Pulmonary angiosarcoma: A case report of surgical treatment.

Pulmonary angiosarcoma (PAS) is a malignant tumor of the vascular wall of mesenchymal origin. PAS is rare and has unknown etiology and poor prognosis. Depending on the location, angiosarcoma can lead to serious obstructive and embolic complications, as well as severe pulmonary hypertension and right ventricular heart failure. Patients with PAS are often mistakenly diagnosed with pulmonary embolism, chronic thromboembolic pulmonary hypertension, or lung tumors. Here, we present a clinical case of combined treatment of PAS.

The recruitment of the U5 snRNP to nascent transcripts requires internal loop 1 of U5 snRNA.

In this study, we take advantage of the high spatial resolution offered by the nucleus and lampbrush chromosomes of the amphibian oocyte to investigate the mechanisms that regulate the intranuclear trafficking of the U5 snRNP and its recruitment to nascent transcripts. We monitor the fate of newly assembled fluorescent U5 snRNP in Xenopus oocytes depleted of U4 and/or U6 snRNAs and demonstrate that the U4/U6.U5 tri-snRNP is not required for the association of U5 snRNP with Cajal bodies, splicing speckles, and nascent transcripts. In addition, using a mutational analysis, we show that a non-functional U5 snRNP can associate with nascent transcripts, and we further characterize internal loop structure 1 of U5 snRNA as a critical element for licensing U5 snRNP to target both nascent transcripts and splicing speckles. Collectively, our data support the model where the recruitment of snRNPs onto pre-mRNAs is independent of spliceosome assembly and suggest that U5 snRNP may promote the association of the U4/U6.U5 tri-snRNP with nascent transcripts.

Lampbrush chromosomes enable study of cohesin dynamics.

The lampbrush chromosomes present in the nuclei of amphibian oocytes offer unique biological approaches for study of the mechanisms that regulate chromatin structure with high spatial resolution. We discuss fundamental aspects of the remarkable organization and plasticity exhibited by lampbrush chromosomes. We then utilize lampbrush chromosomes to characterize the chromosomal distribution and dynamics of cohesin, the four-protein complex (RAD21/MCD1/SCC1, SMC1, SMC3, SCC3/SA2) responsible for sister chromatid cohesion. We find that endogenous SMC3 and newly expressed hRAD21 co-localize on chromosomal axes, sites where sister chromatids are tightly paired. We present evidence suggesting that hRAD21 recruitment to lampbrush chromosomes is modulated by chromosomal SMC1 and SMC3. Notably, using a technique for de novo chromosome assembly, we demonstrate that both SMC3 and hRAD21 are recruited to single, unreplicated lampbrush chromatids. Finally, we used our novel method of analyzing the oocyte nucleus under oil combined with fluorescence recovery after photobleaching, to provide direct evidence that cohesin is highly dynamic at discrete, condensed chromosomal regions. Collectively, these data demonstrate that lampbrush chromosomes provide a unique and powerful tool for combining biochemical and cytological analyses for dissection of complex chromosomal processes.

Live images of RNA polymerase II transcription units.

The nucleus of an amphibian oocyte can be manually isolated in mineral oil where it maintains all its activities for several hours. These undisrupted (live) nuclei have been used successfully in recent years to analyze the dynamic organization of several non-chromosomal nuclear organelles. Here, we describe an improved procedure for imaging an oil-isolated nucleus by light microscopy and we use it to produce the very first images of lampbrush chromosomes in an in vivo-like condition. These chromosomes are morphologically identical to those observed in conventional nuclear spread preparations. Importantly, their lateral loops, which are active RNA polymerase II transcription units, are readily distinguished by differential interference contrast microscopy.

Splicing-independent recruitment of spliceosomal small nuclear RNPs to nascent RNA polymerase II transcripts.

In amphibian oocytes, most lateral loops of the lampbrush chromosomes correspond to active transcriptional sites for RNA polymerase II. We show that newly assembled small nuclear ribonucleoprotein (RNP [snRNP]) particles, which are formed upon cytoplasmic injection of fluorescently labeled spliceosomal small nuclear RNAs (snRNAs), target the nascent transcripts of the chromosomal loops. With this new targeting assay, we demonstrate that nonfunctional forms of U1 and U2 snRNAs still associate with the active transcriptional units. In particular, we find that their association with nascent RNP fibrils is independent of their base pairing with pre-messenger RNAs. Additionally, stem loop I of the U1 snRNA is identified as a discrete domain that is both necessary and sufficient for association with nascent transcripts. Finally, in oocytes deficient in splicing, the recruitment of U1, U4, and U5 snRNPs to transcriptional units is not affected. Collectively, these data indicate that the recruitment of snRNPs to nascent transcripts and the assembly of the spliceosome are uncoupled events.