virus or plasmid DNA.     

Expression of a Cx43 Deletion Mutant in 3T3 A31 Fibroblasts Prevents PDGF-Induced Inhibition of Cell Communication and Suppresses Cell Growth

Communication through gap junctions was first suggested to have a role in the social control of cell growth over 30 years ago. However, despite extensive experimentation, the importance of gap junctions as a general mechanism of growth control remains to be established. A number of different studies have shown that a common early response of cells in culture to polypeptide growth factors such as PDGF is a rapid and transient inhibition of cell communication suggesting that a cell may have to lose communication with its neighbors before it can undergo cell division. Here we show that 3T3 A31 fibroblasts exposed to PDGF exhibit a 50% decrease in cell communication as measured by dye transfer in the absence of significant changes in the cellular content and distribution of Cx43. Likewise, PDGF inhibited cell communication in cells transfected either with a vector which did not contain a cDNA or with an expression vector encoding full-length Cx43 fused to a c-myc tag (Cx43-M). In contrast, 3T3 A31 fibroblasts transfected with an expression construct encoding a deletion mutant of Cx43 (Cx43-256M) consisting of amino acids 1-256 of Cx43 fused to a c-myc tag maintain high levels of gap junction activity following exposure to PDGF. These results suggest that sites which trigger loss of cell communication in response to PDGF are located within amino acids 257 to 382 of the Cx43 molecule. Cells transfected with an expression vector encoding full-length Cx43 fused to a c-myc tail exhibited a reduced basal growth rate compared to both parent cells and cells transfected with a control vector but maintained a strong mitogenic response to PDGF. In contrast, both the basal growth rate and the mitogenic response to PDGF was markedly reduced in cells which expressed Cx43-256M consistent with the hypothesis that loss of cell communication is required before a cell can respond to mitogenic stimuli.     

MspI Allelic Pattern of Bovine Growth Hormone Gene in Indian Zebu Cattle (Bos indicus) Breeds

The MspI allelic variation in intron III of the bovine growth hormone (bGH) gene was explored using PCR-RFLP in 750 animals belonging to 17 well-recognized breeds of Indian zebu cattle (Bos indicus) reared in different geographic locations of the country. Restriction digestion analysis of a 329-bp PCR fragment of the bGH intron III region with MspI restriction enzyme revealed two alleles (MspI− and MspI+) and two genotypes (−/− and +/−) across the 17 cattle breeds studied. The allelic frequency varied from 0.67 to 0.94 for MspI (−) and from 0.06 to 0.33 for MspI (+) across the 17 breeds, with a combined average frequency of 0.87 and 0.13, respectively. No animal with +/+ genotype was detected across the samples analyzed. The chi-square test showed that the difference in MspI allelic frequency was not significant (p > 0.05), regardless of the geographic origin, coat color, or utility of the cattle breed. The high MspI (−) allele frequencies obtained for Indian zebu cattle in this study are in sharp contrast to those reported for taurine breeds from northern Europe, Mediterranean countries, and America. Findings of this study further substantiate the hypothesis that the MspI (−) allele has an Indian origin.     

A Deletion in the Bovine FANCI Gene Compromises Fertility by Causing Fetal Death and Brachyspina

Fertility is one of the most important traits in dairy cattle, and has been steadily declining over the last decades. We herein use state-of-the-art genomic tools, including high-throughput SNP genotyping and next-generation sequencing, to identify a 3.3 Kb deletion in the FANCI gene causing the brachyspina syndrome (BS), a rare recessive genetic defect in Holstein dairy cattle. We determine that despite the very low incidence of BS (<1/100,000), carrier frequency is as high as 7.4% in the Holstein breed. We demonstrate that this apparent discrepancy is likely due to the fact that a large proportion of homozygous mutant calves die during pregnancy. We postulate that several other embryonic lethals may segregate in livestock and significantly compromise fertility, and propose a genotype-driven screening strategy to detect the corresponding deleterious mutations.     

