Modeling the dental development of fossil hominins through the inhibitory cascade

The inhibitory cascade is a mathematical model for interpreting the relative size of the occlusal surfaces of mammalian molars in terms of developmental mechanisms. The cascade is derived from experimental studies of mouse molars developed in culture, and has been tested and applied to the dentitions of rodents, ungulates, carnivores, and platyrrhines. Results from such applications have provided new information regarding the origins of plesiomorphic traits in mammalian clade and how derived morphologies may arise. In this study we apply the inhibitory cascade model to the postcanine dentition of a sample of Old World primates that includes fossil hominins. The results of this study suggest that the inhibitory cascade (i.e. M₁ < M₂ < M₃) describes the relative sizes of the molar occlusal areas of Old World primates and is likely the plesiomorphic condition for this clade. Within that clade, whereas most Old World monkeys have a M₁ < M₂ < M₃ pattern, most apes have a M₁ < M₂ ≈ M₃ pattern. This modified cascade suggests that greater levels of inhibition (or less activation) are acting on the posterior molars of apes, thus facilitating the reduction of M₃s within the apes. With the exception of the baboon genus Papio, extant congeners typically share the same molar inhibitory cascade. The differences in the relative size relationships observed in the molar and premolar-molar cascades of the species included in the fossil hominin genus Paranthropus suggest that although large postcanine teeth are a shared derived trait within this genus, the developmental basis for postcanine megadontia may not be the same in these two Paranthropus taxa. Our results show that phenotypic characters such as postcanine megadontia may not reflect common development.     

Digital Image Analysis in Dental Research Applied for Treatment of Fissures on Occlusal Surfaces of Premolars

The aim of this paper was to quantitatively assess caries changes of teeth by using digital image analysis. Digital images of stained sections of crowns of teeth were acquired with a computer-assisted light microscope. In each image, spots representing the main and total demineralization of enamel were segmented to determine their area. The area of total demineralization was significantly different between premolars with sealed fissures and unprotected premolars as indicated by the Mann–Whitney test. Fissures on occlusal surfaces of premolars were characterized by their width, height, and distance from the bottom of the fissure to the enamel–dentin junction. This distance was also significantly different between protected and unprotected teeth. The results of our in vitro studies of enamel lesions allow us to plan an effective diagnosis, prophylaxis, and treatment of early caries changes in in vivo conditions. © 2003 Biomedical Engineering Society. PAC2003: 8764Rr, 8757Ra, 8757Nk, 8780Pa     

A quantitative approach for analysing bone modelling patterns from craniofacial surfaces in hominins

Bone size and shape arise throughout ontogeny as a result of the coordinated activity of osteoblasts and osteoclasts, responsible for bone deposition and resorption, and growth displacements. The modelling processes leave specific microstructural features on the bone surface, which can be used to infer the mechanisms shaping craniofacial traits in extinct and extant species. However, the analysis of bone surfaces from fossils and archaeological samples faces some difficulties related to the bone loss caused by taphonomic factors, and the lack of formal methods for estimating missing information and comparing the patterns of bone modelling among several specimens and samples. The present study provides a new approach for the quantitative analysis of bone formation and resorption patterns obtained from craniofacial surfaces. First, interpolation techniques were used to estimate missing data on high‐resolution replicas of the left maxilla in a sample of sub‐adult and adult modern humans and sub‐adult fossil hominins. The performance of this approach was assessed by simulating variable amounts of missing data. Then, we applied measures of dispersion and central tendency to represent the variation and average pattern of bone modelling within samples. The spatial interpolation resulted in reliable estimations of the type of cell activity (deposition or resorption) in the missing areas, even when large extensions of the bone surface were lost. The quantification of the histological data allowed us to integrate the information of different specimens and depict the areas with higher and lower variation in the bone modelling pattern of the maxilla among specimens. Overall, the main advantages of the quantitative approach used here for generating bone modelling patterns are the high replicability and the possibility of incorporating variation among specimens into the comparisons among samples.     

