The functional architecture of the nucleus as analysed by ultrastructural cytochemistry

Ultrastructural cytochemistry has been, for many years now, a major tool for investigating structure-function relationships in the cell nucleus. It has been essential in approaching the roles which different nuclear structural constituents can play in nuclear functions. This article briefly summarises transmission electron microscopic studies aimed at characterising in situ nuclear architectural domains and their involvement in main nuclear functions, such as DNA replication, hnRNA transcription and pre-mRNA processing. It discusses the importance of ultrastructural cytochemistry in high resolution analyses of intranuclear distribution of chromatin domains and their topological relationships with other structural interphase nuclear constituents. It puts forward the central role of the perichromatin region as a functional nuclear domain. Finally, it attempts to critically evaluate some future applications of ultrastructural investigations of the nucleus and stresses the importance of combining them with light microscopic analyses of living cell

Cell and tissue structural modifications in hibernating dormice

<strong>Abstract</strong> Tissues and cells of hibernating mammals undergo striking seasonal modifications of their activity through a quiescence-reactivation cycle. During winter, the temperature drastically decreases, the cell timing greatly slows down, the mitotic index sharply falls, DNA, RNA and protein synthesis are drastically reduced; however, upon arousal, all metabolic and physiological activities are quickly restored at the euthermic levels. The physiological, biochemical and behavioural aspects of hibernation have been extensively studied, but data on the morpho-functional relationships of cell and tissue components during the euthermia-hibernation-arousal cycle are rare. In this review, an overview of cell and tissue structural modifications so far reported in hibernating dormice is given and the possible role in the adaptation to the hypometabolic state as well as in the rapid resumption of activities upon arousal is discussed. <strong>Riassunto</strong> <strong>Modificazioni strutturali di cellule e tessuti in Gliridi ibernanti</strong> I tessuti e le cellule dei mammiferi ibernanti subiscono profonde modificazioni stagionali della loro attività attraverso un ciclo di quiescenza-riattivazione. Durante l'inverno, la temperatura corporea si abbassa a valori vicini a quelli ambientali, il ciclo cellulare rallenta, l'indice mitotico si riduce notevolmente e la sintesi di DNA, RNA e proteine è drasticamente ridotta. Tuttavia, al risveglio, tutte le attività metaboliche e fisiologiche sono rapidamente ristabilite ai livelli eutermici. Mentre gli aspetti fisiologici, biochimici e comportamentali dell'ibernazione sono stati ampiamenti studiati, i dati sulle relazioni morfo-funzionali dei componenti cellulari e tessutali durante il ciclo eutermia-ibernazione-risveglio sono piuttosto rari. In questo articolo vengono riassunte le attuali conoscenze sulle modificazioni strutturali di cellule e tessuti nei Gliridi ibernanti e viene discusso il loro possibile ruolo nell'adattamento allo stato ipometabolico e nel rapido ripristino delle attività al risveglio

The kidney during hibernation and arousal from hibernation. A natural model of organ preservation during cold ischaemia and reperfusion

Background. During hibernation the kidney is in a hypothermic condition where renal blood flow is minimal and urine production is much reduced. Periodical arousal from hibernation is associated with kidney reperfusion at increasing body temperature, and restored urine production rate. Methods. To assess the degree of structural preservation during such extreme conditions, the kidney cortex was investigated by means of electron microscopy in the dormouse Muscardinus avellanarius during winter hibernation, arousal from hibernation and the summer active period. Results. Results show that the fine structure of the kidney cortex is well preserved during hibernation. In the renal corpuscle, a sign of slight lesion was the focal presence of oedematous endothelial cells and/or podocytes. Proximal convoluted tubule cells showed fully preserved ultrastructure and polarity, and hypertrophic apical endocytic apparatus. Structural changes were associated with increased plasma electrolytes, creatinine and urea nitrogen, and proteinuria. During the process of arousal the fine structure of the kidney cortex was also well maintained. Conclusion. These results demonstrate that dormice are able to fully preserve kidney cortex structure under extreme conditions resembling e.g. severe ischaemia or hypothermic organ storage for transplantation, and reperfusion. Elucidation of the mechanisms involved in such a natural model of organ preservation could be relevant to human medicin