The per gene is essential for biological clock functions and determines the period length of circadian and ultradian rhythms. The per mutants are characterized by aberrant
rhythms involving eclosion and locomotor activity (Konopka and
Benzer, 1971) and may change the rhythmic component of the
male courtship song (Crossley, 1988; Ewing, 1988; Kyriacou and
Hall, 1980, 1986, 1988). These mutants also affect the rhythm
of the larval heartbeat (Dowse, Ringo, and Kyriacou; Livingstone, 1981, Neurosci. Abstr. 7: 351), the level of tyrosine
decarboxylase [Livingstone and Tempel, 1983, Nature (London)
303: 67-70], and fluctuations in membrane potentials in larval salivary glands (Weitzel and Rensing, 1981, J. Comp. Physiol. 143: 229-35), modulate intercellular junctional communication (Bargiello et al., 1987), and alter the location of
neural secretory cells in the brain (Konopka and Wells, 1980,
J. Neurobiol. 11: 411-15).
In wild-type flies the period length is about 24 hr. In
general, increases in per+ dosage lead to shortened circadian
rhythms and decreases lead to lengthened circadian rhythms
(Baylies et al., 1987; Cote and Brody, 1986; Hamblen et al.,
1986; Smith and Konopka, 1981, 1982; Young et al., 1985).
Females heterozygous for per+ and a deletion of the locus or a
per0 allele show longer-than-normal periods.
per flies can be classified on the basis of their circadian
rhythms as: (1) Cryptic period mutants (per0, per-) which
have a 10-15 hr (ultradian) period and appear
arrhythmic except in special algorhythmic tests (Dowse et al.,
1987); (2) Long period mutants (perL), 29 hr; (3) Long-period
variable mutants (perLvar), which in homozygotes or heterozygotes are arrhythmic but in combination with certain partial
deletions of the per locus result in a 30-34 hr period.
(Konopka, 1987); (4) Short period mutants (pers), 19 hr; (5)
Short period variable mutants (persvar), some flies having a
20 hr period and the others a normal 24 hr period for locomotor activity.
In temperature-change experiments on pers and perL1, the
locomotor activity periods were found to be nearer to 24 hr at
low temperatures, but to diverge further from normal upon
heating (Konopka, Pittendrigh, and Orr; Hamblen, Ewer, and
Hall). perL2 shows lengthening of the periods at high temperatures.
The mutant types affecting circadian rhythms (per0, perL,
and pers) may cause similar kinds of changes in the rhythmic
fluctuations in courtship song interpulse intervals (IPIs) of
the male (Crossley, 1988; Ewing, 1988; Kyriacou and Hall,
1980, 1986, 1988). per0 mutants show nonrhythmic variations
in the interval between pulses of wing vibration.
Neural studies show that transplantation of pers brains into
per01 adult hosts causes some of the hosts to be "rescued";
i.e. to show short-period circadian rhythms for locomotor
activity (Handler and Konopka, 1979). Octopamine synthesis
occurs at subnormal rates in per01 brains, with a corresponding decrease in the enzyme tyrosine decarboxylase (Livingstone
and Tempel, 1983); less severe decrements in tyrosine decarboxylase are found in pers and perL1 flies.
Physiological studies show that per mutations can affect the
level of gap junctional communication among cells in a tissue
(Bargiello et al., 1987). In salivary glands the per0 and
perL1 mutations cause a lowering of the level of junctional
communication, while pers gives a level of communication
higher than wild type. Because electrical synapses are composed of gap junctions, per may influence circadian behavioral
rhythms through altered conductances at the synapse (Bargiello
et al., 1987).
Mosaic analysis of pers mutants indicates that the gene
influences the brain with respect to aberrant locomotor
rhythms (Konopka, Wells, and Lee, 1983, Mol. Gen. Genet.
190: 284-88); per01 and per02 (and, to a lesser degree, pers)
are said to cause anomalous photonegative behavior in light-response tests (Palmer, Kendrick, and Hotchkiss, 1985, Ann.
N.Y. Acad. Sci., pp 323-24), but in general are not defective
in visual responses (phototaxis tests, optomotor behavior, and
electroretinogram) according to Dushay and Hall.