CALBINDIN-D28K, CALRETININ, AND RECOVERIN IMMUNOREACTIVITIES IN DEVELOPING CHICK PINEAL-GLAND

Calbindin-D28k, calretinin, and recoverin, three intracellular calcium -binding proteins belonging to the troponin C/calmodulin superfamily, were immunohistochemically localized in chick pineal during developmen t [from embryonic day 16 (E16) to postnatal day 14 (P14)]. At E18, onl y calretinin immunoreactivity could be detected in nuclei from follicu lar pinealocytes. With development, calretinin immunoreactivity expand ed from nucleus to cytoplasm, and calretinin immune-positive cell numb er increased. At P14 almost all pinealocytes were calretinin positive. Calbindin-D28k immunoreactivity was not detected before E20. During d evelopment, many follicular and parafollicular pinealocytes became str ongly calbindin-D28k positive, reaching a peak both in intensity and i n number at P7; thereafter their number decreased. In addition to pine alocytes, neuron-like cells appeared calbindin-D28k positive at E20 an d calretinin positive at P7. Recoverin, a myristoylated protein isolat ed from vertebrate photoreceptor and which might participate in the in activation of the phototransduction cascade, was transiently expressed in follicular and parafollicular pinealocytes from P1 to P14 with a m aximal expression at P7. This transitory expression may coincide with a transitory light sensitivity period in chick pinealocytes, before co mplete maturity of the pineal gland.