Expression of DM-GRASP/BEN in the developing mouse spinal cord and various epithelia

Transcriptomic landscape of early hair follicle and epidermal development

Morphogenesis of ectodermal organs, such as hair, tooth, and mammary gland, starts with the formation of local epithelial thickenings, or placodes, but it remains to be determined how distinct cell types and differentiation programs are established during ontogeny. Here, we use bulk and single-cell transcriptomics and pseudotime modeling to address these questions in developing hair follicles and epidermis and produce a comprehensive transcriptomic profile of cellular populations in the hair placode and interplacodal epithelium. We report previously unknown cell populations and marker genes, including early suprabasal and genuine interfollicular basal markers, and propose the identity of suprabasal progenitors. By uncovering four different hair placode cell populations organized in three spatially distinct areas, with fine gene expression gradients between them, we posit early biases in cell fate establishment. This work is accompanied by a readily accessible online tool to stimulate further research on skin appendages and their progenitors.

Cell Adhesion Molecules and Ubiquitination-Functions and Significance

Cell adhesion molecules of the immunoglobulin (Ig) superfamily represent the biggest group of cell adhesion molecules. They have been analyzed since approximately 40 years ago and most of them have been shown to play a role in tumor progression and in the nervous system. All members of the Ig superfamily are intensively posttranslationally modified. However, many aspects of their cellular functions are not yet known. Since a few years ago it is known that some of the Ig superfamily members are modified by ubiquitin. Ubiquitination has classically been described as a proteasomal degradation signal but during the last years it became obvious that it can regulate many other processes including internalization of cell surface molecules and lysosomal sorting. The purpose of this review is to summarize the current knowledge about the ubiquitination of cell adhesion molecules of the Ig superfamily and to discuss its potential physiological roles in tumorigenesis and in the nervous system.

CD166 and regulation of hematopoiesis

PURPOSE OF REVIEW

Many surface antigens have been previously used to identify hematopoietic stem cells or cellular elements of the hematopoietic niche. However, to date, not a single surface marker has been identified as a common marker expressed on murine and human hematopoietic stem cells and on cells of the hematopoietic niche. Recently, a few laboratories, including ours, recognized the importance of CD166 as a functional marker on both stem cells and osteoblasts and have begun to characterize the role of CD166 in hematopoiesis.

RECENT FINDINGS

Expression of CD166 on hematopoietic cells and cells in the marrow microenvironment was first reported more than a decade ago. Lately, however, a more prominent role for CD166 in normal hematopoiesis and in cancer biology including metastasis began to emerge. This review will cover the significance of CD166 in identifying normal hematopoietic stem cells and cells of the hematopoietic niche and highlight how CD166-mediated homophilic interactions between both cell types may be critical for stem cell function.

SUMMARY

The conserved homology between murine and human CD166 and its involvement in metastasis provides an excellent bridge for translational investigations aimed at enhancing stem cell engraftment and clinical utility of stem cells and at using CD166 as a therapeutic target in cancer.

ALCAM (CD166) Is a Surface Marker for Early Murine Cardiomyocytes

ALCAM (activated leukocyte cell adhesion molecule, CD166) belongs to the immunoglobulin superfamily and is involved in axon guidance, hematopoiesis, immune response and tumor metastasis. During embryogenesis, mRNA encoding ALCAM was expressed in the cardiac crescent and the neural groove at embryonic day (E) 7.75 and predominately in the tubular heart at E8.5. A newly generated monoclonal antibody against the ALCAM molecule (ALC-48) exclusively stained cardiomyocytes at E8.25-10.5. However, ALCAM expression was lost by cardiomyocytes by E12.5 and its expression shifts to a variety of organs during later stages. ALCAM was found to be a prominent surface marker for cardiomyocytes in early embryonic hearts. The transient expression of ALCAM during early developmental stages marks specific developmental stages in cardiomyocyte differentiation.

Axon fasciculation defects and retinal dysplasias in mice lacking the immunoglobulin superfamily adhesion molecule BEN/ALCAM/SC1

The immunoglobulin superfamily adhesion molecule BEN (other names include ALCAM, SC1, DM-GRASP, neurolin, and CD166) has been implicated in the control of numerous developmental and pathological processes, including the guidance of retinal and motor axons to their targets. To test hypotheses about BEN function, we disrupted its gene via homologous recombination and analyzed the resulting mutant mice. Mice lacking BEN are viable and fertile, and display no external morphological defects. Despite grossly normal trajectories, both motor and retinal ganglion cell axons fasciculated poorly and were occasionally misdirected. In addition, BEN mutant retinae exhibited evaginated or invaginated regions with photoreceptor ectopias that resembled the "retinal folds" observed in some human retinopathies. Together, these results demonstrate that BEN promotes fasciculation of multiple axonal populations and uncover an unexpected function for BEN in retinal histogenesis.

