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PubMed1998

Clonal analysis helps to differentiate aberrant thyroid tissue from thyroid carcinoma.

A rare case of multiple aberrant of thyroid tissues in the tongue and lymph nodes of the bilateral neck was studied by immunohistochemistry and molecular clonal analysis to determine whether these tissues represent aberrant ectopic thyroid or metastases of a thyroid carcinoma. The thyroid tissues in the tongue and lymph nodes were all of polyclonal origins, consistent with ectopic thyroid in the tongue and bilateral cervical lymph nodes, rather than malignant thyroid tissues. This case shows that molecular clonal analysis can be used to distinguish aberrant thyroid from metastases of thyroid carcinoma.

Adult↗
PubMed1997

Clonal analysis of high-grade squamous intra-epithelial lesions of the uterine cervix.

We previously reported that invasive squamous cell carcinomas of the uterine cervix are of monoclonal composition. In the current study, we extended our previous work to determine the clonal composition of cases of high-grade squamous intra-epithelial lesion (HSIL). Clonal analysis targeting the HUMARA locus was performed on cervical tissue from 9 cases, 8 showing heterozygosity at the HUMARA locus and being, therefore, informative for clonality analysis. Uterine cervices were cut into 12 blocks, fixed with formalin and embedded in paraffin, and DNA was extracted from targeted lesions of each block. A total of 30 samples of cervical intra-epithelial neoplasia 3 (CIN3) (14 samples of carcinoma in situ and 16 samples of severe dysplasia) and 1 sample of CIN2 (moderate dysplasia) were analyzed. Monoclonal composition of the lesions was demonstrated in 30/30 cases of CIN3. Polyclonal composition was seen in the single case of CIN2. In 6 uterine cervices, in which dysplastic lesions were present in more than 3 blocks, the pattern of X-chromosome inactivation was the same in all lesions, suggesting that these individual lesions were derived from a single cell, with intraepithelial extension within the cervical mucosa. By contrast, one uterus contained 2 discontinuous dysplastic foci with different patterns of X-chromosome inactivation, indicating that the 2 lesions developed independently from each other. Our results demonstrate that (i) lesions of CIN3 (severe dysplasia and carcinoma in situ) are composed of a clonal neoplastic population of cells and (ii) most cases of HSIL are unifocal in origin.

Carcinoma in Situ↗
PubMed1998

Clonality Analysis of Benign Parathyroid Lesions by Human Androgen Receptor (HUMARA) Gene Assay.

Benign conditions of the parathyroid gland have been classified as adenomas and hyperplasias. These entities however are difficult to distinguish when only a single gland is enlarged. Adenomas are defined as neoplastic clonal growths whereas hyperplasias are considered to be reactive processes of polyclonal origin. In order to analyze the clonal pattern of these lesions, we have studied hyperplasias and adenomas of parathyroid glands from women by the human androgen receptor (HUMARA) assay, a recently reliable and highly-lnformative technique based on the X-chromosome inactivation pattern in females. Samples consisted of formalin-fixed as well as frozen tissues. Informativeness with HUMARA marker was 87% (13/15 cases). All hyperplasias (5/5) and 6/8 adenomas yielded polyclonal results, since two alleles of similar intensity appeared when the lesion was HpaIl-digested. Two parathyroid adenomas had a loss of one X-alIeIe for the HUMARA gene and they were interpreted as monoclonal. These results show that parathyroid hyperplasias and adenomas, considered as multigland or monogland involvement diseases respectively, may be both polyclonal in origin, and that only a small subset of adenomas is found to be clonal. Consequently, clonality analysis cannot allow a clear distinction between these two entities as classically diagnosed. A different approach should be considering hyperplasia or adenoma when a polyclonal or monoclonal result has been obtained by clonality analysis.

Journal Article↗
PubMed2001

Clonal analysis of differentiating embryonic stem cells reveals a hematopoietic progenitor with primitive erythroid and adult lymphoid-myeloid potential.

