Sea urchin testicular cells evaluated by fluorescence microscopy of unfixed tissue

A procedure is presented for rapid, quantitative evaluation of cell and nuclear types present in the male gonad of the sea urchin. Vitally stained whole mounts of tissue fragments or dissociated cells are prepared, which reveal detailed 3-dimensional chromatin patterns and enough cytoplasmic features to provide reliable markers for most of the somatic and germ line cell types. Representative cellular morphologies are described. Nuclear volume changes during spermatogenesis are quantified. Spermatid nuclei contain an apparently interconnected network of heterochromatin. Regions relatively devoid of chromatin decrease in size as nuclear condensation proceeds and spherical nuclear shape is maintained. The major decrease in nuclear volume occurs prior to the late spermatid stage. The volume of the spermatozoan nucleus is achieved by the smallest late spermatid nucleus before the change from spherical to conoid morphology. The relationship of this morphological transition to sperm histone dephosphorylation is discussed.