Temporal‐spatial Pattern of TGFβ1 during Morphogenesis of the Inner Ear

Antibodies raised against TGFβ1 synthetic peptides defined temporal-spatial localization of this growth factor in the epithelial and mesenchymal tissues of the developing inner ears from 10 to 16 GD. TGFβ1 was present in the epithelial cells at the earliest stage (i.e., 10 GD otocyst) of inner ear development studied and persisted until 14 GD when most otic morphogenesis is complete. The developmental stages of greatest stain intensity over the otic epithelium (i.e., 10.5 GD and 13 GD) correlate with the events of initiation of chondrogenesis and inhibition of chondrogenesis, both of which are mediated by epithelial-mesenchymal tissue interactions. TGFβ1 was present in the extracellular matrix of the periotic mesenchyme from the earliest stage studied (i.e., 10 GD, otocyst mesenchyme) through the latest stage examined (i.e., 16 GD, perilymphatic space mesenchyme). There was tremendous variation in the localization of the extracellular TGFβ1 in the otic mesenchyme and its presence correlates with sites of active morphogenesis and differentiation. For example, at 12 GD, extracellular localized growth factor was most concentrated in sites of cellular condensation and S-GAG production while in the 14 GD inner ear, areas of dense staining for TGFβ1 correlate with areas of perilymphatic space formation and otic capsule sculpting where S-GAG production is being turned off. Enzymatic treatment of tissue sections with hyaluronidase to remove matrix in general decreased and in some instances abolished immunolocalization of TGFβ1. The only exception to this was noted at 16 GD where enzymatic treatment enhanced the staining of the matrix of the cartilaginous otic capsule.