B cell precursors are present in the thymus during early development

An in vitro system for transforming immature lymphoid cells present in the thymus at early development has been established. By phenotype analysis of the transformants obtained, we observed that B cell precursors, susceptible to Abelson murine leukemia virus (A-MuLV)- or Harvey murine sarcoma virus (H-MuSV)-induced lymphogenesis, were present at high frequency in the fetal thymus of BALB/c mice. These precursors recolonized alymphoid thymus lobes in vitro, as do T cell precursors. It was further observed that B precursors in the fetal liver were also capable of recolonizing alymphoid thymus lobes and were stored in a thymic environment. These results suggest that stroma cells of the fetal thymus may possess the capacity to support the growth of B precursors. On the other hand, B cell precursors sensitive to the viral transformation were undetectable in the fetal thymus of C57BL/6, although immunohistochemical analysis suggested their presence. However, in the fetal liver of the same strain, B precursors recolonizing alymphoid thymus in vitro were sensitive to the viral transformation. Based on these results, we will discuss both the role and fate of thymic B precursors. In addition, we also obtained T cell lymphomas at different stages of differentiation from the fetal thymus of C57BL/6 infected with A-MuLV or H-MuSV. These data indicate the usefulness of our system in establishing cell lines derived from intrathymic lymphogenesis at early development.     

c-kit阳性细胞和胎儿食管平滑肌发育的关系

目的:探讨c-kit阳性细胞和α-平滑肌肌动蛋白阳性平滑肌细胞(α-SMA)在人胎儿食管中分布关系.方法:采用免疫荧光组织化学双重标记法对8例胎儿食管中c-kit阳性细胞和α-SMA阳性平滑肌细胞的分布进行观察.结果:c-kit阳性细胞在食管上段内肌层内侧有少量分布,肌间层和黏膜下层也可见零星分布,在食管中段外肌层开始有少量分布,内肌层数量中等,至食管下段内外肌层均有大量分布.α-SMA阳性平滑肌细胞在食管肌层由上至下逐渐增加,并由内肌层扩展到外肌层.在食管上端肌间层和黏膜下层可见少量c-kit和α-SMA共同表达.结论:c-kit阳性细胞可能是Cajal间质细胞,在胎儿食管的分布与平滑肌密切相关.食管内平滑肌细胞和Cajal间质细胞可能起源于同一种前体细胞.     

Spatial and temporal distribution of nerves, ganglia, and smooth muscle during the early pseudoglandular stage of fetal mouse lung development.

Neural tissue and smooth muscle appear early in the developing fetal lung, but little is known of their origin and subsequent distribution. To investigate the spatial and temporal distribution of nerves, ganglia, and airway smooth muscle during the early pseudoglandular stage, fetal mouse lungs at embryonic days (E) 11 to 14 were immunostained as whole-mounts and imaged by confocal microscopy. At E11, the primordial lung consisted of the future trachea and two budding epithelial tubules that were covered in smooth muscle to the base of the growing buds. The vagus and processes entering the lung were positive for the neural markers PGP 9.5 (protein gene product 9.5) and synapsin but no neurons were stained at this stage. An antibody to p75NTR revealed neural crest cells on the future trachea as well as in the vagus and in processes extending from the vagus to the lung. This finding indicates that even though neuronal precursors are already present at this stage, they are still migrating into the lung. By E12, neural tissue was abundant in the proximal part of the lung and nerves followed the smooth muscle-covered tubules to the base of the growing buds. At E13 and E14, a neural network of interconnected ganglia, innervated by the vagus, covered the trachea. The postganglionic nerves mainly followed the smooth muscle-covered tubules, but some extended out into the mesenchyme beyond the epithelial buds. Furthermore, we show in a model of cultured lung explants that neural tissue and smooth muscle persist and continue to grow and differentiate in vitro. By using fluorescent markers and confocal microscopy, we present the developing lung as a dynamic structure with smooth muscle and neural tissue in a prime position to influence growth and development.     

