EDITORIAL

We have projected this issue of volume 44 of the European Journal of Histochemistry, the first issue of the third millennium, to celebrate the achievements of the just-ended twentieth century, quite agreed upon as the century of histochemistry. The issue opens with a review by van der Ploeg entitled “Cytochemical nucleic acid research during the twentieth century”. This is the text of a lecture he presented in Camerino to the 1999 Congress of Histochemistry on the occasion of his receiving the 1st International Histochemical Award. The award, in memory of the founder of our Society, Maffo Vialli, was instituted for the express purpose of linking more closely our Society with other European histochemical centers, and more generally with their cell biology activities. Prof. van der Ploeg in his article traces a very analytical history of the last century’s research on nucleic acids and, through this, how our knowledge about cell biology and about how life is regulated, progressed. He begins right from the discovery at the end of the seventeenth century of a simple microscope, “insensitive to optical aberration”, which permitted Van Leeuwenhoek to observe unicellular organisms for the first time. From this follows, clearly and compellingly, the evolution of biological thought about the nucleus and cell life, closely correlating it with the development of the instruments of observation and measurement, and the techniques of imaging and quantification of nucleic acids

Kinetics of DNase I digestion of interphase chromatin in differentiated cell nuclei of the mouse: a flow cytometric study.

The process of DNA digestion with DNase I was monitored in interphase chromatin of differentiated cells by flow cytometry after DNA staining with either the intercalating dye propidium iodide (PI) or the AT specific dye Hoechst 33258 (HO). Nuclei from the liver, kidney and spleen of the mouse were studied after different digestion times (0 to 120 min). During the first 30 min of treatment, a tissue specific digestion pattern was found after PI staining; from 60 min onward, the digestion curves ran parallel, with minor quantitative differences among the cell types. After HO staining, the digestion kinetics appeared to be similar for all the cell types; this is likely due to the peculiar base composition of the mouse genome, where inactive c-heterochromatin is exceptionally AT-rich. No quantitative correlation was found between interphase "heterochromatin" and chromatin DNA which is resistant to DNase I cleavage, while the amount of DNase-I-sensitive DNA does not correspond to the interphase "euchromatic" component. It was confirmed that the flow cytometric approach is a tool for quantifying relative changes in the functional state of chromatin in differentiated cell system

Genome size and constitutive heterochromatin in Hylobates muelleri and Symphalangus syndactylus and in their viable hybrid.

Genome size was measured as the amount of Feulgen-stained DNA in six species of the family Hylobatidae and in a hybrid of the gibbon (Hylobates muelleri) and siamang (Symphalangus syndactylus). The family, on the whole, exhibits a wider range of genome sizes than pongids; in particular, the siamang has about 15% more DNA than the 44-chromosome Hylobates species of the "lar" group. Quantitative analysis of C-heterochromatin in hybrid metaphases showed that the difference in genome size of the parental species correlates with the amount of C-band-positive material. Hylobatids are the only group of primates in which karyotype diversification has taken place with a massive quantitative change in constitutive heterochromatin

Sperm-chromatin maturation in the mouse. A cytochemical approach.

Cytochemical techniques were used to study chromatin during spermiogenesis and sperm maturation in the mouse, starting from the stages at which the substitution of somatic histones by testis-specific proteins occurs. It was possible to distinguish and analyze the different temporal incidence of two processes involved in sperm maturation, i.e. chromatin condensation (a tridimensional highly compacted arrangement) and chromatin stabilization (a tough structure, which protects the genome DNA). The first process, involving a reduction in the nuclear size and a decrease in the amount of sperm DNA accessible to specific cytochemical reactions and stainings, was found to reach its maximum in caput-epididymidis spermatozoa, in which electron microscopy revealed that the sheared chromatin was mainly organized into 120-A-thick knobby fibers. No further changes were found in sperm up to their appearance in the fallopian tubes. On the contrary, chromatin stabilization, the onset of which occurs in the testis (at the late spermatid stage) via the formation of -S-S- cross-links, is completed in the vas deferens, where chromatin has a superstructure consisting of thicker fibers, with diameters of 210 and 350 A. The reductive cleavage of disulfides in vas-deferens spermatozoa does not completely destroy the superstructure of sperm chromatin, which could indicate 'coiling' of the basic knobby fiber. In fact, when the ion concentration was increased, the chromatin of vas-deferens spermatozoa appeared to be organized into fibers with diameters similar to those of the caput epididymidis. This unique organization of mature sperm chromatin should have an essential role in the fast swelling of spermatozoa during fertilization