Richard G. Kessel

The Golgi Apparatus: Structure and Function

Publisher Summary This chapter discusses the structure and function of the Golgi apparatus. The basic ultrastructure of the Golgi apparatus is relatively consistent throughout both the animal and plant kingdoms. The Golgi apparatus is readily observed in the living cell under the phase contrast microscope, where it generally appears comparable to that seen following the metallic impregnation methods. Metallic impregnation shows the Golgi apparatus as a dense, somewhat pleomorphic and ill-defined morphological structure. Early studies revealed its form to vary greatly in different types of cells and in the same cells depending on their state of activity. It may exist as a compact mass or be dispersed through the cytoplasm as isolated fragments. It has been described as a filamentous or platelike reticulum, a network of varying degrees of complexity, an arrangement of clear canals, vacuoles of varying size and crescent, cup or diskshaped bodies (dictyosomes) composed of an outer rim of osmiophilic substance (“Golgi externum”) and an inner central portion of osmiophobic substance (“Golgi internum”). Electron microscope studies served to confirm and strengthen the classical concept of the Golgi apparatus and to clearly show its complex nature. Golgi complex might be involved in the synthesis of this cell product or to what extent it might be dealing with the secretory product in other ways. In some cells, it appears that the Golgi complex may collaborate with other cell organelles in the production of complex or heterogeneous secretory product. Other complex functions are also discussed in the chapter.

The Problem of Germ Cell Determinants

Publisher Summary This chapter discusses the problem of germ cell determinants, it emphasized that the underlying mechanism involved in the origin, deposition, and mode of expression of all localized tissue-determining substances in the oocyte may be similar. The differentiation and organization within the oocyte, whether it involves so-called germ cell determinants, yolk deposition, polarity, or symmetry, depend basically on the nature of the information stored in the genes, and upon a suitable cytoplasmic environment in which they may normally and sequentially express themselves during the development and life cycle of the organism. The experimental studies of chromatin diminution are given. Molecular aspects of chromatin elimination in Ascaris lumbricoides have recently been investigated specifically with respect to a comparison of the informational content of Ascaris cells before and after chromatin elimination. These studies indicate that chromatin elimination in Ascaris leads to a quantitative difference in information content of the somatic cell line versus the germ cell line.

Annulate Lamellae: A Last Frontier in Cellular Organelles

Publisher Summary This chapter highlights annulate lamellae (AL) that are porous and often stacked parallel membranes that are largely confined to the cytoplasm of cells possessing them, but in a few cell types they may also be located inside the nucleus (intranuclear annulate lamellae). The chapter discusses distribution of the organelle, its generalized structure and variations in different cell types, the nature of the pore that characterizes this organelle, the relationships of annulate lamellae to other cellular organelles and cell products, postulated mechanisms involved in the morphogenesis of annulate lamellae, experimental manipulations that have been reported to either increase or decrease the amount of these membranes in cells, and consideration of the broad array of functions proposed for this organelle. AL is partially membranous like the endoplasmic reticulum (ER) and contains numerous pore complexes that are structurally similar to those in the nuclear envelope. The membranes enclose a compartment, a cisterna, and ribosomes are occasionally attached directly to the outer surface of the annulate lamellae. The AL is cyclical or transitory in some cells and variable in quantity. AL appears to be well developed in germ cells (male and female gametes), embryonic cells, and tumor and cancer cells.

The Structure and Function of Annulate Lamellae: Porous Cytoplasmic and Intranuclear Membranes

Publisher Summary This chapter describes the structure and functions of annulate lamellae (AL). AL are membranous organelles that consist of parallel membranes enclosing a cavity or cisterna; they also resemble the nuclear envelope in organization. The membranous components of AL are interrupted by discontinuities called “pores.” The pores in AL are structurally similar or identical to pores in a nuclear envelope but tend to have a higher frequency than the nuclear envelope pores, and the pores of AL are often hexagonally arranged. The function hypothesized that the pores of AL may be involved in the processing and assembly of polyribosomes is similar to the hypothesis proposed as one of the functions for nuclear pores. AL that are present in the nuclei of several different cell types are structurally identical to cytoplasmic AL. Intranuclear AL have their origin from intranuclear vesicles. The function of intranuclear AL is unknown but has been postulated to be similar to certain functions hypothesized for cytoplasmic AL.

An electron microscope study of the process of differentiation during spermatogenesis in the drone honey bee (Apis mellifera L.) with special reference to centriole replication and elimination

Spermatogenesis in the honey bee (Apis mellifera L.) differs from the process in diploid insects in several ways. The primary spermatocytes in the haploid drone undergo an abortive first meiotic division and, further, an unequal division of the secondary spermatocyte occurs. The result is two spermatids rather than the typical four. Associated with the first meiotic division, a centriole replication process occurs resulting in supernumary centrioles; the latter are eliminated from the cells through cytoplasmic blebs prior to the second meiotic division. During the centriole replication process, several single annulate lamellae appear to be differentiated from pre-existing lamellae of endoplasmic reticulum. An amorphous granular material is observed to surround the replicating centrioles, and it is similar to material located in the pores of the annulate lamellae and nuclear envelope. Because of the specific orientation which the annulate lamellae illustrate relative to the replicating centrioles, it is postulated that they are somehow involved in the accumulation of material utilized in centriole replication. The secondary spermatocyte spindle has associated with it a nuclear “wall” composed of alternate vesicular and compact layers of endoplasmic reticulum. The innermost layer of this wall appears to give rise to the spermatid nuclear envelope. Spermatocytes are interconnected by intercellular bridges throughout the process of spermatogenesis and it is postulated that this syncytium synchronizes the division process. Spermiogenesis in the honey bee is similar to that observed in a number of other insects.

