Naslov
A Model For Observing Osteoblast Lineage Progression In Vivo

Autori
Kalajzić, Žana ; Kalajzić, Ivo ; Višnjić, Dora ; Gronowicz, Gloria ; Rowe, W David

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
J Bone Miner Res 15 Suppl 1, S196, 1234, 2000. / - , 2000

Skup
ASBMR, anual meeting, 2000

Mjesto i datum
Toronto, Kanada, 22.09.2000. - 26.09.2000

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
osteoblast; lineage; GFP

Sažetak
Mice harboring a 2.3 kb fragment of the rat collagen promoter driving the herpes thymdine kinase gene (Col2.3 *tk) are a model for conditional ablation of the osteoblast lineage when the mice are exposed to ganciclovir (GCV). Upon termination of GCV treatment, a phase of exaggerated osteogenesis occurs providing a model to examine a defined wave of new bone formation. We performed a molecular and histological analysis on 5 groups of mice that had recovered from GCV exposure for 0 to 4 weeks and compared them with nontreated controls. To assist in recognizing cellular events, mice bearing a 3.6 kb fragment of the rat collagen promoter driving the autofluorescent marker gene GFP were crossed with the Col2.3 *tk mice. This construct activates in preosteoblastic cells and the strength of fluoresence increases with osteoblastic differentiation. Mice heterozygous for both transgenes were injected with GCV for 16 days and then allowed to recover over a 28 day period. Northern analysis of flushed long bones showed a significant reduction of mRNA for *tk, GFP, Col1a1, BSP, OP, OC in samples taken at day 0. There was only a minimal increase of these transcripts after 7 days of recovery. Maximal expression of GFP, *tk, Col1a1, BSP and OP transcripts was observed by day 15 of recovery. While OC was detected by day 15, its maximal expression was achieved on recovery day 21. Histological analysis of paraffin embedded femurs of treated mice at day 0 revealed a complete absence of osteoblasts lining the endosteal and trabecular surfaces and loss of bone marrow cellularity. pOBCol3.6GFP positive cells were only present in the periosteal region. By day 7, scattered GFP positive cells were found in the marrow in close proximity with trabeculae. By day 15 the bone marrow space of recovered animals had developed a hypercellular fibrous tissue that was interlaced with new blood vessels and the marrow was repopulated with hematopoietic elements. The fibroblastic cells strongly expressed GFP but the newly formed blood vessels were GFP negative. By day 21 of recovery the fibroblastic tissue had been replaced with a cellular trabecular bone. The cells within and on the surface of the trabeculae were strongly GFP positive. By day 28, the cellularity within the new trabeculae was reduced and there were areas of fatty accumulation within the marrow. The cells within the trabeculae were no longer GFP positive while those that were positive lined the surface of the trabeculae. Current studies are being repeated with GFP constructs that are activate later in the lineage than pOBCol3.6. The combination of the GFP marked cells and this GCV induced wave of osteogenesis may be a useful method to identify cells within the osteoprogenitor lineage in vivo.

Izvorni jezik
Engleski

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