Molecular and serological dynamics of Chlamydia pecorum infection in a longitudinal study of prime lamb production

Background

Chlamydia pecorum is a globally significant livestock pathogen causing pathology and production losses. The on-farm infection and serological dynamics and the relevance of existing diagnostic tools for diagnosing C. pecorum in livestock remains poorly characterized. In this study, we characterized the antigen and antibody dynamics of this pathogen in a longitudinal study of prime lamb production, utilizing the infection focused C. pecorum-specific 16S rRNA qPCR assay and serology based chlamydial Complement fixation Test (CFT).

Methods

The study consisted of 76 Border Leicester mixed sex lambs (39 females and 37 males) that were sampled bimonthly from 2–10 months of age in a commercial farm operating in Central NSW, Australia. Blood/plasma was analysed for CFT antibodies, and swabs from conjunctival, rectal and vaginal sites were analysed for C. pecorum shedding using qPCR. We assessed the temporal and overall dynamics of C. pecorum in lambs, including detailed description and comparison of qPCR and CFT, the timing of first detection by either diagnostic method, the lag between infection and antibody response; and the distribution of qPCR load and CFT antibody titre over time.

Results

Over the study period, C. pecorum was highly prevalent (71.0% by qPCR, 92.1% by CFT, 96.0% by both), with 21.1% (16/76) lambs shedding ≥1, 000 qPCR copies/µl (denoted as high shedders). C. pecorum shedding (as evidence of infection) were first observed at two months of age (14.4%) with a significant peak of infection occurring at six months of age (34.2%), whereas seroconversions peaked at eight months of age (81.5%). 52.6% of C. pecorum qPCR and CFT positive lambs became qPCR negative by 10 months of age, indicating clearance of chlamydial infection. Although CFT is utilised for on-farm detection of active infection, we confirm that it lagged behind qPCR detection (average lag 1.7 ± 2.1 months) and that the proportion of qPCR positives simultaneously identified by CFT was low with 2/11 (18.1%), 0/13, 17/25 (68.0%), 5/7 (71.4%) and 1/10 (10.0%) concurrent seroconversions occurring at two, four, six, eight and 10 months of age, respectively.

Discussion

This work reveals rapid rates of C. pecorum infection and widespread exposure during lamb production. The comparison of molecular and serological diagnostic agreement longitudinally, supports the use of qPCR as an important ancillary tool for the detection of active infections in conjunction with chlamydial CFT for routine veterinary diagnostics. Development of rapid Point-of-Care (POC) tools for diagnosing active infection would be valuable for producers and veterinarians.

Humoral immune response against two surface antigens of Chlamydia pecorum in vaccinated and naturally infected sheep

Chlamydia pecorum is a globally recognised livestock pathogen due to the significant clinical and economic impact it poses to livestock producers. Routine serological diagnosis is through a complement fixation test (CFT), which is often criticised for cross-reactivity, poor sensitivity and specificity. Although serology remains the preferred method in veterinary diagnostic laboratories, serological assays based on surface antigens of C. pecorum have not been established until now. In this study, we evaluated the use of two chlamydial recombinant protein antigens (PmpG and MOMP-G) by a direct IgG ELISA method for detection of ovine anti-chlamydial antibodies. Using the Pepscan method we then identified B cell epitopes across PmpG and MOMP-G proteins, in lambs with (a) naturally occurring asymptomatic C. pecorum infections (b) C. pecorum-associated polyarthritis and (c) recombinant PmpG and MOMP-G vaccine. Plasma IgG antibodies to PmpG in natural infection of lambs were detected earlier in infection than CFT and served as an acute phase marker. Antibodies to MOMP-G IgG were significantly heightened in lambs with C. pecorum-associated polyarthritis. PmpG and MOMP-G specific B-cell epitope mapping revealed epitope responses in immunised lambs cluster with some of the epitope responses in naturally infected lambs. B-cell epitope mapping further revealed that lambs with polyarthritis recognised several unique PmpG (50% frequency, peptide 8, 25, 40, 41 and 50) and MOMP (50% frequency, peptide 50) epitopes in comparison to asymptomatic infections. The findings of this study will have implications towards improved serodiagnosis of C. pecorum infections in livestock and inform the downstream development of alternative peptide-based antigens for future C. pecorum vaccine studies.

