Regulation of Vertebrate Sensory Organ Development: A Scenario for Growth Hormone and Insulin-Like Growth Factors Action

Abstract

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Peptide hormones as developmental growth and differentiation factors

“…While fetal and postnatal growth is generally regarded as dependent on endocrine GH from pituitary somatotrophs, embryonic development, before the functional differentiation of the pituitary gland, has been regarded as an example of a “growth without growth hormone” syndrome (Geffner,1996). While this may be true for endocrine GH, it is not true at the local paracrine/autocrine level, because GH is produced in extra‐pituitary sites in the embryo and has growth factor‐like effects on certain aspects of differentiation (Harvey and Hull,1997; Sanders and Harvey,2004; Diaz‐Casares, et al,2005). Early embryonic growth in the chick is clearly independent of pituitary GH, because decapitation of early chick embryos at approximately ED1.5 has no effect on the wet weight of the embryo until ED14.5, when decapitated embryos begin to grow more slowly; an effect which is reversed by pituitary GH replacement (Thommes et al,1992).…”

“…Cultured retinal neuroepithelial cells from ED5 embryos are responsive to insulin (Diaz et al,1999), as are retinal ganglion cells in vivo, (Diaz et al,2000), probably by means of Akt and caspase‐dependent and ‐independent pathways (Valenciano et al,2006). To what extent these effects of insulin are distinguishable from those of IGF‐1, which also occurs at this time in development (Diaz‐Casares et al,2005), is not entirely clear.…”