From Kepler's conjecture and fcc lattice to modelling of crowding in living matter.

Up to now, sphere packing has been investigated without any reference to living matter. This study focuses on the void space (VS) of sphere packing to mimic the extracellular spaces of living tissues. It was inspired by the importance of the extracellular matrix, the vehicle of micro and macromolecules involved in cell metabolism, intercellular communication and drug delivery.

Does the cell number 10(9) still really fit one gram of tumor tissue?

A tumor reaching the size of 1 cm(3) (approximately 1 g wet weight) is commonly assumed to contain 1 x 10(9) cells. This paper comments on the probable origin of this "magic" number and on some possible reasons why it has remained in use until now. However, mostly in epithelial tumors (85% of all human tumors) a cell number one order of magnitude smaller would be more realistic.

The puzzle of ploidy of Purkinje neurons.

This paper places attention on the discrepancies existing in the literature on the ploidy of Purkinje neurons and focuses on the special case of partial replication of their genome and on the unequal frequency of polyploid Purkinje neurons in the cerebellar cortex of the lobes and the vermis. Owing to the compartmental structure of the cerebellum, this paper suggests the investigation with modern methods and techniques of other cerebellar regions such as the flocculus, with the aim of establishing whether increased ploidy correlates with cell hypertrophy and/or with stimulation of cerebellar functions.

Drop of connexins: a possible link between aging and cancer?

The incidence of cancer increases with age but we do not know why. As a working hypothesis we propose here that cells somehow initiated in vivo in the course of life and finally engaged in the aging program, which involves a drop of connexins with loss of cell-to-cell communication (equivalent to the promotion phase in the multistep process of carcinogenesis), may recover their growth potential, thus allowing cancer to progress. This is supported by evidence that: (i) connexin 43 (Cx43) acts as a tumor suppressor; (ii) cx43 and gap junction intercellular communication drop in precancerous lesions and in tumors of various origins, as well as in aging cells; (iii) telomerase is activated in cancerous somatic cells.

The expression of the non-receptor tyrosine kinases Arg and c-abl is differently modulated in B lymphoid cells at different stages of differentiation.

The products of the human ARG gene and the human ABL gene characterize the Abelson family of non-receptor tyrosine protein kinases. Both genes are ubiquitously expressed. The interactions of these two similar protein kinases are still not well known, although it has been suggested that they could cooperate, with redundant actions, to provide intracellular signals in the cells.

Drop of connexin 43 in replicative senescence of human fibroblasts HEL-299 as a possible biomarker of senescence.

The expression of connexin 43 (cx43) and cell-cell communication were studied in replicative senescence of cultured HEL-299 fibroblasts. A progressive decrease in fluorescent dye transfer was detected by a scrape-loading technique in aging fibroblasts. This change was accounted for by a marked decrease in the amount of cx43 in aging cells, as detected by western blot analysis (cell extracts) and indirect fluorescence (cells in culture).