Loss-of-function analysis of EphA receptors in retinotectal mapping

Peer reviewedPublisher PD

Qualitative palmar dermatoglyphic patterns in cases of idiopathic generalized epilepsy

Background: Genetic etiology has been proposed for both idiopathic epilepsy and dermatoglyphics. Hence, the present study has been undertaken to find out the existence of any correlation between dermatoglyphics and idiopathic generalized epilepsy.Objective of current study wasto find out an association, if any, between dermatoglyphic patterns of hands in idiopathic generalized epilepsy of both sexes.Methods:The study was conducted in the department of anatomy and department of neurology, Himalayan institute of medical sciences, Swami Ram Nagar, Dehradun. Fingertip patterns (whorls, loops, arches) and Main line (A, B, C, D) terminations were analysed by utilizing finger and palmar prints.Results:The present study showed a significant decrease in whorls and an increase in arches in both the hands of male and female IGE patients. Loops were increased in both hands of female patients. Main line D was mostly confined to sectors 11, 9 and 7 in both sexes among the cases and controls. Main line C terminated quite often in sectors 9 & 7 in males and females of the case series. Main line B terminated most frequently in sectors 5'' & 7 in control and case groups. Main line A terminated most frequently in sector 5' in males and females.  Conclusion: Therefore, we can conclude and hypothesize merely by observing decrease in the whorl and increase in the arch patterns in the fingerprints (as observed in the present study) that persons with high risk of idiopathic generalized epilepsy can be identified early and preventive measures can be taken against serious complications.

Toca-1 Mediates Cdc42-Dependent Actin Nucleation by Activating the N-WASP-WIP Complex

AbstractAn important signaling pathway to the actin cytoskeleton links the Rho family GTPase Cdc42 to the actin-nucleating Arp2/3 complex through N-WASP. Nevertheless, these previously identified components are not sufficient to mediate Cdc42-induced actin polymerization in a physiological context. In this paper, we describe the biochemical purification of Toca-1 (transducer of Cdc42-dependent actin assembly) as an essential component of the Cdc42 pathway. Toca-1 binds both N-WASP and Cdc42 and is a member of the evolutionarily conserved PCH protein family. Toca-1 promotes actin nucleation by activating the N-WASP-WIP/CR16 complex, the predominant form of N-WASP in cells. Thus, the cooperative actions of two distinct Cdc42 effectors, the N-WASP-WIP complex and Toca-1, are required for Cdc42-induced actin assembly. These findings represent a significantly revised view of Cdc42-signaling and shed light on the pathogenesis of Wiskott-Aldrich syndrome

Lateral transport of Smoothened from the plasma membrane to the membrane of the cilium

A distinct pathway for ligand-stimulated lateral trafficking of the hedgehog protein Smoothened into cilia is described

Hedgehog-Interacting Protein is a multimodal antagonist of Hedgehog signalling

Hedgehog (HH) morphogen signalling, crucial for cell growth and tissue patterning in animals, is initiated by the binding of dually lipidated HH ligands to cell surface receptors. Hedgehog-Interacting Protein (HHIP), the only reported secreted inhibitor of Sonic Hedgehog (SHH) signalling, binds directly to SHH with high nanomolar affinity, sequestering SHH. Here, we report the structure of the HHIP N-terminal domain (HHIP-N) in complex with a glycosaminoglycan (GAG). HHIP-N displays a unique bipartite fold with a GAG-binding domain alongside a Cysteine Rich Domain (CRD). We show that HHIP-N is required to convey full HHIP inhibitory function, likely by interacting with the cholesterol moiety covalently linked to HH ligands, thereby preventing this SHH-attached cholesterol from binding to the HH receptor Patched (PTCH1). We also present the structure of the HHIP C-terminal domain in complex with the GAG heparin. Heparin can bind to both HHIP-N and HHIP-C, thereby inducing clustering at the cell surface and generating a high-avidity platform for SHH sequestration and inhibition. Our data suggest a multimodal mechanism, in which HHIP can bind two specific sites on the SHH morphogen, alongside multiple GAG interactions, to inhibit SHH signalling

Functional divergence in the role of N-linked glycosylation in smoothened signaling