Telocytes in human fetal skeletal muscle interstitium during early myogenesis

A new peculiar stromal cell type called telocyte (TC)/CD34-positive stromal cell (i.e. cell with distinctive prolongations named telopodes) has recently been described in various tissues and organs, including the adult skeletal muscle interstitium of mammals. By forming a resident stromal three-dimensional network, TCs have been suggested to participate in different physiological processes within the skeletal muscle tissue, including homeostasis maintenance, intercellular signaling, tissue regeneration/repair and angiogenesis. Since a continuous interplay between the stromal compartment and skeletal muscle fibers seems to take place from organogenesis to aging, the present study was undertaken to investigate for the first time the presence of TCs in the human skeletal muscle during early myogenesis. In particular, we describe the morphological distribution of TCs in human fetal lower limb skeletal muscle during early stages of myogenesis (9–12 weeks of gestation). TCs were studied on tissue sections subjected to immunoperoxidase-based immunohistochemistry for CD34. Double immunofluorescence was further performed to unequivocally differentiate TCs (CD34-positive/CD31-negative) from vascular endothelial cells (CD34-positive/CD31-positive). Our findings provide evidence that stromal cells with typical morphological features and immunophenotype of TCs are present in the human skeletal muscle during early myogenesis, revealing differences in either CD34 immunopositivity or TC numbers among different gestation ages. Specifically, few TCs weakly positive for CD34 were found between 9 and 9.5 weeks. From 10 to 11.5 weeks, TCs were more numerous and strongly reactive and their telopodes formed a reticular network in close relationship with blood vessels and primary and secondary myotubes undergoing separation. On the contrary, a strong reduction in the number and immunopositivity of TCs was observed in fetal muscle sections from 12 weeks of gestation, where mature myotubes were evident. The muscle stroma showed parallel changes in amount, density and organization from 9 to 12 weeks. Moreover, blood vessels appeared particularly numerous between 10 and 11.5 weeks. Taken together, our findings suggest that TCs might play a fundamental role in the early myogenetic period, possibly guiding tissue organization and compartmentalization, as well as angiogenesis and maturation of myotubes.     

Skeletal muscle development and regeneration

In the late stages of muscle development, a unique cell population emerges that is a key player in postnatal muscle growth and muscle regeneration. The location of these cells next to the muscle fibers triggers their designation as satellite cells. During the healing of injured muscle tissue, satellite cells are capable of forming completely new muscle fibers or restoring damaged muscle fibers. A major problem in muscle healing is the formation of dysfunctional scar tissue, which leads to incomplete functional recovery. Therefore, the identification of factors that improve the process of muscle healing and reduce the formation of scar tissue is of great interest. Because satellite cells possess the capability of self-renewal, a unique feature of stem cells, they play a central role in the search for therapies to improve muscle healing. Growth factor-based and (satellite) cell-based therapies are being investigated to treat minor muscle injuries and intrinsic muscle defects. Major muscle injury that involves the loss of muscle tissue requires the use of scaffolds with or without (satellite) cells. Scaffolds are also being developed to generate muscle tissue in vitro. These approaches aim to restore the structure and function of the injured muscle without dysfunctional scarring.     

Clusterin expression during fetal and postnatal CNS development in mouse

Clusterin (or apolipoprotein J) is a widely distributed multifunctional glycoprotein involved in CNS plasticity and post-traumatic remodeling. Using biochemical and morphological approaches, we investigated the clusterin ontogeny in the CNS of wild-type (WT) mice and explored developmental consequences of clusterin gene knock-out in clusterin null (Clu-/-) mice. A punctiform expression of clusterin mRNA was detected through the hypothalamic region, neocortex and hippocampus at embryonic stages E14/E15. From embryonic stage E16 to the first week of the postnatal life, the vast majority of CNS neurons expressed low levels of clusterin mRNA. In contrast, a very strong hybridizing signal mainly localized in pontobulbar and spinal cord motor nuclei was observed from the end of the first postnatal week to adulthood. Astrocytes expressing clusterin mRNA were often detected through the hippocampus and neocortex in neonatal mice. Real-time polymerase chain amplification and clusterin-immunoreactivity dot-blot analyses indicated that clusterin levels paralleled mRNA expression. Comparative analyses between WT and Clu-/- mice during postnatal development showed no significant differences in brain weight, neuronal, synaptic and astrocyte markers as well myelin basic protein expression. However, quantitative estimation of large motor neuron populations in the facial nucleus revealed a significant deficit in motor cells (-16%) in Clu-/- compared with WT mice. Our data suggest that clusterin expression is already present in fetal life mainly in subcortical structures. Although the lack of this protein does not significantly alter basic aspects of the CNS development, it may have a negative impact on neuronal development in certain motor nuclei.     

