Figure 5.

Immunolocalization of alpha melanocyte‐stimulating hormone (αMSH) in mouse and chicken embryonic tissues. a‐f: Each had an adjacent section counterstained but incubated without primary antibody as a negative control (a′‐f′). a. Mouse E13.5 limbs show αMSH in skin, muscles and perichondrium. b. At the same stage, αMSH in the heart. c. By E17.5 in the mouse limb, αMSH production is strong in the epidermis but also in the dermis and all skeletal muscle, but excluded from hypertrophic cartilage. d, e. αMSH is unexpectedly produced by numerous internal organs at the same stage. f. In addition to the skin, interdigital mesenchyme before digit separation is complete, expresses αMSH, in contrast to the digital cartilage. g. Chicken embryonic eye at HH29 shows strong choroidal expression of αMSH in close proximity to the blood vessels and retinal pigmented epithelium. h. At the same stage, immunoreactivity was observed throughout the epidermis but also in discrete limb and flank subectodermal dermis regions (arrowheads), in perineural sheaths but not in dorsal root ganglia. i. αMSH is produced in distal nerves of the forelimb at HH29, in the epidermis with the exception of interdigital skin (brackets). As in the trunk, αMSH is produced by specific domains of underlying dermal mesenchyme at the tips of the growing digits. Abbreviations: A, adrenal; at, atrium; bv, blood vessel; c, cartilage; Ch, ocular choroid; d, dermis; drg, dorsal root ganglia; ep, epidermis; K, kidney; li, liver; m, muscle; n, nerves; P, pancreas; RPE, retinal pigmented epithelium; Scl, sclera; SI, small intestine; ve, ventricle