Progress in understanding hominoid dental development

Teeth preserve a record of the way they grow in the form of incremental markings in enamel, dentine and cementum. These make it possible to reconstruct cellular activity and the timing of dental development in living and fossil primates, including hominids. They also provide a way of exploring the mechanisms that underlie morphological change during evolution and the nature of the relationship between ontogeny and phylogeny. All living great apes are dentally mature by about 11 y, irrespective of their body mass. While the early period of root formation in living great apes is shorter than in modern humans, enamel takes approximately the same time to form, irrespective of how thick it is. In general, differences in the total time taken to form enamel seem not to be due to differences in the rate at which enamel and dentine are secreted, but rather to faster or slower rates of differentiation of ameloblasts and odontoblasts and therefore to the number of secretory cells active at any one time during tooth formation. Tooth size, especially height, may influence the sequence of appearance of tooth mineralisation stages. The space available in the jaws may also have an influence on both the timing of tooth bud/crypt appearance and the sequence of gingival emergence. When each of these potential influences on dental development are carefully considered, and incremental markings used to calibrate key events, the developing dentition can provide an estimate of the period of dental maturation in fossil hominoids. However, the influence of body mass on the period of dental development among primates remains unclear. The earliest hominoids, dated at around 18 Mya, may still have had modern monkey‐like maturational profiles, and the earliest hominids, dated between 1.8 and 3.7 Mya, modern great ape‐like maturational profiles. Exactly when the extended or prolonged modern human‐like maturational profile first appeared remains debatable, but the most secure suggestion might be at the time of the appearance of the earliest archaic Homo sapiens, when brain size and body mass were finally both within the ranges known for modern humans. But at present we should not reject the hypothesis that an extended, modern human‐like, maturational profile arose more than once during human evolution in parallel with an increase in brain size.     

Megadontia, striae periodicity and patterns of enamel secretion in Plio-Pleistocene fossil hominins

Early hominins formed large and thick-enamelled cheek-teeth within relatively short growth periods as compared with modern humans. To understand better the developmental basis of this process, we measured daily enamel increments, or cross striations, in 17 molars of Plio-Pleistocene hominins representing seven different species, including specimens attributed to early Homo. Our results show considerable variation across species, although all specimens conformed to the known pattern characterised by greater values in outer than inner enamel, and greater cuspal than cervical values. We then compared our results with the megadontia index, which represents tooth size in relation to body mass, for each species to assess the effect of daily growth rates on tooth size. Our results indicate that larger toothed (megadont) taxa display higher rates or faster forming enamel than smaller toothed hominins. By forming enamel quickly, large tooth crowns were able to develop within the constraints of shorter growth periods. Besides daily increments, many animals express long-period markings (striae of Retzius) in their enamel. We report periodicity values (number of cross striations between adjacent striae) in 14 new specimens of Australopithecus afarensis, Paranthropus aethiopicus, Paranthropus boisei, Homo habilis, Homo rudolfensis and Homo erectus, and show that long-period striae express a strong association with male and average male–female body mass. Our results for Plio-Pleistocene hominins show that the biological rhythms that give rise to long-period striae are encompassed within the range of variation known for modern humans, but show a lower mean and modal value of 7 days in australopithecines. In our sample of early Homo, mean and modal periodicity values were 8 days, and therefore similar to modern humans. These new data on daily rates of enamel formation and periodicity provide a better framework to interpret surface manifestations of internal growth markings on fossil hominin tooth crowns. Importantly, our data on early hominin cross striation variation may now contribute towards solving difficult taxonomic diagnoses where much may depend on fragmentary molar remains and enamel structure.     