Both smooth and skeletal muscle precursors are present in foetal mouse oesophagus and they follow different differentiation pathways.

Muscularis externa of mouse oesophagus is composed of two skeletal muscle layers in the adult. Unlike rest of skeletal muscle in the body, the oesophageal skeletal muscle in the mouse has been proposed to be derived from fully differentiated smooth muscle cells by transdifferentiation during later foetal and early postnatal development (Patapoutian et al. [1995] Science 270:1818-1821). Here we characterised the nature of cells in muscularis externa of the mouse oesophagus by ultrastructural and immunoctyochemical analyses. The presence of differentiated skeletal muscle cells identified by positive staining for skeletal muscle specific myosin heavy chain became first apparent in the outer layer of cranial oesophagus at 14 days gestation. The transient expression of smooth muscle type alpha-actin in mouse oesophageal muscle was also apparent during foetal development. This isoform, however, was not smooth muscle specific during early development as it was also detected in foetal skeletal muscles. Compared with oesophagus, the suppression of this smooth muscle type alpha-actin during foetal development was faster in non-oesophageal skeletal muscle cells. The development of skeletal muscle in oesophagus showed a cranial to caudal and an outer layer to inner layer progression. During early foetal development, mouse oesophagus is composed of undifferentiated mesenchymal cells that formed cell clusters. Two types of cells with different staining densities could be distinguished within these cell clusters by electron microscopy. The centrally located pale staining cells gave rise to skeletal muscle cells while the peripherally positioned dense staining cells gave rise to smooth muscle cells, indicating the existence of both skeletal and smooth muscle cell precursors in mouse oesophagus during early foetal development. Further development showed an increase in the proportion of skeletal muscle cells and a decrease in size and number of the smooth muscle type cells. Apart from decrease in cell size, some other morphological features of smooth muscle cell degeneration were also observed during later foetal and early neonatal development. No smooth muscle cells undergoing transdifferentiation were observed. Both immunochemical and ultrastructural observations, thus, demonstrated the presence of skeletal muscle cells in early foetal oesophagus. It is concluded that the transient appearance of smooth muscle cells may provide a scaffold for the laying down of skeletal muscle layers in mouse oesophagus, the final disappearance of which may be triggered by lack of smooth muscle innervation.     

Early maturation of force production in pig tracheal smooth muscle during fetal development.

The contractility of airway smooth muscle is fully established at late term at birth but its responsiveness during fetal life has not been defined. In this study, the contractile force of airway smooth muscle to acetylcholine (ACh), K+ depolarizing solution, and electrical field stimulation (EFS) was measured in tracheas from small fetal pigs. Contraction to either agonist and to EFS was detectable in fetuses of as low as 9 g body weight, which corresponds to approximately 36 days of gestation. Isometric force increased progressively with age, reaching 4.1 +/- 0.4 mN for K+ and 5.8 +/- 0.5 mN for ACh (10(-4) M) at 600 g fetal weight (90 days). However, when normalized for cross sectional area of smooth muscle, the stress was essentially the same from 17- to 600-g fetuses. (K+: 17 g = 74.4 +/- 10.6 mN/mm2, 600 g = 89.3 +/- 13.0 mN/mm2; ACh [10(-4) M]: 17 g = 76.3 +/- 16.0 mN/mm2, 600 g = 127.0 +/- 13.0 mN/mm2). The sensitivities of the various groups to ACh were not significantly different (e.g., EC50: 30 g = 4.0 +/- 0.2 x 10(-6) M, 600 g = 3.7 +/- 1.1 x 10(-6) M). EFS produced frequency-dependent contractile responses in all groups. With increasing fetal size, there was a corresponding increase in force. When this force was normalized to a maximum ACh response (10(-4) M), there was no significant difference between groups of fetuses. Histologic examination showed the major tissue components of the trachea were present in fetuses above 7 g. Immunocytochemistry detected myosin, caldesmon, and filamin in the smooth muscle from fetuses of 7 g and above, showing that contractile and actin-binding proteins were present from a very early age. It is concluded that smooth muscle contractile function is well developed very early in fetal life in pigs.     