Mechanisms of protein yolk synthesis and deposition in crustacean oocytes

SummaryElectron microscope studies on the oocytes of several crustacean species demonstrate that the protein yolk arises within vesicular and lamellar forms of the rough-surfaced endoplasmic reticulum. The vesicular form of the endoplasmic reticulum may have its origin from a blebbing process of the outer layer of the nuclear envelope. Disc-shaped granules, representing precursor elements of the yolk granules, appear within the vesicular and lamellar profiles of endoplasmic reticulum. Autoradiographic results suggest that the ribosomes attached to the endoplasmic reticulum take part in the biosynthesis of yolk proteins. Numerous disc-shaped granules accumulate within the cisternae of the endoplasmic reticulum, but eventually they undergo a transformation into a finely granular yolk granule. Thus, both the origin and growth of protein yolk granules occur within membranes constituting the endoplasmic reticulum. The results provide evidence that intra-ooplasmic synthesis of yolk protein occurs in these oocytes.

The association between microtubules and nuclei during spermiogenesis in the dragonfly.

Electron microscope studies on dragonfly spermatids at different stages during their maturation into spermatozoa reveal the nucleus (in transverse section) to be folded, resulting in a number of alternate furrows and ridges. During the elongation of the sperm head, the furrows become deeper and the chromatin of the nucleus is compressed or condensed. The specific orientation of groups of microtubules abotu 250 A in diameter in these furrows throughout spermiogenesis is suggestive that they play a role in the elongation of the nucleus. Microtubules are no longer associated with the nuclei of mature sperm. Microtubules are also associated with elements of the mid-piece and with each of the peripheral filaments in the flagellum.

An electron microscope study of differentiation and growth in oocytes of Ophioderma panamensis.

Electron microscope studies on oocytes of the ophiuroid Ophioderma panamensis indicate the numerous nucleoli to be active throughout much of oogenesis. The nucleoli appear to “spin out” coarse strands of granules and fibers from their periphery (nucleolonema), and become attached at certain points to the inner layer of the nuclear envelope. The nucleolonema appear to fragment into small granular clusters or granule-filament complexes, both of which are also observed in the cytoplasm. During the period of nucleolar activity, mitochondria illustrate a special relationship to the nuclear surface, being preferentially aligned adjacent to the outer layer of the nuclear envelope. Proteid yolk granules first become apparent within certain of the Golgi cisternae. The origin of cortical granules also appears to be associated with the Golgi complexes. During oocyte differentiation an extensive membrane system of vesicles and lamellae, part rough- and part smooth-surfaced, forms in the peripheral portion of the ooplasm. The morphological variations observed during oocyte growth indicate that this membrane system differentiates into (a) annulate lamellae, (b) endoplasmic reticulum which becomes organized into concentric whorls of membranes (within which lipid droplets appear), and (c) single lamellae of endoplasmic reticulum which partially surround each of the Golgi complexes in the cell. The specific arrangement and association between the Golgi complexes and endoplasmic reticulum strongly suggest that the two organelles play a role in the elaboration of proteid yolk granules and cortical granules.

An electron microscope study of spermiogenesis in the grasshopper with particular reference to the development of microtubular systems during differentiation.

Early in spermiogenesis of the grasshopper, numerous microtubules (manchette) develop in association with a perinuclear and pericentriolar granular aggregate. Eventually the microtubules, in a helical configuration, form a layer investing the spermatid nucleus. As the nucleus elongates and the chromatin condenses, the layer of microtubules appears to straighten and form usually three concentric layers around the late spermatid nucleus. The microtubules appear to degenerate following the nuclear elongation process so that they are no longer present in the head region of the completely mature sperm. Microtubules do develop in the midpiece and tail during spermiogenesis and persist in the mature spermatozoa. In these regions they are associated with the nebenkern and flagellar filaments. Those microtubules associated with the peripheral flagellar filaments as well as the two central filaments of the flagellum usually contain a dense internal body about 75 A in diameter.

An electron microscope study of nuclear-cytoplasmic exchange in oocytes of Ciona intestinalis

Electron microscope observations of glutaraldehyde-osmium tetroxide fixed oocytes of the tunicate Ciona intestinalis indicate that nuclear-cytoplasmic exchanges are prominent in young oocytes. Dense granular accumulations are noted at various regions on both sides of the nuclear envelope, and under favorable conditions they can be demonstrated to be continuous through the nuclear pores. The basophilic staining reaction of this product and the structural similarity to nucleolar components suggest that the exchange is from the nucleus to the ooplasm. The product transferred (which is Feulgen negative) appears to accumulate in the ooplasm adjacent to the nuclear envelope. The morphological variations observed suggest a subsequent transformation of this material into particulate ribosomes. Mitochondria often show a close association with the extruded ooplasmic masses.