Apoptosis in the early involuting stellate reticulum of rat molar tooth germs

 When the enamel organ of the rat tooth germ is fully developed at the tip of the prospective cusp, amelogenesis begins, and at this site the overlaying stellate reticulum begins its involution. During the involution process, there is a gradual decrease in intercellular spaces, invasion by blood vessels, appearance of macrophage-like cells and reduction in the number of stellate reticulum cells. Since reduction or disappearance of cells during embryonic development in organs and tissues has been shown to occur by apoptosis, we decided to examine early involuting regions of the stellate reticulum in the hope of detecting apoptosis. For this purpose, upper first molars of Wistar newborn rats aged 1 and 3 days were fixed in formaldehyde for the TUNEL method and in glutaraldehyde-formaldehyde for light and electron microscopy. Paraffin sections revealed TUNEL-positive structures, i.e. brown-yellow-stained bodies, in the central portion of the stellate reticulum, and next to the outer enamel epithelium and stratum intermedium. Examination of ultrathin sections confirmed the TUNEL findings: some stellate reticulum cells showed nuclei containing crescent-like electron-opaque condensed masses of peripheral chromatin, typical of apoptosis. Also, apoptotic bodies of various sizes and appearances were frequently observed within stellate reticulum cells. We should like to suggest that apoptosis is associated with the reduction in the number of cells during regression of the reticulum. Accepted: 7 December 1998     

Hominid mandibular corpus shape variation and its utility for recognizing species diversity within fossil Homo

Mandibular corpora are well represented in the hominin fossil record, yet few studies have rigorously assessed the utility of mandibular corpus morphology for species recognition, particularly with respect to the linear dimensions that are most commonly available. In this study, we explored the extent to which commonly preserved mandibular corpus morphology can be used to: (i) discriminate among extant hominid taxa and (ii) support species designations among fossil specimens assigned to the genus Homo. In the first part of the study, discriminant analysis was used to test for significant differences in mandibular corpus shape at different taxonomic levels (genus, species and subspecies) among extant hominid taxa (i.e. Homo, Pan, Gorilla, Pongo). In the second part of the study, we examined shape variation among fossil mandibles assigned to Homo (including H. habilis sensu stricto, H. rudolfensis, early African H. erectus/H. ergaster, late African H. erectus, Asian H. erectus, H. heidelbergensis, H. neanderthalensis and H. sapiens). A novel randomization procedure designed for small samples (and using group ‘distinctness values’) was used to determine whether shape variation among the fossils is consistent with conventional taxonomy (or alternatively, whether a priori taxonomic groupings are completely random with respect to mandibular morphology). The randomization of ‘distinctness values’ was also used on the extant samples to assess the ability of the test to recognize known taxa. The discriminant analysis results demonstrated that, even for a relatively modest set of traditional mandibular corpus measurements, we can detect significant differences among extant hominids at the genus and species levels, and, in some cases, also at the subspecies level. Although the randomization of ‘distinctness values’ test is more conservative than discriminant analysis (based on comparisons with extant specimens), we were able to detect at least four distinct groups among the fossil specimens (i.e. H. sapiens, H. heidelbergensis, Asian H. erectus and a combined ‘African Homo’ group consisting of H. habilis sensu stricto, H. rudolfensis, early African H. erectus/H. ergaster and late African H. erectus). These four groups appear to be distinct at a level similar to, or greater than, that of modern hominid species. In addition, the mandibular corpora of H. neanderthalensis could be distinguished from those of ‘African Homo’, although not from those of H. sapiens, H. heidelbergensis, or the Asian H. erectus group. The results suggest that the features most commonly preserved on the hominin mandibular corpus have some taxonomic utility, although they are unlikely to be useful in generating a reliable alpha taxonomy for early African members of the genus Homo.     

