Allometric constraints on Sr/Ca and Ba/Ca partitioning in terrestrial mammalian trophic chains

In biological systems, strontium (Sr) and barium (Ba) are two non-essential elements, in comparison to calcium (Ca) which is essential. The Sr/Ca and Ba/Ca ratios tend to decrease in biochemical pathways which include Ca as an essential element, and these processes are termed biopurification of Ca. The quantitative pathway of the biopurification of Ca in relation to Sr and Ba between two biological reservoirs (R _n and R_{n -1}) is measured with an observed ratio (OR) expressed by the (Sr/Ca) _Rn /(Sr/Ca) _Rn-1 and (Ba/Ca) _Rn /(Ba/Ca) _Rn-1 ratios. For a mammalian organism, during the whole biopurification of Ca starting with the diet to the ultimate reservoir of Ca which is the bone, the mean values for OR_Sr and OR_Ba are 0.25 and 0.2, respectively. In this study, published Sr/Ca and Ba/Ca ratios are used for three sets of soils, plants, and bones of herbivorous and carnivorous mammals, each comprising a trophic chain, to illustrate the biopurification of Ca at the level of trophic chains. Calculated OR_Sr and OR_Ba of herbivore bones in relation to plants and of bones of carnivores in relation to bones of herbivores give OR_Sr=0.30±0.08 and OR_Ba=0.16±0.08, thus suggesting that trophic chains reflect the Sr/Ca and Ba/Ca fluxes that are prevalent at the level of a mammalian organism. The slopes of the three regression equations of log(Sr/Ca) vs. log(Ba/Ca) are similar, indicating that the process of biopurification of Ca with respect to Sr and Ba is due to biological processes and is independent of the geological settings. Modifications of the logarithmic expression of the Sr/Ca and Ba/Ca relationship allow a new formula of the biopurification process to be deduced, leading to the general equation OR_Ba=OR_Sr^1.79±0.33,where the allometric coefficient is the mean of the slopes of the three regression equations. Some recent examples are used to illustrate this new analysis of predator-prey relations between mammals. This opens up new possibilities for the utilization of Ba/Ca and Sr/Ca in addition to stable isotope ratios (¹³C and ¹⁵N) for the determination of the relative contribution of different food sources to an animals diet.     

Changes in Sr/Ca, Ba/Ca and 87Sr/86Sr ratios between trophic levels in two forest ecosystems in the northeastern U.S.A.

The variability and biologicalfractionation of Sr/Ca, Ba/Ca and ⁸⁷Sr/⁸⁶Srratios were studied in a soil–plant–invertebrate–bird food chain in two forested ecosystems withcontrasting calcium availability in the northeasternU.S.A. Chemical measurements were made of the soilexchange pool, leaves, caterpillars, snails, and boththe femurs and eggshells of breeding insectivorousmigratory songbirds. ⁸⁷Sr/⁸⁶Sr values weretransferred up the food chain from the soil exchangepool to leaves, caterpillars, snails and eggshellswithout modification. Adult birds were the oneexception; their ⁸⁷Sr/⁸⁶Sr values generallyreflected those of lower trophic levels at each site,but were lower and more variable, probably becausetheir strontium was derived in part from foods intropical winter habitats where lower⁸⁷Sr/⁸⁶Sr ratios are likely to predominate. Sr/Ca and Ba/Ca ratios decreased at each successive trophiclevel, supporting previous suggestions that Sr/Ca andBa/Ca ratios can be used to identify the trophic levelat which an organism is primarily feeding. The changesin Sr/Ca and Ba/Ca ratios we measured for vegetationand insects were comparable to similar measurementsmade previously (but based on single samples of eachorganism) in an alpine ecosystem. Changes in Sr/Ca andBa/Ca ratios between birds and their food have notpreviously been measured, but the values we obtainedwere similar to those for herbivorous and carnivorousmammals at similar trophic levels. Our results provideevidence that supports the use of Sr/Ca ratios in thedetermination of human paleodiets and suggests thatSr/Ca ratios may also provide a useful tool in studiesof modern food webs. Furthermore, our findings suggestthat ⁹⁰Sr from nuclear fallout will notbioaccumulate in forests and that changes in Sr/Caratios between trophic levels will need to beconsidered in some cases when using⁸⁷Sr/⁸⁶Sr as a tracer of calciumbiogeochemistry.     

