Fractal analysis of the Orce skull sutures

Methods of fractal geometry (Mandelbrot, 1983) are used here to analyse the relative complexity of the sagittal and lambdoid sutures visible in the skull fragment formed by parts of an occipital squame and parietals found in a sealed deposit at the early Lower Pleistocene site of Venta Micena (Orce, Granada, Spain), generally regarded as human bone but occasionally suggested as belonging to an equid. For comparison with the fossil, corresponding sutures of various primates (hominids, pongids and cercopithecids) and two other groups of mammals (equids and ruminants) were analysed using the computer program FRACTAL-D (Slice, 1989) in order to determine their fractal dimensions as a measure of differential sutural design complexity. The results show that the fractal dimension of the Venta Micena skull sutures lies within the range of variation for infant specimens of both modern and Plio-Pleistocene hominids. Sutural complexity in young pongids and cercopithecids overlaps the range of fractal dimensions found in hominids, whereas values obtained from equids and ruminants are significantly greater than those for all the primates analysed here. Therefore, in terms of fractal dimension measures of relative complexity, the sutures preserved in the Venta Micena fossil could not have belonged to an equid (pace Agusti & Moyà-Sola, 1987); rather, its fractal dimension is consistent with the attribution of the fossil to an infant of Homo sp.     

Assessment of the role of sutures in a lizard skull: a computer modelling study

Sutures form an integral part of the functioning skull, but their role has long been debated among vertebrate morphologists and palaeontologists. Furthermore, the relationship between typical skull sutures, and those involved in cranial kinesis, is poorly understood. In a series of computational modelling studies, complex loading conditions obtained through multibody dynamics analysis were imposed on a finite element model of the skull of Uromastyx hardwickii, an akinetic herbivorous lizard. A finite element analysis (FEA) of a skull with no sutures revealed higher patterns of strain in regions where cranial sutures are located in the skull. From these findings, FEAs were performed on skulls with sutures (individual and groups of sutures) to investigate their role and function more thoroughly. Our results showed that individual sutures relieved strain locally, but only at the expense of elevated strain in other regions of the skull. These findings provide an insight into the behaviour of sutures and show how they are adapted to work together to distribute strain around the skull. Premature fusion of one suture could therefore lead to increased abnormal loading on other regions of the skull causing irregular bone growth and deformities. This detailed investigation also revealed that the frontal-parietal suture of the Uromastyx skull played a substantial role in relieving strain compared with the other sutures. This raises questions about the original role of mesokinesis in squamate evolution.     

Developmental regulation of skull morphology II: ontogenetic dynamics of covariance

Canalization may play a critical role in molding patterns of integration when variability is regulated by the balance between processes that generate and remove variation. Under these conditions, the interaction among those processes may produce a dynamic structure of integration even when the level of variability is constant. To determine whether the constancy of variance in skull shape throughout most of postnatal growth results from a balance between processes generating and removing variation, we compare covariance structures from age to age in two rodent species, cotton rats (Sigmodon fulviventer) and house mice (Mus musculus domesticus). We assess the overall similarity of covariance matrices by the matrix correlation, and compare the structures of covariance matrices using common subspace analysis, a method related to common principal components (PCs) analysis but suited to cases in which variation is so nearly spherical that PCs are ambiguous. We find significant differences from age to age in covariance structure and the more effectively canalized ones tend to be least stable in covariance structure. We find no evidence that canalization gradually and preferentially removes deviations arising early in development as we might expect if canalization results from compensatory differential growth. Our results suggest that (co)variation patterns are continually restructured by processes that equilibrate variance, and thus that canalization plays a critical role in molding patterns of integration.     