Variability in Premolar and Molar Root Number in a Modern Population of Pan troglodytes verus

While teeth are the most common fossil remains for hominoids, little is known of the tooth root morphology in Primates. With the exception of modern humans, the variability of the number of roots within a species is scarcely documented and not conclusively quantified. This lack of knowledge hinders the interpretation of observed evolutionary trends, such as the reduction of the number of roots of premolars within the hominins. Here, we present the first quantification of the variability of the number of roots in a nonhuman ape population including 405 specimens. Our sample is made of a single biological population of Pan troglodytes verus from Liberia, which is compared to other extant hominoids. Both permanent and deciduous teeth were analyzed and comprise premolars and molars from maxillaries and mandibles. The estimated variability is very low for each tooth position; more than 97% of the specimens displaying the same number of roots except for P₄ (94%), M₁ (89%), and P⁴ (57%). No variability at all was observed for lacteal teeth. Males and females are statistically identical, and no difference linked to the tooth size (estimated by the occlusal surface) was observed. When compared to the observation in other hominoid species, these results emphasize that the difference of the number of roots observed between modern humans and apes is significant, and suggests that the evolution of premolar root number is mosaic, with the common ancestor of Pan and Homo probably displaying a reduced number of roots for P⁴ and maybe P³, but a plesiomorphic morphology of the roots of lower premolars. Anat Rec, 297:1927–1934, 2014. © 2014 Wiley Periodicals, Inc.     

利用光学相干断层图像平均灰度值定量研究牛恒牙早期人工脱矿

目的 研究经酸蚀脱矿后牛恒牙光学相干断层图像平均灰度值的变化,探讨平均灰度值作为一个参数指标定量检测牛恒牙早期脱矿的可行性.方法 以正常离体牛恒牙为样本,采用凝胶酸蚀法制备人工脱矿模型;用光学相干断层摄影术对人工脱矿模型扫描成像,利用Matlab软件计算不同酸蚀时间脱矿区牙体层110 μm范围内的平均灰度值.将测得图像灰度和归一化后图像灰度,分别进行单因素方差分析.结果 牙体表层110 μm范围内不同时间酸蚀脱矿区的平均灰度值从大到小依次为30 min酸蚀脱矿区、1O min酸蚀脱矿区、0 min酸蚀脱矿区,图像灰度归一化后做单因素方差分析,P＜0.05.结论 牙体表层110 μm范围内不同酸蚀时间脱矿区平均灰度值差异有统计学意义,并随脱矿时间增加而增大,即平均灰度值可以用于光学相干断层摄影术定量检测牙齿的早期脱矿.光学相干断层图像灰度归一化使得不同酸蚀脱矿区的平均灰度值更有可比性,减小了由于样本之间差异引起的误差,提高了平均灰度值作为参数指标定量检测牙齿早期脱矿的可靠性.     

