Brown adipocytes local response to thyroid hormone is required for adaptive thermogenesis in adult male mice

Thyroid hormone (T3) and its nuclear receptors (TR) are important regulators of energy expenditure and adaptive thermogenesis, notably through their action in the brown adipose tissue (BAT). However, T3 acts in many other peripheral and central tissues which are also involved in energy expenditure. The general picture of how T3 regulates BAT thermogenesis is currently not fully established, notably due to the absence of extensive omics analyses and the lack of specific mice model. Here, we first used transcriptome and cistrome analyses to establish the list of T3/TR direct target genes in brown adipocytes. We then developed a novel model of transgenic mice, in which T3 signaling is specifically suppressed in brown adipocytes at adult stage. We addressed the capacity of these mice to mount a thermogenic response when challenged by either a cold exposure or a high-fat diet, and analyzed the associated changes in BAT transcriptome. We conclude that T3 plays a crucial role in the thermogenic response of the BAT, controlling the expression of genes involved in lipid and glucose metabolism and regulating BAT proliferation. The resulting picture provides an unprecedented view on the pathways by which T3 activates energy expenditure through an efficient adaptive thermogenesis in the BAT.

Thyroid hormone receptor α in skeletal muscle is essential for T3-mediated increase in energy expenditure

Thyroid hormones are important for homeostatic control of energy metabolism and body temperature. Although skeletal muscle is considered a key site for thyroid action, the contribution of thyroid hormone receptor signaling in muscle to whole‐body energy metabolism and body temperature has not been resolved. Here, we show that T3‐induced increase in energy expenditure requires thyroid hormone receptor alpha 1 (TRα₁) in skeletal muscle, but that T3‐mediated elevation in body temperature is achieved in the absence of muscle‐TRα₁. In slow‐twitch soleus muscle, loss‐of‐function of TRα₁ (TRα^HSACre) alters the fiber‐type composition toward a more oxidative phenotype. The change in fiber‐type composition, however, does not influence the running capacity or motivation to run. RNA‐sequencing of soleus muscle from WT mice and TRα^HSACre mice revealed differentiated transcriptional regulation of genes associated with muscle thermogenesis, such as sarcolipin and UCP3, providing molecular clues pertaining to the mechanistic underpinnings of TRα₁‐linked control of whole‐body metabolic rate. Together, this work establishes a fundamental role for skeletal muscle in T3‐stimulated increase in whole‐body energy expenditure.

Evidence for hormonal control of heart regenerative capacity during endothermy acquisition

Tissue regenerative potential displays striking divergence across phylogeny and ontogeny, but the underlying mechanisms remain enigmatic. Loss of mammalian cardiac regenerative potential correlates with cardiomyocyte cell-cycle arrest and polyploidization as well as the development of postnatal endothermy. We reveal that diploid cardiomyocyte abundance across 41 species conforms to Kleiber's law-the ¾-power law scaling of metabolism with bodyweight-and inversely correlates with standard metabolic rate, body temperature, and serum thyroxine level. Inactivation of thyroid hormone signaling reduces mouse cardiomyocyte polyploidization, delays cell-cycle exit, and retains cardiac regenerative potential in adults. Conversely, exogenous thyroid hormones inhibit zebrafish heart regeneration. Thus, our findings suggest that loss of heart regenerative capacity in adult mammals is triggered by increasing thyroid hormones and may be a trade-off for the acquisition of endothermy.

Neuronal expression of a thyroid hormone receptor α mutation alters mouse behaviour

In humans, alterations in thyroid hormone signalling are associated with mood and anxiety disorders, but the neural mechanisms underlying such association are poorly understood. The present study investigates the involvement of neuronal thyroid hormone receptor α (TRα) in anxiety, using mouse genetics and Cre/loxP technology to specifically alter TRα signalling in neurons. We evaluated the behaviour of mice expressing a dominant negative, neuron-specific mutation of TRα (TRα^AMI/Cre3 mice), using the elevated-plus maze, light-dark box and open-field tests. In a first experiment, mice were housed individually, and the behaviour of TRα^AMI/Cre3 mice differed significantly from that of control littermates in these 3 tests, suggesting heightened anxiety. In a second experiment, designed to evaluate the robustness of the results with the same 3 tests, mice were housed in groups. In these conditions, the behaviour of TRα^AMI/Cre3 mice differed from that of control littermates only in the light-dark box. Thus, TRα^AMI/Cre3 mice appear to be more likely to develop anxiety under stressful housing conditions than control mice. These results suggest that in adult mice, thyroid hormone signalling in neurons, via TRα, is involved in the control of anxiety behaviour.

Genome-wide search reveals the existence of a limited number of thyroid hormone receptor alpha target genes in cerebellar neurons

Thyroid hormone (T3) has a major influence on cerebellum post-natal development. The major phenotypic landmark of exposure to low levels of T3 during development (hypothyroidism) in the cerebellum is the retarded inward migration of the most numerous cell type, granular neurons. In order to identify the direct genetic regulation exerted by T3 on cerebellar neurons and their precursors, we used microarray RNA hybridization to perform a time course analysis of T3 induced gene expression in primary cultures of cerebellar neuronal cell. These experiments suggest that we identified a small set of genes which are directly regulated, both in vivo and in vitro, during cerebellum post-natal development. These modest changes suggest that T3 does not acts directly on granular neurons and mainly indirectly influences the cellular interactions taking place during development.

Profound morphological and functional changes of rodent Purkinje cells between the first and the second postnatal weeks: a metamorphosis?

Between the first and the second postnatal week, the development of rodent Purkinje cells is characterized by several profound transitions. Purkinje cells acquire their typical dendritic "espalier" tree morphology and form distal spines. During the first postnatal week, they are multi-innervated by climbing fibers and numerous collateral branches sprout from their axons, whereas from the second postnatal week, the regression of climbing fiber multi-innervation begins, and Purkinje cells become innervated by parallel fibers and inhibitory molecular layer interneurons. Furthermore, their periods of developmental cell death and ability to regenerate their axon stop and their axons become myelinated. Thus a Purkinje cell during the first postnatal week looks and functions differently from a Purkinje cell during the second postnatal week. These fundamental changes occur in parallel with a peak of circulating thyroid hormone in the mouse. All these features suggest to some extent an interesting analogy with amphibian metamorphosis.