Characterization of Sarcoptes scabiei Tropomyosin and Paramyosin: Immunoreactive Allergens in Scabies

Scabies is a human skin disease due to the burrowing ectoparasite Sarcoptes scabiei var. hominis resulting in intense itching and inflammation and manifesting as a skin allergy. Because of insufficient mite material and lack of in vitro propagation system for antigen preparation, scabies is a challenging disease to develop serological diagnostics. For allergen characterization, full-length S. scabiei tropomyosin (Sar s 10) was cloned, expressed in pET-15b, and assessed for reactivity with IgE antibodies from human sera. IgE binding was observed to Sar s 10 with sera collected from subjects with ordinary scabies, house dust mite (HDM)-positive and naive subjects and a diagnostic sensitivity of < 30% was observed. S. scabiei paramyosin (Sar s 11) was cloned, and expressed in pET-28a in three overlapping fragments designated Sspara1, Sspara2, and Sspara3. IgE and IgG binding was observed to Sspara2 and Sspara3 antigens with sera collected from ordinary scabies, and HDM-positive subjects, but no binding was observed with sera collected from naive subjects. Sspara2 displayed excellent diagnostic potential with 98% sensitivity and 90% specificity observed for IgE binding and 70% sensitivity for IgG. In contrast, the diagnostic sensitivity of Sspara3 was 84% for IgE binding and 40% for IgG binding. In combination, Sspara2 and Sspara3 provided an IgE sensitivity of 94%. This study shows that IgE binding to Sspara2 and Sspara3 is a highly sensitive method for diagnosis of scabies infestation in clinical practice. The developed enzyme-linked immunosorbent assay helps direct future development of a specific diagnostic tool for scabies.

Antibody and Cytokine Responses of Koalas (Phascolarctos cinereus) Vaccinated with Recombinant Chlamydial Major Outer Membrane Protein (MOMP) with Two Different Adjuvants

Developing a vaccine against Chlamydia is key to combating widespread mortalities and morbidities associated with this infection in koalas (Phascolarctos cinereus). In previous studies, we have shown that two or three doses of a Recombinant Major Outer Membrane Protein (rMOMP) antigen-based vaccine, combined with immune stimulating complex (ISC) adjuvant, results in strong cellular and humoral immune responses in koalas. We have also separately evaluated a single dose vaccine, utilising a tri-adjuvant formula that comprises polyphosphazine based poly I: C and host defense peptides, with the same antigen. This formulation also produced strong cellular and humoral immune responses in captive koalas. In this current study, we directly compared the host immune responses of two sub-groups of wild Chlamydia negative koalas in one population vaccinated with the rMOMP protein antigen and adjuvanted with either the ISC or tri-adjuvant formula. Overall, both adjuvants produced strong Chlamydia-specific cellular (IFN-γ and IL-17A) responses in circulating PBMCs as well as MOMP-specific and functional, in vitro neutralising antibodies. While the immune responses were similar, there were adjuvant-specific immune differences between the two adjuvants, particularly in relation to the specificity of the MOMP epitope antibody responses.

Active Rab11 and functional recycling endosome are required for E-cadherin trafficking and lumen formation during epithelial morphogenesis

The correct targeting and trafficking of the adherens junction protein epithelial cadherin (E-cadherin) is a major determinant for the acquisition of epithelial cell polarity and for the maintenance of epithelial integrity. The compartments and trafficking components required to sort and transport E-cadherin to the basolateral cell surface remain to be fully defined. On the basis of previous data, we know that E-cadherin is trafficked via the recycling endosome (RE) in nonpolarized and newly polarized cells. Here we explore the role of the RE throughout epithelial morphogenesis in MDCK monolayers and cysts. Time-lapse microscopy in live cells, altering RE function biochemically, and expressing a dominant-negative form of Rab11 (DN-Rab11), each showed that the RE is always requisite for E-cadherin sorting and trafficking. The RE remained important for E-cadherin trafficking in MDCK cells from a nonpolarized state through to fully formed, polarized epithelial monolayers. During the development of epithelial cysts, DN-Rab11 disrupted E-cadherin targeting and trafficking, the subapical localization of pERM and actin, and cyst lumen formation. This final effect demonstrated an early and critical interdependence of Rab11 and the RE for E-cadherin targeting, apical membrane formation, and cell polarity in cysts.

