Functional modulation of phosphodiesterase-6 by calcium in mouse rod photoreceptors

The dynamic landscape of chromatin accessibility and active regulatory elements in the mediobasal hypothalamus influences the seasonal activation of the reproductive axis in the male quail under long light exposure

BACKGROUND

In cold and temperate zones, seasonal reproduction plays a crucial role in the survival and reproductive success of species. The photoperiod influences reproductive processes in seasonal breeders through the hypothalamic-pituitary-gonadal (HPG) axis, in which the mediobasal hypothalamus (MBH) serves as the central region responsible for transmitting light information to the endocrine system. However, the cis-regulatory elements and the transcriptional activation mechanisms related to seasonal activation of the reproductive axis in MBH remain largely unclear. In this study, an artificial photoperiod program was used to induce the HPG axis activation in male quails, and we compared changes in chromatin accessibility changes during the seasonal activation of the HPG axis.

RESULTS

Alterations in chromatin accessibility occurred in the mediobasal hypothalamus (MBH) and stabilized at LD7 during the activation of the HPG axis. Most open chromatin regions (OCRs) are enriched mainly in introns and distal intergenic regions. The differentially accessible regions (DARs) showed enrichment of binding motifs of the RFX, NKX, and MEF family of transcription factors that gained-loss accessibility under long-day conditions, while the binding motifs of the nuclear receptor (NR) superfamily and BZIP family gained-open accessibility. Retinoic acid signaling and GTPase-mediated signal transduction are involved in adaptation to long days and maintenance of the HPG axis activation. According to our footprint analysis, three clock-output genes (TEF, DBP, and HLF) and the THRA were the first responders to long days in LD3. THRB, NR3C2, AR, and NR3C1 are the key players associated with the initiation and maintenance of the activation of the HPG axis, which appeared at LD7 and tended to be stable under long-day conditions. By integrating chromatin and the transcriptome, three genes (DIO2, SLC16A2, and PDE6H) involved in thyroid hormone signaling showed differential chromatin accessibility and expression levels during the seasonal activation of the HPG axis. TRPA1, a target of THRB identified by DAP-seq, was sensitive to photoactivation and exhibited differential expression levels between short- and long-day conditions.

CONCLUSION

Our data suggest that trans effects were the main factors affecting gene expression during the seasonal activation of the HPG axis. This study could lead to further research on the seasonal reproductive behavior of birds, particularly the role of MBH in controlling seasonal reproductive behavior.

Structural basis of calmodulin modulation of the rod cyclic nucleotide-gated channel

Calmodulin (CaM) regulates many ion channels to control calcium entry into cells, and mutations that alter this interaction are linked to fatal diseases. The structural basis of CaM regulation remains largely unexplored. In retinal photoreceptors, CaM binds to the CNGB subunit of cyclic nucleotide-gated (CNG) channels and, thereby, adjusts the channel's Cyclic guanosine monophosphate (cGMP) sensitivity in response to changes in ambient light conditions. Here, we provide the structural characterization for CaM regulation of a CNG channel by using a combination of single-particle cryo-electron microscopy and structural proteomics. CaM connects the CNGA and CNGB subunits, resulting in structural changes both in the cytosolic and transmembrane regions of the channel. Cross-linking and limited proteolysis-coupled mass spectrometry mapped the conformational changes induced by CaM in vitro and in the native membrane. We propose that CaM is a constitutive subunit of the rod channel to ensure high sensitivity in dim light. Our mass spectrometry-based approach is generally relevant for studying the effect of CaM on ion channels in tissues of medical interest, where only minute quantities are available.