Type 3 deiodinase deficiency causes spatial and temporal alterations in brain T3 signaling that are dissociated from serum thyroid hormone levels

The type 3 deiodinase (D3) is an enzyme that inactivates thyroid hormones (TH) and is highly expressed during development and in the central nervous system. D3-deficient (D3KO) mice develop markedly elevated serum T(3) level in the perinatal period. In adulthood, circulating T(4) and T(3) levels are reduced due to functional deficits in the thyroid axis and peripheral tissues (i.e. liver) show evidence of decreased TH action. Given the importance of TH for brain development, we aimed to assess TH action in the brain of D3KO mice at different developmental stages and determine to what extent it correlates with serum TH parameters. We used a transgenic mouse model (FINDT3) that expresses the reporter gene β-galactosidase (β-gal) in the central nervous system as a readout of local TH availability. Together with experiments determining expression levels of TH-regulated genes, our results show that after a state of thyrotoxicosis in early development, most regions of the D3KO brain show evidence of decreased TH action at weaning age. However, later in adulthood and in old age, the brain again manifests a thyrotoxic state, despite reduced serum TH levels. These region-specific changes in brain TH status during the life span of the animal provide novel insight into the important role of the D3 in the developing and adult brain. Our results suggest that, even if serum concentrations of TH are normal or low, impaired D3 activity may result in excessive TH action in multiple brain regions, with potential consequences of altered neural function that may be of clinical relevance to neurological and neuroendocrine disorders.

Thyroid Hormones Signaling Is Getting More Complex: STORMs Are Coming

T3 regulates many physiological and developmental processes by binding to thyroid hormone receptors (TRs). This induces a conformational change of DNA-bound TRs that releases corepressors in favor of coactivators. The associated chromatin modifications induce polymerase II recruitment. Mouse genetic studies clarified the respective contribution of each receptor isoform and revealed the important activity of unliganded TRs. They also confirm the paradoxical negative regulation of some promoters by liganded TRs. Recent advances place these molecular events in a broader context of extra- and intracellular regulation: control of ligand availability, changes in the cell sensitivity to T3, nongenomic effects, and cross talks with other signaling pathways contribute to increase the diversity and complexity of thyroid hormones signaling. A promising novel class of TRs synthetic ligands, called STORMs (selective TR modulators), might allow for tissue- and promoter-specific interventions.

Thyroid hormone signaling is highly heterogeneous during pre- and postnatal brain development

We have generated transgenic reporter mice to analyze the spatio-temporal distribution of thyroid hormone signaling during mouse brain development. The reporter system, utilizing a chimeric yeast Gal4 DNA-binding domain-thyroid hormone alpha ligand-binding domain fusion protein to drive lacZ expression, revealed that thyroid hormone signaling starts in the midbrain roof several days before the onset of thyroid gland function, and that it remains highly heterogeneous in the central nervous system throughout pre- and postnatal development. We speculate that this heterogeneity might provide neural cells with positional information during development.

The transcription factor RFX3 directs nodal cilium development and left-right asymmetry specification

There are five members of the RFX family of transcription factors in mammals. While RFX5 plays a well-defined role in the immune system, the functions of RFX1 to RFX4 remain largely unknown. We have generated mice with a deletion of the Rfx3 gene. RFX3-deficient mice exhibit frequent left-right (LR) asymmetry defects leading to a high rate of embryonic lethality and situs inversus in surviving adults. In vertebrates, specification of the LR body axis is controlled by monocilia in the embryonic node, and defects in nodal cilia consequently result in abnormal LR patterning. Consistent with this, Rfx3 is expressed in ciliated cells of the node and RFX3-deficient mice exhibit a pronounced defect in nodal cilia. In contrast to the case for wild-type embryos, for which we document for the first time a twofold increase in the length of nodal cilia during development, the cilia are present but remain markedly stunted in mutant embryos. Finally, we show that RFX3 regulates the expression of D2lic, the mouse orthologue of a Caenorhabditis elegans gene that is implicated in intraflagellar transport, a process required for the assembly and maintenance of cilia. In conclusion, RFX3 is essential for the differentiation of nodal monocilia and hence for LR body axis determination.

Effects of ligand and thyroid hormone receptor isoforms on hepatic gene expression profiles of thyroid hormone receptor knockout mice

Little is known about the overall patterns of thyroid hormone (Th)-mediated gene regulation by the main Th receptor (Tr) isoforms, Tr-alpha and Tr-beta, in vivo. We used 48 complementary DNA microarrays to examine hepatic gene expression profiles of wild-type and Thra and Thrb knockout mice under different Th conditions: no treatment, treatment with 3,3',5-triiodothyronine (T(3)), Th-deprivation using propylthiouracil (PTU), and treatment with a combination of PTU and T(3). Hierarchical clustering analyses showed that positively regulated genes fit into three main expression patterns. In addition, only a subpopulation of target genes repressed basal transcription in the absence of ligand. Interestingly, Thra and Thrb knockout mice showed similar gene expression patterns to wild-type mice, suggesting that these isoforms co-regulate most hepatic target genes. Differences in the gene expression patterns of Thra/Thrb double-knockout mice and Th-deprived wild-type mice show that absence of receptor and of hormone can have different effects. This large-scale study of hormonal regulation reveals the functions of Th and of Tr isoforms in the regulation of gene expression patterns.

Florid plaques in ovine PrP transgenic mice infected with an experimental ovine BSE

The occurrence of the variant Creutzfeldt-Jakob disease (vCJD), related to bovine spongiform encephalopathy (BSE), raises the important question of the sources of human contamination. The possibility that sheep may have been fed with BSE-contaminated foodstuff raises the serious concern that BSE may now be present in sheep without being distinguishable from scrapie. Sensitive models are urgently needed given the dramatic consequences of such a possible contamination on animal and human health. We inoculated transgenic mice expressing the ovine PrP gene with a brain homogenate from sheep experimentally infected with BSE. We found numerous typical florid plaques in their brains. Such florid plaques are a feature of vCJD in humans and experimental BSE infection in macaques. Our observation represents the first description, after a primary infection, of this hallmark in a transgenic mouse model. Moreover, these mice appear to be a promising tool in the search for BSE in sheep.

