Inducible cell labeling and lineage tracking during fracture repair. (11th November 2014)

• Record Type: Journal Article
• Authors: Seime, Till; Kolind, Mille; Mikulec, Kathy; Summers, Matthew A.; Cantrill, Laurence; Little, David G.; Schindeler, Aaron
• Is Part Of: Development growth and differentiation. Volume 57:Number 1(2015)
• Page Start: 10
• Page End: 23
• Publication Date: 2014-11-11
• Subjects: Embryology -- Periodicals; Developmental biology -- Periodicals; Growth -- Periodicals; 574.3
• DOI: 10.1111/dgd.12184
• Languages: English
• ISSNs: 0012-1592

Abstract

<abstract abstract-type="main" id="dgd12181-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Mouse models incorporating inducible Cre‐ER<sup>T</sup><sup>2</sup>/LoxP recombination coupled with sensitive fluorescent reporter lines are being increasingly used to track cell lineages <italic>in vivo</italic>. In this study we use two inducible reporter strains, <italic>Ai9</italic><sub><italic>iCol2a1</italic></sub> (<italic>Ai9</italic> × <italic>Col2a1‐cre</italic><italic>ER</italic><sup><italic>T</italic></sup><sup><italic>2</italic></sup>) to track contribution of chondrogenic progenitors during bone regeneration in a closed fracture model and <italic>Ai9</italic><sub><italic>i</italic></sub><sub><italic>UBC</italic></sub> (<italic>Ai9</italic> × <italic>UBC–cre</italic><italic>ER</italic><sup><italic>T</italic></sup><sup><italic>2</italic></sup>) to examine methods for inducing localized recombination. By comparing with <italic>Ai9</italic> littermate controls as well as inducible reporter mice not dosed with tamoxifen, we revealed significant leakiness of the CreER<sup>T2</sup> system, particularly in the bone marrow of both lines. These studies highlight the challenges associated with highly sensitive reporters that may be activated without induction in tissues where the CreER<sup>T2</sup> fusion is expressed. Examination of the growth plate in the <italic>Ai9</italic><sub><italic>iCol2a1</italic></sub> strain showed cells of the osteochondral lineage (cell co‐staining with chondrocyte and osteoblast markers) labeled with the tdTom reporter. However, no such labeling was noted in healing fractures of <italic>Ai9</italic><sub><italic>iCol2a1</italic></sub> mice. Attempts to label a single limb using intramuscular injection of 4‐hydroxytamoxifen in the <italic>Ai9</italic><sub><italic>i</italic></sub><sub><italic>UBC</italic></sub> strain resulted in complete labeling of the entire animal, comparable to intraperitoneal injection. While a challenge to interpret, these data are nonetheless informative regarding the limitations of these inducible reporter models, and justify caution and expansive controls in future studies using such models.</p> </abstract>