Anatomical Sciences Department, Stony Brook University, Stony Brook, NY 11794, USA.
Bone. 2013 Nov;57(1):300-10. doi: 10.1016/j.bone.2013.08.010. Epub 2013 Aug 15.
Basic issues surrounding osteocyte biology are still poorly understood, including the variability of osteocyte morphology within and among bones, individuals, and species. Several studies have suggested that the volume or shape of osteocytes (or their lacunae) is related to bone and/or organismal growth rate or metabolism, but the nature of this relationship, if any, is unclear. Furthermore, several studies have linked osteocyte lacuna volume with genome size or growth rate and suggested that osteocyte lacuna volume is unrelated to body size. Herein the scaling of osteocyte lacuna volume with body mass, growth and basal metabolic rates, genome size, and red blood cell size is examined using a broad sample of extant birds within a phylogenetic framework. Over 12,000 osteocyte lacuna axes were measured in a variety of bones from 34 avian and four non-avian dinosaur species. Osteocyte lacunae in parallel-fibered bone are scalene ellipsoids; their morphology and volume cannot be reliably estimated from any single thin section, and using a prolate ellipsoid model to estimate osteocyte lacuna volume results in a substantial (ca. 2-7 times) underestimate relative to true lacunar volume. Orthogonal thin sections reveal that in birds, even when only observing parallel-fibered, primary, cortical bone, intra-skeletal variation in osteocyte lacuna volume and shape is very high (volumes vary by a factor of 5.4 among different bones), whereas variation among homologous bones of the same species is low (1.2-44%; mean=12%). Ordinary and phylogenetically informed bivariate and multiple regressions demonstrate that in birds, osteocyte volume scales significantly but weakly with body mass and mass-specific basal metabolic rate and moderately with genome size, but not with erythrocyte size. Avian whole-body growth rate and osteocyte lacuna volume are weakly and inversely related. Finally, we present the first three-dimensionally calculated osteocyte volumes for several non-avian dinosaurs, which are much larger than previously reported values and smaller than those of large extant avians. Osteocyte volumes estimated from a single transverse section and assuming prolate morphology, as done in previous studies, are relative underestimates in theropod dinosaurs compared to sauropod dinosaurs, raising the possibility that no major change in osteocyte volumes (and genome size) occurred within Theropoda on the lineage leading to birds. Osteocyte volume is intertwined with several organismal attributes whose relative importance varies at a number of hierarchical levels.
骨细胞生物学的基本问题仍未得到很好的理解,包括骨内和骨间、个体和物种的骨细胞形态的可变性。几项研究表明,骨细胞(或其腔隙)的体积或形状与骨骼和/或生物体的生长速度或代谢有关,但这种关系的性质(如果有的话)尚不清楚。此外,几项研究将骨细胞腔隙体积与基因组大小或生长速度联系起来,并表明骨细胞腔隙体积与体型无关。本文在系统发育框架内,使用大量现生鸟类样本,研究了骨细胞腔隙体积与体重、生长和基础代谢率、基因组大小和红细胞大小的关系。在 34 种鸟类和 4 种非鸟类恐龙的多种骨骼中测量了超过 12000 个骨细胞腔隙轴。平行纤维骨中的骨细胞腔隙是斜椭球体;它们的形态和体积不能仅从单个薄片中可靠地估计,并且使用扁长椭球体模型来估计骨细胞腔隙体积会导致相对于真实腔隙体积的大量(约 2-7 倍)低估。正交薄片显示,在鸟类中,即使只观察平行纤维、初级、皮质骨,骨细胞腔隙体积和形状的骨骼内变异也非常高(不同骨骼之间体积变化高达 5.4 倍),而同一物种同源骨骼之间的变异则很低(1.2-44%;平均值为 12%)。普通和系统发育信息双变量和多元回归表明,在鸟类中,骨细胞体积与体重和体重特定基础代谢率显著但较弱地相关,与基因组大小中度相关,但与红细胞大小无关。鸟类的全身生长速度和骨细胞腔隙体积呈弱负相关。最后,我们提出了几种非鸟类恐龙的第一个三维计算骨细胞体积,这些体积比以前报道的值大得多,比大型现生鸟类的体积小。在以前的研究中,从单个横截面上估计并假设扁长形态的骨细胞体积,与蜥脚类恐龙相比,兽脚类恐龙的相对低估,这增加了在导致鸟类的谱系中,在兽脚类恐龙中,骨细胞体积(和基因组大小)没有发生重大变化的可能性。骨细胞体积与几个生物体属性交织在一起,这些属性的相对重要性在许多层次上有所不同。