Extendend chromatin fibers in spermatozoa of apis mellifera (HYMENOPTERA, APOIDEA)

The flow of chromatin from the nuclei of mouse liver cells and spermatozoa after treatment with concentratedsaline and detergent solutions under the simultaneous action of gravity results in the formation of extendedchromatin fibers (ECF). In mouse somatic nuclei, the increase in chromatin condensation is accompaniedby a decrease in the frequency of ECF formation. Since tightly packed chromatin with a very lysine-richhistone variant that resembles somatic H1 histones occurs in honey bee spermatozoa, we examined theformation of ECF in sperm cells of Apis mellifera, and compared the findings with data for mouse cells.Freshly prepared smears of fixed and unfixed semen from A. mellifera were lysed under the action of gravity,stained with toluidine blue at pH 4.0, and examined with polarized and unpolarized light. A protocol usingunfixed preparations and a short lysis period that resulted in abundant ECF production in mouse hepatocytes(which contain loosely-packed chromatin) and sperm cells produced ECF in only a few spermatozoa of A.mellifera. In contrast, a protocol using fixed preparations and a long lysis period produced fewer ECFs inthe former two cell types and no ECF formation in honey bee spermatozoa. The limited chromatin fluidityin A. mellifera spermatozoa may reflect their special DNA-protein composition and organization in the cellnuclei, the participation of nuclear matrix elements, a less effective disruption of the nuclear envelope andplasmalemmal components during lysis, and/or cytoplasmic spatial constraints resulting from particularitiesin the acrosomal complex.

Extended chromatin fibers in mouse testicular spermatozoa

Since in mouse spermatozoa the somatic histones are replaced by other basic proteins and there are changes in the chromatin supraorganization, different patterns of extended chromatin fiber (ECF) formation would be expected compared with those formed by somatic cells that were previously studied. In this study, we investigated the formation of ECF in mouse testicular spermatozoa after lysis with 2 M NaCl plus 1 por cento Triton X-100, and under the action of gravity. ECFs were observed under polarized light in fixed and unfixed spermatozoa subjected to lysis in a vertical position and stained with toluidine blue at pH 4.0. In unfixed preparations, all of the sperm nuclei showed ECFs, whereas in fixed preparations 60 por cento of the cells had ECF. The latter frequency was much higher than that previously reported for mouse hepatocytes. Even in cells that did not produce ECFs in vertically and horizontally lysed preparations, an ordered reorganization of the chromatin was observed after lysis. The faint positive response to acid fast green at the nuclear periphery in spermatozoa that did not develop ECF after lysis was assumed to represent residual protamine and nuclear matrix proteins. The high frequency of mouse sperm cell nuclei with ECF probably reflected the extraction of protamines from the DNA-protein complexes of sperm cell nuclei facilitated by the specific lysis protocol.