Establishment of a cell line with features of early dendritic cell precursors from fetal mouse skin

During ontogeny, the skin is progressively populated by major histocompatibility complex class II-negative dendritic cell (DC) precursors that then mature into efficient antigen-presenting cells (APC). To characterize these DC progenitors better, we generated myeloid cell lines from fetal mouse skin by infecting cell suspensions with a retroviral vector carrying an env^AKR-myc^MH2 fusion gene. These cells, represented by the line FSDC, displayed a dendritic morphology and their proliferation in serum-free medium was promoted by granulocyte/macrophage colony-stimulating factor (GM-CSF), but not macrophage-CSF. FSDC expressed strong surface-membrane ATP/ADPase activity, intracellular staining for 2A1 antigen, and a surface phenotype consistent with a myeloid precursor: H-2^d.b+, I-A^d.b+, CD54⁺, CD11b⁺, CD11c⁺, 2.4G2⁺, F4/80⁺, CD44⁺, 2F8⁺, ER-MP 12^?, Sca-1⁺, Sca-2⁺, NLDC-145^?, B7.2⁺, B7.1^?, J11d^?, B220^?, Thy-1^?, and CD3^?. FSDC stimulated poorly allogeneic or syngeneic T cells in the primary mixed-leukocyte reaction, and markedly increased this function after treatment with GM-CSF, GM-CSF and interleukin (IL)-4 or interferon-γ (IFN-γ); in contrast, stem cell factor, IL-1α and tumor necrosis factor-α had no effect. Preculture with IFN-γ was required for presentation of haptens to primed T cells in vitro. However, FSDC, even after cytokine activation, were less potent APC than adult epidermal Langerhans cells in both of the above assays. Finally, FSDC derivatized with haptens and injected either intravenously or subcutaneously could efficiently induce contact sensitivity responses in naive syngeneic mice. The results indicate that fetal mouse skin is colonized by myeloid precursors possessing a macrophage/immature DC-like surface phenotype and priming capacity in vivo. These cells need further differentiation and activation signals (e.g. cytokines) to express their antigen presenting potential in vitro.     

Passive stiffness of rat skeletal muscle undernourished during fetal development

OBJECTIVES:

The aim of the study was to investigate the effect of fetal undernutrition on the passive mechanical properties of skeletal muscle of weaned and young adult rats.

INTRODUCTION:

A poor nutrition supply during fetal development affects physiological functions of the fetus. From a mechanical point of view, skeletal muscle can be also characterized by its resistance to passive stretch.

METHODS:

Male Wistar rats were divided into two groups according to their mother''s diet during pregnancy: a control group (mothers fed a 17% protein diet) and an isocaloric low‐protein group (mothers fed a 7.8% protein diet). At birth, all mothers received a standardized meal ad libitum. At the age of 25 and 90 days, the soleus muscle and extensor digitorum longus (EDL) muscles were removed in order to test the passive mechanical properties. A first mechanical test consisted of an incremental stepwise extension test using fast velocity stretching (500 mm/s) enabling us to measure, for each extension stepwise, the dynamic stress (σd) and the steady stress (σs). A second test consisted of a slow velocity stretch in order to calculate normalized stiffness and tangent modulus from the stress–strain relationship.

RESULTS:

The results for the mechanical properties showed an important increase in passive stiffness in both the soleus and EDL muscles in weaned rat. In contrast, no modification was observed in young adult rats.

CONCLUSIONS:

The increase in passive stiffness in skeletal muscle of weaned rat submitted to intrauterine undernutrition it is most likely due to changes in muscle passive stiffness.     

Inhibins are the major activin ligands expressed during early thymocyte development.

Activins are members of the transforming growth factor-beta (TGFbeta) superfamily, which regulate cell differentiation processes. Here we report the first quantitative analysis of the expression of Activin/Inhibin ligands, type I and II receptors, as well as Smad proteins in fetal (E14-E16) and adult thymic subpopulations. Our data showed that Alk4, ActRIIA, ActRIIB, and Smads 2, 3, and 4, are expressed in fetal thymus (E14 > E15 > E16) and in thymocytes from adult mice (mostly in the double negative [DN] subpopulation). Ligand expression analysis showed that betaA, betaB, and alpha subunits were mainly detected in thymic stromal cells. Interestingly, alpha subunits were expressed at much higher levels compared to betaA and betaB subunits, demonstrating for the first time the potential role of Inhibins as important mediators during early T cell development. Our data indicate that Activin/Inhibin signaling could regulate the process of thymus organogenesis and early thymocyte differentiation, as it has been demonstrated for other members of the TGF-beta superfamily.     

