Subcellular distribution and relative expression of fibrocyte markers in the CD/1 mouse cochlea assessed by semiquantitative immunogold electron microscopy

Spiral ligament fibrocytes function in cochlear homeostasis, maintaining the endocochlear potential by participating in potassium recycling, and fibrocyte degeneration contributes to hearing loss. Their superficial location makes them amenable to replacement by cellular transplantation. Fibrocyte cultures offer one source of transplantable cells, but determining what fibrocyte types they contain and what phenotype transplanted cells may adopt is problematic. Here, we use immunogold electron microscopy to assess the relative expression of markers in native fibrocytes of the CD/1 mouse spiral ligament. Caldesmon and aquaporin 1 are expressed more in type III fibrocytes than any other type. S-100 is strongly expressed in types I, II, and V fibrocytes, and α1Na,K-ATPase is expressed strongly only in types II and V. By combining caldesmon or aquaporin 1 with S-100 and α1Na,K-ATPase, a ratiometric analysis of immunogold density distinguishes all except type II and type V fibrocytes. Other putative markers (creatine kinase BB and connective tissue growth factor) did not provide additional useful analytical attributes. By labeling serial sections or by double or triple labeling with combinations of three antibodies, this technique could be used to distinguish all except type II and type V fibrocytes in culture or after cellular transplantation into the lateral wall.

Targeted reduction of oxytocin expression provides insights into its physiological roles

Oxytocin is a nonapeptide hormone that participates in the regulation of parturition and lactation. It has also been implicated in various behaviors, such as mating and maternal, and memory. To investigate whether or not oxytocin (OT) is essential for any of these functions, we eliminated, by homologous recombination, most of the first intron and the last two exons of the OT gene in mice. Those exons encode the neurophysin portion of the oxytocin preprohormone which is hypothesized to help in the packaging and transport of OT. The homozygous mutant mice have no detectable neurophysin or processed oxytocin in the paraventricular nucleus, supraoptic nucleus or posterior pituitary. Interestingly, homozygous mutant males and females are fertile and the homozygous mutant females are able to deliver their litters. However, the pups do not successfully suckle and die within 24 hours without milk in their stomachs. OT injection into the dams or rescue with the rat OT gene restores the milk ejection in response to suckling. OT is also needed for post-partum alveolar proliferation. These results indicate an absolute requirement for oxytocin for successful milk ejection, but not for mating, parturition and milk production, in mice. Furthermore, homozygous mutant mice show reduced aggression in some tests.

Catalytic turnover of substrate benzylamines by the quinone-dependent plasma amine oxidase leads to H2O2-dependent inactivation: evidence for generation of a cofactor-derived benzoxazole

Incubation of bovine plasma amine oxidase (BPAO) with benzylamine and various p-substituted analogues results in a time-dependent inactivation that is attributable to buildup of the H(2)O(2)-turnover product on the basis of protection afforded by coincubation with catalase. The mechanism of inactivation is distinct from that effected by H(2)O(2) itself, which requires higher concentrations. Solution studies using models for the 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor reveal a loss of catalytic activity arising from oxidation of the dihydrobenzoxazole tautomer of the product Schiff base, that competes with hydrolytic release of benzaldehyde product. The resulting stable benzoxazole exhibits a characteristic absorption depending on the nature of the benzylamine p-substituent. For benzylamine itself, the model benzoxazole absorbs at 313 nm, in an area of strong absorption by the enzyme, whereas for 4-nitrobenzylamine, the absorption of the model benzoxazole is sufficiently red-shifted (at 365 nm) to be discerned above the background enzyme absorption. Inactivation of BPAO by 4-nitrobenzylamine is accompanied by loss of the resting TPQ anion absorption at 480 nm concomitant with generation of a new absorption near 360 nm. Resonance Raman spectra of the inactivated enzyme show a close correspondence with those for the model 4-nitrobenzylamine-derived benzoxazole. Substrate-dependent inactivation is also observed for the other two mammalian enzymes examined, equine plasma amine oxidase and human kidney amine oxidase. Catalase provides complete protection in these instances as well. Benzoxazole formation may constitute a common mechanism of inactivation of quinone-dependent amine oxidases by normal substrates in vitro if the product H(2)O(2) is permitted to accumulate. More importantly, the results suggest that the benzoxazole inactivation pathway may be important physiologically and may have influenced the distribution of amine oxidases and catalase in cells.

