No abstract

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.

No abstract

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)