Efficient transmission of two different sheep scrapie isolates in transgenic mice expressing the ovine PrP gene

We produced transgenic mice expressing the sheep prion protein to obtain a sensitive model for sheep spongiform encephalopathies (scrapie). The complete open reading frame, with alanine, arginine, and glutamine at susceptibility codons 136, 154, and 171, respectively, was inserted downstream from the neuron-specific enolase promoter. A mouse line, Tg(OvPrP4), devoid of the murine PrP gene, was obtained by crossing with PrP knockout mice. Tg(OvPrP4) mice were shown to selectively express sheep PrP in their brains, as demonstrated in mRNA and protein analysis. We showed that these mice were susceptible to infection by sheep scrapie following intracerebral inoculation with two natural sheep scrapie isolates, as demonstrated not only by the occurrence of neurological signs but also by the presence of the spongiform changes and abnormal prion protein accumulation in their brains. Mean times to death of 238 and 290 days were observed with these isolates, but the clinical course of the disease was strikingly different in the two cases. One isolate led to a very early onset of neurological signs which could last for prolonged periods before death. Independently of the incubation periods, some of the mice inoculated with this isolate showed low or undetectable levels of PrPsc, as detected by both Western blotting and immunohistochemistry. The development of experimental scrapie in these mice following inoculation of the scrapie infectious agent further confirms that neuronal expression of the PrP open reading frame alone is sufficient to mediate susceptibility to spongiform encephalopathies. More importantly, these mice provide a new and promising tool for studying the infectious agents in sheep spongiform encephalopathies.

Eukaryotic conditional expression system

Existing conditional expression systems can be classified in two major categories that are based either on the induction or on the de-repression of transcription. The system described here combines both mechanisms, since a unique transcription factor can be shifted from a repression to a stimulation activity by simply changing its ligand. The resulting advantage of this system is the complete absence of basal expression before active induction. The principle of this method is based on the unexpected ability of the chimeric protein containing the DNA-binding domain of the yeast Gal4 transcription factor fused to the COOH half of the estradiol receptor (GalER), to act as a repressor when bound to the drug 4OH-tamoxifen, in the context of a previously described optimized Gal4-responsive promoter. The efficacy of this system has been assessed in transient expression assays using the chloramphenicol acetyl transferase (CAT), and in situ, through the activity of a Gal4 responsive beta-galactosidase gene.

Conservative treatment for girls with nonmetastatic rhabdomyosarcoma of the genital tract: A report from the Study Committee of the International Society of Pediatric Oncology

PURPOSE

To report the results of a conservative multimodal approach in girls with nonmetastatic rhabdomyosarcoma (RMS) of the genital tract, treated in International Society of Pediatric Oncology (SIOP) Malignant Mesenchymal Tumors 84 and 89 protocols.

PATIENTS AND METHODS

From 1984 to 1994, 38 girls with RMS of the genital tract (vulva, vagina, uterus) were treated in SIOP protocols. With the exception of patients with rare small tumors, which were resected at the start of the studies, all patients received initial chemotherapy (CHT) (ifosfamide, vincristine, and actinomycin D). Local treatment including surgery, brachytherapy (BT), and external-beam radiotherapy (ERT) was given only to girls who did not achieve complete remission (CR) with CHT or who subsequently relapsed.

RESULTS

The primary tumor originated in the vulva or vagina in 27 girls and in the uterus in 11. The overall survival rate (+/- SE) was 91% +/- 6% at 5 years, and the event-free survival rate was 78% +/- 7%. At a median follow-up of 5 years, 30 girls were alive and in first CR and five were alive and in second CR. Four patients treated with complete resection of the tumor at diagnosis received less CHT. Thirteen patients were treated with CHT alone. In 17 patients, local treatment was necessary to achieve complete local control, for a residual mass after initial CHT (10 patients), for viable tumor on biopsy (three patients), or for local relapse (four patients). The local treatment used was radiotherapy (RT) (ERT in three patients, BT in seven), radical surgery with uterine ablation (three patients), RT and radical surgery (three patients), and conservative surgery with RT (one patient).

CONCLUSION

Girls with nonmetastatic RMS of the genital tract have an excellent prognosis. We found no difference in outcome between uterine and vulvovaginal RMS. Local treatment does not seem necessary in patients who have a complete response to CHT. When a local treatment is needed, BT may be an alternative to radical surgery or ERT.

[Malignant non-seminomatous germinal tumors of the ovary. Experience of the French Society of Pediatric Oncology. 64 cases]

Ovary seminomatous malignant germ cell tumours are a particular histopathologica entity. The presence of yolk salk tumor or choriocarcinoma is respectively correlated with elevation of alpha FP or beta hCG. This markers elevation permits to assess diagnosis, appreciate response to treatment, and detect relapses. The study of 64 patients registered in two successive S.F.O.P. protocols (TGM 85-TGM 90) precise indications of surgery, platin-based chemotherapy and results. Malignant non seminomatous germ cell tumors are separated in not secreting pure immature teratoma and secreting malignant germ cell tumours. Surgery is essential for treatment of not secreting pure immature teratoma. Secreting germ cell tumors are very chemosensitive and surgery must be as conservative as possible in all cases even metastatic tumour or relapse. If markers are normalized second-look surgery of secreting malignant germ cell tumours is only necessary in case of evident residual tumour. However in case of initial chemotherapy, resection of a pathological ovary is always performed at the end of treatment. These tumours have a good prognosis: 5-years overall survival and disease-free survival are 85%.

A novel growth-factor-dependent myeloid cell line derived from mouse bone marrow cells contains progenitors endowed with high proliferative potential

Constitutive expression of human colony-stimulating factor-1 receptor (CSF-1R) confers long-lasting CSF-1-dependent proliferation to mouse myeloid cell lines. We developed mice transgenic for human CSF-1R because mouse CSF-1 cannot activate human CSF-1R. Then bone marrow cells from transgenic mice were plated onto MS-5 stromal cells expressing the membrane form of human CSF-1 (2M-1 cells) in order to combine the hematopoietic supporting properties of stromal cells and the proliferative effects of CSF-1. Thus, we were able to derive a hematopoietic cell line, called 47.10, that grew indefinitely under these conditions, whereas no cell line could be developed from nontransgenic mice. Proliferation of 47.10 cells is severely affected by neutralizing anti-CSF-1R monoclonal antibodies. Morphologic and cytofluorometry analysis established that most 47.10 cells are immature myelomonocytic cells. Consistent with this phenotype, the myeloid transcription factor PU.1, but not the erythroid transcription factor GATA-1, is expressed in 47.10 cells. A few 47.10 cells (3-5%) do not express lineage specific markers; they differentiate spontaneously to lineage-positive cells after replating on 2M-1 cells. In agar cultures, 47.10 cells form 7- and 14-day colonies in response to a cocktail of granulocyte/macrophage colony-stimulating factor (2.5 ng/mL), interleukin-3 (1 ng/mL), and mouse CSF-1 (10 ng/mL). Under these conditions, about 0.5% of 47.10 cells formed large 14-day colonies (>1 mm) composed of mature monocytes and granulocytes, reflecting the presence of progenitors endowed with high proliferative potential (HPP-47.10 cells). In conclusion, we have characterized a novel continuous myeloid cell line presenting a hierarchical structure similar to that of the bone marrow progenitor cell compartment.