Embryonic stem (ES) cells differentiate into multiple hematopoietic lineages during embryoid body formation in vitro, but to date, an ES-derived hematopoietic stem cell has not been identified and subjected to clonal analysis in a manner comparable with hematopoietic stem cells from adult bone marrow. As the chronic myeloid leukemia-associated BCR/ABL oncogene endows the adult hematopoietic stem cell with clonal dominance without inhibiting pluripotent lymphoid and myeloid differentiation, we have used BCR/ABL as a tool to enable engraftment and clonal analysis. We show that embryoid body-derived hematopoietic progenitors expressing BCR/ABL maintain a primitive hematopoietic blast stage of differentiation and generate only primitive erythroid cell types in vitro. These cells can be cloned, and when injected into irradiated adult mice, they differentiate into multiple myeloid cell types as well as T and B lymphocytes. While the injected cells express embryonic (beta-H1) globin, donor-derived erythroid cells in the recipient express only adult (beta-major) globin, suggesting that these cells undergo globin gene switching and developmental maturation in vivo. These data demonstrate that an embryonic hematopoietic stem cell arises in vitro during ES cell differentiation that constitutes a common progenitor for embryonic erythroid and definitive lymphoid-myeloid hematopoiesis.

Animals↗
PubMed2004

Focal nodular hyperplasia with concomitant hepatocellular carcinoma: a case report and clonal analysis.

This report describes a hepatocellular carcinoma (HCC) with concomitant focal nodular hyperplasia (FNH) in a 56 year old Chinese man. There were two well circumscribed tumours measuring 3 x 2.5 x 2 cm and 2 x 1.5 x 1.5 cm. The larger mass was grey and soft with a small area of bleeding and necrosis and an intact capsule. The smaller mass was yellow and had no capsule. Clonal analysis was carried out to clarify the relation between the HCC and the adjacent FNH. The clonal analysis was based on the methylation pattern of the polymorphic X chromosome linked androgen receptor gene (HUMARA). In FNH, after HpaII digestion, the allelic bands showed two well defined peaks. The intensity of the two peaks in the DNA from cirrhotic tissue did not differ significantly, consistent with a random pattern of X chromosome inactivation. However, in HCC, after HpaII digestion, the allelic bands differed significantly in intensity. Therefore, there was a typical polyclonal pattern of inactivation in FNH but the HCC was interpreted as being monoclonal.

Carcinoma, Hepatocellular↗
PubMed1998

Clonal analysis of macronodules in cirrhosis.

Several arguments suggest that most hepatocellular carcinomas (HCCs) occurring in human cirrhotic livers arise from large hepatocellular nodules or macronodules. Except for nodules with obvious features of HCC, there exist no consistent criteria enabling the differentiation between benign regenerative and neoplastic, potentially malignant macronodules. Surrogate markers able to accurately discriminate those lesions that will evolve toward a HCC are required. In this study, we investigated the clonality of 26 macronodules isolated from eight cases of explanted cirrhotic livers in women by analyzing X-chromosome inactivation, as indicated by the methylation status of the human androgen receptor gene (HUMARA). For each macronodule, a large set of pathological features was evaluated and used to classify the macronodules into four groups: entirely benign-looking nodule (type 1), low-grade dysplastic nodule (type 2), high-grade dysplastic nodule (type 3), and HCC (type 4). Clonal analysis showed that 14 macronodules (54%) were monoclonal and 12 (46%) were polyclonal. Monoclonality was detected in 5 of 11 (45%) nodules from groups of entirely benign-looking and low-grade dysplastic nodules (types 1 and 2) and in 9 of 15 (60%) nodules from the group of high-grade dysplastic nodule and HCC (types 3 and 4). Neither the etiology of cirrhosis nor the size or histological classification of macronodules was correlated with the clonal status. In conclusion, clonal analysis of macronodules enables the differentiation between mono- and polyclonal macronodules in cirrhosis. Because monoclonal macronodules are prone to evolve to HCC, the determination of the clonal status of a macronodule could provide additional information for evaluating the prognosis of these lesions.

Adult↗
PubMed2000

Limitations of clonality analysis of B cell proliferations using CDR3 polymerase chain reaction.

