Dev Biol 2005 Jun;282(1):152-62
Department of Pediatrics, Washington University School of Medicine and St. Louis Children's Hospital, St. Louis, MO 63110, USA.
Loss of function mutations in the gene encoding the heparan sulfate proteoglycan Glypican-3 (GPC3) causes an X-linked disorder in humans known as Simpson-Golabi-Behmel Syndrome (SGBS). This disorder includes both pre- and postnatal overgrowth, a predisposition to certain childhood cancers, and a complex assortment of congenital defects including skeletal abnormalities. In this study, we have identified a previously unrecognized delay in endochondral ossification associated with the loss of Gpc3 function. Gpc3 knockout animals show a marked reduction in calcified trabecular bone, and an abnormal persistence of hypertrophic chondrocytes at embryonic day 16.5 (E16.5). These hypertrophic chondrocytes down-regulate Type X collagen mRNA expression and undergo apoptosis, suggesting a normal progression of hypertrophic chondrocyte cell fate. However, replacement of these cells by mineralized bone is delayed in association with a marked delay in the appearance of osteoclasts in the bone in vivo. This delay in vivo correlates with a significant reduction in the capacity to form osteoclasts from bone marrow macrophage precursors in vitro in response to M-CSF and RANKL, and with a reduction in the numbers of bone-marrow-derived cells expressing the markers CD11b and Gr-1. Together, these results indicate selective impairment in the development of the common hematopoietic lineage from which monocyte/macrophages and PMNs are derived. This is the first report of a requirement for heparan sulfate, and specifically Gpc3, in the lineage-specific differentiation of these cell types in vivo.