Treatment of non-metastatic rhabdomyosarcomas in childhood and adolescence. Results of the second study of the International Society of Paediatric Oncology: MMT84

The second International Society of Paediatric Oncology (SIOP) study for rhabdomyosarcoma (MMT84) had several goals. The two principal aims were: (1) to improve the survival of children with rhabdomyosarcoma; and (2) to reduce the late effects from therapy by restricting the indications for surgery and/or radiotherapy after good response to initial chemotherapy. A further aim was to investigate the role of high-dose chemotherapy in young patients with parameningeal primary tumours. 186 previously untreated eligible patients entered the study. Patients with completely resected primary tumour received three courses of IVA (ifosfamide, vincristine and actinomycin D). Patients with incompletely resected tumour received six to 10 courses of IVA according to stage. Patients achieving complete remission with chemotherapy alone did not usually receive radiotherapy or undergo extensive surgery, but patients remaining in partial remission received local therapy with surgery and/or radiotherapy. Only patients over 5 years of age with parameningeal disease and patients over 12 years with tumours at any site were given systematic irradiation. Complete remission was achieved in 91% (170/186) of all patients. With a median follow-up of 8 years, the 5-year overall survival was 68% (+/- 3% standard error of the mean (SEM) and the 5-year event-free survival 53% (+/- 4% SEM). These results show an improvement over previous SIOP study (RMS75) in which survival was 52% and event-free survival was 47%. Among the 54 patients who exhibited isolated local relapse, 35% (19/54) survived in further remission longer than 2 years after retreatment, including local therapy (surgery +/- radiotherapy). Analysis of the overall burden of therapy received by all surviving children (including primary treatment and treatment for relapse if required) showed that 24% (28/116) were treated by limited surgery followed by three courses of IVA, 29% (34/116) were treated by chemotherapy alone (after initial biopsy) and 13% (15/116) received chemotherapy plus conservative local treatment (limited surgery or radiotherapy for residual disease). Only 34% (39/116) received intensive local therapy defined as radical wide field radiotherapy or radical surgery or both. Compared with the results obtained in the previous SIOP study, treatment in MMT84 was based on response to initial chemotherapy and, despite an overall reduction of the use of local therapy, significantly improved survival for patients with non-metastatic disease. This trial, also for the first time, provides evidence that retreatment after local relapse can achieve long-term second remissions.

Involvement of thyroid hormone and its alpha receptor in avian neurulation

We have analyzed the expression pattern of c-erb A alpha and c-erb A beta which encode the thyroid hormone receptors (T3R alpha and T3R beta) during early chicken embryogenesis. Only c-erb A alpha expression was detected by RT-PCR and whole-mount in situ hybridization. c-erb A alpha transcripts were found to be already present at low level in embryos before egg incubation. During neurulation a marked increase was observed in neurectoderm. A reporter cell line was then constructed and used to demonstrate the release of significant amount of thyroid hormone (T3) from egg yolk by area opaca cells before gastrulation. During gastrulation T3 was found to be enriched in the primitive streak and Hensen's node. Introduction of excess T3 frequently resulted in abnormal development of anterior structures, mainly neural tube defects and anencephalia. These observations suggest that T3R alpha, like the closely related retinoic acid receptors, fulfills functions which are important for embryonic development well before the onset of thyroid gland function.

Pheochromocytoma and paraganglioma in children: a report of 24 cases of the French Society of Pediatric Oncology

Pheochromocytoma and paraganglioma of childhood are rare neuroendocrine tumors. Urinary catecholamine measurements, metaiobenzylguanidine (MIBG) scanning, computed tomographic scanning, and magnetic resonance imaging have greatly facilitated diagnosis. Prognosis after surgical resection is excellent. In this retrospective series collected from French oncology centers, the risk of tumor progression was studied in order to assess prognostic factors and the optimal diagnostic and therapeutic management. Medical records of 24 children with paraganglioma were reviewed. This tumor occurred at a median age of 12.5 years and in most cases was revealed by arterial hypertension. The diagnosis was made by the demonstration of urinary excretion of catecholamines and their metabolites. Six patients had bilateral adrenal pheochromocytomas; two patients had extra-adrenal paragangliomas. In eight patients, the paraganglioma occurred as a familial disease. Surgical excision was the only therapeutic procedure. With a follow-up of 5.2 years, 14 of the patients are still in first complete remission and 6 have developed metastases or shown tumor progression. Despite a high long-term survival rate, the risk of malignancy and of multifocal involvement is of concern and is associated with a significant rate of late events. The outcome depends on adequacy of tumor resection and must be serially assessed.

Identification of transcripts initiated from an internal promoter in the c-erbA alpha locus that encode inhibitors of retinoic acid receptor-alpha and triiodothyronine receptor activities

The thyroid hormone receptor-coding locus, c-erbA alpha, generates several mRNAs originating from a single primary transcript that undergoes alternative splicing. We have identified for the first time two new transcripts, called TRdelta alpha1 and TRdelta alpha2 [mRNA for isoform alpha1 and alpha2 of the T3 receptor (TR), respectively], whose transcription is initiated from an internal promoter located within intron 7 of the c-erbA alpha gene. These two new transcripts exhibit tissue-specific patterns of expression in the mouse. These two patterns are in sharp contrast with the expression patterns of the full-length transcripts generated from the c-erbA alpha locus. TR alpha1 and TRdelta alpha2 mRNAs encode N-terminally truncated isoforms of T3R alpha1 and T3R alpha2, respectively. The protein product of TRdelta alpha1 antagonizes the transcriptional activation elicited by T3 and retinoic acid. This protein inhibits the ligand-induced activating functions of T3R alpha1 and 9-cis-retinoic acid receptor-alpha but does not affect the retinoic acid-dependent activating function of retinoic acid receptor-alpha. We predict that these truncated proteins may work as down-regulators of transcriptional activity of nuclear hormone receptors in vivo.

