Lysosomal properties during thyroxine-induced lateral motor column neurogenesis.

This investigation illustrates that thyroid hormones and not prolactin regulate lysosomal activity during hormone-stimulated lateral motor column (LMC) development in Rana pipiens larvae. Administering a single dose of DL-thyroxine to normal or hypophysectomized larvae induces a 4-8 fold increase in lysosomal acid hydrolase activity within 5 or 6 days. During this interval, the physical properties of lysosomes are dramatically altered with the granules becoming extremely labile to treatments known to disrupt membranes. Nevertheless, thyroxine does not directly influence lysosomal stability; it apparently induces the synthesis and packaging of enzymes through a mechanism requiring de movo production of RNA and protein. The subcellular distribution and physical characteristics of the enzymes are then modified during neuronal death. Such information suggests that changes in lysosomal activity which accompany LMC neurogenesis are indicative of neuronal death, and that these events are controlled by thyroid hormones.