Comparative morphology and functional interpretation of the sutures in the dermal skull roof of temnospondyl amphibians

Sutures in the dermal skull roof of several Palaeozoic temnospondyl amphibians were studied, including Archegosaurus decheni, Sclerocephalus haeuseri, Cheliderpeton latirostre (Archegosauridae), Acanthostomatops vorax (Zatrachydidae), Onchiodon labyrinthicus (Eryopidae), Micromelerpeton credneri and Branchierpeton amblystomum (Dissorophoidea). Lamellae, flat bevels, butt joints, steep walls, and grooves are the sutural types occurring. Morphological sutural differences cannot be used as taxonomically relevant characters, as they mainly differ in their functional manifestations. Similarities of sutural patterns in taxa not closely related are most probably based on convergence, therefore sutural morphology allows functional conclusions rather than revealing phylogenetic relationships. The basic sutural pattern is described in Micromelerpeton credneri. Different textures and obliquity patterns of the sutural surfaces are characteristic of each region of the skull roof. In all temnospondyls studied, the median plane and the margin of the skull roof show a nearly uniform sutural morphology; the circumorbital region is most complex. Although the skulls studied are akinetic, mesokinetic movements of dermal elements along their sutures must have been permitted to guarantee the dynamic stability of the skull construction.     

Developmental regulation of skull morphology. I. Ontogenetic dynamics of variance

In the absence of processes regulating morphogenesis and growth, phenotypic variance of a population experiencing no selective mortality should increase throughout ontogeny. To determine whether it does, we measure variance of skull shape using geometric morphometrics and examine its ontogenetic dynamics in the precocial cotton rat (Sigmodon fulviventer) and the altricial house mouse (Mus musculus domesticus). In both species, variance of shape halves between the two youngest samples measured (between 1 and 10 days postnatal and 10 and 15 days postnatal, respectively) and thereafter is nearly constant. The reduction in variance did not appear to result from a general regulation of skull size or developmental timing, although skull size may also be regulated and developmental timing is an important component of the variation in skull shape of young house mice. The ontogenetic dynamics of variance suggest two possible scenarios. First, variation generated during fetal or early postnatal growth is not immediately compensated and therefore accumulates, whereas later in growth, variation is continually generated and rapidly compensated. Second, variation generated during fetal and early postnatal growth is rapidly compensated, after which no new variance is produced. Based on a general model for bone growth, we hypothesize that variance is generated when bone grows under the direction of disorganized muscular movements and decreases with increasing neuromuscular control. Additionally, increasing coherence of signals transmitted by the growing brain and sensory organs, which exert tensile forces on bone, may also canalize skull shape.     

Developmental changes in the skull morphology of common minke whales Balaenoptera acutorostrata

We investigated growth‐related and sex‐related morphological changes in the skulls of 144 North Pacific common minke whales Balaenoptera acutorostrata. Measurement was conducted at 39 points on the skull and mandible to extract individual allometric equations relating the length and zygomatic width of the skull. The results revealed no significant differences in skull morphology by sex except for width of occipital bone. The size relative to the skull of the anatomical parts involved in feeding, such as the rostrum and mandible, increased after birth. In contrast, the sensory organs and the anatomical regions involved in neurological function, such as the orbit, tympanic bullae, and foramen magnum, were fully developed at birth, and their relative size reduced over the course of development. This is the first study to investigate developmental changes in the skull morphology using more than 100 baleen whale specimens, and we believe the results of this study will contribute greatly to multiple areas of baleen whale research, including taxonomy and paleontology. J. Morphol. 275:1113–1121, 2014. © 2014 Wiley Periodicals, Inc.     

Developmental kinetics of bovine nuclear transfer and parthenogenetic embryos

Early developmental kinetics of nuclear transfer (NT) embryos reconstituted with blastomeres and parthenogenones produced by ionophore activation followed by either dimethylaminopurine (DMAP) or cycloheximide (CHX) treatment was studied. In vitro produced (IVP) embryos served as controls. Embryos were cultured to the hatched blastocyst stage, and images were recorded every 0.5 h throughout the culture period. The longest cell cycle shifted from 4th to 5th cycle (26 +/- 4 and 44 +/- 5 h) in NT-embryos compared to IVP-embryos (41 +/- 2 and 20 +/- 3 h) and showed greater asynchrony between blastomeres than any other embryo category. Compared to DMAP, CHX prolonged the 1(st) (23 +/- 1 vs. 33 +/- 1 h) and shortened the 3(rd) cell cycle (17 +/- 2 vs. 13 +/- 1 h). Moreover, though cytoskeleton activity was initialised, a larger proportion of CHX embryos was unable to accomplish first cleavage. The parthegenones differed from IVP embryos with respect to the lengths of the 1st, 3rd, and 4th cell cycles and time of hatching. The findings are discussed in relation to known ultrastructural, chromosomal and genomic aberrations found in NT embryos and parthenogenones. We hypothesize that the shift of the longest cell cycle in NT embryos is associated with a shift in the time of major genomic transition.     