Ectopic Myf5 or MyoD prevents the neuronal differentiation program in addition to inducing skeletal muscle differentiation, in the chick neural tube

Forced expression of the bHLH myogenic factors, Myf5 and MyoD, in various mammalian cell lines induces the full program of myogenic differentiation. However, this property has not been extensively explored in vivo. We have taken advantage of the chick model to investigate the effect of electroporation of the mouse Myf5 and MyoD genes in the embryonic neural tube. We found that misexpression of either mouse Myf5 or MyoD in the chick neural tube leads to ectopic skeletal muscle differentiation, assayed by the expression of the myosin heavy chains in the neural tube and neural crest derivatives. We also showed that the endogenous neuronal differentiation program is inhibited under the influence of either ectopic mouse Myf5 or MyoD. We used this new system to analyse, in vivo, the transcriptional regulation between the myogenic factors. We found that MyoD and Myogenin expression can be activated by ectopic mouse Myf5 or MyoD, while Myf5 expression cannot be activated either by mouse MyoD or by itself. We also analysed the transcriptional regulation between the myogenic factors and the different genes involved in myogenesis, such as Mef2c, Pax3, Paraxis, Six1, Mox1, Mox2 and FgfR4. We established the existence of an unexpected regulatory loop between MyoD and FgfR4. The consequences for myogenesis are discussed.

BEN/DM-GRASP/SC1 expression during mouse facial development: differential expression and regulation in molars and incisors

The cell adhesion molecule BEN/DM-GRASP/SC1 is expressed in a variety of tissues during embryogenesis. Here, we studied the expression pattern of BEN/DM-GRASP/SC1 in different organs involved in facial mouse development, especially in the developing teeth. BEN/DM-GRASP/SC1 was expressed in nose, whisker, gland, and tongue epithelia, as well as in myogenic mesenchyme. In molars, BEN/DM-GRASP/SC1 was firstly expressed in the condensed mesenchyme and thereafter expression was confined to mesenchymal cells of the dental follicle. In contrast, in incisors, transient BEN/DM-GRASP/SC1 expression was restricted to epithelium. In tissue recombination experiments, BEN/DM-GRASP/SC1 expression in mesenchyme was activated by molar, but not incisor epithelium.

Activated leukocyte cell adhesion molecule (CD166/ALCAM): developmental and mechanistic aspects of cell clustering and cell migration

Activated leukocyte cell adhesion molecule (ALCAM/CD166) is a member of the immunoglobulin superfamily and belongs to a recent subgroup with five extracellular immunoglobulin-like domains (VVC2C2C2). ALCAM mediates both heterophilic (ALCAM-CD6) and homophilic (ALCAM-ALCAM) cell-cell interactions. While expressed in a wide variety of tissues, ALCAM is usually restricted to subsets of cells involved in dynamic growth and/or migration, including neural development, branching organ development, hematopoiesis, immune response and tumor progression. Recent structure-function analyses of ALCAM hint at how its cytoskeletal anchoring and the integrity of the extracellular immunoglobulin-like domains may regulate complex cellular properties in regard to cell adhesion, growth and migration. Accumulating evidence suggests that ALCAM expression may reflect the onset of a cellular program for homeostatic control of growth saturation, which induces either growth arrest or cell migration when the upper limits are exceeded.

Identification and characterization of a cell surface marker for embryonic rat spinal accessory motor neurons

The developing mammalian spinal cord contains distinct populations of motor neurons that can be distinguished by their cell body positions, by the expression of specific combinations of regulatory genes, and by the paths that their axons take to exit the central nervous system (CNS). Subclasses of spinal motor neurons are also thought to express specific cell surface proteins that function as receptors which control the guidance of their axons. We identified monoclonal antibody (mAb) SAC1 in a screen aimed at generating markers for specific subsets of neurons/axons in the developing rat spinal cord. During early embryogenesis, mAb SAC1 selectively labels a small subset of Isl1-positive motor neurons located exclusively within cervical segments of the spinal cord. Strikingly, these neurons extend mAb SAC1-positive axons along a dorsally directed trajectory toward the lateral exit points. Consistent with the finding that mAb SAC1 also labels spinal accessory nerves, these observations identify mAb SAC1 as a specific marker of spinal accessory motor neurons/axons. During later stages of embryogenesis, mAb SAC1 is transiently expressed on both dorsally and ventrally projecting spinal motor neurons/axons. Interestingly, mAb SAC1 also labels the notochord and floor plate during most stages of spinal cord development. The mAb SAC1 antigen is a 100-kD glycoprotein that is likely to be the rat homolog of SC1/BEN/DM-GRASP, a homophilic adhesion molecule that mediates axon outgrowth and fasciculation.