Integration of light and circadian signals that regulate chloroplast transcription by a nuclear-encoded sigma factor

We investigated the signalling pathways that regulate chloroplast transcription in response to environmental signals. One mechanism controlling plastid transcription involves nuclear-encoded sigma subunits of plastid-encoded plastid RNA polymerase. Transcripts encoding the sigma factor SIG5 are regulated by light and the circadian clock. However, the extent to which a chloroplast target of SIG5 is regulated by light-induced changes in SIG5 expression is unknown. Moreover, the photoreceptor signalling pathways underlying the circadian regulation of chloroplast transcription by SIG5 are unidentified. We monitored the regulation of chloroplast transcription in photoreceptor and sigma factor mutants under controlled light regimes in Arabidopsis thaliana. We established that a chloroplast transcriptional response to light intensity was mediated by SIG5; a chloroplast transcriptional response to the relative proportions of red and far red light was regulated by SIG5 through phytochrome and photosynthetic signals; and the circadian regulation of chloroplast transcription by SIG5 was predominantly dependent on blue light and cryptochrome. Our experiments reveal the extensive integration of signals concerning the light environment by a single sigma factor to regulate chloroplast transcription. This may originate from an evolutionarily ancient mechanism that protects photosynthetic bacteria from high light stress, which subsequently became integrated with higher plant phototransduction networks.

Circadian regulation of chloroplasts

Circadian rhythms produce a biological measure of time that increases plant performance. The mechanisms that underlie this increase in productivity require investigation to provide information that will underpin future crop improvement. There is a growing body of evidence that a sophisticated signalling network interconnects the circadian oscillator and chloroplasts. We consider this in the context of circadian signalling to chloroplasts and the relationship between retrograde signalling and circadian regulation. We place circadian signalling to chloroplasts by sigma factors within an evolutionary context. We describe selected recent developments in the integration of light and circadian signals that control chloroplast gene expression.

Clinical applications of immunohistochemistry in gynecological malignancies

Over the past two decades, immunohistochemical techniques have improved to such a degree that it is now a common adjuvant test to the traditional hematoxylin and eosin-stained histologic sections. It is used in most realms of surgical pathology and can often aid in final diagnosis and, in some cases, prognosis. However, immunohistochemistry (IHC) is not always helpful and many pitfalls to its use exist. Understanding the basics of IHC, its utility and difficulties will aid clinicians in better understanding how diagnoses are rendered. This study reviews the general principles of IHC and demonstrates its utility with several commonly encountered problematic areas in gynecological pathology.

Liesegang rings in a submental mass: fine-needle aspiration with histologic correlation

Liesegang rings are lamellated concretions commonly found in chronic cystic lesions that are inflamed, necrotic, fibrotic, or hemorrhagic. We report on an unusual case of a 14-yr-old girl with an acute, rapidly enlarging solid submental mass in which Liesegang rings were identified on aspirate smears.

Metastatic hepatocellular carcinoma to the heart

Right ventricular heart involvement of an otherwise unknown hepatocellular carcinoma is presented and the cytologic differential diagnosis is discussed. This tumor displays classic cytologic features of hepatocellular carcinoma, including trabecular arrangements with prominent endothelial cells and numerous intracytoplasmic hyaline bodies. The background contains many "naked nuclei" and extracellular hyaline bodies. The patient is alive with residual disease 4 months after surgical extirpation of the cardiac mass.

Metastatic hepatocellular carcinoma to the heart

Right ventricular heart involvement of an otherwise unknown hepatocellular carcinoma is presented and the cytologic differential diagnosis is discussed. This tumor displays classic cytologic features of hepatocellular carcinoma, including trabecular arrangements with prominent endothelial cells and numerous intracytoplasmic hyaline bodies. The background contains many "naked nuclei" and extracellular hyaline bodies. The patient is alive with residual disease 4 months after surgical extirpation of the cardiac mass.

Mesenteric artery thrombosis: a case report of combined protein S and protein C deficiency

Individuals with more than one defect in natural coagulant/anticoagulant systems have been postulated to be at an increased risk for thrombotic events. We report a case of combined protein S and C deficiency in a young woman, which resulted in fatal arterial mesenteric thrombosis. The role of coagulation defects in arterial thrombosis is discussed.