Development of a functional musculoskeletal system requires coordinated generation of muscles, bones, and tendons. However, how axial tendon cells (tenocytes) are generated during embryo development is still poorly understood. Here, we show that axial tenocytes arise from the sclerotome in zebrafish. In contrast to mouse and chick, the zebrafish sclerotome consists of two separate domains: a ventral domain and a previously undescribed dorsal domain. While dispensable for sclerotome induction, Hedgehog (Hh) signaling is required for the migration and maintenance of sclerotome derived cells. Axial tenocytes are located along the myotendinous junction (MTJ), extending long cellular processes into the intersomitic space. Using time-lapse imaging, we show that both sclerotome domains contribute to tenocytes in a dynamic and stereotypic manner. Tenocytes along a given MTJ always arise from the sclerotome of the adjacent anterior somite. Inhibition of Hh signaling results in loss of tenocytes and enhanced sensitivity to muscle detachment. Together, our work shows that axial tenocytes in zebrafish originate from the sclerotome and are essential for maintaining muscle integrity.

Blood vessels are vital to sustain life in all vertebrates. While it is known that mural cells (pericytes and smooth muscle cells) regulate vascular integrity, the contribution of other cell types to vascular stabilization has been largely unexplored. Using zebrafish, we identified sclerotome-derived perivascular fibroblasts as a novel population of blood vessel associated cells. In contrast to pericytes, perivascular fibroblasts emerge early during development, express the extracellular matrix (ECM) genes col1a2 and col5a1, and display distinct morphology and distribution. Time-lapse imaging reveals that perivascular fibroblasts serve as pericyte precursors. Genetic ablation of perivascular fibroblasts markedly reduces collagen deposition around endothelial cells, resulting in dysmorphic blood vessels with variable diameters. Strikingly, col5a1 mutants show spontaneous hemorrhage, and the penetrance of the phenotype is strongly enhanced by the additional loss of col1a2. Together, our work reveals dual roles of perivascular fibroblasts in vascular stabilization where they establish the ECM around nascent vessels and function as pericyte progenitors.

Lindane (gamma-hexachlorocyclohexane) is a lipid-soluble pesticide that exerts carcinogenic and reprotoxic properties. The mechanisms by which lindane alters testicular function are unclear. Sertoli cells control germ cell proliferation and differentiation through cell-cell communication, including gap junction intercellular communication. Using the 42GPA9 Sertoli cell line, we show that lindane, at a non-cytotoxic dose (50 microM), abolished gap junction intercellular communication (GJIC) between adjacent cells. This change was associated with a time-related diminution and redistribution of Cx43 from the membrane to the cytoplasmic perinuclear region. A similar alteration was observed for ZO-1, a tight junction component associated with Cx43, but not for occludin, an integral tight junction protein. After a 24 h lindane exposure, Cx43 and ZO-1 colocalized within the cytoplasm and no modification of non-phosphorylated and phosphorylated isoforms of Cx43 was observed. By double immunofluorescent labelling we demonstrate that the cytoplasmic Cx43 signal was not present in either the endoplasmic reticulum/Golgi apparatus or lysosomes. These results suggest that lindane inhibits GJIC between Sertoli cells and that aberrant Cx43/ZO-1 localization may be responsible for this effect. The alterations in gap junctions induced by lindane in 42GPA9 Sertoli cells are similar to those observed in tumour cells and may be involved in the pathogenesis of neoplastic seminomal proliferation.