C3  COMPARING THE MORPHOLOGY OF HAIR, FEATHER AND TOOTH DEVELOPMENT

Cheng-Ming Chuong, Department of Pathology, Univ. Southern California, Los Angeles, CA 90033, USA.

The goal of this workshop is to help participants appreciate how skin appendages such as a hair is made by the Nature. Participants will learn characteristic morphology and distinct molecular expression patterns in different stages of skin appendage development, namely the induction, morphogenesis, differentiation, and cycling stages. We will compare the development of several epithelial appendages, mainly the hair, feather, and tooth. First I will use whole mount chicken embryos of different ages as examples to show the formation of skin appendage tracts (specific regions of skin with skin appendages) and regional specification on the body surface. I will then show different stages of feather development, from primordium, to short feather bud, long feather bud, follicle, and feather filament with barb / barbule formation; first as the whole mount view under a dissection microscope, and then as histological sections with H&E staining. Specimens with immuno-staining and in situ hybridization will be used to illustrate molecular expression. Histological sections of different stages of hair and tooth development will also be shown. Hairs go through primordial, peg, and follicle stages. Teeth go through primordial, bud, cap and bell stages. Generally speaking, the morphology of different skin appendages during the inductive stage are very similar: the epithelial placode with condensed mesenchyme. The morphogenesis stage is the time when different appendages take their characteristic shapes. Differences occur such as feather buds protrude out of the skin, whereas hair gem and tooth bud epithelia invaginate  into the mesenchyme. The similarities and differences of these cellular and molecular events will be discussed.