白藜芦醇上调碱性成纤维细胞生长因子、胰岛素样生长因子1表达治疗骨骼肌损伤

文题释义： 白藜芦醇：非黄酮类的多酚化合物,分子式为C₁₄H₁₂O₃,相对分子质量228.25,为白色针状晶体,易溶于乙醚、氯仿、甲醇、乙醇、丙酮、乙酸、乙酯等有机溶剂。别名：3,4',5-三羟基芪、虎杖甙元,是相关植物在受到病菌侵染或环境恶化时产生的植物抗毒素,主要存在于葡萄、虎杖、决明、花生、桑葚等植物中。 骨骼肌急性钝挫伤：钝挫伤指在钝器作用下,造成以皮内或皮下及软组织出血为主要改变的闭合性损伤。骨骼肌急性钝挫伤指钝器在短时间内伤到肌肉层造成皮下及软组织出血,肌肉没有断裂或者撕裂的闭合性损伤。临床上90%的骨骼肌损伤属于钝挫伤与扭伤。 背景：近年来国内外对白藜芦醇抑制机体组织纤维化方面做了大量研究,但其在肌组织损伤康复方面的作用却鲜有报道。 目的：观察骨骼肌急性钝挫伤修复过程中碱性成纤维细胞生长因子、胰岛素样生长因子1蛋白表达规律,探讨白藜芦醇促进受损骨骼肌结构与功能恢复的作用机制。 方法：33只新西兰兔随机分为3组：正常组(3只)、自然恢复组(15只)、白藜芦醇组(15只),除正常组外均采用钝性暴力法制造骨骼肌钝挫伤模型,损伤后自然恢复组不予处理,白藜芦醇组给予白藜芦醇灌胃治疗,分别于伤后1,3,7,14,21 d处死动物,采用苏木精-伊红染色、Masson染色观察炎症细胞浸润情况、胶原纤维形成情况,免疫组织化学、免疫印记法检测骨骼肌中碱性成纤维细胞生长因子、胰岛素样生长因子1蛋白表达。 结果与结论：①苏木精-伊红染色显示：正常组兔肌纤维多边形、形态规则、排列紧密,肌核均匀分布于肌膜下,无增生与固缩,肌膜完整;自然恢复组伤后1 d见血细胞渗出,3 d炎症细胞开始浸润,至7 d达峰值,21 d肌纤维形态基本恢复正常;白藜芦醇组在炎症细胞浸润、修复时间上整体优于自然恢复组;②Masson染色显示：正常肌细胞中胶原纤维含量极少;自然恢复组随着瘢痕组织的形成,胶原纤维逐渐增加,于14 d达高峰;白藜芦醇组胶原纤维含量低于自然恢复组;③免疫组织化学和免疫印记检测显示：碱性成纤维细胞生长因子、胰岛素样生长因子1蛋白在骨骼肌修复过程中呈现先升高后降低的变化规律,两组均于7 d达高峰,21 d时仍高于正常,且白藜芦醇组峰值高于自然恢复组;④整体来看,白藜芦醇组在炎症反应以及修复程度上均优于自然恢复组,白藜芦醇通过上调碱性成纤维细胞生长因子、胰岛素样生长因子1蛋白表达来促进骨骼肌修复,但其并不改变骨骼肌损伤修复过程中蛋白表达量的整体变化规律。 ORCID: 0000-0001-6570-2052(刘杏) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Fibroblast growth factor expression during skeletal fracture healing in mice

Fibroblast growth factors (FGFs) are important signaling molecules that regulate many stages of endochondral bone development. During the healing of a skeletal fracture, several features of endochondral bone development are reactivated. To better understand the role of FGFs in skeletal fracture healing, we quantitatively evaluated the temporal expression patterns of Fgfs, Fgf receptors (Fgfrs), and molecular markers of bone development over a 14‐day period following long bone fracture in a mouse model. These studies identify distinct groups of FGFs that are differentially expressed and suggest active stage‐specific roles for FGF signaling during the fracture repair process. Developmental Dynamics 238:766–774, 2009. © 2009 Wiley‐Liss, Inc.     

Hepatocyte growth factor concentration in the early second-trimester amniotic fluid does not predict fetal growth at birth.

The purpose of this study was to evaluate whether hepatocyte growth factor (HGF) concentrations in the early second-trimester amniotic fluid predict fetal growth at birth. HGF and insulin-like growth factor-I (IGF-I) concentrations in the early second-trimester amniotic fluid were measured in 12 pregnancies with small for gestational age (SGA) infants, 84 pregnancies with appropriate for gestational age (AGA) infants, and eight pregnancies with large for gestational age (LGA) infants. HGF concentrations were measured from the early second-trimester amniotic fluid samples using an enzyme-linked immunosorbent assay. IGF-I concentrations were measured from the early second-trimester amniotic fluid samples using an immunoradiometric assay. Maternal age in AGA group (34.2 +/- 5.5 years) was significantly lower than in SGA (37.9 +/- 3.0 years) and LGA (37.6 +/- 3.3 years) groups (P < 0.05). There were no significant differences for parity or gestational age at amniocentesis among the groups. There were significant differences for birth age, birth weight, neonatal height, and placental weight among the groups (P < 0.05). HGF concentrations in SGA, AGA and LGA groups were 16.9 +/- 6.6, 16.7 +/- 9.0 and 20.2 +/- 14.8 ng/ml respectively (not significant). There was no correlation between amniotic fluid HGF concentrations and birth weight, height or placental weight. There were also no significant differences for amniotic fluid IGF-I concentrations among the three groups. These results suggest that differences in HGF concentrations in the early second-trimester amniotic fluid do not predict fetal growth at birth. Further study is needed to clarify the role of high HGF concentrations in early second-trimester amniotic fluid during pregnancy.     

