Understanding the intricacies of telomerase regulation is crucial due to the potential health benefits of modifying its activity. Telomerase is composed of an RNA component and reverse transcriptase. However, additional factors required during biogenesis vary between species. Here we have identified fission yeast Lar7 as a member of the conserved LARP7 family, which includes the Tetrahymena telomerase-binding protein p65 and human LARP7. We show that Lar7 has conserved RNA-recognition motifs, which bind telomerase RNA to protect it from exosomal degradation. In addition, Lar7 is required to stabilise the association of telomerase RNA with the protective complex LSm2–8, and telomerase reverse transcriptase. Lar7 remains a component of the mature telomerase complex and is required for telomerase localisation to the telomere. Collectively, we demonstrate that Lar7 is a crucial player in fission yeast telomerase biogenesis, similarly to p65 in Tetrahymena, and highlight the LARP7 family as a conserved factor in telomere maintenance.

Non-technical summary Due to the conservation of developmental pathways and genetic material over the course of evolution, non-mammalian 'model organisms' such as the zebrafish embryo are emerging as valuable tools to explore causes and potential treatments for human diseases. Ion channels are proteins that form pores and help to establish and control electrical gradients by allowing the flow of ions across biological membranes. A diverse range of key physiological mechanisms in every organ in the body depends on the activity of ion channels. In this paper, we show that a potassium-selective channel that underlies salt reabsorption and potassium excretion in the human kidney is also expressed in zebrafish in cells that are important regulators of salt balance. Disruption of the channel's expression in zebrafish leads to effects on the activity of the heart, consistent with a role for this channel in the control of potassium balance in the embryo. AbstractThe zebrafish, Danio rerio, is emerging as an important model organism for the pathophysiological study of some human kidney diseases, but the sites of expression and physiological roles of a number of protein orthologues in the zebrafish nephron remain mostly undefined. Here we show that a zebrafish potassium channel is orthologous to the mammalian kidney potassium channel, ROMK. The cDNA (kcnj1) encodes a protein (Kcnj1) that when expressed in Xenopus laevis oocytes displayed pH-and Ba 2+ -sensitive K + -selective currents, but unlike the mammalian channel, was completely insensitive to the peptide inhibitor tertiapin-Q. In the pronephros, kcnj1 transcript expression was restricted to a distal region and overlapped with that of sodium-chloride cotransporter Nkcc, chloride channel ClC-Ka, and ClC-Ka/b accessory subunit Barttin, indicating the location of the diluting segment. In a subpopulation of surface cells, kcnj1 was coexpressed with the a1a.4 isoform of the Na + /K + -ATPase, identifying these cells as potential K + secretory cells in this epithelium. At later stages of development, kcnj1 appeared in cells of the developing gill that also expressed the a1a.4 subunit. Morpholino antisense-mediated knockdown of kcnj1 was accompanied by transient tachycardia followed by bradycardia, effects consistent with alterations in extracellular K + concentration in the embryo. Our findings indicate that Kcnj1 is expressed in cells associated with osmoregulation and acts as a K + efflux pathway that is important in maintaining extracellular levels of K + in the developing embryo. Abbreviations ClC, chloride channel; hpf, hours post fertilization; Kir, inwardly rectifying potassium channel; MO, morpholino antisense oligonucleotide; NCCT, sodium-chloride cotransporter; Nkcc, sodium-potassium-chloride cotransporter; PDB, protein data bank; ROMK, renal outer medullary potassium channel; TAL, thick ascending limb of Henle's loop; TEVC, two-electrode voltage clamp; TPNQ, tertiapin-Q.L. Abbas and S. Hajihashemi contributed equally to this work.

Telomerase is a reverse transcriptase minimally composed of a reverse transcriptase protein subunit and an internal RNA component that contains the templating region. Point mutations of template RNA bases can cause loss of enzymatic activity, reduced processivity and misincorporation in vitro. Here we report the first complete replacement of the nine base TETRAHYMENA: thermophila telomerase templating region in vivo with non-telomeric sequences. Rather than ablating telomerase activity, three such replaced telomerases (U9, AUN and AU4) were effective in polymerization in vitro. In vivo, the AU4 and AUN genes caused telomere shortening. We demonstrated the fidelity of the AUN and U9 telomerases in vitro and utilized AUN telomerase to demonstrate that 5' end primer recognition by telomerase is independent of template base pairing. However, the mutant AUN template telomerase catalyzed an abnormal DNA cleavage reaction. For these U-only and AU- substituted templates, we conclude that base-specific interactions between the telomerase template and protein (or distant parts of the RNA) are not absolutely required for the minimal core telomerase functions of nucleotide addition and base discrimination.