Thymosin β4 is not required for embryonic viability or vascular development.

RATIONALE: Rossdeutsch et al describe a requirement for thymosin β4 (Tβ4) in vascular development. Impaired mural cell migration, differentiation, partial embryonic lethality, and hemorrhaging were observed after analysis of 2 lines of mice, one of which was germline null for Tβ4 and another in which Tβ4 was knocked down by endothelial-specific expression of Tβ4 short hairpin RNA. These data are in direct contrast to our published global and cardiac-specific Tβ4-knockout lines. Thus, the role of Tβ4 needs to be clarified to understand its importance in cardiovascular development. OBJECTIVE: To investigate and clarify the role of Tβ4 in vascular smooth muscle cell development and vessel stability. METHODS AND RESULTS: Examination of Tβ4 global knockouts did not demonstrate embryonic hemorrhaging, altered mural cell development, or lethality. Endothelial-specific knockouts also did not exhibit any embryonic lethality and were viable to adulthood. CONCLUSIONS: Analysis of our Tβ4 global and cardiac- and endothelial-specific knockout models demonstrated that Tβ4 is dispensable for embryonic viability and vascular development.