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Transcriptional regulatory cascades during epicardial and coronary vascular development from proepicardial progenitor cells remain to be defined. We have used immunohistochemistry of human embryonic tissues to demonstrate that the TBX5 transcription factor is expressed not only in the myocardium, but also throughout the embryonic epicardium and coronary vasculature. TBX5 is not expressed in other human fetal vascular beds. Furthermore, immunohistochemical analyses of human embryonic tissues reveals that unlike their epicardial counterparts, delaminating epicardial-derived cells do not express TBX5 as they migrate through the subepicardium before undergoing epithelial-mesenchymal transformation required for coronary vasculogenesis. In the chick, Tbx5is expressed in the embryonic proepicardial organ (PEO), which is composed of the epicardial and coronary vascular progenitor cells. Retrovirus-mediated overexpression of human TBX5 inhibits cell incorporation of infected proepicardial cells into the nascent chick epicardium and coronary vasculature. TBX5 overexpression as well as antisense-mediated knockdown of chick Tbx5 produce a cell-autonomous defect in the PEO that prevents proepicardial cell migration. Thus, both increasing and decreasing Tbx5 dosage impairs development of the proepicardium. Culture of explanted PEOs demonstrates that untreated chick proepicardial cells downregulate Tbx5 expression during cell migration. Therefore, we propose that Tbx5 participates in regulation of proepicardial cell migration, a critical event in the establishment of the epicardium and coronary vasculature.

Mutations in human TBX5,a member of the T-box transcription factor gene family, cause congenital cardiac septation defects and isomerism in autosomal dominant Holt–Oram syndrome. To determine the cellular function of TBX5 in cardiogenesis, we overexpressed wild-type and mutant human TBX5 isoforms in vitroand in vivo.TBX5 inhibited cell proliferation of D17 canine osteosarcoma cells and MEQC quail cardiomyocyte-like cells in vitro.Mutagenesis of the 5′ end of the T-box but not the 3′ end of the T-box abolished this effect. Overexpression of TBX5 in embryonic chick hearts showed that TBX5 inhibits myocardial growth and trabeculation. TBX5 effects in vivowere abolished by Gly80Arg missense mutation of the 5′ end of the T-box. PCNA analysis in transgenic chick hearts revealed that TBX5 overexpression does suppress embryonic cardiomyocyte proliferation in vivo.Inhibitory effects of TBX5 on cardiomyocyte proliferation include a noncell autonomous process in vitroand in vivo.TBX5 inhibited proliferation of both nontransgenic cells cocultured with transgenic cells in vitroand nontransgenic cardiomyocytes in transgenic chick hearts with mosaic expression of TBX5 in vivo.Immunohistochemical studies of human embryonic tissues, including hearts, also demonstrated that TBX5 expression is inversely related to cellular proliferation. We propose that TBX5 can act as a cellular arrest signal during vertebrate cardiogenesis and thereby participate in modulation of cardiac growth and development.

Mutations in the TBX5 transcription factor gene cause human cardiac malformation in Holt‐Oram syndrome. To identify and localize TBX5 during cardiac morphogenesis, we performed immunohistochemical studies of TBX5 protein cardiac expression during human embryogenesis. Specific antibody to human TBX5 was generated in rabbits with a TBX5 synthetic peptide and affinity purification of antiserum. Anti‐TBX5 was used in immunohistochemical analyses of human cardiac tissue. In embryonic and adult heart, TBX5 is expressed throughout the epicardium and in cardiomyocyte nuclei in myocardium of all four cardiac chambers. Endocardial expression of TBX5 is only present in left ventricle. Asymmetric left‐sided transmyocardial gradients of TBX5 protein expression were observed in embryonic but not adult hearts. Human cardiac expression of TBX5 protein correlates with the cardiac manifestations of Holt‐Oram syndrome. TBX5 transmyocardial protein gradients may contribute to normal patterning of the human heart during embryogenesis. © 2000 Wiley‐Liss, Inc.

To generate an in vivo system for investigating the postintegration phase of HIV-1 replication, mouse lines transgenic for a full-length infectious proviral clone of a monocyte-tropic HIV-1 isolate, HIV-1JR-C SF, were constructed. Leukocytes from two independent JR-CSF transgenic mouse lines produced HIV-1 that infected human PBMCs. Plasma viremia was detected in these mice at levels (mean, >60,000 HIV RNA copies/ml) comparable to those reported for HIV-1-infected individuals. The levels of HIV RNA in these mice increased several-fold after either treatment with the superantigen Staphylococcus enterotoxin B or infection with Mycobacterium tuberculosis. Thus, a provirus encoding a monocyte-tropic HIV-1 strain under the control of its LTR expressed as a transgene in mice can proceed through the postintegration replication phase and produce infectious virus. In addition, the presence of plasma viremia that can be monitored by measuring plasma HIV1 RNA levels permits these mice to be used to study the impact of different interventions on modulating in vivo HIV-1 production. Therefore, these mice provide a novel manipulable system to investigate the in vivo regulation of HIV-1 production by factors that activate the immune system. Furthermore, this murine system should be useful in delineating the role of human-specific factors in modulating HIV-1 replication and investigating the in vivo therapeutic efficacy of agents that target the postintegration stages of HIV-1 replication.

We describe an individual in whom molecular genetic testing provided a diagnosis of the Carney complex, an autosomal dominant syndrome comprising cutaneous and cardiac myxomas, spotty pigmentation of the skin, and endocrinopathy. Recently, we localized the Carney complex disease gene to chromosome region 17q2. Our patient was a member of a family segregating the Carney complex, but was not, himself, initially thought to be affected. Haplotype analysis based on genotyping studies with 17q2 microsatellites predicted that this individual was, in fact, affected by Carney complex and was at risk for development of myxomas. Further clinical evaluation and re-review of prior pathologic studies, then, confirmed the DNA-based diagnosis. This report highlights the difficulty in establishing a diagnosis of Carney complex based on clinical and pathologic findings alone, and we suggest that molecular genetic analyses provide an important diagnostic method for this familial myxoma syndrome. Am. J. Med. Genet. 86:62–65, 1999. © 1999 Wiley-Liss, Inc.

Immunohistochemistry is a vastly diverse and essential method for localization of proteins in cells and tissues. This unit presents methods for labeling proteins in suspension and adherent cultures and in tissue sections, using detection methods for both fluorescence and bright‐field microscopy. Choices of antibodies and detection methods are discussed, and detailed troubleshooting guidelines are provided. Curr. Protoc. Mol. Biol. 81:14.6.1‐14.6.23. © 2008 by John Wiley & Sons, Inc.