Nuclei isolated from spermatozoa of various species (golden hamster, mouse, human, rooster, and the fish tilapia) were heated at 60 degrees-125 degrees C for 20-120 min and then microinjected into hamster oocytes to determine whether they could decondense and develop into pronuclei. Mature, mammalian sperm nuclei, which are stabilized by protamine disulfide bonds, were moderately heat resistant. For example, they remained capable of pronucleus formation even after pretreatment for 30 min at 90 degrees C. Indeed, a temperature of 125 degrees C (steam) was required to inactivate hamster sperm nuclei completely. On the other hand, nuclei of rooster and tilapia spermatozoa and those of immature hamster and mouse spermatozoa, which are not stabilized by protamine disulfide bonds, were sensitive to heating; although some of them decondensed after exposure to 90 degrees C, none formed male pronuclei. Furthermore, nuclei of mature hamster sperm became heat labile when they were pretreated with dithiothreitol to reduce their protamine disulfide bonds. These observations suggest that the thermostability shown by the nuclei of mature spermatozoa of eutherian mammals is related to disulfide cross-linking of sperm protamines.

The ultrastructure of the endometrial stroma in rats bearing deciduomata was examined in detail on day 9 (day of vaginal cornification = day 0) of pseudopregnancy, together with the development of deciduomata from day 4 to day 8. Five major regions were recognizable on day 9. 1) In the basal zone, which contributes to endometrial regeneration following decidualization, stromal cells remained fibrocyte-like and were separated by wide bands of collagen fibrils. Capillaries were fenestrated and large. 2) The capsule surrounding the antimesometrial (region of the) deciduoma was composed of flattened cells, showing mitosis, which appeared to provide a source of appositional growth of the deciduoma. 3) The large, tightly packed, polyploid cells of the antimesometrial deciduoma showed morphological evidence of protein synthesis activity, an absence of smooth endoplasmic reticulum, and surface specializations suggestive of adhesion (adherens junctions), communication (gap junctions), and maintenance of an extensive surface area (lamellar processes). These cells came into very close apposition with capillary endothelial cells, which were seldom fenestrated, lacked any continuous basal lamina, and showed evidence of high metabolic activity. 4) The loosely packed mesometrial deciduoma contained a structurally supportive, "fixed" population of spiny cells and a "free" population of granulated cells and their putative precursors, together with a meshwork of large, sinusoidal capillaries whose endothelium was generally supported by a basal lamina. 5) The peripheral parts of the glycogenic area, which was structurally similar to the mesometrial deciduoma, contained many grossly enlarged intercellular spaces of undetermined function. The stromal cells at day 4, which give rise to all non-vascular elements except the granulated cells mentioned above, were structurally simple and fibrocyte-like. Only two distinct regions, subepithelial and deep, were recognizable. Capillaries at day 4 generally possessed a continuous endothelium, with a complete basal lamina and many pericytes. Between days 5 and 8, the stromal cells showed divergent forms of differentiation according to their position in the endometrium. Ultrastructural differentiation of the vasculature also showed divergence according to position, leading to the various types of capillaries seen at day 9. Regional variation, and high levels of structural organization, characterize the "programmed" decidual response in the pseudopregnant rat.

No abstract

PLATE 145Intranuclear inclusions generally concluded to represent a heterogeneous class of bodies are readily distinguishable from nucleoli, fat droplets, crystals, or melanin also found within nuclei. The intranuclear inclusions associated with virus infection have been broadly classified into two types by Cowdry, type A and type B (1). Both A and B inclusions exhibit morphological variations and the few histochemical studies indicate that not all A nor all B inclusions are chemically alike (1-3). The type B inclusion associated with poliomyelitis, Borna disease, Rift Valley fever (1), and salivary gland virus disease (cytomegalia) (4), often appears in cells where no apparent associatlon with virus etiology could be established. This led Cowdry in 1934 (1) to state, "Consequently with these type B inclusions the existence of a virus should not be taken for granted. They may be simply the expression of nuclear modifications occurring not only in some virus diseases but also in many conditions for which viruses are probably not responsible." Typical intranuclear inclusions have been reported to occur spontaneously in liver and kidney cells of several wild mammals and birds (5), in liver cells of "normal stock" mice (6-8), and in tissue culture cells of foetal leptomeninges (3). Similar nuclear inclusions have been experimentally induced by injections of aluminum hydroxide, ferric hydroxide and carbon (9), by lead poisoning and irradiation (10), and treatment with thioacetamide (11, 12).In a cytochemical study of nuclear inclusions of human, rat, and mouse liver with the light microscope (13) the inclusions were found to be round and to vary in size. They were acidophilic, Feulgen negative, and contained variable levels of basophilic material identified as ribonucleic acid, protein, and occa-

In the polytenc chromosomes of Sdara coprophila, in addition to a nucleolus, large numbcrs of nucleolarlike structures or micronuclcoli are formed. A detailed mapping localized the nuclcolar organizer at one end of thc X chromosome and revealcd that approximately 18 % of the bands of each chromosome are potentially capable of producing micronucleoli. Most of these sites are in regions known from a previous study to show asynchronous DNA replication: DNA puffs and certain hcterochromatic regions. Micronucleoli are rarely found in association with bulbs. The RNA metabolism of the polytene chromosomes during late fourth instar was studied using radioautographic techniques. Isolated glands were incubated in tritiated uridine for l0 to 30 rain, and radioautographs were made of squash preparations. Despite the wide range of variation found among different larval cultures, the iollowing pattern was observed. Just prior to and at the beginning of DNA puff formation, a period of intense extrachromosomal nucleolar and micronucleolar RNA synthesis occurs. After maximal development of the DNA puffs, the synthcsis of extrachromosomal RNA is at a low point, while incorporation into bulbs and DNA puffs remains high. With the onsct of the prcpupal stage, all nuclear RNA synthesis ceases.