The DEAD-box protein DP103 (Ddx20 or Gemin-3) represses orphan nuclear receptor activity via SUMO modification

Structural analysis of nuclear receptor subfamily V orphan nuclear receptors suggests that ligand-independent mechanisms must regulate this subclass of receptors. Here, we report that steroidogenic factor 1 (SF-1) and liver receptor homolog 1 are repressed via posttranslational SUMO modification at conserved lysines within the hinge domain. Indeed, mutating these lysines or adding the SUMO isopeptidase SENP1 dramatically increased both native and Gal4-chimera receptor activities. The mechanism by which SUMO conjugation attenuates SF-1 activity was found to be largely histone deacetylase independent and was unaffected by the AF2 corepressor Dax1. Instead, our data suggest that SUMO-mediated repression involves direct interaction of the DEAD-box protein DP103 with sumoylated SF-1. Of potential E3-SUMO ligase candidates, PIASy and PIASxalpha strongly promoted SF-1 sumoylation, and addition of DP103 enhanced both PIAS-dependent receptor sumoylation and SF-1 relocalization to discrete nuclear bodies. Taken together, we propose that DEAD-box RNA helicases are directly coupled to transcriptional repression by protein sumoylation.

Steroidogenic factor-1 and the gonadotrope-specific element enhance basal and pituitary adenylate cyclase-activating polypeptide-stimulated transcription of the human glycoprotein hormone alpha-subunit gene in gonadotropes

In the anterior pituitary, expression of the common glycoprotein hormone alpha-subunit (alphaGSU) is mediated in part by multiple response elements residing in the distal promoter (-435 bp). One such site is the gonadotrope-specific element (GSE), which is bound by the orphan nuclear receptor steroidogenic factor-1 (SF-1) and confers pituitary adenylate cyclase-activating polypeptide (PACAP)-stimulated alphaGSU expression. Here we investigated the functional importance of the GSE and SF-1 phosphorylation in both basal and stimulated alphaGSU transcription. Mutation of the GSE reduced basal and PACAP-stimulated alphaGSU promoter activity in the alphaT3-1 gonadotrope cell line. Overexpression of wild-type SF-1, but not an S203A mutant form of SF-1, enhanced basal and PACAP-stimulated alphaGSU promoter activity. The effect of PACAP on alphaGSU promoter activity was inhibited after overexpression of MAPK phosphatase. Helix assembly of the SF-1 ligand-binding domain was stimulated by PACAP in vitro via a MAPK-dependent pathway, as determined using a mammalian two-hybrid assay. PACAP quickly activated MAPK (within 5 min) and also resulted in elevated levels of phospho-cAMP response element-binding protein and phospho-SF-1, as judged by a specific antiphospho-S203 antibody; this effect was blocked by the MAPK kinase inhibitor, UO126. Collectively, these data demonstrate that SF-1 binds to the GSE and activates both basal and PACAP-stimulated alphaGSU transcription, which is further increased by phosphorylation at Ser203 via MAPK. These data suggest strongly that the induction of alphaGSU gene expression by peptide hormone signaling is coupled directly to the posttranslational status of SF-1.

