Biology subjects

Lamb, M. C.

Publications and source records attributed to Lamb, M. C..

5 recordsLinked to original sources

bioRxiv2022

rRNA transcription is integral to liquid-liquid phase separation and maintenance of nucleolar structure

Beginning with transcription of ribosomal RNA (rRNA) by RNA Polymerase (Pol) I in the nucleolus, ribosome biogenesis is intimately tied to cell growth and proliferation. Perturbation of ribosome biogenesis has been previously shown to affect nucleolar structure, yet the underlying mechanism is unknown. We generated loss-of-function mouse mutants of Pol I subunits, Polr1a, Polr1b, Polr1c and Polr1d, thereby genetically inhibiting rRNA transcription and ribosome biogenesis. Pol I mutant embryos are preimplantation lethal and have fewer nucleoli. Using hiPSCs triple labeled for the three nucleolar compartments, we observe two phenotypes upon Pol I inhibition: a single condensed nucleolus, and fragmented nucleoli. We find that when rRNA transcription is inhibited, the viscosity of the granular compartment of the nucleolus is increased disrupting its liquid-liquid phase separation properties, which results in a condensed nucleolus. Taken together, our data suggests that Pol I function and rRNA transcription are required for maintaining nucleolar structure and integrity.

developmental biology↗

bioRxiv2021

Fascin limits Myosin activity within Drosophila border cells to control substrate stiffness and promote migration

A key regulator of collective cell migrations, which drive development and cancer metastasis, is substrate stiffness. Increased substrate stiffness promotes migration and is controlled by Myosin. Using Drosophila border cell migration as a model of collective cell migration, we identify, for the first time, that the actin bundling protein Fascin limits Myosin activity in vivo. Loss of Fascin results in: increased activated Myosin on the border cells and their substrate, the nurse cells; decreased border cell Myosin dynamics; and increased nurse cell stiffness as measured by atomic force microscopy. Reducing Myosin restores on-time border cell migration in fascin mutant follicles. Further, Fascins actin bundling activity is required to limit Myosin activation. Surprisingly, we find that Fascin regulates Myosin activity in the border cells to control nurse cell stiffness to promote migration. Thus, these data shift the paradigm from a substrate stiffness-centric model of regulating migration, to uncover that collectively migrating cells play a critical role in controlling the mechanical properties of their substrate in order to promote their own migration. This new means of mechanical regulation of migration is likely conserved across contexts and organisms, as Fascin and Myosin are common regulators of cell migration.

cell biology↗

bioRxiv2019

Prostaglandins regulate invasive, collective border cell migration

While prostaglandins (PGs), short-range lipid signals, regulate cell migration, their mechanisms of action are poorly understood in collective migration. To address this, we use Drosophila border cell migration during Stage 9 of oogenesis. The border cells delaminate from the epithelium, and migrate collectively and invasively between the nurse cells. Pxt is the Drosophila cyclooxygenase-like enzyme responsible for all PG synthesis. Loss of Pxt results in both a significant delay in border cell migration during Stage 9 and an increase in cluster length compared to wild-type controls. Contributing to these phenotypes is altered integrin localization. Integrins are enriched on the border cell membranes, and this enrichment is lost in pxt mutants. Active integrins require interaction with the actin cytoskeleton. As we previously found PGs regulate the actin bundler Fascin and Fascin is required for border cell migration, we hypothesized PGs regulate Fascin to control integrins. Supporting this, loss of Fascin results in a pxt-like integrin localization, and dominant genetic interaction studies reveal that co-reduction of Pxt and Fascin results in delayed and elongated border cell clusters. Together these data lead to the model that PG signaling controls Fascin, and thereby integrins, to mediate on-time border cell migration and maintain cluster cohesion.

cell biology↗

bioRxiv2019

Fascin regulates protrusions and delamination to promote invasive, collective cell migration in vivo.

Fascin is an actin bundling protein that is essential for developmental cell migrations and promotes cancer metastasis. In addition to bundling actin, Fascin has several actin-independent roles. Border cell migration during Drosophila oogenesis provides an excellent model to study Fascins various roles during invasive, collective cell migration. Border cell migration requires Fascin. Fascin functions not only within the migrating border cells, but also within the nurse cells, the substrate for this migration. Loss of Fascin results in increased, shorter and mislocalized protrusions during migration. Data supports the model that Fascin promotes the activity of Enabled, an actin elongating factor, to regulate migration. Additionally, loss of Fascin inhibits border cell delamination. These defects are partially due to altered E-cadherin localization in the border cells; this is predicted to be an actin-independent role of Fascin. Overall, Fascin is essential for multiple aspects of this invasive, collective cell migration, and functions in both actin-dependent and -independent manners. These findings have implications beyond Drosophila, as border cell migration has emerged as a model to study mechanisms mediating cancer metastasis.

cell biology↗

bioRxiv2019

Pharmaco-genetic screen to uncover actin regulators targeted by prostaglandins during Drosophila oogenesis

Prostaglandins (PGs) are lipid signaling molecules with numerous physiologic functions, including pain/inflammation, fertility, and cancer. PGs are produced downstream of cyclooxygenase (COX) enzymes, the targets of non-steroidal anti-inflammatory drugs (NSAIDs). In numerous systems, PGs regulate actin cytoskeletal remodeling, however, their mechanisms of action remain largely unknown. To address this deficiency, we undertook a pharmaco-genetic interaction screen during late-stage Drosophila oogenesis. Drosophila oogenesis is as an established model for studying both actin dynamics and PGs. Indeed, during Stage 10B, cage-like arrays of actin bundles surround each nurse cell nucleus, and during Stage 11, the cortical actin contracts, squeezing the cytoplasmic contents into the oocyte. Both of these cytoskeletal properties are required for follicle development and fertility, and are regulated by PGs. Here we describe a pharmaco-genetic interaction screen that takes advantage of the facts that Stage 10B follicles will mature in culture and COX inhibitors, such as aspirin, block this in vitro follicle maturation. In the screen, aspirin was used at a concentration that blocks 50% of the wild-type follicles from maturing in culture. By combining this aspirin treatment with heterozygosity for mutations in actin regulators, we quantitatively identified enhancers and suppressors of COX inhibition. Here we present the screen results and initial follow-up studies on three strong enhancers - Enabled, Capping protein, and non-muscle Myosin II Regulatory Light Chain. Overall, these studies provide new insight into how PGs regulate both actin bundle formation and cellular contraction, properties that are not only essential for development, but are misregulated in diseases.

cell biology↗