Sr/Ca and early hominin diets revisited: new data from modern and fossil tooth enamel

A previous study of strontium/calcium (Sr/Ca) ratios in Paranthropus suggested that it consumed more animal foods than was previously believed. However, that study looked at Sr/Ca in fossil bone, which is known to be highly susceptible to diagenesis. Enamel, in contrast, is resistant to post-mortem alteration making it a more appropriate material for Sr/Ca analysis of Plio-Pleistocene fossils. Yet, we know virtually nothing about Sr/Ca in the enamel of modern African mammals, much less fossil taxa. To address this gap, we studied Sr/Ca in tooth enamel from modern mammals in the greater Kruger National Park, South Africa, as well as fossil fauna from the Sterkfontein Valley. Grazing herbivores have the highest Sr/Ca, followed by browsers and carnivores in both modern and fossil fauna. This similarity in ecological Sr/Ca patterning between modern and fossil fauna shows that diagenesis has not obscured the primary dietary signals. Australopithecus has significantly higher Sr/Ca than Paranthropus, and higher Sr/Ca than fossil papionins, browsers, and carnivores. Paranthropus has lower Sr/Ca than grazers, but its Sr/Ca is higher or equal to that of fossil papionins, browsers, and carnivores. Thus, Sr/Ca for both hominins is relatively high, and provides no direct evidence for omnivory in either taxon. The consumption of underground resources or insects are among the possible explanations for the highly elevated Sr/Ca in Australopithecus.     

Tracking dietary transitions in weanling baboons (Papio hamadryas anubis) using strontium/calcium ratios in enamel

Strontium and calcium are incorporated into developing teeth in a manner that reflects changing physiological concentrations in the body. A new model predicts changes in strontium/calcium (Sr/Ca) ratios in response to dietary transitions experienced at birth and during the weaning period. Microsampling of longitudinal thin sections of tooth enamel using laser ablation inductively coupled plasma mass spectrometry provides a basis for the systematic evaluation of variation in Sr/Ca ratios within the tooth crown. Incremental growth markers in enamel are used to determine the age of onset of enamel mineralization at each sampling point. Thin sections of 5 teeth from 2 wild-caught baboons (Papio hamadryas anubis) were systematically analysed using this technique. Intra- and intertooth analyses of Sr/Ca ratios reveal a pattern of dietary development during the period of enamel formation that is consistent with observational data on the timing of weaning behaviour in anubis baboons.     

青海喇家遗址人类遗骸的锶同位素比值分析

喇家遗址位于青海省民和县,主体为齐家文化的遗存,距今大约3900~4300年。喇家遗址古代人类迁移活动的研究,对于探索黄河上游古代文明,推动该地区齐家文化研究,有着积极的学术意义。本文首先采用电感耦合等离子体质谱技术对喇家遗址出土的22个个体的44份牙釉质和骨骼样品进行了元素分析,根据检测结果排除了受到污染的2份骨骼样品。其次,通过热电离质谱分析方法对喇家遗址出土22个个体的42份牙釉质和骨骼样品及8个猪牙釉质样品的锶同位素比值进行了测定。检测数据表明,猪牙釉质的锶同位素比值的标准偏差远小于其他动物,可以推断猪由当地饲养的可能性是最大的,因此其牙釉质锶同位素比值可以代表当地的锶同位素水平。经过计算得到8个猪牙釉质的锶同位素比值的平均值为0.710930,将该平均值加或减2倍标准偏差可以得到喇家遗址当地的锶同位素比值范围在0.711058~0.710802之间。以此为前提可以推测,本次检测的22个个体中,有17个个体牙釉质的锶同位素比值在遗址当地的锶同位素比值范围内,可能为本地出生。还有2个个体牙釉质在当地的锶同位素比值范围上下限附近,姑且存疑;仅有3个个体牙釉质的锶同位素比值在遗址当地的锶同位素比值范围以外,表明这些个体可能在其他地区出生,去世后埋葬在遗址中。此外,数据分析还显示,本地出生人群牙釉质的锶同位素比值平均值与骨骼的锶同位素比值平均值比较接近,暗示喇家遗址当地古人类生活方式可能比较统一。     