Mutations in the Myp1 Gene of Ustilago Maydis Attenuate Mycelial Growth and Virulence

Mating between haploid, budding cells of the dimorphic fungus Ustilago maydis results in the formation of a dikaryotic, filamentous cell type. Mating compatibility is governed by two mating-type loci called a and b; transformation of genes from these loci (e.g., a1 and b1) into a haploid strain of different mating type (e.g., a2 b2) allows filamentous growth and establishes a pathogenic cell type. Several mutants with a nonmycelial colony morphology were isolated after insertional mutagenesis of a filamentous, pathogenic haploid strain. The mutagenized region in one such mutant was recovered by plasmid rescue and employed to isolate a gene involved in conditioning the mycelial phenotype (myp1). An 1150 amino acid open reading frame is present at the myp1 locus; the predicted polypeptide is rich in serine residues and contains short regions with similarity to SH3 domain ligands. Construction of myp1 disruption and deletion mutants in haploid strains confirmed that this gene plays a role in mycelial growth and virulence.     

A Mutant with Expression Deletion of Gene Sec-1 in a 1RS.1BL Line and Its Effect on Production Quality of Wheat

The chromosome arm 1RS of rye (Secale cereal L.) has been used worldwide as a source of genes for agronomic and resistant improvement. However, the 1RS arm in wheat has end-use quality defects that are partially attributable to the presence of ω-secalins, which are encoded by genes at the Sec-1 locus. Various attempts in removing the Sec-1 genes from the 1RS.1BL translocation chromosome have been made. In the present study, two new primary 1RS.1BL translocation lines, T917-26 and T917-15, were developed from a cross between wheat variety “{"type":"entrez-nucleotide","attrs":{"text":"A42912","term_id":"2298361"}}A42912” and Chinese local rye “Weining.” The lines T917-15 and T917-26 carried a pair of intact and homogeneous 1RS.1BL chromosomes. The line T917-26 also harbored an expression deletion of some genes at the Sec-1 locus, which originated from a mutation that occurred simultaneously with wheat-rye chromosome translocations. These results suggest that the accompanying mutations of the evolutionarily significant translocations are remarkable resources for plant improvement. Comparison of translocation lines with its wheat parent showed improvements in the end-use quality parameters, which included protein content (PC), water absorption (WA), sodium dodecyl sulfate sedimentation (SDSS), wet gluten (WG), dry gluten (DG) and dough stickiness (DS), whereas significant reduction in gluten index (GI) and stability time (ST) were observed. These findings indicate that 1RS in wheat has produced a higher amount of protein, although these comprised worse compositions. However, in the T917-26 line that harbored an expression deletion mutation in the Sec-1 genes, the quality parameters were markedly improved relative to its sister line, T917-15, especially for GI and DS (P < 0.05). These results indicated that expression deletion of Sec-1 genes significantly improves the end-use quality of wheat cultivars harboring the 1RS.1BL translocation. Strategies to remove the Sec-1 genes from the 1RS.1BL translocation in wheat improvement are discussed.     

Genetic Variants in ADD1 Gene and their Associations with Growth Traits in Cattle

The α-adducin (ADD1) is a subunit of adducin which is a cytoskeleton heterodimeric protein. Adducin participates in oocytes chromosome meiosis of mice, prompting adducin has an effect on embryonic development. Adducin gene mutation has significantly functional change. So the present study was to identify and characterize polymorphisms within the coding region of the bovine ADD1 gene among different cattle breeds. Here, 11 novel single nucleotide polymorphisms (SNPs 1–11) were identified by DNA sequencing and polymerase chain reaction-single stranded conformational polymorphism, there were one synonymous mutation in exon 1 (SNP1); four missense mutations in exons 4, 7, and 8 (SNPs 3–6); and six mutations in introns 4, 12, 13, and 14 (SNPs 2, 7–10). The statistical analyses indicated that the some SNPs are associated with the growth traits (body length, body height, chest circumference, and hucklebone width) in Chinese Jiaxian cattle population. Our results provide evidence that polymorphisms in the ADD1 gene are associated with growth traits, and may be used for marker-assisted selection in beef cattle breeding program.     

