Developmentally programmed genome rearrangement accompanies differentiation of the silent germline micronucleus into the transcriptionally active somatic macronucleus in the ciliated protozoan Tetrahymena thermophila. Internal eliminated sequences (IES) are excised, followed by rejoining of MAC-destined sequences, while fragmentation occurs at conserved chromosome breakage sequences, generating macronuclear chromosomes. Some macronuclear chromosomes, referred to as non-maintained chromosomes (NMC), are lost soon after differentiation. Large NMC contain genes implicated in development-specific roles. One such gene encodes the domesticated piggyBac transposase TPB6, required for heterochromatin-dependent precise excision of IES residing within exons of functionally important genes. These conserved exonic IES determine alternative transcription products in the developing macronucleus; some even contain free-standing genes. Examples of precise loss of some exonic IES in the micronucleus and retention of others in the macronucleus of related species suggest an evolutionary analogy to introns. Our results reveal that germline-limited sequences can encode genes with specific expression patterns and development-related functions, which may be a recurring theme in eukaryotic organisms experiencing programmed genome rearrangement during germline to soma differentiation.

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Operating on the aortic arch is a formidable challenge. Open operations remain the gold standard, but despite improvement in technique and outcomes, they are still associated with significant morbidity and mortality. The last 20 years have seen a remarkable reduction in the operative morbidity associated with treatment of the descending thoracic aorta using thoracic endovascular aneurysm repair (TEVAR). To improve outcomes following arch repair, new TEVAR devices, including both single-branched and multibranched designs, have come to clinical trial. This review discusses the modern state of open and hybrid repairs while introducing the reader to technology for endovascular therapy of the aortic arch. We describe important anatomical and operative considerations for the devices. Given these nuances, we believe the future of the aortic arch to be patient-individualised hybrid repairs, involving both open and endovascular options with a multidisciplinary ‘thoracic aorta team’ at the helm.

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