Gli2 and Gli3 are primary transcriptional regulators that mediate hedgehog (Hh) signaling. Mechanisms that stabilize and destabilize Gli2 and Gli3 are essential for the proteins to promptly respond to Hh signaling or to be inactivated following the activation. In this study, we show that loss of suppressor of fused (Sufu; an inhibitory effector for Gli proteins) results in destabilization of Gli2 and Gli3 full-length activators but not of their C-terminally processed repressors, whereas overexpression of Sufu stabilizes them. By contrast, RNAi knockdown of Spop (a substrate-binding adaptor for the cullin3-based ubiquitin E3 ligase) in Sufu mutant mouse embryonic fibroblasts (MEFs) can restore the levels of Gli2 and Gli3 full-length proteins, but not those of their repressors, whereas introducing Sufu into the MEFs stabilizes Gli2 and Gli3 full-length proteins and rescues Gli3 processing. Consistent with these findings, forced Spop expression promotes Gli2 and Gli3 degradation and Gli3 processing. The functions of Sufu and Spop oppose each other through their competitive binding to the N- and C-terminal regions of Gli3 or the C-terminal region of Gli2. More importantly, the Gli3 repressor expressed by a Gli3 mutant allele (Gli3Δ699) can mostly rescue the ventralized neural tube phenotypes of Sufu mutant embryos, indicating that the Gli3 repressor can function independently of Sufu. Our study provides a new insight into the regulation of Gli2 and Gli3 stability and processing by Sufu and Spop, and reveals the unexpected Sufu-independent Gli3 repressor function.

Summary In mice, Gli2 and Gli3 are the transcription factors that mediate the initial Hedgehog (Hh) signaling. In the absence of Hh signaling, the majority of the full-length Gli3 protein undergoes proteolytic processing into a repressor, while only a small fraction of the full-length Gli2 protein is processed. Gli3 processing is dependent on phosphorylation of the first four of the six protein kinase A (PKA) sites at its C-terminus. However, whether the same phosphorylation of Gli2 by PKA is required for Gli2 processing and, if so, whether such phosphorylation regulates additional Gli2 function are unknown. To address these questions, we mutated these PKA sites in the mouse Gli2 locus to create the Gli2P1-4 allele. Gli2P1-4 homozygous embryos die in utero and exhibit exencephaly, defects in neural tube closure, enlarged craniofacial structures, and an extra anterior digit. Analysis of spinal cord patterning shows that domains of motoneurons and V2, V1, and V0 interneurons are expanded to different degrees in both Gli2P1-4 single and Gli2P1-4;Shh double mutants. Furthermore, Gli2P1-4 expression prevents massive cell death and promotes cell proliferation in Shh mutant. Analysis of Gli2P1-4 protein in vivo reveals that the mutant protein is not processed and is twice as stable as wild type Gli2 protein. We also show that the Gli2 repressor can effectively antagonize Gli2P1-4 activity. Together, these results indicate that phosphorylation of Gli2 by PKA induces Gli2 processing and destabilization in vivo and plays an important role in the Hh-regulated mouse embryonic patterning.

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Primary cilia are assembled and maintained by evolutionarily conserved intraflagellar transport (IFT) proteins that are involved in the coordinated movement of macromolecular cargo from the basal body to the cilium tip and back. The IFT machinery is organized in two structural complexes named complex A and complex B. Recently, inactivation in the mouse germline of Ift genes belonging to complex B revealed a requirement of ciliogenesis, or proteins involved in ciliogenesis, for Sonic Hedgehog (Shh) signaling in mammals. Here we report on a complex A mutant mouse, defective for the Ift122 gene. Ift122-null embryos show multiple developmental defects (exencephaly, situs viscerum inversus, delay in turning, hemorrhage and defects in limb development) that result in lethality. In the node, primary cilia were absent or malformed in homozygous mutant and heterozygous embryos, respectively. Impairment of the Shh pathway was apparent in both neural tube patterning (expansion of motoneurons and rostro-caudal level-dependent contraction or expansion of the dorso-lateral interneurons), and limb patterning (ectrosyndactyly). These phenotypes are distinct from both complex B IFT mutant embryos and embryos defective for the ciliary protein hennin/Arl13b, and suggest reduced levels of both Gli2/Gli3 activator and Gli3 repressor functions. We conclude that complex A and complex B factors play similar but distinct roles in ciliogenesis and Shh/Gli3 signaling.

