Commitment of human mesenchymal stromal cells to skeletal lineages is independent of their morphogenetic capacity.

Background: Mesenchymal stromal cells (MSCs) are multipotent cell populations obtained from fetal and adult tissues. They share some characteristics with limb bud mesodermal cells such as differentiation potential into osteogenic, chondrogenic, and tenogenic lineages and an embryonic mesodermal origin. Although MSCs differentiate into skeletal-related lineages , they have not been shown to self-organize into complex skeletal structures or connective tissues, as in the limb.

Chicken Recombinant Limbs Assay to Understand Morphogenesis, Patterning, and Early Steps in Cell Differentiation.

Cell differentiation is the fine-tuned process of cell commitment leading to the formation of different specialized cell types during the establishment of developing tissues and organs. This process is actively maintained in adulthood. Cell differentiation is an ongoing process during the development and homeostasis of organs.

Analysis of Cell Differentiation, Morphogenesis, and Patterning During Chicken Embryogenesis Using the Soaked-Bead Assay.

A multitude of genetic programs is activated during embryonic development that orchestrates cell differentiation to generate an astounding diversity of somatic cells, tissues, and organs. The precise activation of these genetic programs is regulated by morphogens, diffusible molecules that direct cell fate at different thresholds. Understanding how genetic activation coordinates morphogenesis requires the study of local interactions triggered by morphogens during development.

Activation of the WNT-BMP-FGF Regulatory Network Induces the Onset of Cell Death in Anterior Mesodermal Cells to Establish the ANZ.

The spatiotemporal control of programmed cell death (PCD) plays a significant role in sculpting the limb. In the early avian limb bud, the anterior necrotic zone (ANZ) and the posterior necrotic zone are two cell death regions associated with digit number reduction. In this study, we evaluated the first events triggered by the FGF, BMP, and WNT signaling interactions to initiate cell death in the anterior margin of the limb to establish the ANZ.

SCA-1/Ly6A Mesodermal Skeletal Progenitor Subpopulations Reveal Differential Commitment of Early Limb Bud Cells.

At early developmental stages, limb bud mesodermal undifferentiated cells are morphologically indistinguishable. Although the identification of several mesodermal skeletal progenitor cell populations has been recognized, in advanced stages of limb development here we identified and characterized the differentiation hierarchy of two new early limb bud subpopulations of skeletal progenitors defined by the differential expression of the SCA-1 marker. Based on tissue localization of the mesenchymal stromal cell-associated markers (MSC-am) CD29, Sca-1, CD44, CD105, CD90, and CD73, we identified, by multiparametric analysis, the presence of cell subpopulations in the limb bud capable of responding to inductive signals differentially, namely, sSca and sSca cells.

The spatiotemporal expression patterns of MSC-associated markers contribute to the identification of progenitor subpopulations in developing limbs.

During limb development, skeletal tissues differentiate from their progenitor cells in an orchestrated manner. Mesenchymal stromal cells (MSCs), which are considered to be adult undifferentiated/progenitor cells, have traditionally been identified by the expression of MSC-associated markers (MSC-am) and their differentiation capacities. However, although MSCs have been isolated from bone marrow and a variety of adult tissues, their developmental origin is poorly understood.

WNT5A-Ca-CaN-NFAT signalling plays a permissive role during cartilage differentiation in embryonic chick digit development.

During digit development, the correct balance of chondrogenic signals ensures the recruitment of undifferentiated cells into the cartilage lineage or the maintenance of cells at the undifferentiated stage. WNT/β catenin maintains the pool of progenitor cells, whereas TGFβ signalling promotes cartilage differentiation by inducing Sox9 expression. Moreover, WNT5A promotes the degradation of β catenin during mouse limb development.

Understanding the Cellular and Molecular Mechanisms That Control Early Cell Fate Decisions During Appendicular Skeletogenesis.

The formation of the vertebrate skeleton is orchestrated in time and space by a number of gene regulatory networks that specify and position all skeletal tissues. During embryonic development, bones have two distinct origins: bone tissue differentiates directly from mesenchymal progenitors, whereas most long bones arise from cartilaginous templates through a process known as endochondral ossification. Before endochondral bone development takes place, chondrocytes form a cartilage analgen that will be sequentially segmented to form joints; thus, in the cartilage template, either the cartilage maturation programme or the joint formation programme is activated.

A small population of resident limb bud mesenchymal cells express few MSC-associated markers, but the expression of these markers is increased immediately after cell culture.

Skeletal progenitors are derived from resident limb bud mesenchymal cells of the vertebrate embryos. However, it remains poorly understood if they represent stem cells, progenitors, or multipotent mesenchymal stromal cells (MSC). Derived-MSC of different adult tissues under in vitro experimental conditions can differentiate into the same cellular lineages that are present in the limb.

Interdigital tissue remodelling in the embryonic limb involves dynamic regulation of the miRNA profiles.

Next-generation sequencing in combination with quantitative polymerase chain reaction analysis revealed a dynamic miRNA signature in the interdigital mesoderm of the chick embryonic hinlimb in the course of interdigit remodelling. During this period, 612 previously known chicken miRNAs (gga-miRNAs) and 401 non-identified sequences were expressed in the interdigital mesoderm. Thirty-six microRNAs, represented by more than 750 reads per million, displayed differential expression between stages HH29 (6 id) and HH32 (7.