Two FGF receptor genes are differentially expressed in epithelial and mesenchymal tissues during limb formation and organogenesis in the mouse

Differential expression of two members of FGF receptor gene family, FGFR-1 and FGFR-2 mRNA, in the adult rat central nervous system

The fibroblast growth factor (FGF) receptor gene family now contains four members that encode homologous receptor-tyrosine kinases (RTKs) to each other. We have demonstrated that one of the members, FGFR-1 (also termed as flg), is expressed in the widespread but specific neuronal populations in the adult rat central nervous system (CNS). In the present study, we examined the expression pattern of another member, FGFR-2 (also termed as bek) and compared it with that of FGFR-1. In contrast with FGFR-1, we detected FGFR-2 expression primarily in the fiber tracts of the adult rat CNS, suggesting that the oligodendrocytes are the main sites of the FGFR-2 expression. These findings indicate that FGF may regulate neurons and glial cells through different subtypes of its cognate receptor.

Restoration of hair growth by surgical implantation of follicular dermal sheath

The capacity of lower follicle dermal sheath to restore hair growth was tested by removing the lower halves of follicles, and then immediately implanting material containing dermal sheath cells from these bases, into the remaining upper epidermal follicle cavity. Over 60% of recipient follicles produced stout emergent vibrissa fibres and some operations resulted in multiple hair production from a single follicle. Histological examination revealed new dermal papillae within large bulb structures which were sited below the level of amputation--a feature that indicated that the new dermal papilla was derived from implanted material. For many follicles, the failure to produce emergent fibres could be accounted for after histological examination. These results provide clear evidence that lower follicle dermal sheath cells are capable of replacing those of the dermal papilla and it shows that they can do so in the context of the upper follicle. However, because elements of lower follicle epidermis were present in the implant material, the interactive sequence of events cannot be established. Dermal sheath cells have immense potential for papilla cell replacement: questions remain as to whether the distinction between sheath and papilla cells is one of context, or whether the transition requires specific external influences.

FGF-mediated aspects of skeletal muscle growth and differentiation are controlled by a high affinity receptor, FGFR1

Fibroblast growth factors (FGFs) and FGF receptors (FGFRs) play major roles in vertebrate embryogenesis, including control of skeletal muscle growth and differentiation. Understanding their roles requires delineating the specific FGF and FGFR isoforms involved. This study analyzes the FGFR transcripts found in a model mouse skeletal myoblast cell line (MM14) during growth and terminal differentiation. MM14 cells express transcripts for FGFR1 (flg) but not FGFR2 (bek). The predominate FGFR1 transcript contains three immunoglobulin (Ig)-like domains in the extracellular ligand binding region. Approximately one-fourth of the three Ig-like domain transcripts possess a 6-nt deletion between the first and second Ig-like domains which after translation would result in deletion of an Arg-Arg pair. Cloning of mouse genomic DNA surrounding the region of the FGFR1 6-nt deletion indicates that the deletion is derived by alternative splicing of FGFR1 transcripts. Transcripts containing two Ig-like domains account for less than 5% of total FGFR1 mRNA in MM14 cells. A survey of RNA from mouse tissues indicated that two Ig-like domain FGFR1 transcripts are rare in all tissues except in lung, in which the two Ig-like domain form accounts for roughly 70% of the lung FGFR1 mRNA. PCR RACE cloning studies disclosed 162 nt of additional FGFR1 5'-flanking RNA which was highly GC-rich. FGFR1 transcripts decline 8- to 10-fold during low serum, (-)FGF-mediated differentiation of MM14 cultures. The kinetics of the FGFR1 mRNA decline is similar to the previously described differentiation-dependent decrease in cell surface FGF receptors.

Differential expression and regulation of two distinct fibroblast growth factor receptors during early development of the urodele amphibian Pleurodeles waltl

Fibroblast growth factor (FGF) has been shown to be involved in mesoderm induction during amphibian development. Its presence in the embryo suggests that FGF is an endogenous inducer. By polymerase chain reaction (PCR) methods and by screening a Pleurodeles waltl tail-bud cDNA library with a cDNA probe for human FGF receptor, we have isolated two full-length cDNA clones, which we designate PFR1 and PFR4 based on their homology to the human FGF receptors FGFR-1 and FGFR-4. Both cDNA clones encode Pleurodeles FGF receptors that share characteristics common to members of the FGF receptor superfamily. The deduced amino acid sequence of PFR1 is 85% identical overall with the human fms-like-gene (FLG). PFR4 is most closely related to the human FGFR-4 (66% overall identity). The tyrosine kinase catalytic domains of both receptors are remarkably conserved. The two receptors show distinct patterns of regulation during early development. PFR1 first appears as a maternally derived mRNA and mRNA levels remain constant during early developmental stages. However, PFR4 mRNA is first expressed at the late blastula stage, which suggests that its expression is a result of zygotic transcription. Furthermore, northern blot analysis indicates that PFR1 mRNA is distributed evenly in the early gastrula while PFR4 mRNA is predominantly localized to the presumptive ectoderm. At tail-bud stage, PFR1 transcripts are localized primarily to the neural and mesodermal tissues, PFR4 transcripts are most abundantly expressed in neural tissue, and more transcripts are detected in lateral plate mesoderm than in the somites. When animal cap explants of blastulae are cultured in the presence of mesoderm-inducing factors, PFR1 mRNA levels are maintained by bFGF and activin A. In contrast, PFR4 mRNA levels are significantly down-regulated. These observations suggest a differential expression and regulation of FGF receptors in early amphibian development.