protein are made in salivary glands, eyes, optic 
lobes, and the thoracic central nervous system. Un- 
expected locations also are found; high levels of 
protein are made in pupal and adult ovaries and 
testes, and the gene is expressed in some endocrine 
organs. 
Some of the major sites of per RNA and protein 
^-synthesis can be correlated with genetically defined 
per-dependent functions, and this suggests that 
some phenotypes may be autonomously controlled 
by the identified cells. For example, the localization 
of per RNA and protein in the thoracic ganglia fits 
v^^ell with the observation that per is required in the 
thorax for production of ultradian rhythms con- 
nected with male courtship song, per RNA and pro- 
tein are expressed in the adult optic lobes. Muta- 
tions affecting optic lobe development alter (and in 
some cases may eliminate) adult locomotor activity 
rhythms. 
Some sites of expression suggest a wider range of 
phenotypic effects than previously reported. Syn- 
PUBLICATIONS 
thesis in the ring gland complex is correlated with 
rhythmic secretion of an eclosion hormone, gating 
adult emergence from pupation. Possibly a per- 
dependent, autonomous pacemaker in this cell 
complex controls eclosion timing. Expression of 
per was found in gonads, and it has recently been 
shown that sperm release in some insects is con- 
trolled by a circadian pacemaker that functions in 
vitro in isolated testes. 
A curious feature of the protein's expression is 
location in different subcellular compartments in 
different tissues. The protein is associated with nu- 
clei in photoreceptor cells, optic lobes, and ring 
gland. It is cytoplasmic, and possibly on cell sur- 
faces, in the embryonic nervous system, gonads, 
salivary glands, and certain cells of the central 
brain. The different localizations could point to in- 
volvement in more than one cellular process. 
Dr. Young is also Professor of Genetics at The 
Rockefeller University. 
Books and Chapters of Books 
Young, M.W 1989. Molecular aspects of biological clocks. In McGraw-Hill Yearbook of Science and Technol- 
ogy. New York: McGraw-Hill, 6th ed, pp 60-63. 
Articles 
Kidd, S., Baylies, M.K., Gasic, G.E, and Young, M.W 1989. Structure and distribution of the Notch protein in 
developing Drosophila. Genes Dev 3:1 113-1 129. 
Saez, L., and Young, M.W 1988. In situ localization of the per clock protein during development of Dro- 
sophila melanogaster. Mol Cell Biol 8:5378-5385. 
Young, M.W , Bargiello, T.A., Baylies, M.K., Saez, L., Spray D.C., and Jackson, F.R. 1988. The molecular genetic 
approach to a study of biological rhythms in Drosophila. Adv Biosci 73:43-53. 
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