Acute resistance exercise increases skeletal muscle angiogenic growth factor expression

AIMS: Both aerobic and resistance exercise training promote skeletal muscle angiogenesis. Acute aerobic exercise increases several pro-angiogenic pathways, the best characterized being increases in vascular endothelial growth factor (VEGF). We hypothesized that acute resistance exercise also increases skeletal muscle angiogenic growth factor [VEGF and angiopoietin (Ang)] expression. METHODS: Seven young, sedentary individuals had vastus lateralis muscle biopsies and blood drawn prior to and at 0, 2 and 4 h post-resistance exercise for the measurement of VEGF; VEGF receptor [KDR, Flt-1 and neuropilin 1 (Nrp1)]; Ang1 and Ang2; and the angiopoietin receptor--Tie2 expression. Resistance exercise consisted of progressive knee extensor (KE) exercise to determine one repetition maximum (1-RM) followed by three sets of 10 repetitions (3 x 10) of KE exercise at 60-80% of 1-RM. RESULTS: Resistance exercise significantly increased skeletal muscle VEGF mRNA and protein and plasma VEGF protein at 2 and 4 h. Resistance exercise increased KDR mRNA and Tie2 mRNA at 4 h and Nrp1 mRNA at 2 and 4 h. Skeletal muscle Flt-1, Ang1, Ang2 and Ang2/Ang1 ratio mRNA were not altered by resistance exercise. CONCLUSIONS: These findings suggest that acute resistance exercise increases skeletal muscle VEGF, VEGF receptor and angiopoietin receptor expression. The increases in muscle angiogenic growth factor expression in response to acute resistance exercise are similar in timing and magnitude with responses to acute aerobic exercise and are consistent with resistance exercise promoting muscle angiogenesis.     

Hominin life history: reconstruction and evolution

In this review we attempt to reconstruct the evolutionary history of hominin life history from extant and fossil evidence. We utilize demographic life history theory and distinguish life history variables, traits such as weaning, age at sexual maturity, and life span, from life history-related variables such as body mass, brain growth, and dental development. The latter are either linked with, or can be used to make inferences about, life history, thus providing an opportunity for estimating life history parameters in fossil taxa. We compare the life history variables of modern great apes and identify traits that are likely to be shared by the last common ancestor of Pan-Homo and those likely to be derived in hominins. All great apes exhibit slow life histories and we infer this to be true of the last common ancestor of Pan-Homo and the stem hominin. Modern human life histories are even slower, exhibiting distinctively long post-menopausal life spans and later ages at maturity, pointing to a reduction in adult mortality since the Pan-Homo split. We suggest that lower adult mortality, distinctively short interbirth intervals, and early weaning characteristic of modern humans are derived features resulting from cooperative breeding. We evaluate the fidelity of three life history-related variables, body mass, brain growth and dental development, with the life history parameters of living great apes. We found that body mass is the best predictor of great ape life history events. Brain growth trajectories and dental development and eruption are weakly related proxies and inferences from them should be made with caution. We evaluate the evidence of life history-related variables available for extinct species and find that prior to the transitional hominins there is no evidence of any hominin taxon possessing a body size, brain size or aspects of dental development much different from what we assume to be the primitive life history pattern for the Pan-Homo clade. Data for life history-related variables among the transitional hominin grade are consistent and none agrees with a modern human pattern. Aside from mean body mass, adult brain size, crown and root formation times, and the timing and sequence of dental eruption of Homo erectus are inconsistent with that of modern humans. Homo antecessor fossil material suggests a brain size similar to that of Homo erectus s. s., and crown formation times that are not yet modern, though there is some evidence of modern human-like timing of tooth formation and eruption. The body sizes, brain sizes, and dental development of Homo heidelbergensis and Homo neanderthalensis are consistent with a modern human life history but samples are too small to be certain that they have life histories within the modern human range. As more life history-related variable information for hominin species accumulates we are discovering that they can also have distinctive life histories that do not conform to any living model. At least one extinct hominin subclade, Paranthropus, has a pattern of dental life history-related variables that most likely set it apart from the life histories of both modern humans and chimpanzees.     

