Biology subjects

Cross, F.

Publications and source records attributed to Cross, F..

3 recordsLinked to original sources

bioRxiv2023

The Hedgehog receptors PTCH1 and PTCH2 exist as active homomeric and heteromeric complexes

With the importance of Hedgehog signalling in embryonic development, tissue homeostasis and disease, understanding the molecular mechanisms of signal transduction is paramount for the design of specific, effective therapeutics. The Hedgehog receptor PTCH1 and the less studied PTCH2 isoform are evolutionarily related to bacterial RND permeases and sterol sensing proteins, which mobilise hydrophobic compounds powered by a cation gradient. Here we demonstrate that, in the active state, PTCH1 and PTCH2 form homomeric and heteromeric complexes that are inhibited by binding of Sonic Hedgehog. We show that PTCH2, unlike PTCH1, appears to have minimal cholesterol transport activity, but that conserved residues involved in cation transport are essential for its function. Heteromeric PTCH1-PTCH2 complexes depend on PTCH1s cholesterol transport capacity, but the cation transport can be provided in trans by PTCH2, suggesting that some deleterious mutations in either isoform can be silenced by formation of heteromers, enhancing the robustness of this signal transduction system. These findings provide the molecular basis for the intriguing behaviour of PTCH2 as semi-redundant and partially overlapping in function with PTCH1 and explain the dominant negative effect of mutations that disrupt the PTCH2 cation transport triad in rare cases of cancer.

biochemistry↗

bioRxiv2021

Systems-wide Analysis Revealed Shared and Unique Responses to Moderate and Acute High Temperatures in the Green Alga Chlamydomonas reinhardtii

Different intensities of high temperatures affect the growth of photosynthetic cells in nature. To elucidate the underlying mechanisms, we cultivated the unicellular green alga Chlamydomonas reinhardtii under highly controlled photobioreactor conditions and revealed systems-wide shared and unique responses to 24-hour moderate (35{degrees}C) and acute (40{degrees}C) high temperatures and subsequent recovery at 25{degrees}C. We identified previously overlooked unique elements in response to moderate high temperature. Heat at 35{degrees}C transiently arrested the cell cycle followed by partial synchronization, up-regulated transcripts/proteins involved in gluconeogenesis/glyoxylate-cycle for carbon uptake, promoted growth, and increased starch accumulation. Heat at 40{degrees}C arrested the cell cycle, inhibited growth, resulting in carbon uptake over usage and increased starch accumulation. Both high temperatures induced photoprotection, while 40{degrees}C decreased photosynthetic efficiency, distorted thylakoid/pyrenoid ultrastructure, and affected the carbon concentrating mechanism. We demonstrated increased transcript/protein correlation during both heat treatments, suggesting reduced post-transcriptional regulation during heat may help coordinate heat tolerance activities efficiently. During recovery after both heat treatments, transcripts/proteins related to DNA synthesis increased while those involved in photosynthetic light reactions decreased. We propose down-regulating photosynthetic light reactions during DNA replication benefits cell cycle resumption by reducing ROS production. Our results provide potential targets to increase thermotolerance in algae and crops.

cell biology↗

bioRxiv2021

Control of division and microtubule dynamics in Chlamydomonas by cyclin B/CDKB1 and the anaphase-promoting complex

In yeast and animals, cyclin B binds and activates the cyclin-dependent kinase ( CDK) CDK1 to drive entry into mitosis. We show that CYCB1, the sole cyclin B in Chlamydomonas, activates the plant-specific CDKB1 rather than the CDK1 ortholog CDKA1. Time-lapse microscopy shows that CYCB1 is synthesized before each division in the multiple fission cycle, then is rapidly degraded 3-5 minutes before division occurs. CYCB1 degradation is dependent on the anaphase-promoting complex (APC). Like CYCB1, CDKB1 is not synthesized until late G1; however, CDKB1 is not degraded with each division within the multiple fission cycle. The microtubule plus-end-binding protein EB1 labeled with mNeonGreen (EB1-NG) allowed detection of mitotic events in live cells. The earliest detectable step in mitosis, splitting of polar EB1-NG signal into two foci, likely associated with future spindle poles, was dependent on CYCB1. CYCB1-GFP localized close to these foci immediately before spindle formation. Spindle breakdown, cleavage furrow formation and accumulation of EB1 in the furrow were dependent on the APC. In interphase, rapidly growing microtubules are marked by comets of EB1; comets are absent in the absence of APC function. Thus CYCB1/CDKB1 and the APC mitosis modulate microtubule dynamics while regulating mitotic progression.

cell biology↗