Parameningeal rhabdomyosarcoma: results of an international workshop

PURPOSE

A retrospective analysis was performed on children with nonmetastatic rhabdomyosarcomas (RMS) involving a parameningeal site treated by one of the four major cooperative groups: Intergroup Rhabdomyosarcoma Study (IRS), International Society of Pediatric Oncology (SIOP), German Cooperative Group (CWS), and Italian Cooperative Group (ICS) to analyse survival and prognostic factors.

METHODS AND MATERIALS

Between 1979 and 1989, 230 children (median age 6 years) were treated in the IRS III, SIOP 84, CWS 81, and ICS 79 studies. All patients received chemotherapy, and 203 were irradiated. Radiotherapy doses were similar in the four studies, although treatment volumes were not similar. The SIOP patients had smaller volumes treated. In addition, the SIOP patients with a low risk of meningeal involvement and children under 5 years of age were not irradiated if they had a complete response (CR) to chemotherapy. Time to initiation of irradiation was earlier in the IRS and Italian studies.

RESULTS

Median follow-up was 62 months (range 22-140). The 5-year survival and 5-year event-free survival were better for the IRS study (74% and 71%) than for the other study groups (55% and 36% for SIOP, 47% and 47% for CWS, and 39% and 39% for ICS). The low-risk (LR) patients in the IRS study had improved survival. However, patients with high risk of meningeal involvement had similar survival in all four studies. The most significant prognostic factor was the size of tumor (> 5 cm).

CONCLUSION

The improved results from the IRS group, especially among the LR patients, could be related to the IRS treatment employed, particularly the systematic use of radiation, to the inclusion of patients with smaller tumors, and to the routine use of quality control of radiation.

The osteoclast generation: an in vitro and in vivo study with a genetically labelled avian monocytic cell line

Osteoclasts are multinucleate giant cells responsible for bone resorption. Osteoclast precursors are hematopoietic mononucleate cells, which give rise to osteoclasts after fusion. Nevertheless, the precise stage of differentiation where osteoclast precursors diverge from other hematopoietic lineages is still debated. We describe here both in vitro and in vivo approaches to the study of the osteoclast differentiation pathway. We used cells of the BM2 avian monocytic cell line, which are able to differentiate into macrophages both in vitro and in vivo. In order to follow the progeny of BM2 monocytes, we have derived a BM2 cell clone expressing the nlslacZ gene (BM2nlslacZ) which has still retained the main features of the parental cell line. In vitro, when BM2nlslacZ cells were triggered toward macrophages, they participated in the formation of multinucleate osteoclast-like cells as seen by their blue nuclei. Furthermore, when BM2nlslacZ cells were injected into the blood stream of chicken embryos, they could give rise to blue nucleate macrophages in the bone marrow, as well as to osteoclasts with blue nuclei in bone. Finally, we have shown that fusion of tagged mononucleate precursor cells not only occurs with other mononucleate precursor cells but also with mature multinucleate osteoclasts. This work shows that cells already engaged in the late stages of the monocytic differentiation pathway are able to differentiate into osteoclasts and that osteoclast divergence takes place after the monocyte stage.

Virofection: a one-step procedure for using replication-defective retrovirus vectors

Virofection is a simple new way to use replication-defective vectors. It consists of the cotransfection of two plasmids: one plasmid bearing the genome of the replication-defective retrovirus vector and a second "helper" plasmid expressing the gag, pol, and env retrovirus sequences. It provides stable integration into the chromosome and long-term expression of only vector-borne sequences. We present here several helper plasmids derived from avian leukosis viruses, which we have used for the virofection of the lacZ reporter gene in chicken cell cultures. Expression can be stabilized at a very high rate in both chicken fibroblasts and blastoderm cells, without giving rise to replication-competent virus.

Phase II study of rapid-scheduled etoposide in paediatric soft tissue sarcomas

Twenty three patients with paediatric soft tissue sarcomas who had relapsed or refractory disease were treated with a rapid schedule of intravenous etoposide (100 mg/m2 daily on three consecutive days, weekly over 3 weeks). The regimen was well tolerated with predictable myelotoxicity. In 19 patients with rhabdomyosarcoma, there was a response rate of 42%. This appears to be better than previously reported with conventional three weekly schedules. These data indicate that for rhabdomyosarcoma, as for some other tumours, a divided dose regimen may be the optimal schedule and is worthy of further evaluation.

Virofection: a new procedure to achieve stable expression of genes transferred into early embryos

A new procedure, virofection, designed to stabilize the expression of transfected DNA has been developed. It exploits the capacity of retroviruses to integrate their genome into the chromosomes of host cells. The co-transfection of two plasmids, one carrying the genome of a defective retrovirus vector, the other one encoding all the retroviral proteins, results in a transient production of infectious virus particles. These particles can infect the neighboring cells and this leads to the stable integration of the vector genome. This procedure is time-saving and appears to be quite efficient. When applied to chicken embryonic fibroblasts cultured in vitro, it resulted in the stable expression of the lacZ gene in more than 30% of the cells, and did not induce chronic viremia. Stable lacZ expression was also achieved in chicken embryos in ovo. Virofection appears to be a promising and generally applicable method for implementing stable, safe and efficient gene transfer in vitro and in vivo.

[Pneumothorax revealing pneumoblastoma in an infant]

BACKGROUND

Pulmonary blastoma is a tumor with bad prognosis that is exceptionally seen before the age of 2 years.

CASE REPORT

A 3 1/2 month-old infant was admitted because she suffered from tachypnea. A left pneumothorax with shift of the mediastinum was recognized that required insertion of a chest tube followed by ventilation and pleural drainage. X rays and CT scan showed a round bullous lesion in the left lung that persisted at the age of 5 months. At that time, clinical deterioration led to thoracotomy allowing excision of a bullous tumor; histological examination showed that this tumor was a pulmonary blastoma. Recurrence of this tumor, 16 months later, required chemotherapy and surgical excision. The patient is normal at the age of 4 years.

CONCLUSION

Pulmonary blastoma is exceptional in infancy; it may be revealed by pneumothorax. Its bad prognosis requires aggressive therapy.

