The pineal and others tissues produced hormone melatonin synchronizes biological clocks with dark light environmental cycle. This hormone has functions on development via Mel1a melatonin receptor and NRH: quinona redutase 2 (QR2) enzyme. The present aim was to initiate an investigation about the localization of the both Mel1a melatonin receptor and QR2 enzyme melatonin binding site in vertebrate development. We taken as a model the fresh water turtle Kinosternon scorpioides (muçuã). Whole 21 days embryos (E21) and retinas from E21 and 60 days posthatched (PH) muçuãs respectively were assayed by immunoassays and immunohistochemistry, using commercial antibodies and the results were revealed by Texas red fluorescence. As Mel1a melatonin receptor as QR2 enzyme were localized in important external morphological characters in E21 and in retinas from both E21 and PH. Results showed Mel1a melatonin receptor in maxillary, mandibula, eye contour, Iris, choroide fissure, neck, elongated forelimb and hindlimb, developing carapace, beyond of the internal part of the tail bud. QR2 fluorescent signals in whole E21 embryos were in the following morphological external characters. In head, QR2 is at maxillary region; in the eye at lens and iris; in elongated forelimb and hindlimb; and in tail bud. No fluorescence was observed in negative controls incubated without the primary antibody. In conclusion, our achievers suggest that melatonin participates in Kinosternon scorpioides development as in ossification, hole of the Mella receptor, as in xenobiotic protection, hole of the QR2 enzyme. Melatonin functions on turtle development disclose are only starting, but we found some interesting answers and future investigations arise from these studies.
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