Targeted Disruption of the Inhibitor of DNA Binding 4 (Id4) Gene Alters Photic Entrainment of the Circadian Clock.

Giles E Duffield,Maricela Robles-Murguia,Kathleen A Mcdonald,Tim Y Hou

doi:10.3390/ijms22179632

Giles E Duffield, Maricela Robles-Murguia + Show 2 more

Open Access

https://doi.org/10.3390/ijms22179632

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Abstract

Inhibitor of DNA binding (Id) genes comprise a family of four helix–loop–helix (HLH) transcriptional inhibitors. Our earlier studies revealed a role for ID2 within the circadian system, contributing to input, output, and core clock function through its interaction with CLOCK and BMAL1. Here, we explore the contribution of ID4 to the circadian system using a targeted disruption of the Id4 gene. Attributes of the circadian clock were assessed by monitoring the locomotor activity of Id4−/− mice, and they revealed disturbances in its operation. Id4-mutant mice expressed a shorter circadian period length, attenuated phase shifts in responses to continuous and discrete photic cues, and an advanced phase angle of entrainment under a 12:12 light:dark cycle and under short and long photoperiods. To understand the basis for these properties, suprachiasmatic nucleus (SCN) and retinal structures were examined. Anatomical analysis reveals a smaller Id4−/− SCN in the width dimension, which is a finding consistent with its smaller brain. As a result of this feature, anterograde tracing in Id4−/− mice revealed retinal afferents innovate a disproportionally larger SCN area. The Id4−/− photic entrainment responses are unlikely to be due to an impaired function of the retinal pathways since Id4−/− retinal anatomy and function tested by pupillometry were similar to wild-type mice. Furthermore, these circadian characteristics are opposite to those exhibited by the Id2−/− mouse, suggesting an opposing influence of the ID4 protein within the circadian system; or, the absence of ID4 results in changes in the expression or activity of other members of the Id gene family. Expression analysis of the Id genes within the Id4−/− SCN revealed a time-of-day specific elevated Id1. It is plausible that the increased Id1 and/or absence of ID4 result in changes in interactions with bHLH canonical clock components or with targets upstream and/or downstream of the clock, thereby resulting in abnormal properties of the circadian clock and its entrainment.

Highlights

Many aspects of biochemistry, physiology, and behavior are organized around a 24-h rhythm, which is driven by an endogenous circadian clock [1,2]
We show distinct alterations in the entrainment properties of the clock in Id4−/− mice that are observed when the circadian system is probed with continuous light, discrete pulses of either saturating or sub-saturating light, which likely explain the advanced phase angle of entrainment observed under different photoperiods
ID1 can interact with CLOCK and BMAL1, these data suggest the possibility for an indirect effect of ID4 upon the circadian clock via changes in levels of ID1

Summary

Introduction

Physiology, and behavior are organized around a 24-h rhythm, which is driven by an endogenous circadian clock [1,2]. Inhibitor of DNA binding (ID) proteins (ID1, ID2, ID3, and ID4) comprise a family of four helix–loop–helix (HLH) transcriptional inhibitors, and they regulate development and tumorigenesis [6] They function at the molecular level as dominant negative transcriptional regulators of specific bHLH transcription factors. Mice lacking Id2 exhibit abnormally rapid entrainment in response to a large change in the photoschedule, corresponding to an increased magnitude of light-induced phase delays and a delayed phase angle of entrainment [7,17] These phaseshifting responses are correlated with increased per clock gene expression in both SCN and in cell lines derived from Id2−/− mice that are stimulated by an entrainment signal (zeitgeber) [13,17]

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