A dynamic regulation of GDNF-family receptors correlates with a specific trophic dependency of cranial motor neuron subpopulations during development

Glial cell line-derived neurotrophic factor (GDNF) family ligands promote the survival of developing motor neurons in vivo and in vitro. However, not all neurons survive with any single ligand in culture and GDNF null mutant mice display only a partial motor neuron loss. An interesting possibility is that subpopulations of motor neurons based on their function and/or their myotopic organization require distinct members of GDNF family ligands. Because responsiveness to the different ligands depends on the expression of their cognate ligand-binding receptor we have herein addressed this issue by examining the expression of GDNF-family receptors (gfr) during development and in the adult in cranial motor nuclei subpopulations. We have furthermore examined the in vivo role of GDNF for cranial motor neuron subpopulations. The shared ret receptor was expressed in all somatic, branchial and visceral cranial embryonic motor nuclei examined, showing that they are all competent to respond to GDNF family ligands during development. At early stages of development both the GDNF receptor, gfralpha1, and the neurturin (NTN) receptor, gfralpha2, were expressed in the oculomotor, facial and spinal accessory, and only gfralpha1 in the trochlear, superior salivatory, trigeminal, hypoglossal and weakly in the dorsal motor nucleus of the vagus and the ambiguous nucleus. The abducens nucleus was negative for both gfralpha1 and gfralpha2. The artemin (ART) receptor, gfralpha3, was expressed only in the superior salivatory nucleus. A motor neuron subnuclei-specific expression of gfralpha1 and gfralpha2 was seen in the facial and trigeminal nuclei which corresponded to their dependence on GDNF in null mutant mice. We found that the expression was dynamic in these nuclei, which may reflect developmental changes in their trophic factor dependency. Analysis of GDNF null mutant mice revealed that the dynamic receptor expression is regulated by the ligand in vivo, indicating that the attainment of changes in dependency could be ligand induced. Our results indicate that specific GDNF family ligands support selective muscle-motor neuron circuits during development.

Amplification of FGF-related genes in human tumors: possible involvement of HST in breast carcinomas

In order to document a possible involvement of structural alterations of FGF (Fibroblast Growth Factor)-like genes in human oncogenesis, we have screened a large series of human tumors for amplification of five FGF-related genes (Basic-FGF, INT2, HST, FGF5 and FGF6). None of 37 hematopoietic neoplasms, one out of 13 melanomas (8%), three out of 43 bladder tumors (7%) and 41 out of 238 breast carcinomas (17%) contained amplified FGF-related sequences, namely HST and INT2. Only these two genes, both located on band q13 of chromosome 11 have been found amplified. In all cases they were co-amplified and in only one instance did amplification extend to the ETS1 locus at position 11q23. INT2 and HST RNA could be evidenced by RNA/RNA in situ hybridization in breast carcinomas. Our results indicate a correlation between RNA expression and gene amplification in the case of HST but not of INT2. Although evaluation of the clinical significance of HST amplification and expression must await long-term follow-up of the patients, we suggest that HST gene product could play a role in development and/or progression of human breast cancer.

Relationship between cellular adhesiveness and metastatic activity in polyomavirus-transformed FR3T3 rat cell lines

A series of polyomavirus-transformed rat cells with varying tumorigenic potential were tested for biophysical parameters possibly related to metastatic properties: adhesive capacity and strength of adhesion to different substrates (laminin, fibronectin and albumin), cell deformability and spreading. Two groups of cell lines were defined according to their higher or lower adhesive capacity. Adhesivity did not appear to be related to cell deformability and spreading. A weak correlation was suggested between low adhesivity and high metastatic potential. A selection method was devised to separate cell samples into 3 subpopulations with different adhesive strength. Two cell lines, originally different, were chosen for this study: Py-tsa A25 cells were less adherent and highly metastatic, and Py-WTA2 cells were more adherent and less metastatic. After s.c. inoculation into syngeneic Fisher rats, the 3 selected subpopulations of the 2 cell lines induced pulmonary nodules to varying degrees, but only the less adherent ones were able to induce visceral metastasis located in stomach and intestine. In this case, animal survival time was 30% lower than for the highly adherent selected cells. After 10 culture passages, the same subpopulations were able to metastasize only in the lungs. However, when the selection procedure was repeated, the less adherent cells were again able to yield visceral nodules. Tumorigenicity remained unchanged in all cases. Study of cell dissemination and arrest in vivo showed a rapid targeting of labelled tumor cells toward lungs and stomach 5 hr after intradermal injection, where they remained up to 72 hr. More adherent cells displayed delayed localization after injection (24 hr) and radioactivity decreased more rapidly.