Cytoplasmic cylinders in bullfrog oocytes

Historical survey on chromatoid body research

The chromatoid body (CB) is a male reproductive cell-specific organelle that appears in spermatocytes and spermatids. The cytoplasmic granule corresponding to the CB was first discovered some 130 years ago by von Brunn in 1876. Thirty years later the German term "chromatoide Körper" (chromatoid body) was introduced to describe this granule and is still used today. In this review, first, the results obtained by light microscopic studies on the CB for the first 60 years are examined. Next, many findings revealed by electron microscopic studies are reviewed. Finally, recent molecular cell biological studies concerning the CB are discussed. The conclusion obtained by exploring the papers on CB published during the past 130 years is that many of the modern molecular cell biological studies are undoubtedly based on information accumulated by vast amounts of early studies.

The ultrastructure of germinal beds in the ovary of Gerrhonotus coeruleus (Reptilia: Anguidae)

A study of ovarian structure in adult Alligator Lizards (Gerrhonotus coeruleus) was conducted by light microscopy and transmission electron microscopy. Particular attention was directed to characterizing the ultrastructure of germ-line cells, prior to follicle formation. General ovarian structure in this lizard is similar to that of other lizards. The paired organs are hollow, thin-walled sacs containing follicles in roughly 3 to 4 size classes. Ovarian germinal tissue consists of oogonia (diploid cells which divide mitotically) and oocytes (meiotic cells), intermixed with ovarian surface epithelial cells. Germ cells reside in two dorsal patches of epithelium per ovary (germinal beds), as is common in lizards. Oogonia in interphase show a highly dispersed chromatin pattern. Within oogonia cytoplasm, Golgi complexes are scarce, rough endoplasmic reticulum is absent, and lipid droplets are rare. Ribosomes are scattered in small clusters. Small, round vesicles are common in all oogonia; glycogen-like granules are present in some. Mitochondria form a juxta-nuclear mass within which groups of several mitochondria surround a dense granule. 'Nuage' granules also are found unassociated with mitochondria. Oocytes are present in stages of meiotic prophase up to diplotene. Synaptinemal complexes are seen in several (pachytene) cells. The cytoplasm of oocytes differs from that of oogonia in that mitochondria do not form groups, and nuage and glycogen are absent, whereas small round vesicles and large irregular vesicles are common. The ultrastructural similarities in germ cells of a reptile as compared to those of other vertebrates strengthens the notion that germ-line cells possess (or lack) qualities related to the undifferentiated state of these cells.

The relationship between the nuage and the chromatid body during spermatogenesis in the rat

Cytoplasmic structures ultrastructurally similar to the nuage are present in the cytoplasm of all spermatogenic cells in adult rats. The nuage is a discrete organelle which should not be confused with the chromatoid body. In step 7-8 spermatids transient contact is established between the nuage by the chromatoid body. This indicates a very specific recognition of the nuage by the chromatoid body. It is suggested that the nuage and the chromatoid body are separate cell organelles the functions of which are somehow related to each other.

Occurrence of nuage in fetal human germ cells

Germ cells of human fetuses aged 7-13 weeks were studied. Dense fibrous material called nuage was found in the cytoplasm of human fetal germ cells. The nuage increased in frequency in the germ cells during the interval studied. In oogonia the nuage occurred much more frequently than in spermatogonia and the frequency of nuage in oogonia increased earlier than in spermatogonia. The number of nuage was continuously at a higher level in oogonia than in spermatogonia. It is suggested that these findings support the theory that the nuage may act as a germ cell determinant.

Distribution of nuclear pores and perinuclear dense substances in spermatocytes I of some Oedionychina fleabeetles

The nuclear envelope of growing postpachytene spermatocyte I differs notably in structure between the fleabeetles Omophoita cyanipennis and Oedionychus bicolor. The former species shows a more conventional structure with an even and probably random distribution of nuclear pores, and a strongly electron-opaque layer of fibrogranular material (FM) separated from the outer nuclear membrane by an intermediate layer of about 40 nm thickness. Peripherally from the FM layer, a continuous corona of granular dense material (GM) is accumulated around the nucleus. In Oedionychus, all nuclear pores are clustered in "nuclear sieves", i.e., shallow, cup-like indentations of the nuclear envelope. The sieves are filled with an electron-opaque substance resembling the FM of the Omophoita spermatocytes. This substance is kept at a distance of about 40 nm from the outer nuclear membrane. GM is produced only at the sives, and is thus discontinuous. The sieves with their contents are called nuclear sieve complexes (NSC).

Ultrastructural characterization of nuage in spermatocytes of the rat testis

At least six different types of nuage, as judged by morphological appearance, were found in spermatocytes of the adult rat testis. These were characterized by form, distribution, and association with other organelles. The appearance (with time) and the dissociation of some nuage types were recorded in conjunction with other events of the spermatogenic cycle. The data indicate that all types of nuage behave in a dynamic way. Especially interesting were the findings concerning the chromatoid body. This structure was first observed in mid-pachytene spermatocytes. By late diplotene and during the first meiotic division, it had lost its prominence such that its eventual fate could not be determined. Large dense (0.5 micrometer) bodies appeared de novo in the cytoplasm of newly formed secondary spermatocytes. They were seen scattered throughout the cell and in association with mitochondria. With time these bodies appeared to coalesce to form the large definitive chromatoid of a type similar to that known to be present throughout most of the remainder of spermiogenesis.

Fine structural and radioautographic observations on dense perinuclear cytoplasmic material in tadpole oocytes

Dense fibrous material is first seen in association with mitochondria in tadpole oogonia but is most prominent in oocytes during the extended first meiotic prophase when it aggregates into dense bodies in the perinuclear cytoplasm. The origin of this material has been attributed to 350-A nuclear granules which form cytoplasmic streamers of fibrous material upon passage through nuclear pores. This has commonly been interpreted as the transfer of ribonucleoprotein to the cytoplasm for storage. However, cytochemical reactions for nucleic acids have indicated an absence of detectable RNA in this dense material, and the results of radioautographic studies with labeled uridine, thymidine, or actinomycin D argue against the presence of nucleic acids. When sites of incorporation of tritiated amino acids were radioautographically localized, an appreciable number of silver grains were present over the dense bodies. Uptake of certain amino acids occurs fairly promptly but the degree of labeling levels off after about 6 hr, suggesting a rapid turnover of the material in the dense bodies. Attention is drawn to the similarity of the dense bodies to structures present in germ cells of a number of other species, and possible functions of the dense bodies in germ cell differentiation are considered.

Intramitochondrial yolk-crystals of frog oocytes. I. Formation of yolk-crystal inclusions by mitochondria during bullfrog oogenesis

Electron microscope examination of thin sections of bullfrog (Rana catesbeiana) ovarian oocytes has shown the presence of mitochondria containing yolk-crystal inclusions in oocytes of all sizes, from 160 to 1500 micro mean diameter. The hexagonally shaped yolk-crystals have major periodicities of 73.8 +/- 10.7 A (n = 100). Several forms of modified mitochondria, observed in the smaller oocytes, may be arranged into a series of structurally intermediate forms between standard oocyte mitochondria and the typical mitochondria with yolk-crystal inclusions. The observation of such intermediate forms is consistent with proposals that the yolk-crystal inclusions arise within a limited portion of the oocyte chondriome by a complex process of mitochondrial differentiation.