Localization of Type IV Collagen in the Myotome Cells during the Somite Differentiation in the Chick Embryo. (type IV collagen/chick embryo/myotome/dermatome/immunohistochemistry)

Unilateral Basement Membrane Zone Alteration of the Regenerated Laminar Region in Equine Chronic Laminitis

Between the laminar epidermis and the laminar dermis of laminar region (LR) in equine foot, it can be observed the basement membrane zone (BMZ), which is composed of a basement membrane and its accompaniments like the hemidesmosome and anchoring fibril. Alteration in the BMZ in equine laminitis is possibly related with not only development but also recovery outcome and recurrence of this disease. However, there is little known about the structure of the BMZ during the recovery phase of this disease. To assess the condition of the BMZ of LR affected by chronic laminitis, the tissue was examined in three cases at two weeks, four weeks and three months after the onset of laminitis, using pathological, immunohistochemical and electron microscopic techniques. Histologically in all laminitis cases, there was a regenerated laminar epidermis with proliferating keratinocytes between the Stratum medium and the dermis, but it included the undeveloped secondary epidermal laminae (ud-SELs) structure in one side of the primary epidermal laminae, especially in the part of the deep area of LR. Immunohistochemical results were positive for the anti-type IV collagen, anti-type VII collagen and anti-laminin 5 antibodies in the most BMZs. However, partial BMZs adjacent to the ud-SELs were negative for the anti-type VII collagen and anti-laminin 5 antibodies. Ultrastructurally, in the BMZ of the ud-SEL, the lamina densa and the lamina lucida were present. In contrast, the anchoring fibrils and the hemidesmosomes were either absent, or present at lower than normal levels. In conclusion, the present study indicated that the part of regenerated LR in chronic laminitis was not able to fully restore to construct the BMZ for a long time, especially in the unilateral side of laminar epidermis. It might be related with recurrence of this disease.

The growth of the dermomyotome and formation of early myotome lineages in thoracolumbar somites of chicken embryos

Myotome formation in the epaxial and hypaxial domains of thoraco-lumbar somites was analyzed using fluorescent vital dye labeling of dermomyotome cells and cell-fate assessment by confocal microscopy. Muscle precursor cells for the epaxial and hypaxial myotomes are predominantly located in the dorsomedial and ventrolateral dermomyotome lips, respectively, and expansion of the dermomyotome is greatest along its mediolateral axis coincident with the dorsalward and ventralward growth directions of the epaxial and hypaxial myotomes. Measurements of the dermomyotome at different stages of development shows that myotome growth begins earlier in the epaxial than in the hypaxial domain, but that after an initial lag phase, both progress at the same rate. A combination of dye injection and/or antibody labeling of early and late-expressed muscle contractile proteins confirms the myotome mediolateral growth directions, and shows that the myotome thickness increases in a superficial (near dermis) to deep (near sclerotome) growth direction. These findings also provide a basis for predicting the following gene expression sequence program for the earliest muscle precursor lineages in mouse embryos: Pax-3 (stem cells), myf-5 (myoblast cells) and myoD (myocytes). The movements and mitotic activity of early muscle precursor cells lead to the conclusion that patterning and growth in the myotome specifically, and in the epaxial and hypaxial domains of the body generally, are governed by morphogenetic cell movements.