Figure 4.

Embryonic mouse Pomc transcription and embryonic chicken Pomc expression as relates to Mc1r and/or Sox10 transcription (blue). a. Frontal section, E11.5; strong expression in rib cartilage and intercostal and limb muscle masses, mandibular mesenchyme, and gut. a′. Hybridization of adjacent section to sense‐transcribed probe (negative control). b. Oblique parasagittal section through upper dorsal trunk at E13.5; strong expression in central and peripheral nervous systems and lung mesenchyme. c. Transverse section through trunk at same stage, showing widespread additional transcription by smooth and skeletal muscle and liver. d. E13.5 head in sagittal section, showing hypothalamic, cerebellar, pontine and pituitary transcription of Pomc, as well as in heart and tongue muscle. e. Coronal section of an embryonic chicken at stage HH31 with extremely strong transcription by hypothalamic neurons in addition to expression throughout the brain. f. Mouse E17.5 coronal section through the level of the eye with striking Pomc expression in the neural retina, facial muscles but not cartilage, and nasal glands. g. The hypothalamus, cerebellum and select hindbrain nuclei express relatively more Pomc transcript at E17.5. h, i: Adjacent sections of chicken forelimb at HH29, hybridized respectively with probes against Pomc and Mc1r. Pomc (h) is more broadly expressed throughout connective tissues, cartilage and the dermis and intense staining is present in skeletal muscle. i. Mc1r is also expressed in muscle masses but also regions of perichondrium and a specific zone of dermis (arrow) not anatomically distinguished. j‐l: Tangential sections through wing skin and feather follicles at HH37, with probes against (j) Pomc ‐ asymmetric dermal expression indicated by arrows, (k) Mc1r ‐ artifact labeled with orange asterisk ‐ or (l) Sox10 (melanoblasts). Abbreviations: ah, adenohypophysis; c, cartilage; cb, cerebellum; cp, choroid plexus; dia, diaphragm; drg, dorsal root ganglon; g, gut; h, heart; hb, hindbrain; hp, hippocampus; hy, hypothalamus; lb, forelimb bud; li, liver; lu, lung; m, muscle; md, mandible; ne, nasal epithelium; ng, nasal gland; on, optic nerve; pons, pontine flexure; ret, retina; sc, spinal cord; st, stomach; tg, tongue; v, vertebra; vib, vibrissa