Amounts of Sr and Ca Eluted from Deciduous Enamel to Artificial Saliva Related to Dental Caries

This study was performed to elucidate the relationship between dental caries and the levels of Sr and Ca eluted from enamel, and to examine whether these elements are useful as factors to assess caries risk. The available 103 (Sr) and 108 (Ca) samples were obtained among 111 collected deciduous teeth. The healthy regions of enamel were decalcified in artificial saliva at pH 6.2 and 5.5. The eluted levels of these elements from enamel were determined using atomic absorption spectrophotometry. Sr and Ca levels were not affected by the sex nor tooth type. Sr levels of the caries-experienced tooth (CE) group were 2.6-fold (pH 6.2) and 2.2-fold (pH 5.5) higher than those of the sound tooth (ST) group, respectively. Furthermore, the Sr levels were significantly higher in the teeth with treated than in those with untreated caries. Only at pH 6.2 was a significant difference found in Ca levels between the ST and CE groups. In the ST group, at pH 5.5, both the Sr and Ca levels significantly increased when the children had six or more carious teeth. The Sr and Ca elution levels were significantly inhibited in the teeth receiving fluoride application every 3 or 4 months compared to those that were not. These findings indicate that Sr can be an indicator of the acid resistance of teeth, and a useful factor to assess future caries risk.     

Evaluation of the mobility and discrimination of Ca, Sr and Ba in forest ecosystems: consequence on the use of alkaline-earth element ratios as tracers of Ca

A comprehensive understanding of Ca cycling in an ecosystem is desirable because of the role of this element in tree mineral nutrition and its status as a major base cation on the soil exchange complex. The determination of the origin of Ca in forests is particularly indicated in regard of important changes linked to acid inputs and intensive logging. Natural strontium isotopes are increasingly used as tracers of Ca in forest ecosystems for qualitative and quantitative assessments. Nevertheless this method is limited to relatively simple systems with two sources of nutrients. Some recent studies coupled Sr/Ca or Sr/Ba ratios to Sr isotopic measurements in order to solve more complex systems. Such method has however associated with it some uncertainties: this approach assumed that Ca, Sr and Ba behave similarly throughout the ecosystem and does not take into account the Ca biopurification processes occurring in some tree’s organs which can alter element ratio. The present work focuses on two deciduous species covering large areas in Europe: European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.). In order to test the similarity of behaviour between Ca, Sr and Ba, their concentrations were measured extensively in the major compartments of two forest ecosystems. In parallel, the discrimination process inside tree organs was studied in 23 stands for beech and 10 stands for oak. We found that Sr and Ca behave similarly in all soil and tree compartments. By contrast, Ba and Ca appear to have contrasting behaviours, especially in streams, soil solution and soil exchange complex (no correlations between element concentrations). Sr/Ba and Ba/Ca ratios must therefore be used with care as tracer of Ca. The Ca biopurification is absent in roots and slight in bole wood but is large in bark, twigs and leaves. The discrimination factors (DF) between wood and leaves are characteristic of the two species studied and do not change significantly as a function of the soil Ca status (acidic or calcareous soils). Therefore, strontium–calcium DF can be used as a correction factor of the Sr/Ca ratio of leaves when this ratio is used in connection with Sr isotopic ratios. This correction allows to solve systems of tree nutrition with more than two sources of Ca.     

Otolith Sr/Ca ratio complements Sr isotopes to reveal fish migration in large basins with heterogeneous geochemical landscapes

Environmental Biology of Fishes - The potential use of Sr/Ca and Ba/Ca ratios in fish otolith, as a complement to 87Sr/86Sr to study movements of Prochilodus lineatus, was evaluated in the La Plata...     

