SUMMARYPrimary cilia are sensory organelles that protrude from the cell membrane. Defects in the primary cilium cause ciliopathy disorders, with retinal degeneration as a prominent phenotype. Here, we demonstrate that the retinal pigment epithelium (RPE), essential for photoreceptor development and function, requires a functional primary cilium for complete maturation and that RPE maturation defects in ciliopathies precede photoreceptor degeneration. Pharmacologically enhanced ciliogenesis in wild-type induced pluripotent stem cells (iPSC)-RPE leads to fully mature and functional cells. In contrast, ciliopathy patient-derived iPSC-RPE and iPSC-RPE with a knockdown of ciliary-trafficking protein remain immature, with defective apical processes, reduced functionality, and reduced adult-specific gene expression. Proteins of the primary cilium regulate RPE maturation by simultaneously suppressing canonical WNT and activating PKCδ pathways. A similar cilium-dependent maturation pathway exists in lung epithelium. Our results provide insights into ciliopathy-induced retinal degeneration, demonstrate a developmental role for primary cilia in epithelial maturation, and provide a method to mature iPSC epithelial cells for clinical applications.

During avian erythropoiesis, the blast cells of the bone marrow mature into polychromatic erythrocytes (late stages knwon as reticulocytes) and then into mature red blood cells. When chickens are made anemic, the proportion of immature cells in the anemic bone marrow increases dramatically. The level of the lysine-rich histones. H1 and H5, has been found to be constant in the blood and bone marrow of normal and anemic chickens. This implies that H5 replaces H1 quantitatively. Urea-aluminum-lactate starch gel electrophoresis of H5 from these sources show that the degree of phosphorylation of H5 is proportional to the number of immature cells. About 70% of the H5 from the most immature bone marrow is phosphorylated, while 50% of the H5 from anemic blood is phosphorylated and H5 in normal blood is almost completely devoid of phosphate. When immature cells of the anemia bone marrow are incubated in the presence of inorganic 32P and [3H]lysine and [3H]arginine, extensive 32P incorporation is found in the phospho species. A minimum of nine phosphorylated components have been demonstrated by starch gel electrophoresis. The incorporation of 3H is time dependent. After 1.5 h of labeling, 3H is found in H5 containing 0, 1, 2, and 3 phosphates. tthe combined data suggest that newly synthesized H5 becomes progressively phosphorylated and that at the terminal stage of development, the phosphorylated H5 is completely dephosphorylated. These events may be important in controlling the timing of chromatin condensation.

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