Developmental defects of the facial the skull in some forms of craniosynostosis]

Changes in the facial skull of 74 patients with untimely synostosis of craniocerebral sutures and pathologic shape of the cerebral skull are characterized. All the patients presented with shortened base of the skull, gross deformations of the facial skull. Certain regularities in the formation of these defects were distinguished.     

Developmental kinetics of hemopoietic progenitors in the avian embryo spleen

By means of plasma clot clonal cultures, the content of the avian spleen in granulomonocytic progenitors was studied during ontogeny. Serum-free media were used that were supplemented with growth activities produced either by embryonic fibroblasts or adult spleen cells. These two conditioned media not only permitted the growth of M-CFC, G-CFC, and GM-CFC but also F-CFU (fibroblast colony-forming units) from quail or chick embryonic spleen cells. The presence of spleen cell-conditioned medium promoted the development of large colonies of immature granulocytes. In the chick the first hemopoietic progenitors appeared at E9 and their number displayed two peaks, one at E15 and a smaller one at E18. In the quail the first progenitors were detected as early as E7 and their number peaked at E10. In this species, hemopoietic progenitors disappeared definitively before hatching while in the chick some were still present at P3. The progenitor content of the chick embryo spleen was compared to that of the bone marrow. This content remained stable during all of embryonic life, while the bone marrow exhibited a very different profile, where a sharp peak at E16 was followed by an acute decline and a stabilization at a rather low level. The particular profile in the spleen speaks in favor of a special role of this organ in the development of the hemopoietic system.     

Bioactive sutures

With the first wave of bioactive sutures already in the marketplace, research is ongoing in the development of future products. Such sutures could potentially have not only antimicrobial activity but also anesthetic and antineoplastic functions. Some clinical trials have already been completed in Russia. This technology is likely to become commonplace. This article reviews the progress made to date in the development of this technology.     

Development of lens sutures

Cylindrical map projections (CMPs) have been used for centuries as an effective means of plotting the features of a 3D spheroidal surfaces (e.g. the earth) on a 2D rectangular map. We have used CMPs to plot primate fiber cell organization from selected growth shells as a function of growth, development and aging. Lens structural parameters and features were derived from slit-lamp, light and transmission and scanning electron micrographs. This information was then used to create CMPs of lenses that were then correlated with azimuthal map projections (AMPs; projections that are radially symmetric around a central point [the poles]) to reveal different suture patterns during distinct time periods. In this manner, both lens fiber and suture branch locations are defined by degrees of longitude and latitude. CMPs and AMPs confirm that throughout defined periods of development, growth and ageing, increasingly complex suture patterns are formed by the precise ordering of straight and opposite end curvature fibers. However, the manner in which additional suture branches are formed anteriorly and posteriorly is not identical. Anteriorly, new branches are added between extant branches. Posteriorly, pairs of new branches are formed that progressively overlay extant branches. The advantage of using CMPs is that the shape and organization of every fiber in a growth shell can be observed in a single image. Thus, the use of CMPs to plot primate fiber cell organization has revealed more complex aspects of fiber formation that may explain, at least in part, changes in lens optical quality as a function of age and pathology. In addition, more accurate measurements of fiber length will be possible by incorporating the latitudinal and longitudinal locations of fibers.     

Flexure of cranial sutures

Beam samples containing cranial sutures were prepared from embalmed and unembalmed cranial bone and were tested to determine their flexural stiffness and strength. With the aid of layered beam theory, the flexural stiffnesses of beams containing cranial sutures were compared to hypothetical layered cranial bone beams which did not contain sutures. The bending stiffnesses and strengths of cranial sutures were found to be generally the same as comparable layered cranial bone structures. Embalmed samples were slightly stiffer and stronger in bending than unembalmed samples.     