Anterior-posterior (A/P) limb patterning in vertebrates is determined by the counteraction between the Sonic Hedgehog (Shh) and the Gli3 transcription factor. Shh exerts its effect on Gli3 by regulating the full-length Gli3 protein processing to generate a Gli3 repressor gradient along the A/P axis of the limb. However, it is not clear whether the full-length Gli3 is an activator in vivo and plays any role in the limb patterning. Here we show that mouse limbs expressing only a Gli3 repressor form exhibit mild polysyndactyly and a partial loss of digit identity, while limbs expressing only a full-length Gli3 protein display severe polysyndactyly and a complete loss of digit identity. Interestingly, when the full-length Gli3 and the repressor are equally expressed in the limb, the digit patterning is overall normal except for an extra anterior digit. Furthermore, in the presence of one Gli3 wild type allele, a Gli3 mutant allele that expresses only the full-length form can rescue the Shh mutant digit phenotype to a great extent. The full-length Gli3 protein can also activate Shh target gene expression without Shh. Thus, our data indicate that the full-length Gli3 protein is an activator in vivo and that the ratio of the Gli3 activator to repressor, but neither the Gli3 repressor gradient nor the Gli3 activator/repressor ratio gradient, determines limb digit patterning.

The lack of fresh water resources is attracting concern worldwide. Recently, to address this global issue, researchers proposed the heat localization concept for interfacial solar seawater desalination in 2014. Since then, interfacial solar steam generation (ISSG) devices have attracted much attention, due to their potential for achieving highly enhanced optical‐thermal conversion through a single interface as compared with traditional solar seawater desalination. To date, the promising prospect of ISSG systems in seawater desalination has stimulated the rapid development of solar desalination technology based on heat localization. To comprehensively recognize ISSG devices and acquire more insights into their design associated with biological relevance, efficiency improvement, and applications, this review summarizes the progresses and prospects of ISSG devices in relation to the evolution of advanced materials, the engineering architecture, the collaborative application, and the current challenges.

Solar‐driven interfacial desalination (SDID), which is based on localized heating and interfacial evaporation, provides an opportunity for developing environmentally friendly and cost‐effective seawater thermal desalination. However, localized heating and rapidly generated interfacial steam may cause salt to accumulate on the evaporator's surface and block the channel of steam evaporation. Salt accumulation inevitably reduces the light absorption and service period of the solar absorber, resulting in a significant decrease in evaporation efficiency over time. Salt accumulation makes it difficult to produce SDID devices with high energy efficiency and long‐term stability for large‐scale use in remote poverty‐stricken areas. Therefore, the exploration of novel and effective strategies for addressing salt accumulation through both material design and structural engineering has attracted more attention in recent years. This review presents an overview of the state‐of‐the‐art advancements in salt‐resistant photothermal evaporation and discusses the critical issues for achieving salt mitigation SDID, focusing on the classification of salt mitigation strategies based on photothermal evaporation configurations, the basic mechanism of salt mitigation, and the architectural design of photothermal materials. Finally, the important challenges and prospects of SDID are discussed to providing a meaningful roadmap to efficient salt mitigation SDID.

Interfacial solar steam generation (ISSG) has received increasing attention in both industry and academia, and is considered a method with great potential for wastewater treatment and desalination. These practical applications require materials that fulfil several requirements: being low cost, being scalable in terms of processing, being environmentally friendly, and having a high, stable optical–thermal conversion efficiency of solar vaporization. Currently, biomass materials show very promising prospects for ISSG systems. Here, it is observed that bamboo charcoal (BC) possesses a series of unique advantages that make it a highly efficient ISSG device. The broadband light absorption and the arched and porous structural features of BC fulfil all the basic requirements of an ISSG device in localized heating, heat management, and water supply. The self‐contained arched BC device demonstrates high evaporation efficiency (84% under 1 sun radiation) and superb stability under strongly acidic, strongly alkaline, and intense light environment conditions. More importantly, the porous BC device can provide stable fresh water production that simultaneously promotes the purification of water via evaporation by heating. Finally, the low cost, environmentally sustainable, mechanically robust, and long‐term stable BC device is a potential opportunity for wastewater treatment and desalination in underdeveloped areas.