Understanding and exploiting nature's chemical arsenal: the past, present and future of calicheamicin research

The enediyne antitumor antibiotics are appreciated for their novel molecular architecture, their remarkable biological activity and their fascinating mode of action and many have spawned considerable interest as anticancer agents in the pharmaceutical industry. Of equal importance to these astonishing properties, the enediynes also offer a distinct opportunity to study the unparalleled biosyntheses of their unique molecular scaffolds and what promises to be unprecedented modes of self-resistance to highly reactive natural products. Elucidation of these aspects should unveil novel mechanistic enzymology, and may provide access to the rational biosynthetic modification of enediyne structure for new drug leads, the construction of enediyne overproducing strains and eventually lead to an enediyne combinatorial biosynthesis program. This article strives to compile and present the critical research discoveries relevant to the clinically most promising enediyne, calicheamicin, from a historical perspective. Recent progress, particularly in the areas of biosynthesis, self-resistance, bio-engineering analogs and clinical studies are also highlighted.

The mechanism of delayed selfing in Collinsia verna (Scrophulariaceae)

Collinsia verna, blue-eyed Mary, has floral attributes of an outcrossing species, yet most flowers readily self-pollinate under greenhouse conditions. Here we describe the mechanism of self-pollination in C. verna via changes in relative positions of the stigma and anthers and late timing of receptivity, resulting in delayed selfing. Each flower contains four anthers that dehisce sequentially over ∼1 wk. Pollen that is not collected by pollinators accumulates in the keel petal and retains high viability (>80% pollen germination) up to the time of corolla abscission. The stigmatic surface does not become receptive until after the third anther dehisces. This overlap in the sexual phases is concurrent with a change in herkogamy during floral development. In most flowers (70%), the stigma has moved to the front of the keel and is positioned near the anthers when the third anther dehisces. Under field conditions, fruiting success of plants within pollinator exclosures was ∼75% of the fruiting success in open-pollinated plants (33% fruiting success via autogamy vs. 44% fruiting success, respectively). Collinsia verna plants in pollinator exclosures exhibit variation in autogamy rates within natural populations (range 0-80%). In addition, only half of naturally pollinated, receptive flowers examined had pollen tubes growing in their styles. In contrast, shortly after corolla abscission, nearly all flowers examined (96%) had pollen tubes in their styles. Thus we find that in C. verna, autogamy occurs late in floral development, which has the potential to provide substantial reproductive assurance, and that individuals vary in their ability to set fruit through this mechanism. We suggest that delayed selfing mechanisms may be overlooked in other species and that variable pollinator availability may play a significant role in the maintenance of mixed mating in species with delayed selfing, such as C. verna.

Deficiency in mouse oxytocin prevents milk ejection, but not fertility or parturition

Oxytocin is a nonapeptide hormone that participates in the regulation of parturition and lactation. It has also been implicated in various behaviors, such as mating and maternal, and memory. To investigate whether or not oxytocin (OT) is essential for any of these functions, we eliminated, by homologous recombination, most of the first intron and the last two exons of the OT gene in mice. Those exons encode the neurophysin portion of the oxytocin preprohormone which is hypothesized to help in the packaging and transport of OT. The homozygous mutant mice have no detectable neurophysin or processed oxytocin in the paraventricular nucleus, supraoptic nucleus or posterior pituitary. Interestingly, homozygous mutant males and females are fertile and the homozygous mutant females are able to deliver their litters. However, the pups do not successfully suckle and die within 24 h without milk in their stomachs. OT injection into the dams restores the milk injection in response to suckling. These results indicate an absolute requirement for oxytocin for successful milk injection, but not for mating, parturition and milk production, in mice.