Developmental stages of cucumber seedlings: kinetics of chlorophyll accumulation and other growth parameters

The changes in morphology during dark germination and subsequent growth of cucumber (Cucumis sativus) seedlings in the light go through three different phases described as latent, active, and steady-state. This pattern is consistently observed for several related developmental processes. The latent period lasts about 2 days following water imbibition after which the following capabilities appear in concert: (a) root and stem elongation, (b) pigment synthesis including protochlorophyll, chlorophyll, carotenoid, and phytochrome, (c) synthesis of ribulose-1,5-bisphosphate carboxylase/oxygenase, and (d) enhancement of greening by excision. Following the active phase, which lasts for another 2 to 3 days, these processes slow to a steady-state. Inhibition of chlorphyll accumulation by SO₂ was only observed for seedlings in the steady-state phase.     

Mechanical properties of cranial sutures

Many bones in mammalian skulls are linked together by cranial sutures, connective tissue joints that are morphologically variable and show different levels of interdigitation among and within species. The goal of this investigation was to determine whether sections of skull with cranial sutures have different mechanical properties than adjacent sections without sutures, and if these properties are enhanced with increased interdigitation. To test these hypotheses, bending strength and impact energy absorption were measured for samples of goat (Capra hircus) cranial bone without sutures and with sutures of different degrees of interdigitation. Bending strength was measured under both dynamic (9.7 mm displacement s-1) and relatively static (0.8 mm s-1) conditions, and at either speed, increased sutural interdigitation provided increased strength during three-point bending. However, except for very highly interdigitated sutures loaded slowly, sutures were not as strong in bending as bone. In contrast, sutures absorbed from 16% to 100% more energy per unit volume during impact loading than did bone. This five-fold increase in energy absorption by the sutures was significantly correlated with increased sutural interdigitation.     

Linking form and function of the fibrous joints in the skull: a new quantification scheme for cranial sutures using the extant fish Polypterus endlicherii

The aim of this study is to connect specific sutural morphologies with the specific types of deformation they experience. To meet this goal, we quantified the morphologies of the interfrontal (IF), interparietal (IP), and frontoparietal (FP) sutures in the extant fish Polypterus endlicherii, and used our published measurements of in vivo deformation of these sutures during feeding to infer how suture morphology and function are connected. Specifically, we found that three relatively simple measures of cross-sectional suture complexity (i.e., the ratio of total sutural length to its shortest end-to-end length; amount of sutural overlap; and size of the largest interdigitation) can be used to distinguish between the IF, FP, and IP sutures, which exhibit very different cross-sectional shapes and responses to loading. Interestingly, these differences in cross-sectional morphology are not reflected by the linear traces of these sutures on the surface of the skull, implying that cross-sectional shape of a suture must be known to infer the loading conditions it experiences. Plotting the three cross-sectional metrics against one another to yield a sutural morphospace shows that the IF, IP, and FP sutures define regions that are largely distinct from one another. Our previous measurements of strain across these sutures suggested that the FP region would lie between the IF and IP regions; instead, the FP region is largely set apart from the other two fields. Based on this discovery, and on the locations of cranial muscles, we propose a new model of deformation in the skull of P. endlicherii during feeding, in which rotation parallel to the skull roof is combined with bending, subjecting the FP suture to complex shearing. Finally, although the sutures of P. endlicherii appear to be significantly less complex than those of mammals, these fish sutures show a similar range of morphologies and perform similar functions as do mammalian sutures.     

Developmental changes in chromatin organization in rat cerebral hemisphere neurons and analysis of DNA reassociation kinetics

Previous reports have demonstrated that neuronal nuclei of rabbit, mouse and rat cerebral hemispheres exhibit a short DNA repeat length of 160 bp compared to the more typical repeat size of 200 bp found in glial nuclei and other cell types of higher eukaryotes. In this study we report that the conversion of chromatin to a short DNA repeat length in rat cerebral hemisphere neurons is a gradual process which begins between the first and second day after birth and is complete by 8 days. In these neurons, histone H1 appears to be less accessible to degradation by trypsin in the newborn rat brain compared to the 8 day old rat. This suggests that the developmental shift to a short DNA repeat length may be accompanied by a dispersal or decondensation of neuronal chromatin which results in an increased accessibility of neuronal histone H1 to degradation by trypsin. The increase in nuclear DNA content to 3.5C which has been reported in rat cortical neurons during early postnatal development does not appear to be associated with a selective amplification of a subset of DNA sequences as determined by DNA reassociation kinetics.