Papers by K VijayRaghavan
Development, 2019
, passed away on the 13th of June 2019 after a prolonged illness. Heinrich described himself as '... more , passed away on the 13th of June 2019 after a prolonged illness. Heinrich described himself as 'a hedonist when it came to science' because he said it gave him great pleasure. It was this quality that made working with Heinrich thrilling and deeply fulfilling. Heinrich's long and versatile career spanned the breadth of neurosciencefrom development, to evolution and behaviour. In his passing we have lost not just an astute scientist, but also an impassioned educator and an adventurer of science.
Development, 1997
Several recent studies have provided clues to the molecular mech-anisms that operate during myoge... more Several recent studies have provided clues to the molecular mech-anisms that operate during myogenesis (Molkentin and Olson, 1996). The development of muscles to give rise to the precise pattern observed in the mature animal involves the function of myogenic regulatory genes ...
Development, 1997
We have investigated the roles of homeotic selector genes in the migration and fusion of myoblast... more We have investigated the roles of homeotic selector genes in the migration and fusion of myoblasts, and in the differentiation of adult muscle fibres of Drosophila. Altering intrinsic homeotic identities of myoblasts does not affect their segment-specific migration patterns. By transplanting meso - and metathoracic myoblasts into the abdomen, we demonstrate that the fusion abilities of myoblasts are independent of their segmental identities. However, transplanted thoracic myoblast nuclei are 'entrained' by those of the host abdominal muscles to which they fuse and are unable to 'switch on' a thoracic muscle-specific reporter gene. This process is likely to be mediated by homeotic repression because mis-expression of an abdominal muscle-specific homeotic gene, Ultrabithorax, in the thoracic muscles results in the repression of the thoracic muscle-specific reporter gene. Finally, we show that removal of Ultrabithorax function specifically from muscle cells of the first...
We have followed the pupal development of the indirect flight muscles (IFMs) of Drosophila melano... more We have followed the pupal development of the indirect flight muscles (IFMs) of Drosophila melanogaster. At the onset of metamorphosis larval muscles start to histolyze, with the exception of a specific set of thoracic muscles. Myoblasts surround these persisting larval muscles and begin the formation of one group of adult indirect flight muscles, the dorsal longitudinal muscles. We show that the other group of indirect flight muscles, the dorsoventral muscles, develops simultaneously but without the use of larval templates. By morphological criteria and by patterns of specific gene expression, our experiments define events in IFM development.
The correct patterning of muscles in the Drosophila embryo depends on the migration of developing... more The correct patterning of muscles in the Drosophila embryo depends on the migration of developing muscles over the ectoderm and on the attachment of these muscles to specific attachment sites. We investigate the mechanisms that are involved in this process and describe experiments that allow a genetic dissection of the role of the ectoderm in muscle migration and attachment. We show that cells along the segmental border in the ectoderm are used by the developing muscles to reach their attachment sites. These segment border cells are recognized by dissociated myotubes in single suspensions in culture. Thus, developing muscles have properties that allow the specific recognition of the segment border cells and migrate to attach to these cells. The segment border cells are absent in the mutant wingless and naked. In these mutants, the muscles are severely disorganized. We show that this is not a mere consequence of disruption of the epidermis, since, in the mutant patched, where segment...
Development
We have examined the development of innervation to the indirect flight muscles of Drosophila. Dur... more We have examined the development of innervation to the indirect flight muscles of Drosophila. During metamorphosis, the larval intersegmental nerve of the mesothorax is remodelled to innervate the dorsal longitudinal muscles and two of the dorsoventral muscles. Another modified larval nerve innervates the remaining dorsoventral muscle. The dorsal longitudinal muscles develop using modified larval muscles as templates while dorsoventral muscles develop without the use of such templates. The development of innervation to the two groups of indirect flight muscles differs in spatial and temporal patterns, which may reflect the different ways in which these muscles develop. The identification of myoblasts associated with thoracic nerves during larval life and the association of migrating myoblasts with nerves during metamorphosis indicate the existence of nerve-muscle interactions during indirect flight muscle development. In addition, the developing pattern of axonal branching suggests ...
eLife
Blood cells arise from diverse pools of stem and progenitor cells. Understanding progenitor heter... more Blood cells arise from diverse pools of stem and progenitor cells. Understanding progenitor heterogeneity is a major challenge. TheDrosophilalarval lymph gland is a well-studied model to understand blood progenitor maintenance and recapitulates several aspects of vertebrate hematopoiesis. However in-depth analysis has focused on the anterior lobe progenitors (AP), ignoring the posterior progenitors (PP) from the posterior lobes. Using in situ expression mapping and developmental and transcriptome analysis, we reveal PP heterogeneity and identify molecular-genetic tools to study this abundant progenitor population. Functional analysis shows that PP resist differentiation upon immune challenge, in a JAK-STAT-dependent manner. Upon wasp parasitism, AP downregulate JAK-STAT signaling and form lamellocytes. In contrast, we show that PP activate STAT92E and remain undifferentiated, promoting survival.Stat92Eknockdown or genetically reducing JAK-STAT signaling permits PP lamellocyte differ...
