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Figure 3 | BMC Developmental Biology

Figure 3

From: Analysis of chick (Gallus gallus) middle ear columella formation

Figure 3

Timeline of chondrogenesis of the columella condensation. Transverse paraffin sections at the level of the second pharyngeal arch, 12 μm. Counterstaining of sectioned heads, E6-E12 with Alcian Blue/Chlorantine Fast Red (AB/CFR), SafraninO (SafO), and Hematoxylin and Eosin (H&E). Columella columns 1, 3, 5; extracolumella columns 2, 4, 6. The columella is marked by black arrowheads in SafO sections (column 3), the extracolumella by white arrowheads (column 4). (A) Initially, few chondrocytes are detected by Alcian Blue in the columella at E6 and none in the extracolumella. (B) By E7, the perichondrium is forming around the condensation (white arrowhead), with Alcian Blue stained chondrocytes in the columella, but absent in the extracolumella. (C) Note the expanding tubotympanic sulcus (a) and ingressing external auditory meatus, which appose to form the tympanic membrane at E8. (C-E) E8-E10, staining refines and the extent of chondrogenesis in the columella and extracolumella is evident. Note the dorsal expansion of the tubotympanic sulcus forming the pneumatic middle ear cavity around the columella (labeled a, b, c - columns 1/2) (F, G). E11 and E12 counterstaining detects chondrocytes of both persistent and replacement cartilage. The columella is now transversely oriented with respect to the notochord. The supracolumella arm is dorsal, and infracolumella arm ventral. Abbreviations: eam-external auditory meatus, tm-tympanic membrane.

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