Retinoic acid stimulates the synthesis of a novel heat shock protein in the regenerating forelimb of the newt.

Morphogenetic effects of retinoic acid (RA) on the urodele amphibian limb regenerate pattern have been well documented, but little is known regarding the mechanism of this action of RA at the molecular level. Since exogenous RA, at concentrations sufficient to cause proximalization, represents a significant stress to newts and has been shown previously to elicit increased synthesis of heat shock proteins (HSPs) in mouse embryo limb buds, we investigated the effects of this putative morphogen on the synthesis of members of the 70-kilodalton (70-kDa) stress protein family in amputated forelimbs of the newt Notophthalmus viridescens. Injection (i.p.) of RA in dimethyl sulfoxide (DMSO), at a dose sufficient to cause significant proximal-distal reduplication of the pattern in 50% of animals treated, resulted in increased synthesis and accumulation of a 73-kDa protein with a pI of approximately 6.75. The synthesis of this same protein is increased in limb tissues as a result of a brief 35 degrees C heat shock. This protein is electrophoretically distinct from the newt HSP 70 family members, displays a different partial peptide map, and shows no immunological cross-reactivity with an anti-human HSP 70 monoclonal antibody. It may be a member of a separate family of 70- to 73-kDa HSPs. Interestingly, the synthesis of this protein is increased and it is more abundant in control, proximal moderate-early bud stage regenerates at 6 days after i.p. injection of DMSO than in similarly treated distal regenerates. This protein is, in addition, increased in distal regenerates to proximal levels by a prior injection of RA.(ABSTRACT TRUNCATED AT 250 WORDS)

A low-molecular weight chick brain-derived growth factor is mitogenic for cultured astroglia from the chick embryo.

Immunohistochemically defined astrocytes from the 10-day chick embryo were stimulated to incorporate increased levels of [3H]thymidine when a low-molecular weight peptide growth factor, chick brain-derived growth factor (CBGF), was added to the cultures. Treatment of these GFAP-positive astrocytes with 10 ng/ml CBGF in medium supplemented with 1% fetal bovine serum resulted in a 3.5-4-fold increase in [3H]thymidine incorporation when compared to astrocytes cultured in defined medium supplemented with 1% serum alone. CBGF had no effect on the survival, proliferation or differentiation of a number of other cell types from the 10-day chick embryo brain, including neurons and meningeal fibroblasts. CBGF was also ineffective as a mitogen for chick embryo skeletal muscle myoblasts, primary mouse embryo fibroblasts and one murine teratocarcinoma-derived cell line (STO). We suggest that CBGF might act as a mitogenic signal for astroglia during central nervous system development and repair.

Clonal origin of haematopoietic colonies in the postnatal mouse liver.

The liver of the neonatal mouse continues to show haematopoietic activity for up to 2 weeks after birth and morphological analysis has shown that this activity becomes focused in discrete haematopoietic colonies by the end of the first week postnatal. Furthermore, each colony contains cells of one haematopoietic lineage only, that is, erythroid, myeloid or pre-B-lymphoid cells. This pattern of differentiation suggests that each colony is derived from a single committed precursor cell, which, if true, would represent the first demonstration of non-mixed haematopoietic colonies in normal development and would provide a useful system for studying the factors affecting the clonal diversity of haematopoietic stem cells and their lineage-committed progeny. Here we have analysed the haematopoietic foci in the liver of neonatal mouse chimaeras, using a newly developed ubiquitous in situ cell marker system which clearly demonstrates the clonal origin of these colonies.

In vivo and in vitro development of mouse embryos homozygous for the embryonic lethal velvet coat (Ve) mutation.

Embryos homozygous for the velvet coat mutation, Ve/Ve, were recognized at 6.5 days post coitum by the reduced size of the ectodermal portions of the egg cylinder and the loose, columnar nature of the overlying endoderm. Later in development ectoderm tissues were sometimes entirely absent. Abnormalities appeared in the ectoplacental cone at 8.5 days but trophoblast giant cells and parietal endoderm appeared unaffected. Homozygotes could not be unequivocally identified at 5.5 days nor at the blastocyst stage but were recognized in blastocyst outgrowths by poor development of the inner cell mass derivatives. It has previously been suggested that Ve may exert its action at the blastocyst stage by reducing the size of the inner cell mass, but no evidence for such a reduction was found. Most of the observations on Ve/Ve homozygotes are, however, consistent with the hypothesis that Ve exerts its action primarily on later primitive ectoderm development.