Small Noncoding RNAs Encoded within the Bovine Herpesvirus 1 Latency-Related Gene Can Reduce Steady-State Levels of Infected Cell Protein 0 (bICP0)

Following acute infection in mucosal epithelium, bovine herpes virus 1 (BHV-1) establishes lifelong latency in sensory neurons within trigeminal ganglia. The latency-related RNA (LR-RNA) is abundantly expressed in sensory neurons of latently infected calves. Expression of LR proteins is necessary for the latency reactivation cycle because a mutant virus that does not express LR proteins is unable to reactivate from latency after dexamethasone treatment. LR-RNA sequences also inhibit bICP0 expression, productive infection, and cell growth. However, it is unclear how LR-RNA mediates these functions. In this study, we identified a 463-bp region within the LR gene (the XbaI-PstI [XP] fragment) that inhibited bICP0 protein and RNA expression in transiently transfected mouse neuroblastoma cells. Small noncoding RNAs (sncRNAs) encoded within the XP fragment (20 to 90 nucleotides in length) were detected in transiently transfected mouse neuroblastoma cells. Two families of sncRNAs were cloned from this region, and each family was predicted to contain a mature microRNA (miRNA). Both miRNAs were predicted to base pair with bICP0 mRNA sequences, suggesting that they reduce bICP0 levels. To test this prediction, sequences encompassing the respective sncRNAs and mature miRNAs were synthesized and cloned into a small interfering RNA expression vector. Both sncRNA families and their respective miRNAs inhibited bICP0 protein expression in mouse neuroblastoma cells and productive infection in bovine cells. In trigeminal ganglia of latently infected calves, an sncRNA that migrated between nucleotides 20 and 25 hybridized to the XP fragment. During dexamethasone-induced reactivation from latency, XP-specific sncRNA levels were reduced, suggesting that these sncRNAs support the establishment and maintenance of lifelong latency in cattle.Bovine herpes virus 1 (BHV-1) infection leads to respiratory and genital disorders, abortion, conjunctivitis, and/or multisystemic infection in small calves (19-21, 23). Consequently, BHV-1 infections are a significant economic loss to the cattle industry. As with other Alphaherpesvirinae subfamily members, the primary site for a BHV-1 latent infection is sensory ganglionic neurons (19, 20, 23). Virus reactivation from latency can occur after stress, suggesting that corticosteroids play a role in this process.During latency, viral gene expression is restricted to the latency-related (LR) gene and open reading frame E (ORF-E) (13, 23, 35, 36). The LR gene contains two open reading frames (ORF1 and ORF2) and two reading frames (RF-B and RF-C) (24). A fraction of LR-RNA is polyadenylated and alternatively spliced in trigeminal ganglia (TG), suggesting that more than one protein is expressed (4, 5, 12). A peptide antibody directed against ORF2 recognizes a protein encoded by the LR gene (12, 17, 18). LR protein expression is necessary for the latency reactivation cycle because a mutant BHV-1 strain with three stop codons at the N terminus of ORF2 does not reactivate from latency (14, 33). Furthermore, the LR mutant virus has diminished clinical symptoms and reduced shedding of infectious virus from the eye, TG, and tonsil (14, 15, 33). Finally, the LR mutant virus induces higher levels of apoptosis in TG neurons, in part because a protein encoded by the LR gene (ORF2) inhibits apoptosis (3, 14, 15, 26, 40). Three LR proteins, including ORF2, have reduced or no expression in cells infected with the LR mutant virus (18, 27).Although proteins encoded by the LR gene are necessary for the latency reactivation cycle, non-protein coding functions within LR-RNA have also been identified. For example, the intact LR gene inhibits the ability of bICP0 to stimulate productive infection in a dose-dependent manner (1, 9). Insertion of three in-frame stop codons at the amino terminus of the first ORF within the LR gene (ORF2) inhibited bICP0 repression with an efficiency similar to that of the wild-type (wt) LR gene, suggesting that expression of an LR protein is not required (9). Since the LR gene is antisense to bICP0 coding sequences, we assumed that LR-RNA hybridized to bICP0 RNA sequences and interfered with bICP0 expression. However, we were unable to obtain data suggesting that antisense repression was the major reason why the LR gene inhibited bICP0 expression. LR gene products also inhibit mammalian cell growth (8, 38), and the cell growth-inhibitory function of the LR gene maps to a 463-bp XbaI-PstI (XP) fragment (8). Sequences within the XP region have the potential to form stem-loop secondary structures, suggesting that there are small noncoding RNAs (sncRNAs) expressed from the XP region.In this study, we demonstrated that the XP fragment efficiently inhibits bICP0 protein levels and, to a lesser extent, bICP0 RNA levels. Northern blot analysis using the XP fragment as a probe detected sncRNAs migrating between 20 and 90 nucleotides (nt). Two families of sncRNAs with the same 5′ terminus but different 3′ termini were cloned from this region. Members of these two families of sncRNAs inhibited bICP0 expression with an efficiency similar to that of the XP fragment. Each family of sncRNAs has the potential to generate a mature microRNA (miRNA). Sequences encompassing the mature miRNA also inhibited bICP0 expression in transiently transfected cells. Although the miRNA sequences have the potential to base pair with bICP0 mRNA, the miRNA sequences do not overlap bICP0 RNA sequences. Finally, LR-specific sncRNAs and miRNAs inhibited productive infection approximately 2-fold, suggesting that LR-specific sncRNAs support the establishment and maintenance of lifelong latency in cattle.     