Muscle heterogeneity has been explored in terms of fiber-type distribution, structural organisati... more Muscle heterogeneity has been explored in terms of fiber-type distribution, structural organisation, and differences at their junctions with neurons and tendons. We amplify on such observation to additionally suggest that muscle syncytia have nonuniform protein requirements along their length, deployed for developmental and functional uses. An exploration of regionalized proteins or their mRNA across muscle syncytia has not been done. We investigated mRNA localization in regions of Drosophila melanogaster dorsal longitudinal muscle (DLM) syncytia over their entire transcriptome. Dissection of muscle regions, their RNA-seq and stringent Differential Gene Expression analysis indeed reveals statistically significant regionalization of nearly a hundred mRNA over the length of DLMs. Functions of over half of these genes require experimental verification. A preponderance of mRNA coding for catabolic and proteolytic enzymes is conspicuous among transcripts enriched in the posterior of DLMs...
Scientific reports, Jan 4, 2018
Rudhira/Breast Carcinoma Amplified Sequence 3 (BCAS3) is a cytoskeletal protein that promotes dir... more Rudhira/Breast Carcinoma Amplified Sequence 3 (BCAS3) is a cytoskeletal protein that promotes directional cell migration and angiogenesis in vitro and is implicated in human carcinomas and coronary artery disease. To study the role of Rudhira during development in vivo, we generated the first knockout mouse for rudhira and show that Rudhira is essential for mouse development. Rudhira null embryos die at embryonic day (E) 9.5 accompanied by severe vascular patterning defects in embryonic and extra-embryonic tissues. To identify the molecular processes downstream of rudhira, we analyzed the transcriptome of intact knockout yolk sacs. Genome-wide transcriptome analysis showed that Rudhira functions in angiogenesis and its related processes such as cell adhesion, extracellular matrix organization, peptidase activity and TGFβ signaling. Since Rudhira is also expressed in endothelial cells (ECs), we further generated Tie2Cre-mediated endothelial knockout (CKO) of rudhira. CKO embryos surv...
Neuron, Jan 16, 2018
Human Ataxin-2 is implicated in the cause and progression of amyotrophic lateral sclerosis (ALS) ... more Human Ataxin-2 is implicated in the cause and progression of amyotrophic lateral sclerosis (ALS) and type 2 spinocerebellar ataxia (SCA-2). In Drosophila, a conserved atx2 gene is essential for animal survival as well as for normal RNP-granule assembly, translational control, and long-term habituation. Like its human homolog, Drosophila Ataxin-2 (Atx2) contains polyQ repeats and additional intrinsically disordered regions (IDRs). We demonstrate that Atx2 IDRs, which are capable of mediating liquid-liquid phase transitions in vitro, are essential for efficient formation of neuronal mRNP assemblies in vivo. Remarkably, ΔIDR mutants that lack neuronal RNP granules show normal animal development, survival, and fertility. However, they show defects in long-term memory formation/consolidation as well as in C9ORF72 dipeptide repeat or FUS-induced neurodegeneration. Together, our findings demonstrate (1) that higher-order mRNP assemblies contribute to long-term neuronal plasticity and memor...
Walking is a complex rhythmic locomotor behaviour generated by sequential and periodical contract... more Walking is a complex rhythmic locomotor behaviour generated by sequential and periodical contraction of muscles essential for coordinated control of movements of legs and leg joints. Studies of walking in vertebrates and invertebrates have revealed that premotor neural circuitry generates a basic rhythmic pattern that is sculpted by sensory feedback and ultimately controls the amplitude and phase of the motor output to leg muscles. However, the identity and functional roles of the premotor interneurons that directly control leg motoneuron activity are poorly understood. Here we take advantage of the powerful genetic methodology available in Drosophila to investigate the role of premotor inhibition in walking by genetically suppressing inhibitory input to leg motoneurons. For this, we have developed a novel algorithm for automated analysis of leg motion to characterize the walking parameters of wildtype flies from high speed video recordings. Further, we use genetic reagents for targ...
Science (New York, N.Y.), Jan 20, 2016
Peer review and preprints. Preprints accelerate dissemination, whereas manuscripts are being impr... more Peer review and preprints. Preprints accelerate dissemination, whereas manuscripts are being improved through peer review.
Journal of Cancer Policy, 2015
In 2011, the National Cancer Institute (NCI, USA) introduced the Provocative Questions (PQ) Initi... more In 2011, the National Cancer Institute (NCI, USA) introduced the Provocative Questions (PQ) Initiative, a new approach allowing active researchers to define major unsolved or neglected problems in oncology unaddressed by existing funding. Last year, the U.S. NCI teamed up with the Indian Department of Biotechnology (DBT) to pilot the PQ approach in three cities in India. Workshop outcomes includedthe generation of fundable "PQs" (perplexing questions understudied by the international scientific community), as well as the identification of several non-PQ projects and research-related issues of importance to DBT and other Indian funding groups. The workshops clearly indicated the need to expand beyond crafting "PQs" when considering the best areas for research funding in international settings. Nonetheless, the first set of PQ workshops provided a forum to discuss key issues regarding cancer research in India, including the paucity of cancer research funding, and the lack of relevant human resource training and technology sharing platforms. Continued open debate between researchers, funders and policymakers will be essential to effectively strengthen the cancer research portfolio in India.