Analysis of otolith chemistry in Nassau grouper (Epinephelus striatus) from the Bahamas and Belize using solution-based ICP-MS

 We examined the utility of otolith minor and trace element chemistry, assayed with inductively coupled plasma mass spectrometry (ICP-MS), as a means of delineating population structure in the Nassau grouper (Epinephelus striatus). We characterized the elemental composition of otoliths collected in 1993 from three locations in Exuma Sound, Bahamas and from Glover Reef, Belize in 1995. A single location in Exuma Sound was sampled in 1994 to test temporal variability in otolith composition. Five elements (Ca, Zn, Sr, Ba and Pb) were routinely detected, at levels significantly above background, by solution-based ICP-MS. Results from analysis of variance of elemental data, expressed as a ratio to Ca, indicated that there were no significant differences among the Exuma locations for any element, but significant variability was found between Glover Reef and the pooled Exuma localities for Zn/Ca, Sr/Ca and Ba/Ca ratios. Significant inter-annual differences at one Exuma Sound location was restricted to Ba/Ca ratios. Discriminant function analysis correctly classified 86% and 95% of the Belize and pooled Exuma sites, respectively. Otoliths from Belize were characterized by low Zn/Ca and high Ba/Ca and Pb/Ca ratios compared to otoliths from fish collected in Exuma Sound. Although differences in Ba levels may be related to upwelling at Glover Reef, more data are needed to definitely link otolith composition with regional differences in water chemistry. Accepted: 15 February 1999     

Coccolith Sr/Ca ratios in the eastern Mediterranean: Production versus export processes

Samples collected by two sediment traps located southwest of Crete in the eastern Mediterranean (EMED) [48A (1953 m) and 48B (950 m)] from June 2005 to May 2006 were used to study fluxes of organic carbon, carbonate and coccolithophores in combination with the variations of Sr/Ca ratios in different individually picked coccolith species. Considering the complexity of the EMED, we validate the use of Sr/Ca ratios as productivity proxy and unravel the varied processes which may influence it. We examined the relationship between the seasonal peaks in export fluxes and the Sr/Ca ratio in coccoliths of three upper photic zone coccolithophores species collected in the traps, Calcidiscus leptoporus, Helicosphaera carteri and Emiliania huxleyi. We aimed at testing whether high export fluxes are correlated with high Sr/Ca ratios, suggestive of higher nutrient-stimulated production, or Sr/Ca ratios are unchanged during high export periods, suggestive of increased export efficiency or scavenging. Periods of enhanced trap fluxes in March and June result from surface water blooms recognized in satellite imagery. An additional peak flux was found in January, but this peak represents re-suspended or recycled material in the water column.The amplitude of seasonal variations in the Sr/Ca ratios of the three investigated species is small in both traps. In the shallow trap, a decrease in the Sr/Ca ratio of C. leptoporus occurred synchronously with minimal fluxes. The other two species were not measured for this period. In the deep trap, no such decrease in Sr/Ca was observed during minimal fluxes, in either C. leptoporus or H. carteri, probably due to a long residence of coccoliths in the water column, recycling and low export efficiency. Absolute Sr/Ca ratios for all species are lower than in other more productive environments like the Bay of Bengal, Arabian Sea, or Sargasso Sea. We conclude that Sr/Ca ratios in coccoliths of surface sediments in the EMED reflect mainly spring–summer bloom conditions averaged over hundreds to thousands of years.In addition, the origin of varying calcite thickness in H. carteri was investigated. The similarity of average Sr/Ca ratios in differently-calcified specimens confirms that coccolith thickness variations in this species result from primary biomineralization processes and not from variable overgrowth by (low Sr) abiogenic calcite in the water column or the sediments.     

Factors influencing Sr/Ca ratios in otoliths of Girella elevata: an experimental investigation

The utility of Sr/Ca ratios in otoliths as indicators of thermal history in fish was investigated for juvenile Girella elevata . There was no direct relationship between ratios of Sr/Ca and temperature of the water, as has been assumed in many previous studies. Sr/Ca ratios did not decrease when water temperature was elevated from 19 to 28° C. Elevation of ambient Sr levels in the sea water caused a significant increase in Sr/Ca ratios in otoliths, and there was a detectable increase in Sr/Ca ratios in otoliths of some individuals fed an Sr-enriched diet. Multiple factors may influence natural Sr/Ca ratios in otoliths of juvenile G. elevata and their interactions make it difficult to interpret the chronology of conditions experienced by an individual fish during early life in the pelagic or benthic environment.     