BACKGROUND/AIMS: Detection of clonal immunoglobulin heavy chain (IgH) rearrangements by the polymerase chain reaction (PCR) is an attractive alternative to Southern blotting in lymphoma diagnostics. However, the advantages and limitations of PCR in clonality analysis are still not fully appreciated. In this study, clonality was analysed by means of PCR, focusing in particular on the sample size requirements when studying extremely small samples of polyclonal and monoclonal lesions. MATERIALS/METHODS: High resolution complementarity determining region 3 (CDR3) PCR was used to investigate the minimum number of cells and the amount of tissue required for the detection of a polyclonal population, both for fresh cells and formalin fixed, paraffin wax embedded tissue. Subsequently, frozen and paraffin wax embedded samples of 76 B cell lymphoproliferative disorders, 43 of which were tested by means of Southern blotting, were analysed to establish the sensitivity of this assay. These specimens included 12 chronic lymphocytic leukaemias (CLLs), nine mantle cell lymphomas (MCLs), 10 follicular lymphomas (FLs), and 45 mucosa associated lymphoid tissue (MALT) lymphomas. The specificity was tested on reactive lymph nodes (n = 19), tonsils (n = 4), peripheral blood lymphocyte fractions (n = 4), and biopsies with gastritis (n = 21). RESULTS: In reactive tissue, 20 ng of high molecular weight DNA derived from 6.5-9 x 10(3) B cells was sufficient to obtain a polyclonal PCR result. With smaller amounts "pseudoclonality" could be induced. When using paraffin wax blocks, undiluted DNA isolated from tonsillar tissue of at least 1 mm2 was necessary to obtain a polyclonal pattern. The sensitivity required to detect clonality in paraffin wax embedded and frozen tissue by PCR for FL (40% and 60%, respectively) was lower than that for MALT lymphomas (60% and 86%, respectively), CLL (78% and 89%, respectively), and MCL (88% and 100%, respectively). PCR specificity was 96% and 100% for frozen and paraffin wax embedded tissue, respectively. CONCLUSION: The minimum amount of template for CDR3 PCR is approximately 20 ng of high molecular weight DNA or 1 mm3 of B cell rich paraffin wax embedded normal tonsillar tissue, but care has to be taken to avoid pseudoclonality when low numbers of B cells are present. Duplicate or triplicate tests should be performed to avoid misinterpretation. The specificity of the PCR assay is almost 100%, whereas sensitivity depends on a combination of factors, such as lymphoma type and tissue fixation. Because frozen samples yield better results, obtaining fresh material for the PCR assay is recommended, especially when analysing FL and MALT lymphomas.

Blotting, Southern↗
PubMed1994

Clonal analysis of parathyroid adenomas by means of the polymerase chain reaction.

Clonality of parathyroid adenomas and normal parathyroid glands was analyzed by a method based on restriction fragment length polymorphism of the X-chromosome-linked phosphoglycerokinase (PGK) gene and on random inactivation of the gene by methylation. Through the introduction of the polymerase chain reaction to this method, clonal analysis could be performed on small DNA samples prepared from cryostat sections of these specimens. Every normal parathyroid gland was found to be polyclonal while every parathyroid adenoma was found to be monoclonal. When DNA samples obtained from four widely separated sites of an adenoma were independently analyzed, each sample was found to be monoclonal and, in addition, the same allele of PGK gene was inactivated. These results suggest that parathyroid adenoma, which has a single cell origin, is a true neoplasm and that its pathogenesis is probably different from that of parathyroid hyperplasia which is polyclonal in origin.

Adenoma↗
PubMed1994

Preoperative Discrimination of Fibroadenoma Which Is Clinically and Cytologically Indistinguishable from Breast Carcinoma through Clonal Analysis of Fine Needle Aspirate of Tumor: Report of a Case.

Recently, it has been demonstrated that breast carcimoma is monoclonal and fibroadenoma is polyclonal in origin. In the present case report, this observation was successfully applied to a preoperative differential diagnosis of a fibroadenoma clinically and cytologically indistinguishable from carcimoma. Case report: A45-year old female presented for clinical examination with a history of breast lump. A firm tumor measuring 2 x 2 cm was palpable in the upper-outer quadrant of @the left breast. The margin of the tumor was partially ill-defined and its mobility was restricted. A tumor shadow with a partially ill-defined margin was revealed by mammography. Ultrasonographic examination showed and irregularly-shaped, hypo-echoic tumor accompanied by an acoustic shadow. Fine needle aspiration biopsy yielded positive cytology. Based on these results, the tumor was diagnosed as breast carcinoma. However, clonal analysis of fine needle aspirates showed a polyclonal pattern, strongly indicating that the tumor was not a carcinoma but benign disease; most probably fibroadenoma. Thus, an open surgical biopsy was performed. Histoglogical examination revealed that the tumor was indeed a fibroadenoma with epithelial hyperplasia. This case suggests the usefulness of clonal analysis of fine needle aspirates in differentiating fibroadenoma from carcinoma of the breast.

