A conserved transcription factor regulatory program promotes tendon fate

Creators: Niu, Xubo^{1, 2}; Melendez, Delmy L.^{3, 2}; Raj, Suyash^{3, 2}; Cai, Junming^{3, 2}; Senadeera, Dulanjalee^{3, 2}; Mandelbaum, Joseph^{3, 2}; Shestopalov, Ilya A.^{3, 2}; Martin, Scott D.¹; Zon, Leonard I.^{3, 2, 4}; Schlaeger, Thorsten M.^{3, 2}; Lai, Lick Pui⁵; McMahon, Andrew P.⁵; Craft, April M.^{3, 2}; Galloway, Jenna L.^{1, 2}

1. Massachusetts General Hospital
2. Harvard University
3. Boston Children's Hospital
4. Howard Hughes Medical Institute
5. University of Southern California

Abstract

Tendons, which transmit force from muscles to bones, are highly prone to injury. Understanding the mechanisms driving tendon fate would impact efforts to improve tendon healing, yet this knowledge is limited. To find direct regulators of tendon progenitor emergence, we performed a zebrafish high-throughput chemical screen. We established forskolin as a tenogenic inducer across vertebrates, functioning through Creb1a, which is required and sufficient for tendon fate. Putative enhancers containing cyclic AMP (cAMP) response elements (CREs) in humans, mice, and fish drove specific expression in zebrafish cranial and fin tendons. Analysis of these genomic regions identified motifs for early B cell factor (Ebf/EBF) transcription factors. Mutation of CRE or Ebf/EBF motifs significantly disrupted enhancer activity and specificity in tendons. Zebrafish ebf1a/ebf3a mutants displayed defects in tendon formation. Notably, Creb1a/CREB1 and Ebf1a/Ebf3a/EBF1 overexpression facilitated tenogenic induction in zebrafish and human pluripotent stem cells. Together, our work identifies the functional conservation of two transcription factors in promoting tendon fate.

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Acknowledgement

We would like to thank Jennifer Smith, Stewart Rudnicki, Rachel Warden, and Richard Siu from ICCB-Longwood Screening Facility for help with the chemical screen; Tiao Xie from Image and Data Analysis Core for help in developing a CellProfiler pipeline for data analysis; and Daniel Richard from Harvard University and Andrew Zhu from Craft lab for bioinformatic analyses. We thank Galloway lab members, Eric Liao, and Liao lab members for helpful suggestions. We thank Renee Daigle and Jessica Bethoney for their help with the fish facility. We are thankful for support from the HSCI, the Arthritis National Research Foundation, and NIH/NIAMS for J.L.G. (AR074541 and AR079495) and A.M.C. (AR073821).

Funding

We are thankful for support from the HSCI, the Arthritis National Research Foundation, and NIH/NIAMS for J.L.G. (AR074541 and AR079495) and A.M.C. (AR073821).

Contributions

J.L.G. and X.N. conceived the project, designed the experiments, discussed, analyzed data, and prepared the manuscript. X.N. made all transgenic constructs and generated the transgenic lines. D.L.M., S.R., J.C., and D.S. performed the mESCs and hESCs experiments and analyzed and generated the data under the supervision of A.M.C., and A.M.C. provided the human DARs information. J.M., I.A.S., and L.I.Z. provided the incubator for blastomere cell culture during the screen and helped set up and troubleshoot the initial blastomere cell culture. S.D.M. provided the BMAC. T.M.S. helped train the Yokogawa CV7000 Cell Voyager high-content confocal imager. L.P.L. and A.P.M. generated the mESCs line. J.L.G. directed the study, and X.N. performed all the remaining experiments and statistical analyses.

Data Availability

Raw RNA sequencing data generated in this study has been deposited in the GEO repository database under accession codes “GSE252165”. Any additional information required to reanalyze the data reported in this paper is available from the lead contact upon request.

Conflict of Interest

L.I.Z. is a founder and stockholder of Fate Therapeutics, CAMP4 Therapeutics, Amagma Therapeutics, and Scholar Rock and is a consultant for Celularity.

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