Tissue growth and remodeling of the embryonic and adult adrenal gland

The adrenal gland provides a model system for the study of tissue remodeling in endocrine physiology. For example, proper adrenal development requires proliferation of the adrenogonadal primordia, separation of adrenal and gonadal precursors, and cell migration that unites the adrenal cortex and adrenal medulla. In the adult, normal adrenal function is assured by the adrenal gland's unique capacity for growth in response to both tissue injury and physiological demand. Identification of the molecular and genetic programs underlying tissue remodeling in the adrenal is important for understanding basic aspects of development and regeneration, as well as adrenal disease. Here, we will highlight the roles that nuclear receptors and pituitary hormones play in regulating fetal adrenal development and adult adrenal growth. In addition, we will review the most current data on how extracellular signaling pathways are coupled to the function of these important regulators of adrenal development and function.

Thyroid hormone receptor-beta mutations conferring hormone resistance and reduced corepressor release exhibit decreased stability in the N-terminal ligand-binding domain

Resistance to thyroid hormone (RTH) syndrome is associated with mutations in the human thyroid hormone receptor-beta (hTRbeta), many of which show marked reduction in hormone binding. Here, we investigated the structural consequences of two RTH mutants (A234T and R243Q), residing in the flexible N-terminal portion of the ligand binding domain (LBD), which exhibit modestly reduced hormone binding with impaired release of corepressor. X-ray crystallography analyses revealed that these two RTH mutants modulate the position of this flexible region by either altering the movement of helix 1 (A234T) or disrupting a salt bridge (R243Q). The subsequent increased flexibility and mobility in regions after the two sites of mutation coincided with a disorganized LBD. Consistent with this finding, the ability of these mutant N-terminal regions (234-260) to recruit the remaining LBD was decreased in a ligand-dependent helix assembly assay. Collectively, these data suggest that structural information imparted by the flexible segment in the N-terminal LBD is critical for overall stability of the LBD. Thus, these structural analyses provide mechanistic insight into the etiology of RTH disease in human TRbeta mutants that exhibit hormone binding with decreased ligand-dependent corepressor release.

Phosphorylation and intramolecular stabilization of the ligand binding domain in the nuclear receptor steroidogenic factor 1

Steroidogenic factor 1 (SF-1) is an orphan nuclear receptor with no known ligand. We showed previously that phosphorylation at serine 203 located N'-terminal to the ligand binding domain (LBD) enhanced cofactor recruitment, analogous to the ligand-mediated recruitment in ligand-dependent receptors. In this study, results of biochemical analyses and an LBD helix assembly assay suggest that the SF-1 LBD adopts an active conformation, with helices 1 and 12 packed against the predicted alpha-helical bundle, in the apparent absence of ligand. Fine mapping of the previously defined proximal activation function in SF-1 showed that the activation function mapped fully to helix 1 of the LBD. Limited proteolyses demonstrate that phosphorylation of S203 in the hinge region mimics the stabilizing effects of ligand on the LBD. Moreover, similar effects were observed in an SF-1/thyroid hormone LBD chimera receptor, illustrating that the S203 phosphorylation effects are transferable to a heterologous ligand-dependent receptor. Our collective data suggest that the hinge together with helix 1 is an individualized specific motif, which is tightly associated with its cognate LBD. For SF-1, we find that this intramolecular association and hence receptor activity are further enhanced by mitogen-activated protein kinase phosphorylation, thus mimicking many of the ligand-induced changes observed for ligand-dependent receptors.

Direct interaction of SRY-related protein SOX9 and steroidogenic factor 1 regulates transcription of the human anti-Müllerian hormone gene

For proper male sexual differentiation, anti-Müllerian hormone (AMH) must be tightly regulated during embryonic development to promote regression of the Müllerian duct. However, the molecular mechanisms specifying the onset of AMH in male mammals are not yet clearly defined. A DNA-binding element for the steroidogenic factor 1 (SF-1), a member of the orphan nuclear receptor family, located in the AMH proximal promoter has recently been characterized and demonstrated as being essential for AMH gene activation. However, the requirement for a specific promoter environment for SF-1 activation as well as the presence of conserved cis DNA-binding elements in the AMH promoter suggest that SF-1 is a member of a combinatorial protein-protein and protein-DNA complex. In this study, we demonstrate that the canonical SOX-binding site within the human AMH proximal promoter can bind the transcription factor SOX9, a Sertoli cell factor closely associated with Sertoli cell differentiation and AMH expression. Transfection studies with COS-7 cells revealed that SOX9 can cooperate with SF-1 in this activation process. In vitro and in vivo protein-binding studies indicate that SOX9 and SF-1 interact directly via the SOX9 DNA-binding domain and the SF-1 C-terminal region, respectively. We propose that the two transcription factors SOX9 and SF-1 could both be involved in the expression of the AMH gene, in part as a result of their respective binding to the AMH promoter and in part because of their ability to interact with each other. Our work thus identifies SOX9 as an interaction partner of SF-1 that could be involved in the Sertoli cell-specific expression of AMH during embryogenesis.

