Light-Sheet Microscopy Enables Three-Dimensional Fluorescence Imaging and Live Imaging of Satellite Cells on Skeletal Muscle Fibers.

The ex vivo myofiber culture system has proven to be a useful methodology to explore the biology and behavior of satellite cells within their niche environment. However, a limitation of this system is that myofibers and their associated satellite cells are commonly examined using conventional fluorescence microscopy, which renders a three-dimensional system into two-dimensional imaging, leading to the loss of precious information or misleading interpretation of observations. Here, we report on the use of light-sheet fluorescence microscopy to generate three-dimensional and live imaging of satellite cells on myofibers.

Basal lamina remodeling at the skeletal muscle stem cell niche mediates stem cell self-renewal.

A central question in stem cell biology is the relationship between stem cells and their niche. Although previous reports have uncovered how signaling molecules released by niche cells support stem cell function, the role of the extra-cellular matrix (ECM) within the niche is unclear. Here, we show that upon activation, skeletal muscle stem cells (satellite cells) induce local remodeling of the ECM and the deposition of laminin-α1 and laminin-α5 into the basal lamina of the satellite cell niche.

Hedgehog signalling acts upstream of Laminin alpha1 transcription in the zebrafish paraxial mesoderm.

Laminin-111 (α1β1γ1) is a member of the Laminin family of extra-cellular matrix proteins that comprises 16 members, components of basement membranes. Laminin-111, one of the first Laminin proteins synthesised during embryogenesis, is required for basement membrane deposition and has essential roles in tissue morphogenesis and patterning. Yet, the mechanisms controlling Laminin-111 expression are poorly understood.

Asymmetric Distribution of Primary Cilia Allocates Satellite Cells for Self-Renewal.

Regeneration of vertebrate skeletal muscles requires satellite cells, a population of stem cells that are quiescent in normal conditions and divide, differentiate, and self-renew upon activation triggered by exercise, injury, and degenerative diseases. Satellite cell self-renewal is essential for long-term tissue homeostasis, and previous work has identified a number of external cues that control this process. However, little is known of the possible intrinsic control mechanisms of satellite cell self-renewal.

The myotomal basement membrane: insight into laminin-111 function and its control by Sonic hedgehog signaling.

The importance of laminin-containing basement membranes (BM) for adult muscle function is well established, in particular due to the severe phenotype of congenital muscular dystrophies in patients with mutations disrupting the BM-muscle cell interaction. Developing muscles in the embryo are also dependent on an intact BM. However, the processes controlled by BM-muscle cell interactions in the embryo are only beginning to be elucidated.

Sonic hedgehog acts cell-autonomously on muscle precursor cells to generate limb muscle diversity.

How muscle diversity is generated in the vertebrate body is poorly understood. In the limb, dorsal and ventral muscle masses constitute the first myogenic diversification, as each gives rise to distinct muscles. Myogenesis initiates after muscle precursor cells (MPCs) have migrated from the somites to the limb bud and populated the prospective muscle masses.

FatJ acts via the Hippo mediator Yap1 to restrict the size of neural progenitor cell pools.

The size, composition and functioning of the spinal cord is likely to depend on appropriate numbers of progenitor and differentiated cells of a particular class, but little is known about how cell numbers are controlled in specific cell cohorts along the dorsoventral axis of the neural tube. Here, we show that FatJ cadherin, identified in a large-scale RNA interference (RNAi) screen of cadherin genes expressed in the neural tube, is localised to progenitors in intermediate regions of the neural tube. Loss of function of FatJ promotes an increase in dp4-vp1 progenitors and a concomitant increase in differentiated Lim1(+)/Lim2(+) neurons.

A novel Gli3 enhancer controls the Gli3 spatiotemporal expression pattern through a TALE homeodomain protein binding site.

The zinc finger transcription factor Gli3 is an essential mediator of hedgehog signaling. Gli3 has a dynamic expression pattern during embryonic development. In the neural tube, Gli3 transcripts are patterned along the anteroposterior and dorsoventral axes such that the initial broad expression in the posterior neural tube becomes dorsally restricted as neurogenesis takes place.

Expression analysis of TALE family transcription factors during avian development.

The TALE family of homeodomain containing transcription factors consists of the Meis, Prep and Tgif, and the Pbx subfamily of proteins. Several TALE orthologues have been identified in amniotes, but no comprehensive analysis of their expression pattern during embryogenesis has been performed. Here, we report on TALE gene expression in the avian embryo.

Sonic hedgehog-dependent synthesis of laminin alpha1 controls basement membrane assembly in the myotome.

Basement membranes have essential structural and signalling roles in tissue morphogenesis during embryonic development, but the mechanisms that control their formation are still poorly understood. Laminins are key components of basement membranes and are thought to be essential for initiation of basement membrane assembly. Here, we report that muscle progenitor cells populating the myotome migrate aberrantly in the ventral somite in the absence of sonic hedgehog (Shh) signalling, and we show that this defect is due to the failure to form a myotomal basement membrane.

Sequence analyses to study the evolutionary history and cis-regulatory elements of Hedgehog genes.

Sequence analysis and comparative genomics are powerful tools to gain knowledge on multiple aspects of gene and protein regulation and function. These have been widely used to understand the evolutionary history and the biochemistry of Hedgehog (Hh) proteins, and the molecular control of Hedgehog gene expression. Here, we report on some of the methods available to retrieve protein and genomic sequences.

Dystroglycan protein distribution coincides with basement membranes and muscle differentiation during mouse embryogenesis.

Using immunohistochemistry, we have examined beta-Dystroglycan protein distribution in the mouse embryo at embryonic stages E9.5 to E11.5.

Expression of avian C-terminal binding proteins (Ctbp1 and Ctbp2) during embryonic development.

C-terminal binding proteins (CtBPs) are transcriptional corepressors of mediators of Notch, Wnt, and other signalling pathways. Thus, they are potential players in the control of several developmentally important processes, including segmentation, somitogenesis, and neural tube and limb patterning. We have cloned the avian orthologues of Ctbp1 and Ctbp2 and examined their expression pattern by whole-mount in situ hybridization between Hamburger and Hamilton (HH) stages 3 and 24.

Expression of avian Groucho-related genes (Grgs) during embryonic development.

Groucho-related genes (Grgs) encode transcriptional co-repressors of Lef/Tcf and Hes proteins, which are mediators of Wnt and Notch signalling, respectively. Thus, they are important players in the developmental processes controlled by Wnt and Notch signalling, including lateral inhibition, segmentation and dorso-ventral patterning. We have cloned the avian homologues of Grg genes and examined their expression pattern by whole-mount in situ hybridisation between Hamburger-Hamilton (HH) stages 3 and 24.

Gli2 and Gli3 have redundant and context-dependent function in skeletal muscle formation.

The Gli family of zinc finger transcription factors are mediators of Shh signalling in vertebrates. In previous studies, we showed that Shh signalling, via an essential Gli-binding site in the Myf5 epaxial somite (ES) enhancer, is required for the specification of epaxial muscle progenitor cells. Shh signalling is also required for the normal mediolateral patterning of myogenic cells within the somite.