A distinct regulatory region of the Bmp5 locus activates gene expression following adult bone fracture or soft tissue injury

Abstract

Bone morphogenetic proteins (BMPs) are key signaling molecules required for normal development of bones and other tissues. Previous studies have shown that null mutations in the mouse Bmp5 gene alter the size, shape and number of multiple bone and cartilage structures during development. Bmp5 mutations also delay healing of rib fractures in adult mutants, suggesting that the same signals used to pattern embryonic bone and cartilage are also reused during skeletal regeneration and repair. Despite intense interest in BMPs as agents for stimulating bone formation in clinical applications, little is known about the regulatory elements that control developmental or injury-induced BMP expression. To compare the DNA sequences that activate gene expression during embryonic bone formation and following acute injuries in adult animals, we assayed regions surrounding the Bmp5 gene for their ability to stimulate lacZ reporter gene expression in transgenic mice. Multiple genomic fragments, distributed across the Bmp5 locus, collectively coordinate expression in discrete anatomic domains during normal development, including in embryonic ribs. In contrast, a distinct regulatory region activated expression following rib fracture in adult animals. The same injury control region triggered gene expression in mesenchymal cells following tibia fracture, in migrating keratinocytes following dorsal skin wounding, and in regenerating epithelial cells following lung injury. The Bmp5 gene thus contains an “injury response” control region that is distinct from embryonic enhancers, and that is activated by multiple types of injury in adult animals.

Modulation of tissue repair by regeneration enhancer elements

“…Recently, a ~18 kb region of the murine Bmp5 locus was reported to activate expression from minimal promoters in injury contexts 33 , suggesting it may harbor a TREE analogous to the LEN element we describe here. We suspect that diverse classes of TREEs exist, including elements activated during development and re-activated by injury 34 or during regeneration, elements that activate expression preferentially during regeneration in multiple tissues, and regeneration-specific elements that are more tissue-restricted.…”

Regeneration Genetics

“…This study provides a molecular basis to explain how some epicardial genes that are transcriptionally activated during embryonic development can be re-induced after injuries; that is, by sharing regulatory sequences. Similarly, by deleting different genomic regions surrounding mouse Bmp5, essential for skeletal development and bone repair, Guenther et al identified separable genomic regions responsible for Bmp5 expression in discrete anatomic domains during normal development or following injuries (38). Intriguingly, the 18-kb injury-responsive region is sufficient to trigger gene expression in mesenchymal or epithelial cells in multiple tissues, suggesting it might contain an injury-responsive enhancer element.…”

A Regeneration Toolkit

“…These sequences, in combination with a minimal promoter, were sufficient to direct and maintain expression of a transgenic reporter or even a potent mitogen in regeneration settings but not in uninjured adult tissue. Together, these studies and others, like those identifying injury-responsive sequences near the murine BMP5 gene or chromatin regions that are modulated by exposure to inflammation in murine skin epithelial stem cells (Guenther et al, 2015; Naik et al, 2017), indicate that there may exist thousands of cis -regulatory elements that activate gene expression after tissue injury or stress, and/or during regeneration. Elements like these provide ways researchers can further probe gene function during regeneration through their inherent ability to turn on and off in response to injury and regeneration (Kang et al, 2016).…”

“…Images in (B) are adapted from Kang et al, 2016. Images in (C) are adapted from Guenther et al, 2015. Image in (D) is adapted from Liu et al, 2017.…”