A Blog Around The Clock

An Autonomous Circadian Clock in the Inner Mouse Retina Regulated by Dopamine and GABA:

The circadian clock in the mammalian retina regulates many retinal functions, and its output modulates the central circadian clock in the brain. Details about the cellular location and neural regulation of the mammalian retinal circadian clock remain unclear, however, largely due to the difficulty of maintaining long-term culture of adult mammalian retina and the lack of an ideal experimental measure of the retinal clock. We have circumvented these limitations by developing a protocol for long-term culture of intact mouse retinas to monitor circadian rhythms of clock gene expression in real time. Using this protocol, we have localized expression of molecular retinal circadian rhythms to the inner nuclear layer. We find molecular retinal rhythms generation is independent of many forms of signaling from photoreceptors and ganglion cells, or major forms of neural communication within the inner nuclear layer, and have characterized light-induced resetting of the retinal clock. Retinal dopamine and GABA, although not necessary for the generation of molecular retinal rhythms, were revealed to regulate the phase and amplitude of retinal molecular rhythms, respectively, with dopamine participating in light-induced resetting. Our data indicate that dopamine and GABA play prominent roles in the organization of the retinal circadian clock.

A New View of Embryogenesis--Connective Fibers Join the Dance:

When you climb into bed tonight, you'll be hurtling through space at 18 miles per second (~30 km/s) around the sun. You don't notice this pace, of course, because everything around you moves at the same speed. Although Galileo recognized motion relativity as far back as the 17th century, new research suggests that it may have been overlooked by those seeking to explain one of the most fundamental of all processes in biology--how embryos develop. Early in their development, animal embryos undergo a restructuring process called gastrulation, characterized by a coordinated movement of cells ultimately to form three distinct layers. These layers--the ectoderm, mesoderm, and endoderm--later give rise to tissues such as the nervous system, circulatory system, and intestine, respectively. A key feature of gastrulation in birds and mammals is the formation of the primitive streak, a structure that changes the embryo from a bundle of cells into something with a defined longitudinal axis around which other features can orientate. Scientists have shown that formation of the streak requires mass migration of cells in a uniform direction, but how this procession is regulated remains unclear.