Urotensin II-related peptide (Urp) is expressed in motoneurons in zebrafish, but is dispensable for locomotion in larva.

The urotensin 2 (uts2) gene family consists of four paralogs called uts2, uts2-related peptide (urp), urp1 and urp2. uts2 is known to exert a large array of biological effects, including osmoregulation, control of cardiovascular functions and regulation of endocrine activities. Lately, urp1 and urp2 have been shown to regulate axial straightening during embryogenesis.

Conserved role of the urotensin II receptor 4 signalling pathway to control body straightness in a tetrapod.

Urp1 and Urp2 are two neuropeptides of the urotensin II family identified in teleost fish and mainly expressed in cerebrospinal fluid (CSF)-contacting neurons. It has been recently proposed that Urp1 and Urp2 are required for correct axis formation and maintenance. Their action is thought to be mediated by the receptor Uts2r3, which is specifically expressed in dorsal somites.

The HisCl1 histamine receptor acts in photoreceptors to synchronize Drosophila behavioral rhythms with light-dark cycles.

In Drosophila, the clock that controls rest-activity rhythms synchronizes with light-dark cycles through either the blue-light sensitive cryptochrome (Cry) located in most clock neurons, or rhodopsin-expressing histaminergic photoreceptors. Here we show that, in the absence of Cry, each of the two histamine receptors Ort and HisCl1 contribute to entrain the clock whereas no entrainment occurs in the absence of the two receptors. In contrast to Ort, HisCl1 does not restore entrainment when expressed in the optic lobe interneurons.

Four of the six Drosophila rhodopsin-expressing photoreceptors can mediate circadian entrainment in low light.

Light is the major stimulus for the synchronization of circadian clocks with day-night cycles. The light-driven entrainment of the clock that controls rest-activity rhythms in Drosophila relies on different photoreceptive molecules. Cryptochrome (CRY) is expressed in most brain clock neurons, whereas six different rhodopsins (RH) are present in the light-sensing organs.