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Fleas (Siphonaptera) are holometabolous insects with larval and adult stages that exhibit vastly different ecologies from each other. Adult fleas are parasitic and feed exclusively on the blood of a vertebrate host, whereas flea larvae do not live on hosts and consume dried faecal blood from adult fleas. Because flea larvae rely on adult flea faeces for food, excrement and eggs must fall in the same location; thus, larval density is likely high in these restricted habitats. However, the influence of larval density on the subsequent adult stage has not been examined. In the present study, we utilized egg density to investigate density‐dependent effects on larval development and adult body size in the cat flea (Ctenocephalides felis Bouché) (Siphonaptera: Pulicidae). Specifically, eggs were collected to create three different larval densities (n = 50, 100 and 150 per 56.7 cm2), and hatched larvae from all groups were fed an excess amount of adult faecal pellets. Larval development was measured by recording the proportion of eggs that developed to the pupal stage and the proportion of eggs that reached adulthood (eclosion). The body size of eclosed adults was quantified for both sexes using head length and length of the total body. We found that the number of eggs had no effect on the proportion of larvae that pupated or the proportion of larvae that eclosed; however, higher egg densities resulted in larger body sizes for both sexes. Overall, these data yield significant insight into how the ecology of larval fleas impacts the biology of the resultant adults. [ABSTRACT FROM AUTHOR]

[Ca.sup.+] sparks are rare in healthy adult mammalian skeletal muscle but may appear when adult fiber integrity is compromised, and occur in embryonic muscle but decline as the animal develops. Here we used cultured adult mouse flexor digitorum brevis muscle fibers to monitor occurrence of [Ca.sup.2+] sparks during maintenance of adult fiber morphology and during eventual fiber morphological dedifferentiation after various times in culture. Fibers cultured for up to 3 days retain normal morphology and striated appearance. [Ca.sup.2+] sparks were rare in these fibers. At 5-7 days in culture, many of the original muscle fibers exhibit sprouting and loss of striations, as well as the occurrence of spontaneous [Ca.sup.2+] sparks. The average rate of occurrence of [Ca.sup.2+] sparks is > 10-fold higher after 5-7 days in culture than in days 1-3. With the use of fibers cultured for 7 days, application of the [Ca.sup.2+] channel blockers [Co.sup.2+] or nifedipine almost completely suppressed the occurrence of [Ca.sup.2+] sparks, as previously shown in embryonic fibers, suggesting that [Ca.sup.2+] sparks may be generated by similar mechanisms in dedifferentiating cultured adult fibers and in embryonic fibers before final differentiation. The sarcomeric disruption observed under transmitted light microscopy in dedifferentiating fibers was accompanied by morphological changes in the transverse (T) tubular system, as observed by fluorescence confocal imaging of both an extracellular marker dye and membrane staining dyes. Changes in T tubule morphology coincided with the appearance of [Ca.sup.2+] sparks, suggesting that [Ca.sup.2+] sparks may either be a signal for, or the result of, disruption of DHPR-ryanodine receptor 1 coupling. calcium ion signaling; muscle remodeling; fluo 4; calcium ion imaging

Morgan State University is a public urban research university in Maryland, with a current enrollment of 7,689 students, known for its excellence in teaching, research, public service, and community engagement. [...]

Two Ca2+-dependent signaling pathways, mediated by the Ca2+-activated phosphatase calcineurin and by the Ca2+-activated kinase Ca2+/calmodulin- dependent kinase (CaMK), are both believed to function in fast-to-slow skeletal muscle fiber type transformation, but questions about the relative importance of the two pathways still remain. Here, the differential gene expression during fast-to-slow fiber type transformation was studied using cultured adult flexor digitorum brevis (FDB) fibers and a custom minimicroarray system containing 21 fiber type-specific marker genes. After 3 days of culture, unstimulated fibers showed a generally slower gene expression profile; 3 days of electric field stimulation of cultured FDB fibers with a slow fiber-type pattern transformed the fibers to an even slower gene expression profile. Unstimulated FDB fibers overexpressing constitutively active calcineurin featured a slower gene expression profile, except four genes, indicating that transformation occurred, but was incomplete with activation of the calcineurin pathway alone. In both unstimulated FDB fibers and slow-type electrically stimulated FDB fibers, blocking of CaMK pathway with KN93 generated a faster gene expression profile compared with the negative control KN92, indicating that CaMK pathway functions during the transformation induced by both unstimulated culturing and slow fiber-type electrical stimulation. Moreover, neither the calcineurin nor the CaMK pathway alone could maximally activate the transformation, and coordination of the two pathways is required to accomplish a complete fast-to-slow fiber type transformation. [ABSTRACT FROM AUTHOR]

Ca+ sparks are rare in healthy adult mammalian skeletal muscle but may appear when adult fiber integrity is compromised, and occur in embryonic muscle but decline as the animal develops. Here we used cultured adult mouse flexor digitorum brevis muscle fibers to monitor occurrence of Ca2+ sparks during maintenance of adult fiber morphology and during eventual fiber morphological dedifferentiation after various times in culture. Fibers cultured for up to 3 days retain normal morphology and striated appearance. Ca2+ sparks were rare in these fibers. At 5-7 days in culture, many of the original muscle fibers exhibit sprouting and loss of striations, as well as the occurrence of spontaneous Ca2+ sparks. The average rate of occurrence of Ca2+ sparks is >10-fold higher after 5-7 days in culture than in days 1-3. With the use of fibers cultured for 7 days, application of the Ca2+ channel blockers Co2+ or nifedipine almost completely suppressed the occurrence of Ca2+ sparks, as previously shown in embryonic fibers, suggesting that Ca2+ sparks may be generated by similar mechanisms in dedifferentiating cultured adult fibers and in embryonic fibers before final differentiation. The sarcomeric disruption observed under transmitted light microscopy in dedifferentiating fibers was accompanied by morphological changes in the transverse (T) tubular system, as observed by fluorescence confocal imaging of both an extracellular marker dye and membrane staining dyes. Changes in T tubule morphology coincided with the appearance of Ca2+ sparks, suggesting that Ca2+ sparks may either be a signal for, or the result of, disruption of DHPR-ryanodine receptor 1 coupling. [ABSTRACT FROM AUTHOR]