Dental Maturation,Eruption, and Gingival Emergence in the Upper Jaw of Newborn Primates

In this report we provide data on dental eruption and tooth germ maturation at birth in a large sample constituting the broadest array of non‐human primates studied to date. Over 100 perinatal primates, obtained from natural captive deaths, were screened for characteristics indicating premature birth, and were subsequently studied using a combination of histology and micro‐CT. Results reveal one probable unifying characteristic of living primates: relatively advanced maturation of deciduous teeth and M1 at birth. Beyond this, there is great diversity in the status of tooth eruption and maturation (dental stage) in the newborn primate. Contrasting strategies in producing a masticatory battery are already apparent at birth in strepsirrhines and anthropoids. Results show that dental maturation and eruption schedules are potentially independently co‐opted as different strategies for attaining feeding independence. The most common strategy in strepsirrhines is accelerating eruption and the maturation of the permanent dentition, including replacement teeth. Anthropoids, with only few exceptions, accelerate mineralization of the deciduous teeth, while delaying development of all permanent teeth except M1. These results also show that no living primate resembles the altricial tree shrew (Tupaia) in dental development. Our preliminary observations suggest that ecological explanations, such as diet, provide an explanation for certain morphological variations at birth. These results confirm previous work on perinatal indriids indicating that these and other primates telegraph their feeding adaptations well before masticatory anatomy is functional. Quantitative analyses are required to decipher specific dietary and other influences on dental size and maturation in the newborn primate. Anat Rec, 298:2098–2131, 2015. © 2015 Wiley Periodicals, Inc.     

Combining radiographic and histological data for dental development to compare growth in the past and the present

Background: Being able to estimate the age at death of fossil hominins enables meaningful comparisons of both dental and general growth, past and present.

Aim: The aim of this study was to use data for modern permanent canine formation derived from separate histological and radiographic studies to estimate the age at death of an early African Homo erectus specimen (KNM-WT 15?000) with a developing permanent maxillary canine.

Methods: Ground sections of 18 sexed modern human canines were used to reconstruct growth in tooth height along the enamel–dentine junction (EDJ) and onwards into root formation along the cement–dentine junction (CDJ). Daily rates of enamel and dentine formation were used to put a time scale to cumulative fractions of tooth height.

Results: Age estimates for KNM-WT 15?000 averaged 7.89–8.8 years of age (range?=?6.6–10.3 years) and were close to previous histological estimates for this individual (7.6–8.8 years).

Conclusions: Stages of dental development in KNM-WT 15?000 were easily accommodated within this age distribution of a modern sample. However, body mass and stature estimates for KNM-WT 15?000 fell well beyond those reported for a modern sample of 438 Sudanese children aged between 7.0–10 years.     

An apparently phylogeny-independent method for identification of skeletal (longitudinal) growth cessation (skeletal maturity) in birds

