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Biomedical subjects

R J Kallenbach

Publications and source records attributed to R J Kallenbach.

8 recordsLinked to original sources
PubMed1985

Ultrastructural analysis of the initiation and development of cytasters in sea-urchin eggs.

Two approaches were used to study the origin and overall development of cytasters in relation to the emergence and maturation of new centrioles in sea-urchin eggs. A continuous hypertonic treatment was used to gather information on cytoplasmic areas of potential cytaster formation and the subsequent development of these cytastral areas. A two-step parthenogenetic stimulation procedure was used to analyse various cytastral changes during and after mitosis. Potential cytastral areas are associated with extensive Golgi complexes and astral formation occurs only about newly induced centrioles. The construction of a single aster involves a large redistribution of local cytoplasmic structures, concentrating some components, excluding others and orienting more and more microtubules in an increasingly focussed arrangement. These events are correlated with an extensive accumulation of astral endoplasmic reticulum, an increase in the size of the astral area, and a gradual acquisition of a more typical radial configuration. The astral shape becomes more pronounced during mitosis, after which the cytasters regress, but retain the mature centrioles. The data reveal that cytaster formation is initiated after the activation and appearance of centriolar precursor bodies, and that both centrioles and associated cytasters are complementary structures, which develop in unison. The results suggest that developing centrioles, from the moment of their emergence, control and direct the events of cytastral formation.

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PubMed1984

Endoplasmic reticulum whorls as a source of membranes for early cytaster formation in parthenogenetically stimulated sea urchin eggs.

Sea urchin eggs exposed to a continuous hypertonic treatment rapidly form many concentric whorls of endoplasmic reticulum (ER) during the pre-activation period of the parthenogenetic development. These whorls, however, are only a temporary configurational alteration of ER which begin to break up just prior to egg activation. The conversion back to normal vesicles and lamellae occurs not only concurrently with the appearance of early cytastral areas, but also frequently in close association with the formation of these membranous areas. It is revealed here that membrane elements from disrupting whorls may become incorporated into adjacent, developing clear areas, early cytastral areas, and that this ER constitutes an initial major source of membranes for these early astral areas. Having previously suggested that the actual formation of ER whorls occurs in direct response to released intracellular calcium in hypertonic stressed eggs, the new findings, along with other related data and correlations, further suggest that whorl disruption and the formation of associated astral areas can be correlated with a corresponding decrease in the concentration of this released calcium in the cytoplasm.

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PubMed1983

Do centrioles contain ribosomes?

Centrioles induced via a number of parthenogenetic agents regularly reveal the presence of one or more granules within their central cores. Though not a new discovery, these centriolar granules have carefully been re-evaluated here. Considering various criteria, it is proposed that these granules are intra-centriolar ribosomes. More specifically, they are more comparable to 70S ribosomes than to 80S cytoribosomes. The data suggest that within the lumen of centrioles, certain centriolar proteins are synthesized on ribosomes that may be uniquely centriolar.

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PubMed1983

Distinctive subcellular alterations induced by hypertonic stress in sea urchin eggs.

Sea urchin eggs continuously exposed to a hypertonic solution were ultrastructurally examined for osmotic-stress induced alterations. No fertilization membranes formed during the treatment and the surface-cortex complexes remained unaltered from the unfertilized state. However, the osmotic stress did induce a number of subcellular changes. During the first 30 minutes of the treatment the eggs formed many endoplasmic reticulum whorls and compacted Golgi body aggregations. Both of these new formations can be correlated with rapid changes in intracellular calcium, known to occur in hypertonic stressed eggs. Aggregations of mitochondria could be observed at later stages; these aggregations can also be related to subcellular stress and possible changes in internal calcium concentrations. The various morphological transitions within the cytoplasm, along with the lack of a cortical reaction in these eggs, not only supports the idea that calcium is released during parthenogenetic activation, but also suggests that this free calcium originates from stores other than the stores that are involved during fertilization or simple artificial activation.

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PubMed1983

The induction of de novo centrioles in sea urchin eggs: a possible common mechanism for centriolar activation among parthenogenetic procedures.

Eggs from two species of sea urchins were subjected to a variety of novel two-step parthenogenetic activation procedures. These treatments readily resulted in the formation of cytasters and centrioles. Centrioles are restricted to the cytasters, as well as to the broad perinuclear zone, and it appears that all cytasters contain one or more centrioles. The mode of centriolar origin and maturation, as revealed by these new procedures, is identical to that of centrioles induced by other procedures. Both centriolar and cytastral development are retarded by the parthenogenetic treatments; also, mitosis is generally delayed. These results, along with those of others, reveal that parthenogenetic agents have opposing effects on eggs. The agents are stimulatory in that they activate latent centrioles and the cell cycle, in general. They are inhibitory in that they suppress a variety of physiochemical events. Of these events, only one appears to be common to all parthenogenetic agents: the inhibition of protein synthesis. Egg centrioles may be kept in a latent state by repressor proteins. If these proteins normally cycle rapidly, then an inhibition of their continuous synthesis will disrupt their normal replacement rate. As such, a delay in replacement will allow functioning repressor proteins, associated with latent centrioles, to become nonfunctional, which in turn allows latent centrioles to become derepressed. This deblocking reaction would then activate the appearance of de novo centrioles in eggs.

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PubMed1982

Origin and maturation of centrioles in association with the nuclear envelope in hypertonic-stressed sea urchin eggs.

Unfertilized sea urchin eggs were parthenogenetically activated via a prolonged hypertonic treatment. The continuous subjection to the osmotic stress turned on the cell cycle and brought about the very slow development of mature centrioles. Within 1 h of the exposure, large osmiophilic aggregates were detected at the nuclear surface and were interpreted as early centriolar precursor forms. Ultrastructural examination of eggs during the 8 h of treatment revealed that the precursor forms systematically converted into mature centrioles which then produced daughter centrioles. All centriolar precursor bodies were associated with microtubules; cartwheel structures were the earliest morphological feature of centrioles detected within the osmiophilic bodies. Nascent centrioles appeared at the nuclear surface and, during their development into centrioles, continually maintained intimate associations with the nuclear envelope. We suggest that the resultant modification of the intracellular environment via the hypertonic stress promotes the activation of centriolar 'information-bearing-residues' or 'seeds' located at the nuclear envelope. The oocyte centrioles, before disappearing from the maturing egg, may have produced these 'seeds' and left them at the nuclear surface.

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