Virulence and Pathogenesis of Yellow Fever Virus Serially Passaged in Cell Culture

Viscerotropic virulence of the Asibi strain of yellow fever virus (YFV) for monkeys has been known to be lost after serial passage in HeLa cell monolayers. This phenomenon was investigated in several other mammalian and insect tissue cell lines. Assay in monkeys of original seed virus and of virus after 7 and 11 passages in a porcine kidney cell line (PK) indicated essentially equal infectivity and mortality. Moreover, monkeys receiving the passaged virus exhibited more rapid onset of disease and death than animals infected with original seed virus. Histological changes in animals inoculated with passaged virus were identical to those in animals receiving the seed virus. Virus from later passages in PK cells was also lethal for approximately 50% of the monkeys; however, evidence for progressive attenuation was seen in these preparations. Similar results were obtained with a mosquito (Aedes aegypti) cell line. In contrast to results obtained in PK and mosquito cells, YFV became essentially avirulent (nonlethal and less infective) for monkeys after only seven passages in HeLa cell cultures.     

Derepressed Hyphal Growth and Reduced Virulence in a VH1 Family-related Protein Phosphatase Mutant of the Human Pathogen Candida albicans

Mitogen-activated protein (MAP) kinases are pivotal components of eukaryotic signaling cascades. Phosphorylation of tyrosine and threonine residues activates MAP kinases, but either dual-specificity or monospecificity phosphatases can inactivate them. The Candida albicans CPP1 gene, a structural member of the VH1 family of dual- specificity phosphatases, was previously cloned by its ability to block the pheromone response MAP kinase cascade in Saccharomyces cerevisiae. Cpp1p inactivated mammalian MAP kinases in vitro and acted as a tyrosine-specific enzyme. In C. albicans a MAP kinase cascade can trigger the transition from the budding yeast form to a more invasive filamentous form. Disruption of the CPP1 gene in C. albicans derepressed the yeast to hyphal transition at ambient temperatures, on solid surfaces. A hyphal growth rate defect under physiological conditions in vitro was also observed and could explain a reduction in virulence associated with reduced fungal burden in the kidneys seen in a systemic mouse model. A hyper-hyphal pathway may thus have some detrimental effects on C. albicans cells. Disruption of the MAP kinase homologue CEK1 suppressed the morphological effects of the CPP1 disruption in C. albicans. The results presented here demonstrate the biological importance of a tyrosine phosphatase in cell-fate decisions and virulence in C. albicans.