Biology subjects

Konjikusic, M. J.

Publications and source records attributed to Konjikusic, M. J..

5 recordsLinked to original sources

bioRxiv2025

Primary cilia and BBS4 are required for postnatal pituitary development

Primary cilia orchestrate several signaling pathways, and their disruption results in pleiotropic disorders called ciliopathies. Bardet Beidl syndrome (BBS), one such ciliopathy, provides insights into cilia function in many tissues. Using a mouse model of BBS, Bbs4 knockout (Bbs4-/-), and conditional deletion of pituitary cilia, we found that adult Bbs4-/- and cilia-less pituitaries are hypoplastic and have increased gonadotroph populations. The developing Bbs4-/- pituitary experiences mildly reduced Hedgehog signaling. Isolated Bbs4-/- pituitary stem cells exhibited reduced Hedgehog signal responsiveness and expression of stem cell markers. These data demonstrate that cilia and BBS function are necessary for pituitary growth. We propose that altered pituitary cilia-mediated patterning contribute to physiological features of ciliopathies such as BBS. Summary statementA mouse model of BBS reveals that ciliary Hedgehog signaling is necessary for postnatal pituitary development.

developmental biology↗

bioRxiv2025

Smoothened inhibition of PKA at cilia transduces Hedgehog signals

Hedgehog (HH) signaling in vertebrates is dependent on the primary cilium, an organelle that scaffolds signal transduction. HH signals induce Smoothened (SMO) enrichment in the cilium and indirectly triggers the conversion of GLI proteins into transcriptional activators of HH target genes. Recently, SMO has been shown to inhibit protein kinase A (PKA). To test the hypothesis that SMO specifically inhibits PKA at cilia to activate the HH signal transduction pathway, we developed a ciliary PKA biosensor. Activation of the HH signal transduction pathway by either Sonic hedgehog (SHH) or SMO agonist (SAG) inhibited ciliary PKA activity. Blocking SMO phosphorylation by GRK2/3 prevented ciliary SMO from inhibiting ciliary PKA activity. Gi was dispensable for SMO inhibition of ciliary PKA. In contrast, mutating the SMO C-terminal tail protein kinase inhibitor (PKI) pseudosubstrate site interfered with the ability of SMO to inhibit ciliary PKA. Therefore, HH signaling is transduced via SMO direct inhibition of PKA at cilia, in a manner dependent on GRK2/3.

biochemistry↗

bioRxiv2019

A Comparative Study of the Turnover of Multiciliated Cells in the Mouse Trachea, Oviduct and Brain

In mammals, multiciliated cells (MCCs) line the lumen of the trachea, oviduct, and brain ventricles, where they drive fluid flow across the epithelium. Each MCC population experiences vastly different local environments that may dictate differences in their lifetime and turnover rates. However, with the exception of MCCs in the trachea, the turnover rates of these multiciliated epithelial populations at extended time scales are not well described. Here, using genetic lineage-labeling techniques we provide a direct comparison of turnover rates of MCCs in these three different tissues. We find that oviduct turnover is similar to that in the airway ([~]6 months), while multiciliated ependymal cells turnover more slowly.

developmental biology↗

bioRxiv2019

The Reissner Fiber is Highly Dynamic in vivo and Controls Morphogenesis of the Spine

