Development of the male pronucleus
Frank J. Longo in Fertilization, 2020
Changes in the sperm chromatin consistent with development into a male pronucleus may occur prior to gamete membrane fusion. Segments of the sperm nuclear envelope formerly associated with the acrosome and centrioles are left intact; subsequently they become incorporated into the nuclear envelope of the male pronucleus. Evidence that sperm nuclear envelope breakdown is required for development of a male pronucleus also comes from observations of gynogenetic fish. Models for the organization of chromatin and genes within sperm have been proposed in order to better understand genome function and are particularly relevant to an understanding of sperm chromatin dispersion at fertilization. With the formation of the pronuclear envelope, transformation of the sperm nucleus into a male pronucleus is essentially completed. However, the male pronucleus continues to undergo morphogenetic changes which may include further enlargement, the continuation of chromatin dispersion and the acquisition of internuclear structures such as nucleoli, annulate lamellae and aggregations of tubular inclusions.
Epigenetic Control of Cell-Specific Gene Expression
Lyle Armstrong in Epigenetics, 2020
The greater part of epigenetic control is aimed at repression or activation of specific genes, and there are several mechanisms by which this may be achieved. The cell nucleus is currently considered to be highly complex and organized compartment in which nuclear components tend to occupy nonrandom positions, leading to precise definition of nuclear architecture concept. The chromatin contained within each chromosome is not randomly distributed in the nucleus but occupies a specific location known as the chromosome territory or domain, a feature that constrains the whole spatial organization inside the nuclear compartment. A well-characterized example of multiple chromatin loops-that is, one created by the interaction of gene regulatory elements-is the nucleolus, in which the ribosomal RNA genes are located in clusters. The mechanisms described in this chapter are the basis of the epigenetic control of gene expression; having understood these concepts, we can proceed to examine how epigenetic control is exerted over diverse cellular functions such as mitosis.
Protozoology, Taxonomy, and Nomenclature of Free-Living Amebas
A. Julio Martinez in Free-Living Amebas: Natural History, Prevention, Diagnosis, Pathology, and Treatment of Disease, 2019
The amebas causing meningoencephalitis in humans and lower mammals belong to Acanthamoeba and not Hartmannella. These two genera are also distinct serologically and nutritionally. The light microscopic features of trophozoites and cysts of free-living amebas should be supplemented with transmission and scanning electron microscopy. There are different proteins forming the cytoplasm of free-living amebas. These proteins may be detected and characterized by different variants of Immunoelectrophoresis. The immunoelectrophoretic profiles are useful for taxonomy and classification of genera and species. The cysts are very useful in classification of free-living amebas because there is no distinctive or specific features to differentiate genera and species. The most characteristic features of the cysts are the shape, the appearance of the wall, and the number and morphology of the pores. The nucleus is usually centrally located, relatively small, with a centrally placed nucleolus. An interesting feature is the sharp separation between the nuclear membrane and the cytoplasm.
Nucleolar Adaptation in Human Cancer
Published in Cancer Investigation, 2005
Leonard B. Maggi, Jason D. Weber
While the nucleolus was first observed over two hundred years ago, its role in human cancers is only now being appreciated. Long thought to be a static, ribosome-producing, subnuclear organelle, recent investigations have shown a more dynamic and adaptable side of the nucleolus. Containing not only proteins for the production of ribosomes but also newfound nucleolar oncogenes and tumor suppressors, mechanistic links between the nucleolus and cancer are now more evident. In this regard, much of the work from the past decade has focused on the ability of these proteins to promote and suppress tumorigenesis from the nucleolus. In this review, we will discuss how historical measurements of the nucleolus are being translated into contemporary studies of nucleolar dysfunction in human cancer.
Targeting RNA polymerase I transcription and the nucleolus for cancer therapy
Published in Expert Opinion on Therapeutic Targets, 2013
Ross D Hannan, Denis Drygin, Richard B Pearson
The nucleoli are the site of the production of ribosomes, the protein synthetic apparatus of the cell. The presence of enlarged nucleoli, reflecting increased ribosomal gene transcription, has long been used by pathologists as an indicator of aggressive tumors. However, over the last 10 years a growing body of evidence has revealed that the nucleolus contains a dynamic cohort of over 4500 proteins, the majority of which have no function in ribosome production. The activity of some of these proteins is modulated by their regulated sequestration and release from the nucleolus. In particular, the nucleolus plays a central role in sensing cellular stress to modulate the abundance of the critical tumor suppressor protein p53. The finding that p53 activity is dysregulated in up to 50% of all human cancers highlights the importance of the nucleolar stress response in limiting malignant transformation. The development of drugs to selectively inhibit transcription of the ribosomal RNA genes in the nucleolus has paved the way for a new therapeutic approach to hijack nucleolar stress to selectively and non-genotoxically activate p53 in tumor cells. Here, we describe the potential application of this exciting new class of drugs for the treatment of human cancer.
Changes in the Nucleolar Organizer Regions in the Tuberomammillar Region after Dehydration
Published in Archives Of Physiology And Biochemistry, 1997
S Rubio, A Begega, L.J. Santín, J.L. Arias
The existence of efferent connections between tuberomammillary (TM) and the supraoptic (SON) nuclei led us to study the morphological changes at these levels during dehydration induced in rats by repeated administration of hypertonic saline. The dehydration effects are evaluated by three parameters: nucleus area, argyrophilic nucleolar organizer regions (Ag-NOR) area, and mean number of Ag-NORs. These parameters reflect the level of transcriptional activity of the rRNA genes, which in turn is closely related to the protein synthesis activity of the cell. The technique used is argyrophilic staining which labels the nucleolar organizer regions (NORs) of the nucleoli in the neurons and their area, permitting their quantification with an image analysis system. The statistical analysis reflects the sensitivity to dehydration of these structures at TM level. Our results support the regulatory role of vasopressin secretion by SON through the histaminergic pathways arising from TM in rat dehydration processes.
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