Primary chemotherapy in rhabdomyosarcomas and other malignant mesenchymal tumors of the orbit: results of the International Society of Pediatric Oncology MMT 84 Study

PURPOSE

The MMT 84 multicentric prospective trial of the International Society of Pediatric Oncology (SIOP) was designed to (1) test the effectiveness of ifosfamide 3 g/m2 on days 1 and 2, vincristine 1.5 mg/m2 on days 1 and 14, and dactinomycin 0.9 mg/m2 on days 1 and 2 (IVA) repeated every 21 days; and (2) reduce late effects of treatment by reserving radiation therapy to the primary site for patients not achieving a complete response (CR) to primary chemotherapy.

MATERIALS AND METHODS

Between 1984 and 1989, the MMT 84 study registered 34 children with nonmetastatic rhabdomyosarcomas (RMSs) and other malignant mesenchymal tumors (MMTs) of the orbit in this trial.

RESULTS

The 4-year event-free survival rate is 62% +/- 9% (SD) and the 4-year survival rate 86% +/- 7% (SD). A total of 11 local recurrences occurred, 10 among 22 patients treated without initial radiation. Salvage of local failure was achieved in nine of 11 patients with the use of radiation and additional chemotherapy, but three later developed distant metastases and two have died. One isolated regional lymph node failure has occurred, while no patient relapsed with isolated distant metastases. Six of 12 patients who failed are alive with no evidence of disease from 16 to 50 months after relapse. The treatment was well tolerated in all patients, except for one with renal tubular acidosis and one who died of cardiotoxicity. Twelve patients remain in first remission without the use of radiation to the primary tumor from 27 to 84 months.

CONCLUSION

Despite a higher incidence of local recurrence when treated by primary chemotherapy, early survival rates were not compromised and a significant number of patients avoided the late effects of radiation. However, longer follow-up is required to assess the ultimate outcome of patients treated in this manner.

Value of postchemotherapy bioptical verification of complete clinical remission in previously incompletely resected (stage I and II pT3) malignant mesenchymal tumors in children: International Society of Pediatric Oncology 1984 Malignant Mesenchymal Tumors Study

Bioptical verification of complete clinical remission achieved with postoperative chemotherapy in 140 pediatric patients with nonradically resected stages I and II nonparameningeal malignant mesenchymal tumors was evaluated. Tumor histology was rhabdomyosarcoma in 92 and nonrhabdomyosarcoma in 48 patients. All were included in the International Society of Pediatric Oncology "1984 Malignant Mesenchymal Tumors Study." Treatment given after nonradical surgery and before the biopsy consisted of 3 to 6 IVA courses (ifosfamide, vincristine, actinomycin D). Complete clinical remission (no tumor at physical examination, X-rays, sonography, computed tomography, scintigraphy) was bioptically confirmed in 52 rhabdomyosarcoma and 23 nonrhabdomyosarcoma cases, whereas in all the remaining patients (39 rhabdomyosarcoma and 22 nonrhabdomyosarcoma) complete clinical remission was not bioptically verified. Forty-eight-month local relapse rates were 51% in bioptically confirmed and 48% in nonbiopsied rhabdomyosarcoma patients. In nonrhabdomyosarcoma cases, relapse rates were 25% and 14%, respectively. In 4 cases, bioptical specimens contained tumor cells. In spite of aggressive treatment, only 1 is actually in remission. The total 48-month relapse rate (biopsied and nonbiopsied) was significantly higher in rhabdomyosarcoma patients (50%) than in nonrhabdomyosarcoma patients (26%). The value of bioptical verification of complete clinical remission seems to be limited in our series, when known that relapse rate in bioptically confirmed complete remission cases remained high and the outcome in rare "positive biopsy patients" was poor.

Pure dysgerminoma of the ovary in childhood: treatment results and sequelae

Thirty-five children with pure dysgerminoma of the ovary were all treated at the Institut Gustave Roussy (IGR) from 1956-1985. The median follow-up is 8.5 years. The crude 5-year survival rate is 94.1% (+/- 4.1). The disease-free 5-year survival rate is 81.8% (+/- 6.7). Fourteen patients who had stage I disease were treated by unilateral salpingooophorectomy and prophylactic radiotherapy (20 Gy) to ipsilateral iliac, lumbar-aortic, and subclavicular lymph nodes. All are alive without sequelae. Eighteen patients with stage II and III disease were treated by surgery and radiotherapy (30-40 Gy) to the tumor volume. All are alive but radio-induced sequelae are severe. Five relapses of stage I, II, and III tumors occurred and were cured by a second line treatment. Two of the three patients with stage IV disease died. Four patients received a cisplatinum-containing regimen for disseminated disease or because of a relapse before radiotherapy. Three achieved a complete response of measurable tumor. Given the high efficacy of this kind of chemotherapy and the severe sequelae induced by abdomino-pelvic irradiation, we propose initial chemotherapy for widespread disease and radiotherapy in the event of residual tumor.

Multidrug resistance gene transcript level, and P-glycoprotein expression in paediatric malignant mesenchymal tumours

Twenty-four malignant mesenchymal tumour specimens were analysed for human multidrug resistance (MDRI) gene transcript levels using Northern and slot blot techniques. The presence of P-glycoprotein was assessed in 12 of the 24 samples by immunohistochemistry using the monoclonal antibody (MAb) C219. Increased MDRI transcript levels were found in 2 (8.3%), while, using immunohistochemistry, 2 samples were positive and 3 faintly positive (41.6%). Overall, elevated P-glycoprotein or MDRI transcript levels were found in tumours of 6 patients, 3 of whom are dead. The relationship to MDRI expression and subsequent resistance to chemotherapy has to be established.

Bone metastases as the presenting manifestation of rhabdomyosarcoma in childhood

Rarely, rhabdomyosarcoma can present with bone pain and bone lesions on radiographs without evidence of a primary tumor. Of 428 children with biopsy-proven rhabdomyosarcoma, four presented with radiographic evidence of bone metastases, but no primary tumor was found on subsequent evaluation. On radiographs, these metastases, located most commonly in the metaphyses of the extremities and in the spine, displayed a destructive or diffusely permeative pattern without sclerotic margins and mimicked the more common neuroblastoma. One patient also had diaphyseal cortical lytic metastases of the tibia. Radiographs defined metastases of the extremities better than the correlative bone scans. In the spine, on T2-weighted magnetic resonance (MR) images, metastases displayed high signal intensity which contrasted with the low-signal-intensity marrow in these pediatric patients. On histopathologic examination, metastatic rhabdomyosarcoma was composed of small cells of variable size, shape, and growth pattern similar to other round cell tumors. A positive desmin immunohistochemical test helped to establish the diagnosis. The radiologist, pathologist, and clinician should be aware of this unusual presentation of rhabdomyosarcoma so that suitable immunohistochemical tests are performed and appropriate chemotherapy given.