Effect of salinity on the skeletal chemistry of cultured scleractinian zooxanthellate corals: Cd/Ca ratio as a potential proxy for salinity reconstruction

The effect of salinity on the elemental and isotopic skeletal composition of modern zooxanthellate scleractinian corals (Acropora sp., Montipora verrucosa and Stylophora pistillata) was investigated in order to evaluate potential salinity proxies. Corals were cultured in the laboratory at three salinities (36, 38 and 40). The other environmental parameters were kept constant. For all species analyzed, Sr/Ca, Mg/Ca, U/Ca and Li/Ca ratios were not influenced by salinity changes. The Ba/Ca ratio also lacks a systematic relationship with salinity and exhibits high inter-generic variations, up to one order of magnitude. On the contrary, the Cd/Ca ratio decreases as a function of increasing salinity, and δ¹⁸O and δ¹³C also presented a significant response, but with opposite trends to salinity variations. Since Cd/Ca is usually considered as an upwelling proxy, its salinity dependence could compromise the upwelling signal, unless some corrections can be carried out. Regardless, if the dependence found in the present dataset proved to be widespread and systematic, the Cd/Ca ratio could represent a promising salinometer awaiting further investigation. This study also confirmed the reliability of the well-established temperature proxies Sr/Ca, Mg/Ca and U/Ca, as these ratios were insensitive to salinity variations. Moreover, our results showed that δ¹⁸O or δ¹³C can be considered as reliable temperature recorders as far as the salinity effect is removed from the parameter reconstructed (e.g., temperature). Investigating the influence of salinity on the skeletal chemistry of scleractinian corals grown under controlled environmental conditions confirmed previous results, validated isotopic corrections, and identified a promising proxy of salinity.     

Test of soil extractants for their suitability in predicting Ca/Sr ratios in leaves and stems of sugar maple seedlings

Differential uptake and translocation of Ca and Sr in organisms have been reported, calling into question the use of Sr to track Ca cycling in the environment. We investigated the relationship between Ca/Sr ratios in soil extracts of various strengths (H₂O, NH₄Cl, and NH₄EDTA) and seedlings of sugar maple (Acer saccharum Marsh.) grown from natural regeneration on 37 sites. Our objectives were to determine if Ca/Sr ratios in soil extracts are correlated with those in sugar maple tissues, and what soil extractant best duplicate plant tissue Ca/Sr ratios. Leaves had higher Ca/Sr ratios than stems and the extractants did not produce equal Ca/Sr ratios: H₂O had the lowest Ca/Sr, and NH₄EDTA the highest. The relationships between soil extract Ca/Sr ratios and leaf and stem Ca/Sr ratios were significant and linear, but the slopes differed among extractants. The lowest slope (0.45) was observed for the water extract/leaves and the highest (2.15) for the NH₄EDTA extract/stem with discrimination factors ranging from 0.22 with NH₄EDTA to 1.59 for water. Leaf extracts were more strongly correlated with soil Ca/Sr than stem extracts (R ² of 0.57–0.7 vs. R ² of 0.45–0.6, respectively). These findings support the use of Ca/Sr ratios in plants to track their source of soil Ca, but they highlight the need to calibrate the relationships for the plant tissue and soil extractant used.     

Spatial and temporal variations in otolith chemistry and relationships with water chemistry: a useful tool to distinguish Atlantic salmon Salmo salar parr from different natal streams

Otolith elemental (Sr:Ca, Ba:Ca, Mn:Ca, Mg:Ca and Rb:Ca) and isotopic (⁸⁷Sr:⁸⁶Sr) profiles from several annual cohorts of juvenile Atlantic salmon Salmo salar were related to the physico‐chemical characteristics (chemical signatures, flow rate, temperature and conductivity) of their natal rivers over an annual hydrological cycle. Only Sr:Ca, Ba:Ca and ⁸⁷Sr:⁸⁶Sr in otoliths were determined by their respective ratios in the ambient water. Sr:Ca ratios in stream waters fluctuated strongly on a seasonal basis, but these fluctuations, mainly driven by water flow regimes, were not recorded in the otoliths. Otolith Sr:Ca ratios remained constant during freshwater residency at a given site and were exclusively related to water Sr:Ca ratios during low flow periods. While interannual differences in otolith elemental composition among rivers were observed, this variability was minor compared to geographic variability and did not limit classification of juveniles to their natal stream. Success in discriminating fish from different sites was greatest using Sr isotopes as it remained relatively constant across years at a given location.     

