Smoc2 modulates embryonic myelopoiesis during zebrafish development.

Background: SMOC2 is a member of the BM-40 (SPARC) family of matricellular proteins, reported to influence signaling in the extracellular compartment. In mice, Smoc2 is expressed in many different tissues and was shown to enhance the response to angiogenic growth factors, mediate cell adhesion, keratinocyte migration, and metastasis. Additionally, SMOC2 is associated with vitiligo and craniofacial and dental defects. The function of Smoc2 during early zebrafish development has not been determined to date.

Results: In pregastrula zebrafish embryos, smoc2 is expressed ubiquitously. As development progresses, the expression pattern becomes more anteriorly restricted. At the onset of blood cell circulation, smoc2 morphants presented a mild ventralization of posterior structures. Molecular analysis of the smoc2 morphants indicated myelopoietic defects in the rostral blood islands during segmentation stages. Hemangioblast development and further specification of the myeloid progenitor cells were shown to be impaired. Additional experiments indicated that Bmp target genes were down-regulated in smoc2 morphants.

Conclusions: Our findings reveal that Smoc2 is an essential player in the development of myeloid cells of the anterior lateral plate mesoderm during embryonic zebrafish development. Furthermore, our data show that Smoc2 affects the transcription of Bmp target genes without affecting initial dorsoventral patterning or mesoderm development.