Use of helper cells with two host ranges to generate high-titer retroviral vectors

We have recently described Avian Leukosis Virus (ALV)-based packaging cell lines that can produce helper-free ALV-based retrovirus vectors with A, B, C, and E envelope host ranges. Here, we report that lacZ retroviral vectors of subgroup C or E can infect helper cells of subgroup A (Isolde) which are then able to produce high titers of lacZ recombinant viruses of subgroup A. Superinfection of helper cells by lacZ recombinant virus was performed by cocultivating packaging cells with two subgroup specificities (A and E), but this did not result in increased recombinant virus titers. This "ping-pong" process caused the emergence of replication-competent (RC) viruses which are shown to result from recombination between the viral sequences of the helper cell lines and the cis-acting sequences of the lacZ recombinant virus.

Radiotherapy after ovarian transposition: ovarian function and fertility preservation

The outcome of ovarian function preservation and fertility after ovarian transposition was examined in women treated for cancer. Of 134 patients, 126 were treated with radiotherapy and 72 with chemotherapy. In a multivariate analysis, three factors appeared to be prognostic of ovarian castration: the age over 25, MOPP chemotherapy and a total dose to the ovaries higher than 5 Gy. The incidence of birth was lower in the general population but no abnormality was observed.

Screening for germ line p53 mutations in children with malignant tumors and a family history of cancer

We have undertaken a routine investigation of the p53 status for all the children treated at our institution either affected by multiple tumors or whose family displays at least one second degree relative or less, affected by cancer before the age of 45 years. We report here on the first set of ten such families, eight of which were identified through a proband with sarcoma. p53 exons 5 to 8 have been sequenced following polymerase chain reaction amplification performed on DNA isolated from total blood. A missense mutation affecting codons 248, 273, and 282 was identified in three families. The mutation was inherited in these three families and was detected in unaffected members. In seven families no mutation was detected in exons 5 to 8.

Translocation t(11;19) (q23;p13) in a child with myelomonocytic leukemia following 2 years after chemotherapy for pneumoblastoma

A child, who received successful chemotherapy for pneumoblastoma, developed a myelomonocytic leukemia with translocation t(11;19)(q23;p13) 2 years later. Although this leukemia did not present with features generally associated with therapy-related leukemias, we think this hematologic disease to be secondary to previous chemotherapy. Involvement of chromosome 11q23 is common in acute leukemia and seems to be more significantly related to ANLL in young children (M4 and M5 FAB classification). However, our observation and previous reports suggest that this chromosomal abnormality might be more frequent in therapy-related leukemias. The responsibility of etoposide and cisplatin may be discussed in such secondary malignancies.

Importance of 3' non-coding sequences for efficient retrovirus-mediated gene transfer in avian cells revealed by self-inactivating vectors

Avian leukosis virus-derived vectors were constructed with an internal transcriptional promoter and various 3' non-coding sequences. Deletions were introduced into the downstream U3 long terminal repeat (LTR) to obtain self-inactivation of LTR-mediated transcription after one round of replication. However, 3' non-coding sequences appeared to determine not only self-inactivation of the vectors but also gene transfer efficiency. Further analysis revealed the influence of these sequences on both internal gene expression and RNA packaging. One construct permitted gene transfer while inactivating 5' LTR-promoted transcription.

[Arterial lesions after radiotherapy in children. Apropos of 16 cases]

BACKGROUND

Arterial occlusive disease is an uncommon and rather unpredictable complication of radiotherapy in childhood.

CASE REPORTS

Sixteen children (10 under 5 years of age and 7 under 3 years of age) who underwent radiotherapy for tumors between 1967 and 1983 developed an arterial occlusion with clinical manifestations during their follow-up. The radiotherapy dose was 25-55 Gy, and the fractionation was "conventional". The clinical manifestations depended on the site of arterial stenosis, including aorta and/or its branches (11 cases), carotid artery (3 cases) and limb arteries (2 cases). The delay before onset of clinical manifestations was variable, but generally very long (median: 13 years). Eight patients required surgical rehabilitation.

CONCLUSION

Better management of this type of complication should benefit from the early screening of irradiated children, especially young children, given even moderate doses, and particularly those having received more than 40 Gy.

Treatment of non-metastatic, non-seminomatous malignant germ-cell tumours in childhood: experience of the "Société Française d'Oncologie Pédiatrique" MGCT 1985-1989 study

The members of the French Society of Pediatric Oncology treated, between January 1985 and June 1989, 67 cases of non-metastatic, non-seminomatous malignant germ cell tumours (nSGCT) in sites other than the brain. They used a clinical pre- and postsurgical TNM-type classification in order to standardize the treatment regardless of tumour site. The intensity of the treatment was decreased in comparison with the previous regimen (elimination of adriamycin, reduction in the length of treatment). The actuarial 2-year disease-free survival rate is 80%; results are excellent for patients with clinical stage I and II tumours and permit cure with moderate chemotherapy, avoiding undesirable late effects. On the other hand it is inadequate for patients with stage III suggesting that the initial chemotherapy should be intensified for these latter patients in future protocols.

Primitive malignant nonepithelial hepatic tumors in children

Primary intrahepatic malignant nonepithelial tumors are very rare in children and account for 2% of all malignant mesenchymatous tumors under the age of 15 years. Clinical presentation, radiologic features, and histologic types are not unequivocal. The predominant role of surgery takes place either initially in small localized tumors or later, after initial reductive chemotherapy. In all cases, complete resection is the necessary but not sufficient condition for cure. Additional radiotherapy seems ineffective. High-dose chemotherapy and/or liver transplantation can be proposed for resistant cases. The disease-free survival rate is 37% at 2 years for the whole series.