Spine morphogenesis requires the integration of multiple musculoskeletal tissues with the nervous system. Cerebrospinal fluid (CSF) physiology is important for development and homeostasis of the central nervous system and its disruption has been linked to scoliosis in zebrafish [1, 2]. Suspended in the CSF is an enigmatic glycoprotein thread called the Reissner fiber, which is secreted from the subcomissural organ (SCO) in the brain and extends caudally through the central canal to where it terminates at the base of the spinal cord. In zebrafish, scospondin null mutants are unable to assemble the Reissner fiber and fail to extend a straight body axis during embryonic development [3]. Here, we describe zebrafish hypomorphic missense alleles, which assemble the Reissner fiber and straighten the body axis during early embryonic development, yet progressively lose the fiber, concomitant with the emergence of body curvature, alterations in neuronal gene expression, and scoliosis in adults. Using an endogenously tagged scospondin-GFP zebrafish knock-in line, we directly visualized Reissner fiber dynamics during the normal development and during the progression of scoliosis, and demonstrate that the Reissner fiber is critical for the morphogenesis of the spine. Our study establishes a framework for future investigations of mechanistic roles of the Reissner fiber including its dynamic properties, molecular interactions, and how these processes are involved in the regulation of spine morphogenesis and scoliosis. HighlightsO_LIHypomorphic mutations in zebrafish scospondin result in progressive scoliosis C_LIO_LIThe disassembly of the Reissner fiber in scospondin hypomorphic mutants results in the strong upregulation of neuronal receptors and synaptic transport components C_LIO_LIAn endogenous fluorescent knock-in allele of scospondin reveals dynamic properties of the Reissner fiber during zebrafish development C_LIO_LILoss of the Reissner fiber during larval development is a common feature of zebrafish scoliosis models C_LI

genetics↗

bioRxiv2018

Mutations in Kinesin Family Member 6 Reveal Specific Role in Ependymal Cell Function and Human Neuro-Cranial Development

Cerebrospinal fluid flow is crucial for neurodevelopment and homeostasis of the ventricular system of the brain, with localized flow being established by the polarized beating of the ependymal cell (EC) cilia. Here, we report a homozygous one base-pair deletion, c.1193delT (p.Leu398Glnfs*2), in the Kinesin Family Member 6 (KIF6) gene in a child displaying neurocranial defects and intellectual disability. To test the pathogenicity of this novel human KIF6 mutation we engineered an analogous C-terminal truncating mutation in mouse. These mutant mice display severe, postnatal-onset hydrocephalus. We generated a Kif6-LacZ transgenic mouse strain and report expression specifically and uniquely within the ependymal cell (EC) layer of the brain, without labeling other multiciliated mouse tissues. Analysis of Kif6 mutant mice with scanning electron microscopy (SEM) and immunofluorescence (IF) revealed a reduction in EC cilia, without effect on other multiciliated tissues. Consistent with our findings in mice, defects of the ventricular system and EC cilia were observed in kif6 mutant zebrafish. Overall, this work describes the first clinically-defined KIF6 homozygous null mutation in human and defines KIF6 as a conserved mediator of neuro-cranial morphogenesis with a specific role in the maintenance of EC cilia in vertebrates.\n\nAUTHOR SUMMARYCerebrospinal fluid flow is crucial for neurodevelopment and homeostasis of the ventricular system of the brain. Localized flows of cerebrospinal fluid throughout the ventricular system of the brain are established from the polarized beating of the ependymal cell (EC) cilia. Here, we identified a homozygous truncating mutation in KIF6 in a child displaying neuro-cranial defects and intellectual disability. To test the function of KIF6 in vivo, we engineered mutations of Kif6 in mouse. These Kif6 mutant mice display severe hydrocephalus, coupled with a loss of EC cilia. Similarly, we observed hydrocephalus and a reduction in EC cilia in kif6 mutant zebrafish. Overall, this work describes the first clinically-defined KIF6 mutation in human, while our animal studies demonstrate the pathogenicity of mutations in KIF6 and establish KIF6 as a conserved mediator of neuro-cranial development and EC cilia maintenance in vertebrates.\n\n\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=183 SRC=\"FIGDIR/small/350140_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (58K):\norg.highwire.dtl.DTLVardef@d36bc6org.highwire.dtl.DTLVardef@48cbfborg.highwire.dtl.DTLVardef@147e273org.highwire.dtl.DTLVardef@641ce3_HPS_FORMAT_FIGEXP M_FIG C_FIG

genetics↗