The G protein-coupled receptor (GPCR) Smoothened (Smo) is the requisite signal transducer of the evolutionarily conserved Hedgehog (Hh) pathway. Although aspects of Smo signaling are conserved from Drosophila to vertebrates, significant differences have evolved. These include changes in its active sub-cellular localization, and the ability of vertebrate Smo to induce distinct G protein-dependent and independent signals in response to ligand. Whereas the canonical Smo signal to Gli transcriptional effectors occurs in a G protein-independent manner, its non-canonical signal employs Gαi. Whether vertebrate Smo can selectively bias its signal between these routes is not yet known. N-linked glycosylation is a post-translational modification that can influence GPCR trafficking, ligand responsiveness and signal output. Smo proteins in Drosophila and vertebrate systems harbor N-linked glycans, but their role in Smo signaling has not been established. Herein, we present a comprehensive analysis of Drosophila and murine Smo glycosylation that supports a functional divergence in the contribution of N-linked glycans to signaling. Of the seven predicted glycan acceptor sites in Drosophila Smo, one is essential. Loss of N-glycosylation at this site disrupted Smo trafficking and attenuated its signaling capability. In stark contrast, we found that all four predicted N-glycosylation sites on murine Smo were dispensable for proper trafficking, agonist binding and canonical signal induction. However, the under-glycosylated protein was compromised in its ability to induce a non-canonical signal through Gαi, providing for the first time evidence that Smo can bias its signal and that a post-translational modification can impact this process. As such, we postulate a profound shift in N-glycan function from affecting Smo ER exit in flies to influencing its signal output in mice

Bile acid biosynthesis in Smith-Lemli-Opitz syndrome bypassing cholesterol: Potential importance of pathway intermediates

Bile acids are the end products of cholesterol metabolism secreted into bile. They are essential for the absorption of lipids and lipid soluble compounds from the intestine. Here we have identified a series of unusual Δ5-unsaturated bile acids in plasma and urine of patients with Smith-Lemli-Opitz syndrome (SLOS), a defect in cholesterol biosynthesis resulting in elevated levels of 7-dehydrocholesterol (7-DHC), an immediate precursor of cholesterol. Using liquid chromatography – mass spectrometry (LC-MS) we have uncovered a pathway of bile acid biosynthesis in SLOS avoiding cholesterol starting with 7-DHC and proceeding through 7-oxo and 7β-hydroxy intermediates. This pathway also occurs to a minor extent in healthy humans, but elevated levels of pathway intermediates could be responsible for some of the features SLOS. The pathway is also active in SLOS affected pregnancies as revealed by analysis of amniotic fluid. Importantly, intermediates in the pathway, 25-hydroxy-7-oxocholesterol, (25R)26-hydroxy-7-oxocholesterol, 3β-hydroxy-7-oxocholest-5-en-(25R)26-oic acid and the analogous 7β-hydroxysterols are modulators of the activity of Smoothened (Smo), an oncoprotein that mediates Hedgehog (Hh) signalling across membranes during embryogenesis and in the regeneration of postembryonic tissue. Computational docking of the 7-oxo and 7β-hydroxy compounds to the extracellular cysteine rich domain of Smo reveals that they bind in the same groove as both 20S-hydroxycholesterol and cholesterol, known activators of the Hh pathway

In Vivo Formation of Vacuolated Multi-phase Compartments Lacking Membranes

Eukaryotic cells contain membrane-less organelles, including nucleoli and stress granules, that behave like liquid droplets. Such endogenous condensates often have internal substructure, but how this is established in the absence of membrane encapsulation remains unclear. We find that the N- and C-terminal domains of TDP43, a heterogeneous nuclear ribonucleoprotein implicated in neurodegenerative diseases, are capable of driving the formation of sub-structured liquid droplets in vivo. These droplets contain dynamic internal “bubbles” of nucleoplasm, reminiscent of membrane-based multi-vesicular endosomes. A conserved sequence embedded within the intrinsically disordered region (IDR) of TDP43 promotes the formation of these multi-phase assemblies. Disease-causing point mutations in the IDR can change the propensity to form bubbles, protein dynamics within the phase, or phase-environment exchange rates. Our results show that a single IDR-containing protein can nucleate the assembly of compartmentalized liquid droplets approximating the morphological complexity of membrane-bound organelles