Identification of skeletal maturity is of interest as a measure of species longevity and for identifying its maximal achievable size/mass. Measurement of age on the basis of growth arrest/accentuation lines and external fundamental system evidences cessation or at least extreme slowing of circumferential bone growth. Such intramembranous (periosteal)-derived growth is distinct from the endochondral ossification responsible for longitudinal growth and therefore achievable organismal size/mass. As subchondral transcortical channels are required for nourishment, their loss should identify cessation of longitudinal growth. Predicated on phylogenetic bracketing/relationship and shared anatomical structures with and without growth plates, birds represent an appropriate model for the study of dinosaur ontogeny. Persistence of transcortical subchondral channels in the long bones of birds are examined at ×100–200 magnification and correlated with bone length. Transcortical channels are present in subchondral articular surfaces, but disappear when terminal longitudinal growth is achieved. Articular vascular channels perforating articular surfaces from within the bone are detected. Loss of penetrating channels is interpreted as evidence of skeletal growth cessation, identifying the longitudinal bone length at which skeletal growth cessation has been achieved. The current study provides evidence that maximal bone length does correlate with endochondral cessation growth. Failure of circumferential growth reduction/cessation to correlate with bone length may be related to lack of synchronicity of periosteal-based circumferential growth with the endochondral process responsible for bone lengthening. Loss/closure of articular vascular channels may be the most reliable measure of a bird's achievement of maximal growth (indicating cessation of appendicular element lengthening).     

The expression of IGF-I and myostatin mRNAs in skeletal muscle of hypophysectomized and underfed rats during postnatal growth

Aim: To determine the roles of myostatin and insulin‐like growth factor‐I (IGF‐I) during postnatal growth, we examined IGF‐I and myostatin mRNA expression in the skeletal muscles of hypophysectomized and underfed rats during postnatal growth. Methods: Five‐week‐old rats were divided into four groups: freely fed control, moderately underfed, severely underfed and hypophysectomized. Four weeks later, blood and muscle samples were gathered to determine serum IGF‐I, myosin heavy chain (MHC) isoforms, IGF‐I Ea, IGF‐I Eb and myostatin mRNA. Results: The weights of soleus, plantaris and masseter muscles were decreased in underfed and hypophysectomized rats. Hypophysectomy resulted in significant increases of type I MHC at the expense of type IIx in plantaris muscle and of neonatal MHC at the expense of types IIx and IIb in masseter muscle. Serum IGF‐I was decreased by underfeeding and hypophysectomy. Plantaris muscle IGF‐I Ea mRNA in underfed and hypophysectomized rats was significantly lower than in normal controls. Plantaris muscle IGF‐I Eb mRNA in underfed rats was significantly lower than in normal controls. Masseter muscle IGF‐I Eb mRNA in severely underfed rats was significantly lower than in normal control and hypophysectomized rats. Soleus muscle myostatin mRNA in hypophysectomized rats was significantly higher than in normal and significantly underfed rats. No significant differences in plantaris and masseter muscle myostatin mRNA were observed between groups. Conclusion: Suppressed muscle growth caused by hypophysectomy and underfeeding may be attributed mainly to reduced circulating IGF‐I and partially to reduced IGF‐I mRNA, rather than to a change in myostatin.     

Prenatal expression of growth hormone receptor/binding protein and insulin-like growth factor-I (IGF-I) in the enamel organ

Immunohistochemistry was used to study the ontogeny of GH receptor/binding protein (GHR/BP) and IGF-I from the 13-day-old embryo (E13) to the E19 rat fetus in the developing incisor and molar. Analysis of serial sections revealed diffuse staining of GHR/BP and IGF-I at the bud and early cap stages within both the mesenchyme of the dental papilla and the ectodermal-erived enamel organ. Just before transition to the cap stage, immunoreactivity of GHR/BP and IGF-I increased in the epithelial bud and extended to the condensed dental mesenchyme. At the cap stage, the dental epithelium showed an intense expression of GHR/BP and IGF-I, whereas the dental mesenchymal cells showed very weak staining. The inner enamel epithelium and the outer enamel epithelium were positive for both GHR/BP and IGF-I in the bell stage. Differentiating ameloblasts, odontoblasts and the secretory ameloblasts and odontoblasts continued to express GHR/BP and IGF-I in incisors. These findings support the premise that growth hormone and IGF-I may play a role in embryonic tooth development by regulating the epithelial-mesenchymal interactions that influence events in growth and cytodifferentiation.