Morphology of the development of the sagittal suture of mice

Abstract

Syndesmotic sutures of the skull are formed by dense connective tissue and called "open"; they are "closed" by formation of a synostosis between adjacent bones. Open sutures are considered as areas of growth and as hinges. The importance of open sutures during the period of skull growth is reflected by pathological situations in which premature closure of the sutures occurs. As alterations of the FGF receptor have been reported in genetical disorders accompanied by premature suture closure (Bellus et al. 1996), the role of fibroblasts and connective tissue in the development of the sagittal suture of mice has been investigated by light and electron microscopy. Morphological changes of the sagittal suture at the following stages are reported: at embryonic day 18, days 1, 5, 9, 14, 20, 26, 28 after birth and in adult mice. Two skulls per stage were investigated. Early osteogenesis appeared in a thin plate, followed by a second plate underneath the first one. Both were separated by blood vessels. In general, vascularization preceded desmoid mineralization; the space around blood vessels was occupied by non-bone-forming cells leaving cavities for the presumptive bone marrow. Mineralization of the collagen-rich osteoid at the mineralizing rim of the bone plates was accompanied by apoptoses and cell disintegration. Newly formed bone was immediately covered by osteoblasts forming a sheet of bone-lining cells. At day 9, the double-layered bone plates of both sides reached the median area of the skull but were separated by non-mineralizing, collagen-rich connective tissue. From day 14 onwards, the bone plates thickened. Bone apposition, recognizable by the formation of collagen-rich osteoid and proceeding from day 14 pp onwards, occurred mainly at the outer and inner surfaces of the calvariae, but neither at bone marrow surfaces nor at the medial edges of the parietal bones. These opposite bone faces showed fewer osteoblasts and bone-lining cells, but an increased number of fibroblasts. Tendon-like collagen bundles connected both bone plates of the open suture of day 26 pp as well as in the adult mice, whereby synostotically closed areas alternated. Formation of an open, syndesmotic suture can, therefore, be described as a transition of bone-forming tissue into a bone-tendon junction. The results indicate the importance of the replacement of osteoblasts by fibroblasts at the sutural front of the bone plates in order to prevent a premature suture closure.

The Zebrafish <i>(Danio rerio):</i> A Model System for Cranial Suture Patterning

“…In humans, at around 18 weeks of gestation, the mineralizing bone fronts meet and sutures are induced along the lines of approximation [Shapiro and Robinson, 1980], while in mice, the sutures are induced around day 15 postconception [Johansen and Hall, 1982;Zimmermann et al, 1998]. Our data suggest that in zebrafi sh, cranial suture patterning is an autonomous process, independent of osteogenesis, and that it is an 'active' process occurring within the mesenchymal blastema.…”

“…Understanding how skull vault and cranial sutures normally develop is fundamental for gaining insights into pathological mechanisms. The ability to visualize skull vault development and suture patterning as they occur in vivo in both wild-type and craniofacial muson, 1980;Johansen and Hall, 1982;Zimmermann et al, 1998]. The osteogenesis data presented in this paper demonstrate that, like mammalian skull vault bones, the zebrafi sh skull roof bones are intramembranous in origin, fl anking the cranial sutures.…”

Magnetic resonance imaging and micro-computed tomography combined atlas of developing and adult mouse brains for stereotaxic surgery

“…The lambda junction was defined as the point of intersection of the best fit lines passing through the sagittal and lamboid sutures, as in the Franklin and Paxinos atlas. During early stages of postnatal development of the mouse skull, there is rapid ongoing appositional growth along the suture margins leading to progressive narrowing of the sutures (Zimmermann et al, 1998). Therefore, at postnatal day 7, limited ossification of the neurocranium and existence of wide sagittal and lamboid sutures (Fig.…”

“…First, we developed stereotaxic atlases for six different developmental stages of the C57BL/6J mouse, starting from postnatal day 7 (P7). During the early postnatal period, rapid age-related morphological changes in the brain occur concurrently with the growth of bony plates at the cranial sutures (Zimmermann et al, 1998). The most obvious postnatal changes relate to myelination (Barbarese et al, 1978; Carson et al, 1983; Vincze et al, 2008) which begins in the mouse spinal cord on about the day of birth, and then advances into the mouse brain more or less progressively in the rostral direction beginning at about P10, proceeding rapidly from P10–P30 with a peak rate of formation at about P17, then progressing at a slower rate from P30–P60 and probably continuing at a very slow rate thereafter.…”

AtlasGuide: Software for stereotaxic guidance using 3D CT/MRI hybrid atlases of developing mouse brains

“…For stereotaxic guidance in AtlasGuide, the atlases are oriented in the bregma-lambda horizontal position. At P7, the bregma and lambda cannot be clearly identified due to wide sagittal and lamboid cranial sutures at this stage (Zimmermann et al, 1998), hence approximate coordinates for the bregma junction are provided. Although MRI/DTI data of earlier developmental stages are available, the bregma/lamda-based coordinate system is not applicable at these earlier developmental stages because the neonatal mouse skull is not completely ossified.…”