Development of dermal ridges in the volar skin of fetal pigtailed macaques (Macaca nemestrina).

Development of the dermal ridges in volar skin was investigated in 28 pigtailed macaque (Macaca nemestrina) fetuses of known gestational age, ranging from 51 days postconception to newborn. Histology, scanning electron microscopy, and staining of the abraded dermal surface were used in the study. Morphological features of the dermal-epidermal system and their changes with advancing age are described. Chronology was established for stages in the development of the volar skin, i.e., the differentiation of the primary and secondary epidermal ridges (PER and SER) at the undersurface of the epidermis corresponding to the formation of primary and secondary dermal ridges (PDR and SDR) and the development of the dermal papillae. PDRs were first seen at 55 gestational days and SDRs at 93 days. Differentiation of sweat ducts occurred over the period between 60 and 119 gestational days. A regional sequence of differentiation starting with the digital apices of the hand and ending in the calcar area and the phalanges of the foot was documented. Generally, morphogenesis in the macaque was accelerated relative to that in the human fetus by approximately 3 weeks.

Ventral duplication of the autopod: chemical induction by methoxyacetic acid in rat embryos.

Administration of 2-methoxyethanol to pregnant rats on day 12 of gestation induced ventral duplication of the autopod, presumably via its oxidative metabolite, methoxyacetic acid. Morphological observations indicate that the limb bud periderm is severely damaged by methoxyacetic acid so that large patches of this structure are actually missing during an extended period of limb bud development. A high concentration of methoxyacetic acid (10 mM) was found in the extraembryonic fluid and we postulate that the damage to the periderm was initiated from this extraembryonic exposure. The ventral duplication of the autopod is thought to arise through an attempt by the embryo to repair the periderm lesion.

Early development of the vertebrate limb: an introduction to morphogenetic tissue interactions using scanning electron microscopy.

The developing limbs of most vertebrates serve as a model system for studies of morphogenesis, pattern formation, cell and tissue interactions and cell differentiation. Mesoderm in the flank of the embryo induces overlying ectoderm to form a thickened, stratified or pseudo-stratified epithelium which becomes the highly specialized apical ectodermal ridge. In turn, the apical ridge specifies individual limb parts (first from structures proximal to the body axis, then to more distal components) and is required for those elements to form. If the ridge is removed, subsequent limb development ceases and no further limb parts appear. The series of ectodermal-mesodermal interactions is poorly understood at the molecular level, but scanning electron microscopy permits the visualization of tissues and cells which participate in this remarkable process of morphogenesis and differentiation. This paper is intended to serve as an introduction for the student beginning an investigation into the multiple, integrated biological processes which culminate in the establishment of a normal vertebrate limb.

Syndactyly induced by Janus Green B in the embryonic chick leg bud: a reexamination.

In an attempt to clarify the mechanism of production of the syndactyly induced by Janus Green B (JGB) we have studied the morphology and structural modifications of the chick embryo leg bud after JGB administration by means of neutral red vital staining, whole-mount cartilage staining and light microscopy and transmission and scanning electron microscopy. The results show that the well-known inhibition of interdigital cell death is accompanied by a precocious alteration of the epithelial tissue and especially of the epithelial-mesenchymal interface. 24 h after JGB administration the cells of the AER reduce the number of junctions and the basal ectodermal cells are detached into the mesenchymal tissue in zones in which the basal lamina undergoes disruption. In addition the interdigital mesenchymal cells diverted from the dying program are able to undergo a rapid differentiation into cartilage. It is proposed that the mechanism of production of JGB-induced syndactyly might be due to an alteration of the normal epithelial-mesenchymal interactions rather than to a direct inhibitory effect of the JGB on the dying program.

Fine structure of the interdigital membranes during the morphogenesis of the digits of the webbed foot of the duck embryo.

Fine structural study of interdigital membranes during formation of the digits of the duck foot reveals that the interdigital necrosis is accompanied by a high deposition of collagenous material in the epithelio-mesenchymal interface, rupture of the basal lamina and detachment of ectodermal cells into the amniotic sac. These changes are similar to those observed in the regressing interdigital membrane of the chick although their intensity and temporal extension are less pronounced in the duck. It is suggested that these changes account for the disappearance of the marginal zone of the duck interdigital membranes. The possible causal relationship between the different structural changes are discussed.

The histopathology of tissues in "resistant" and "susceptible" strains of mice infected with a moderate dose of Mycobacterium lepraemurium.

A systematic study by light and electron microscopy of tissues from BALB/c and C57BL/6 mice infected subcutaneously with 10(7) Mycobacterium lepraemurium organisms was carried out at various times throughout the infection. The relatively resistant C57BL/6 mice had an earlier inflammatory response at the site of the infection than did the susceptible BALB/c mice. The infiltration in the former strain contained fibroblast-like cells and epithelioid cells early on in the infection. Few lymphocytes were observed in both strains throughout the infection. The spread of acid-fast bacilli was slower in the resistant strain (C57BL/6). The findings indicated that the rate of cellular infiltration at the infection site and the nature of the cells in the infiltration may determine the outcome of this infection.

Surface changes in the embryonic interdigital epithelium during the formation of the free digits: a comparative study in the chick and duck foot.

The formation of the free digits of the chick is accompanied by conspicuous surface changes of the interdigital ectoderm. These changes were much less pronounced or absent in the duck. As early as the interdigital grooves were detected in the chick, the morphological features of the ectodermal cells changed from a polygonal shape and flattened appearance to a rounded shape and bulging appearance. These changes were not present in the webbed foot of the duck. On the other hand the development of the interdigital commissures was accompanied by the formation of ectodermal ridges consisting of an accumulation of rounded cells which were in some cases in course of detachment to the amniotic cavity. These ridges were very prominent in all the interdigital commissures of the chick. In the duck they were less pronounced and were only present in the first and third commissure. From these results it is suggested that in addition to the well-known interdigital mesenchymal necrotic process (INZ) the ectodermal tissue of the interdigits might also be actively involved in the formation of free digits.

Ultrastructural site variations in mouse epidermal organization.

Mouse dorsal, ear, tail and foot epidermis are compared according to their tissue architecture and cell kinetics. Cell proliferation is expected in terms of the daily volume of keratin replaced. The stratum corneum may be organized into vertical columns of squames, which may have minimal overlap as in dorsum and ear, or maximal overlap as in tail. Individual areas are adapted to their function both in squame fine structure and rate of cell replacement. The surface keratin loss/replacement rate is at its highest in foot and tail, and lowest in ear and dorsum. Observations on hairless mouse dorsum are also included.