MEPE Localization in the Craniofacial Complex and Function in Tooth Dentin Formation

Matrix extracellular phosphoglycoprotein (MEPE) is an extracellular matrix protein found in dental and skeletal tissues. Although information regarding the role of MEPE in bone and disorders of phosphate metabolism is emerging, the role of MEPE in dental tissues remains unclear. We performed RNA in situ hybridization and immunohistochemistry analyses to delineate the expression pattern of MEPE during embryonic and postnatal development in craniofacial mineralizing tissues. Mepe RNA expression was seen within teeth from cap through root formation in association with odontoblasts and cellular cementoblasts. More intense expression was seen in the alveolar bone within the osteoblasts and osteocytes. MEPE immunohistochemistry showed biphasic dentin staining in incisors and more intense staining in alveolar bone matrix and in forming cartilage. Analysis of Mepe null mouse molars showed overall mineralized tooth volume and density of enamel and dentin comparable with that of wild-type samples. However, Mepe^-/- molars exhibited increased thickness of predentin, dentin, and enamel over controls and decreased gene expression of Enam, Bsp, Dmp1, Dspp, and Opn by RT-PCR. In vitro Mepe overexpression in odontoblasts led to significant reductions in Dspp reporter activity. These data suggest MEPE may be instrumental in craniofacial and dental matrix maturation, potentially functioning in the maintenance of non-mineralized matrix.     

Partitioning of the source of leaf calcium of American beech and sugar maple using leaf Ca/Sr ratios: a predominantly surficial but variable depth of Ca uptake

Background and Aims

Reduced availability of calcium (Ca) has been linked to maple forest decline. We therefore aimed at assessing the contribution of the different soil horizons to leaf Ca of competing beech (Fagus grandifolia Ehrh.) and sugar maple (Acer saccharum Marsh.) to better understand the dynamics of Ca uptake.

Methods

Leaf Ca was partitioned using the Ca/Sr ratio approach in two mature forests of southern Quebec. A mass balance was also used at one site to validate the results obtained with the Ca/Sr approach.

Results

The L and F horizons contributed most of the leaf Ca of beech and maple with likely small contributions from the upper B and/or H/Ahe horizons. Leaf Ca/Sr ratios of beech were however more variable than those of maple. Using a mass balance, the organic horizons and upper mineral soil horizons were found to provide ca. 80 and 20 % of tree Ca uptake, respectively.

Conclusion

Beech and maple Ca uptake depth apportionment is on average similar but beech is likely more plastic in sourcing soil Ca. The low contribution of the mineral soil to leaf Ca at our sites can be linked to less favorable conditions for Ca uptake likely associated with low Ca/Al ratios.     

Ca/Ba/Sr-induced conformational changes of ciliary axonemes

Macrocilia of the ctenophore Bero? undergo Ca/Ba/Sr-dependent activation of ciliary beating and microtubule sliding disintegration [Tamm, J. Comp. Physiol. A163:23-31, 1988a; Tamm, Cell Motil. Cytoskeleton 11:126-138, 1988b; Tamm, Cell Motil. Cytoskeleton 12:104-112, 1989; Tamm and Tamm, Proc. Natl. Acad. Sci. U.S.A. 86:6987-6991, 1989]. Here we report that detergent-extracted macrocilia show an ATP-independent conformational change in response to high concentrations of Ca, Ba, or Sr ions. When applied locally by iontophoresis, these ions induce a rapid planar curvature of the distal end of the macrociliary shaft, followed by a slower relaxation to the rest position. Tip curling occurs in a direction opposite to the physiological Ca/Ba/Sr response. When applied uniformly in the bath, a threshold concentration of 10(-1) M Sr is required to induce curling of the tip, and the distal ends remain curved. Calmodulin antagonists do not inhibit the tip curling response. Previous workers found that Ca induces changes in the helical shape of isolated doublet microtubules [Miki-Noumura and Kamiya, Exp. Cell Res. 97:451-453, 1976; Miki-Noumura and Kamiya, J. Cell Biol. 81:355-360, 1979; Takasaki and Miki-Noumura, J. Mol. Biol. 158:317-324, 1982] and sperm axonemes [Okuno and Brokaw, Cell Motil. 1:349-362, 1981] and suggested that conformational changes in microtubules may play a role in Ca regulation of ciliary motility. We propose that the Ca/Ba/Sr-induced curling of the macrociliary tip is due to similar helical changes of doublet microtubules, some of which in macrocilia are prevented from sliding by permanent connections (compartmenting lamellae) between adjacent axonemes within the shaft. Although the tip curling response does not appear to be directly relevant to the physiological Ca response of macrocilia, it provides a novel system for investigating Ca-induced conformational changes of microtubules independent of dynein-powered active sliding.     

