International Journal of Marine Science, 2024, Vol.14, No.4, 256-265 http://www.aquapublisher.com/index.php/ijms 260 the LRO, Inhibition of dynein function disrupts ciliary movement and consequently the establishment of L-R asymmetry (Yamada et al., 2019), Kinesin motor proteins also play a role in the transport of signaling molecules within cilia, contributing to the overall process of L-R patterning (Zhu et al., 2019). Cilia are integral to the establishment of L-R asymmetry through their role in generating directional fluid flow and facilitating the asymmetric expression of key signaling molecules. The interplay of various genetic and molecular mechanisms ensures the precise regulation of this process, which is essential for proper organ development and function. 5 Cilia and Anterior-Posterior Axis Development primary cilia are essential for the proper development of the anterior-posterior axis by mediating key signaling pathways and interacting with morphogen gradients. The dynamic and coordinated output of ciliary signaling is crucial for the spatial and temporal regulation of gene expression during embryogenesis, highlighting the importance of cilia in developmental processes. 5.1 Involvement of cilia in anterior-posterior patterning Cilia play a crucial role in the development of the anterior-posterior (AP) axis by mediating the signaling pathways that are essential for the spatial and temporal regulation of gene expression during embryogenesis. Primary cilia, which are immotile and project from the surface of most vertebrate cells, act as sensory organelles that detect and transmit extracellular signals to regulate cellular processes critical for AP patterning (Anvarian et al., 2019; Kopinke et al., 2020), Mutations in ciliary trafficking genes can differentially affect Sonic Hedgehog (Shh)-dependent neural tube patterning along the AP axis, highlighting the importance of cilia in this developmental process (Legué and Liem, 2020). 5.2 Key signaling pathways Several key signaling pathways are coordinated by primary cilia to control AP axis development. These include the Hedgehog (Hh), Wnt, fibroblast growth factor (FGF), and bone morphogenetic protein (BMP) pathways. The canonical Hh pathway, for instance, is a well-established ciliary signaling system that regulates cell fate and tissue homeostasis (Anvarian et al., 2019; Kopinke et al., 2020), Additionally, the Wnt and FGF pathways are critical for posteriorizing signals, while BMP signaling is involved in ventralizing signals along the AP axis (Tuazon and Mullins, 2015; Carron and Shi, 2016). 5.3 Interaction with morphogen gradients Cilia interact with morphogen gradients to facilitate the precise patterning of the AP axis. These interactions are essential for the proper spatial distribution of signaling molecules and the subsequent activation of downstream genetic programs. 5.3.1 Wnt signaling The Wnt signaling pathway is integral to AP axis patterning, with primary cilia playing a role in modulating Wnt activity. In planarians, for example, Wnt signaling establishes anterior versus posterior pole identities, and cilia are involved in the regulation of this pathway (Bonar et al., 2022), Additionally, the inhibition of Wnt signaling is necessary for the formation of anterior neural tissue during vertebrate development (Carron and Shi, 2016). 5.3.2 Hedgehog pathway The Hedgehog (Hh) pathway is closely associated with cilia, as the majority of Hh signaling components are localized within the cilium-centrosome complex. Cilia are required for both the repression and activation of Hh signaling, which is crucial for the patterning of various tissues along the AP axis (Kopinke et al., 2020), For instance, proper ciliary assembly is critical for restricting Hh activity during early eye development, ensuring the correct formation of optic structures (Burnett et al., 2017). 5.3.3 FGF and BMP pathways The FGF and BMP pathways also interact with cilia to influence AP patterning. FGF signaling, which acts downstream of Hh signaling, is necessary for anterior mesoderm morphogenesis during gastrulation (Guzzetta et
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