Characterization of two Sp1 binding sites of the human sex determining SRY promoter

To investigate the molecular basis of the human SRY gene regulation, we have examined the significance of two potential binding sites for the transcription factor Sp1 (Sp1A: -124 to -131 and Sp1B: -147 to -154) by DNase I footprinting and gel mobility shift assays. Cotransfection experiments in Drosophila SL2 cells implicated Sp1 protein in the transcriptional activation of the SRY promoter.

Phosphorylation of an N-terminal motif enhances DNA-binding activity of the human SRY protein

Of the several strategies that eukaryotes have evolved to modulate transcription factor activity, phosphorylation is regarded as one of the major mechanisms in signal-dependent transcriptional control. To conclusively demonstrate that the human sex-determining gene SRY is affected by such a post-translational control mechanism, we have analyzed its phosphorylation status in living cells. In the present study, we show that the cyclic AMP-dependent protein kinase (PKA) phosphorylates the human SRY protein in vitro as well as in vivo on serine residues located in the N-terminal part of the protein. This phosphorylation event was shown to positively regulate SRY DNA-binding activity and to enhance the ability of SRY to inhibit a basal promoter activity located downstream of an SRY DNA-binding site concatamer. Together these results strongly support the hypothesis that human SRY is a natural substrate for PKA in vivo and that this phosphorylation significantly modulates its major activity, DNA-binding, thereby possibly altering its biological function.

The human testis determining factor SRY binds a nuclear factor containing PDZ protein interaction domains

The human Y-linked testis determining gene SRY encodes a protein with a DNA binding domain from the high mobility group box family. To date, no function has been assigned to amino acid sequences located outside this DNA binding motif. Here, we identify in a yeast two-hybrid screen a PDZ protein termed SIP-1, as an interacting protein with human SRY. In vitro, biochemical analysis, immunoprecipitation experiments, as well as expression of SIP-1 in human embryonic testis confirm that the two proteins can interact together. Interacting domains were mapped to the C-terminal seven amino acids of SRY and to the PDZ domains of SIP-1, respectively. We hypothesize that SIP-1 could connect SRY to other transcription factors providing SRY for its missing trans-regulation domain.

Overexpression of c-erbA proto-oncogene enhances myogenic differentiation

Triiodothyronine (T3) positively regulates both the expression of the MyoD gene, a key myogenic regulator, and C2 muscle cell differentiation. To directly examine the role of its nuclear receptors in the control of myogenesis, we introduced a c-erbA expression vector into C2 muscle cells by transient or stable transfection. Our results show that c-erbA can play a potent role in the triggering of muscle terminal differentiation since its overexpression leads to: (1) a complete abrogation of the activity of the myogenesis inhibitor AP-1 (fos/jun) transcription factor; (2) an enhanced induction of MyoD expression upon T3 treatment; (3) the acquisition by T3 of the ability to trigger both growth arrest and terminal differentiation in the presence of large amounts of serum mitogens, a property that is otherwise specific to retinoic acid (RA). Thus, c-erbA is one of the two protooncogenes (with c-ski) that acts as positive regulator of muscle differentiation. Furthermore, the fact that c-erbA overexpression allows T3 to largely mimic the RA effects indicates that their biological differences in the modulation of myogenic program primarily rely on the differential expression of their receptors in C2 muscle cells rather than on an intrinsic specificity of their target genes.