FAM20C Plays an Essential Role in the Formation of Murine Teeth

FAM20C is highly expressed in bone and tooth. Previously, we showed that Fam20C conditional knock-out (KO) mice manifest hypophosphatemic rickets, which highlights the crucial roles of this molecule in promoting bone formation and mediating phosphate homeostasis. In this study, we characterized the dentin, enamel, and cementum of Sox2-Cre-mediated Fam20C KO mice. The KO mice exhibited small malformed teeth, severe enamel defects, very thin dentin, less cementum than normal, and overall hypomineralization in the dental mineralized tissues. In situ hybridization and immunohistochemistry analyses revealed remarkable down-regulation of dentin matrix protein 1 (DMP1) and dentin sialophosphoprotein in odontoblasts, along with a sharply reduced expression of ameloblastin and amelotin in ameloblasts. Collectively, these data indicate that FAM20C is essential to the differentiation and mineralization of dental tissues through the regulation of molecules critical to the differentiation of tooth-formative cells.     

Anatomical variations in primary teeth microelements with known differences in lead content by micro-Synchrotron Radiation X-Ray Fluorescence (μ-SRXRF) – A preliminary study

Shed teeth have been proposed as trace element biomarkers. This study determined variations in the spatial distribution of Ca, K, Zn, Pb, Mn, Cu, and Sr in four anatomical locations: superficial enamel (SE, 0–10 μm), subsuperficial enamel (SSE, 10–30 μm), primary dentin (PD), and secondary dentin (SD). Five primary incisors were analyzed by micro Synchrotron Radiation X-Ray Fluorescence (μ-SRXRF). Two teeth had low concentrations of lead in the SE (<250 μg/g), while three contained very high lead concentrations in the SE (>2000 μg/g). Teeth were sliced, and five spot measurements (20 μm beam diameter) were accomplished in each location. The data are shown as absolute values and as the ratio between the different elements and Ca. The distribution of K was close to that of Ca. Zn was the third most abundant element, with the highest levels being found in the SE and SD and low levels detected in the PD. Increasing Sr levels were found progressing from the enamel to the dentin, with the highest levels being found in the SD, a distribution that was unique. Pb, Mn, and Cu exhibited a similar trend, with higher signals for these elements detected in the SE. This study provides preliminary data on the heterogeneous distribution of different elements in the tooth, highlighting the importance of the first 10 μm of the SE for determination of some elements, such as Zn, Pb, Mn, and Cu.     

Periodic variation in Sr/Ca ratios in statoliths of the Japanese Common Squid Todarodes pacificus Steenstrup, 1880 (Cephalopoda: Ommastrephidae) maintained under constant water temperature

The Japanese Common Squid, Todarodes pacificus Steenstrup, 1880, moves vertically in the water column in time with the natural day-night cycle and this exposes the animal to considerable temperature changes throughout the 24-h period. We considered that this behavior could result in daily fluctuations of the statolith strontium/calcium ratio (Sr/Ca ratio), if this ratio is thermally sensitive, as is found for coral skeletons. To investigate this hypothesis, Japanese Common Squid were reared under constant temperature (15 °C) for 64 days and their statolith Sr/Ca ratios, in the area that had been deposited while in captivity, measured by wavelength dispersive spectrometer. Small repetitive fluctuations were observed in the statolith Sr/Ca ratios of the captive squid (N=5, 2.7-day cycle) but similar fluctuations were also observed in the statoliths of Japanese Common Squid collected from the wild (N=5, 2.4-day cycle). These results imply that the daily vertical movements in the water column are not reflected in the statolith Sr/Ca ratios in the Japanese Common Squid. The observed small repetitive fluctuations are discussed in relation to the periodic feeding activity of the captive squid (1.9-day cycle).