Preservation of ovarian function by ovarian transposition performed before pelvic irradiation during childhood

Ovarian transposition in adults has been shown to protect ovarian function in about 60% of cases by reducing ovarian exposure to less than 4 to 7 Gy. We therefore evaluated the effect of ovarian transposition during childhood or adolescence. Eighteen girls had ovarian transposition performed at a mean (+/- SEM) age of 9.4 +/- 1.2 years (range, 1.2 to 16 years). Twelve were prepubertal and six had menstruated at the time of ovarian transposition. The initial abnormalities were Hodgkin disease (5 cases), iliac Ewing sarcoma (3), medulloblastoma (2), ovarian seminoma (1), and vaginal or uterine tumor (7). The irradiation was external in 11 cases and local by vaginal curietherapy in 7 cases. Fifteen girls received chemotherapy. The ovarian transposition was bilateral in 15 patients and unilateral in 3 cases; in the latter the other ovary had been destroyed by the tumor or by abdominal irradiation. Ovaries were placed just below the iliac crest (15 cases) or posterolateral to the uterus (3); thus, the calculated ovarian radiation dose was up to 9.5 Gy. At the time of evaluation (8.6 +/- 0.9 years after ovarian transposition), 16 girls had menstruated and 2 remained amenorrheic because of major lesions of the vagina and uterus caused by the vaginal curietherapy. Basal plasma gonadotropin values were normal. Ovulation was documented in seven cases. Two pregnancies occurred. Complications of ovarian transposition were present in four patients: intestinal occlusion, dyspareunia, functional ovarian cysts, and pelvic adhesions with tubal obstruction. We conclude that ovarian transposition, performed before abdominopelvic irradiation during childhood, can preserve ovarian function. Longer follow-up is required to assess the risk of ovarian dystrophy because of vascular lesions or chemotherapy.

XY sex reversal associated with a deletion 5' to the SRY "HMG box" in the testis-determining region

The human testis-determining factor resides within a 35-kilobase (kb) region of the Y chromosome immediately adjacent to the pseudoautosomal boundary. A candidate gene for human sex determination (SRY) was isolated in this region. Here, we describe a study of 25 cases of XY females with pure gonadal dysgenesis for mutations on the Y chromosome short arm, including SRY. Southern blotting revealed a sex-reversed female harboring a deletion extending from approximately 8 kb from the pseudoautosomal boundary of the Y chromosome to at least 33 kb and no more than 60 kb upstream, toward the centromere. The deletion begins no more than 1.8 kb upstream from the first ATG of the SRY open reading frame present in the clone pY53.3. To our knowledge, no mutation has been described previously outside the SRY "HMG box" on the short arm of the Y chromosome, which is associated with sex reversal. Since the 5' extent of the SRY transcriptional unit has not been defined, the deletion may remove upstream exons of SRY and/or transcriptional regulatory motifs, either situation resulting in lack of testicular development. It cannot be formally excluded that the mutation removes a second locus, independent of SRY, that is critical for sex determination. Denaturant gradient gel electrophoresis analysis of the SRY open reading frame in the remaining 24 cases revealed de novo single base-pair transitions in the SRY conserved domain in 4 cases.

[Granulosa cell tumors of the ovary in children and adolescents. Multicenter retrospective study in 40 patients aged 7 months to 22 years]

BACKGROUND

Juvenile granulosa cell tumors (JGCT) of the ovary are rare in children. The over-all outcome after surgery is relatively good, but the indication and type of complementary treatment for severe forms are still unclear.

POPULATION

A retrospective survey of the majority of patients with JGCT of the ovary admitted between 1965 and 1990 to 11 French oncologic pediatric centers was carried out. Medical records including surgical and histological data, were analyzed and each tumor was retrospectively classified by the same pathologist according to the Wollner classification.

RESULTS

There were 40 patients aged 7 months to 22 years (mean: 6 years); 28 were less than 10 year old at diagnosis. Three had enchondromatosis (Ollier's disease). At diagnosis, all patients presented with an abdominal tumor, 23 had developed manifestations of precocious pseudopuberty, 2 had signs of virilization after a normal puberty and 2 had secondary amenorrhea. Surgery was always the primary treatment: unilateral ovariectomy in 35 cases, bilateral in 4 and biopsy alone in 1 case. There were 21 stage I, 1 stage II, 16 stage III and 2 stage IV cases. 13 patients received combined chemotherapy and 2 abdominal radiotherapy. 34 patients were alive and disease-free 10 months to 26 years after surgery and 6 died. All 23 patients with precocious pseudopuberty had a favorable outcome.

CONCLUSIONS

This study confirms earlier reports. Unilateral ovariectomy is the first-choice therapy. There is no evidence that tumors complicated by rupture and hemoperitoneum require chemotherapy. Combined chemotherapy does not appear to improve the prognosis for the rare malignant forms. The factors of good prognosis are age less than 10 years and the presence of precocious pseudopuberty.

Identifying genes involved in the variability of genetic fatness in the growing chicken

A precise knowledge of the genome involved in the expression of a quantitative trait could provide a useful tool in breeding programs; molecular genetic methods are capable of yielding this kind of information. An experimental procedure is presented here for identifying genes whose expression is related to weight variability of abdominal adipose tissue in the growing chicken. Quantitative traits are the result of metabolic pathways exhibiting some major regulation stages that are controlled genetically. These steps involve genes that may act as "major genes". With regard to chicken fat metabolism, most fatty acids are synthesized in the liver and incorporated into very low density lipoprotein (VLDL) particles before their secretion into the plasma. Accordingly, the present study focused on the expression of liver genes. The mRNA of lipogenic enzymes (acetyl-coenzyme-A carboxylase, fatty acid synthase, malic enzyme, and delta 9-desaturase) were analyzed. Also studied were apoprotein (apo)A1, apoVLDL-II, and apoB mRNA from 9-wk-old male chickens from two lines selected for high and low abdominal fat pads. Significant differences for apoA1 mRNA levels occurred between fat and lean birds. Moreover, the total quantity of mRNA provided an accurate estimation of the abdominal fat pad (r = .74 with P < .05).

Packaging cells for avian leukosis virus-based vectors with various host ranges

Using our previously described Haydée semipackaging cell line (F. L. Cosset, C. Legras, Y. Chebloune, P. Savatier, P. Thoraval, J. L. Thomas, J. Samarut, V. M. Nigon, and G. Verdier, J. Virol. 64:1070-1078, 1990) which produces avian leukosis virus gag and pol proteins, we have constructed packaging cells with subgroups B, C, and E envelope specificities. This allows us to produce helper-free avian leukosis virus particles carrying the lacZ reporter gene and the A, B, C, or E subgroup specificities. Titers of the recombinant lacZ virus are shown to be dependent upon the type of the env subgroup and the target avian cell.