Growth hormone size variants: changes in the pituitary during development of the chicken.
There is considerable evidence for the existence of structural variants of growth hormone (GH). The chicken is a useful model for investigating GH heterogeneity as both size and charge immunoreactive-(ir) variants have been observed in the pituitary and plasma. The present study examined the size distribution of ir-GH in the pituitary gland of chicken, from late embryogenesis through adulthood. Pituitaries were homogenized in the presence of protease inhibitor, and the GH size variants were separated by SDS-PAGE, transferred by Western blotting, immunostained with a specific antiserum to chicken GH, and quantitated by chemiluminescence followed by laser densitometry (chemiluminescent assay). Under nonreducing conditions ir-GH bands of 15, 22, 25, 44, 50, 66, 80, 98, 105 and >110 kDa were observed. Both the relative proportion of the GH size variants and the total pituitary content varied with developmental stage and age. The proportion of the 15-kDa fragment was greatest in the embryonic stage, and then it decreased. The proportion of the monomeric 22-kDa form was lowest at 18 days of embryogenesis (dE) and highest at 20 dE. In contrast, the high MW forms (>/=66 kDa) were lowest in embryos, and they increased (P < 0.05) after hatching. The 22-, 44-, 66-, and 80-kDa forms were assayed for activity by radioreceptor assay following isolation by semipreparative SDS-PAGE. Only the 22-kDa GH variant showed radioreceptor activity. Under reducing conditions for SDS-PAGE, ir-GH bands of 13, 15, 18, 23, 26, 36, 39, 44, 48, 59 and 72 kDa were oberved, but most of the high MW form disappeared. There was a concomitant increase in the proportion of the monomeric band and of several submonomeric forms. The present data indicate that the expression, processing, and/or release of some if not all size variants are under some differential control during growth and development of the chicken.
Arámburo
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Centro de Neurobiología, Campus UNAM-UAQ Juriquilla, Universidad Nacional Autónoma de México, Querétaro, México. aramburo@servidor.unam.mx
Luna
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Carranza
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Reyes
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Martínez-Coria
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Scanes
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D000375:Aging; D000818:Animals; D002642:Chick Embryo; D002645:Chickens; D004591:Electrophoresis, Polyacrylamide Gel; D013006:Growth Hormone / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D008163:Luminescent Measurements; D008970:Molecular Weight; D010902:Pituitary Gland / Q000196:embryology / Q000254:growth & development / Q000378:metabolism*; D020033:Protein Isoforms / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism
D020033:Protein Isoforms; D013006:Growth Hormone