The Drosophila genome contains >13,000 protein coding genes, the majority of which remain poor... more The Drosophila genome contains >13,000 protein coding genes, the majority of which remain poorly investigated. Important reasons include the lack of antibodies or reporter constructs to visualise these proteins. Here we present a genome-wide fosmid library of ≈10,000 GFP-tagged clones, comprising tagged genes and most of their regulatory information. For 880 tagged proteins we have created transgenic lines and for a total of 207 lines we have assessed protein expression and localisation in ovaries, embryos, pupae or adults by stainings and live imaging approaches. Importantly, we can visualise many proteins at endogenous expression levels and find a large fraction of them localising to subcellular compartments. Using complementation tests we demonstrate that two-thirds of the tagged proteins are fully functional. Moreover, our clones enable interaction proteomics from developing pupae and adult flies. Taken together, this resource will enable systematic analysis of protein expres...
Biophysical Journal, 2014
that the neonatal cardiac isoform of TnI, ssTnI, confers pH-insensitivity in this regard compared... more that the neonatal cardiac isoform of TnI, ssTnI, confers pH-insensitivity in this regard compared to the adult cTnI isoform. However ssTnI confers deleterious effects of impaired relaxation in the adult myocyte. Alignment and functional studies have demonstrated that this pH-insensitivity is derived from ssTnI residue H132. Introduction of a histidine at the cognate position in cTnI (A164H) mitigates the pH-sensitivity of the calcium-force relationship in cardiac myocytes while retaining relaxation enhancement via the Nterm domain relative to ssTnI. We are establishing a time-resolved fluorescence methodology for detecting alterations in the calcium sensitivity of the thin filament during ischemia. We have engineered a single cysteine mutation for labeling with environmentally sensitive fluorophores designed to detect Ca 2þ and pH-sensitive structural changes in cTnI and cTnC. We will discuss progress using this approach to interrogate troponin function in ischemia mimetic conditions.
eLife, 2014
How myoblast populations are regulated for the formation of muscles of different sizes is an esse... more How myoblast populations are regulated for the formation of muscles of different sizes is an essentially unanswered question. The large flight muscles of Drosophila develop from adult muscle progenitor (AMP) cells set-aside embryonically. The thoracic segments are all allotted the same small AMP number, while those associated with the wing-disc proliferate extensively to give rise to over 2500 myoblasts. An initial amplification occurs through symmetric divisions and is followed by a switch to asymmetric divisions in which the AMPs self-renew and generate post-mitotic myoblasts. Notch signaling controls the initial amplification of AMPs, while the switch to asymmetric division additionally requires Wingless, which regulates Numb expression in the AMP lineage. In both cases, the epidermal tissue of the wing imaginal disc acts as a niche expressing the ligands Serrate and Wingless. The disc-associated AMPs are a novel muscle stem cell population that orchestrates the early phases of a...
Development (Cambridge, England), 1998
Twist is required in Drosophila embryogenesis for mesodermal specification and cell-fate choice. ... more Twist is required in Drosophila embryogenesis for mesodermal specification and cell-fate choice. We have examined the role of Twist and Notch during adult indirect flight muscle development. Reduction in levels of Twist leads to abnormal myogenesis. Notch reduction causes a similar mutant phenotype and reduces Twist levels. Conversely, persistent expression, in myoblasts, of activated Notch causes continued twist expression and failure of differentiation as assayed by myosin expression. The gain-of-function phenotype of Notch is very similar to that seen upon persistent twist expression. These results point to a relationship between Notch function and twist regulation during indirect flight muscle development and show that decline in Twist levels is a requirement for the differentiation of these muscles, unlike the somatic muscles of the embryo.
Proceedings of the National Academy of Sciences of the United States of America, 1991
We describe a method of screening for transposon insertions in or near Drosophila loci that corre... more We describe a method of screening for transposon insertions in or near Drosophila loci that correspond to cloned DNA sequences. We mobilize a modified P element transposon that carries a bacterial plasmid origin of replication and a drug-resistance marker. The genomic sequences flanking each transposon insertion site can then be rescued as a plasmid in Escherichia coli. Libraries of such plasmids, representing pools of transposon-mutagenized individuals, are used as hybridization probes against cloned sequences to determine whether a transposon has inserted next to a particular site in the genome. The number of loci that can be screened simultaneously by this procedure is quite large. We have screened an array of cDNA clones representing almost 700 distinct loci against libraries representing 760 mutagenized flies, and we obtained hybridization signals to 7 different cDNAs. Three of these events have been analyzed in detail and represent genuine insertions near genomic sequences tha...
Uploads
Papers by K VijayRaghavan