Skeletal muscle damage during tourniquet-induced ischaemia

Summary Muscle biopsies from the vastus lateralis muscle of patients who had undergone anterior cruciate ligament surgery under conditions of tourniquet-induced ischaemia were examined under the electron microscope at different periods of time up to 90 min of ischaemia. The severity of the alterations in ultrastructure appeared to depend on the period of ischaemia. The pathological changes consisted of accumulation of lysosomes, persistent intrafibre oedema, and some extracellular oedema. Signs of fibre necrosis were found after 90 min of ischaemia. Capillary ultrastructure was only altered with regard to some swelling of the endothelium and marked thickening of the basement membrane. It was concluded that skeletal muscle could be severely affected even during relatively short periods of ischaemia, which might facilitate the development of muscle atrophy during immobilization after orthopaedic surgery.     

Comparative expression of mouse and chicken Shisa homologues during early development.

During vertebrate embryogenesis, fibroblast growth factor (FGF) and Wnt signaling have been implicated in diverse cellular processes, including cell growth, differentiation, and tissue patterning. The recently identified Xenopus Shisa protein promotes head formation by inhibiting Wnt and FGF signaling through its interaction with the immature forms of Frizzled and FGF receptors in the endoplasmic reticulum, which prevents their posttranslational maturation. Here, we describe the mouse and chicken homologues of Xenopus Shisa. The mouse and chicken Shisa proteins share, respectively, 33.6% and 33.8% identity with the Xenopus homolog. In situ hybridization analysis shows that mouse shisa is expressed throughout embryonic development, predominantly in the anterior visceral endoderm, headfolds, somites, forebrain, optic vesicle, and limb buds. Cross-species comparison shows that the expression pattern of cshisa closely mirrors that of mshisa. Our observations indicate that the Shisa family genes are typically expressed in tissues known to require the modulation of Wnt and FGF signaling.     

Skeletal muscle development in normal and double-muscled cattle

This study examined the effect of genotype on prenatal muscle development in both normal-muscled (NM) animals and in double-muscled (DM) animals harboring a mutation in the gene for myostatin that results in the production of a functionally inactive protein. The following muscle development parameters were analyzed at four gestational ages: muscle weight, fiber type, by both enzyme histochemistry and myosin heavy-chain (MHC) immunocytochemistry, and average fiber area. The weights of both M. vastus lateralis and M. vastus medialis were greater throughout prenatal development in the DM animals compared to NM. The percentage of type 1 muscle fibers initially declined with gestational age and subsequently increased in both NM and DM. The percentage of type 1 fibers was consistently lower in DM than in NM. A pattern of MHC isoform localization was shown in DM muscle that is indicative of a delay in muscle development relative to NM. Muscle fiber size was differentially regulated in NM and DM, depending on fiber type. Type 1 fibers were smaller in DM than NM in late gestation, while type 2 fibers were smaller throughout gestation. This study suggests that the inactivating myostatin mutation in DM animals may be associated with changes in both skeletal muscle fiber type and fiber size during bovine muscle development.     

TCR repertoire in early fetal mouse thymus

We investigated the rearrangement and expression of TCR genesin mouse fetal thymus organ culture, a system that avoids subsequententry of hematopoietic precursor cells. The first observablerearranged TCR gene was homogeneous V2-J2, detectable as earlyas fetal day 11 (d11) in the thymic primordla. The productiveTCR was homogeneous V5-J1, first detectable in d13 thymocytes,followed by adult-type TCR (V4 and V7). Sequence analysis ofTCR revealed five types of V-J junctional sequences. In thevery early stage, a homogeneous V-J junction is generated viaa short homology sequence in the coding region (Type I), whilea short homology sequence in the P-nucleotlde rather than thecoding region is used in the following stage (Type II). In thelater embryonic stages, diverse V-J junctions are generatedby well-known mechanisms, such as P-nucleotide (Type III), N-regioninsertion (Type IV) or trimming of the coding ends (Type V).These findings suggest that the generation of homogeneous TCR (V2 and V5) in the early fetal stages is due to the intrinsicrearrangement mechanisms and is in stage specific manner.