Journal Article↗
PubMed1997

Clonality analysis as a tool to study the biology and response to therapy in myelodysplastic syndromes.

We examined the bone marrow of 45 patients with MDS at the time of diagnosis and in the course of the disease by means of Southern blot analysis and cytogenetic studies to detect and evaluate clonal markers and their implication on the prognosis of the disease and the response to treatment. All patients were enrolled in an EORTC study and received low-dose Ara-C with or without growth factors according to the study protocol. Thirty patients (67%) were characterized by different clonal markers, such as various gene rearrangements (eg Ig-JH, tcR-beta, bcr, GM-CSF, G-CSF or IL-3) and/or chromosomal markers at the time of diagnosis or early in the course of the disease. In 23 of 30 cases that could be studied in the course of the disease, a statement about the clonal situation was possible: in three cases (8%) the clonal situation did not change, in nine cases (39%) at least a transient reduction of clonal cells could be demonstrated, suggesting partial or complete response to therapy. In eight cases (35%) a change for the worse could be seen. In four cases (17%) involvement of multiple clones could be demonstrated with the clones exhibiting different susceptibilities to treatment. Clinical evaluation showed that patients without clonal markers at diagnosis had a better prognosis as compared to patients who presented with clonal markers. We suggest that clonality analysis at diagnosis and in the course of the disease will be a useful tool to study the biology and response to treatment in MDS.

Blotting, Southern↗
PubMed1997

Clonal analysis and identification of epidemic strains of methicillin-resistant Staphylococcus aureus by antibiotyping and determination of protein A gene and coagulase gene polymorphisms.

Forty-three methicillin-resistant Staphylococcus aureus (MRSA) isolates with known genetic and epidemiological relatedness and different degrees of transmission were analyzed by antibiotyping, protein A gene polymorphism analysis, and coagulase gene polymorphism analysis. The three typing systems were evaluated for their performance and convenience to define clones and to discriminate between epidemic MRSA (EMRSA) and sporadic MRSA (SMRSA). Antibiotyping and AluI restriction fragment length polymorphism analysis of the coagulase gene were able to define clones in the same way as DNA macrorestriction analysis (SmaI). However, both techniques presented disadvantages, making neither of them useful as a single typing method. Protein A gene polymorphism analysis appeared to be of no value for clonal analysis. None of the three typing methods was able to differentiate between EMRSA and SMRSA.

Bacterial Typing Techniques↗
PubMed1995

Quantitative non-radioactive clonality analysis of human leukemic cells and progenitors using the human androgen receptor (AR) gene.

Clonal analysis of FACS-purified primitive hematopoietic stem cells and of their progeny as assessed by the progenitors obtained from long-term cultures requires PCR-based approaches, mainly because of the low number of cells available. We have developed a non-radioactive androgen receptor (AR) assay which allows a simple and quantitative evaluation of the clonality of hematopoietic cells and progenitors. In this approach 5' AR primer is labelled by fluorescein and the amplified product is run on a sequencing gel which allows evaluation of the intensity of the fluorescent peaks generated. A computer software then analyzes the reduction of the intensity of the peaks on HpaII-digested samples. In order to determine the feasibility of the technique, we analyzed the clonality of leukemic cells from a patient with an acute-phase CMML which showed a typical clonal pattern of her leukemic DNA sample (WBC = 300 x 10(9)/I) using phosphoglycerate kinase (PGK) analysis. The same sample was then analyzed with either radioactive- or fluorescein-labelled AR primers, showing a typical clonal pattern (complete disappearance of one allele after HpaII digestion). A short-term clonogenic assay was then set up on methylcellulose and clonogenic progenitors were individually analyzed. All 24 colonies tested showed a typical clonal pattern with the disappearance of the same allele on each sample after HpaII digestion, indicating that they all derived from the same leukemic stem cell. Using this approach we then analyzed 94 patients with several hematologic malignancies and quantification of their fluorescent peaks. Fifty-four percent of the patients were clearly heterozygous (ie, a difference of > or = 2 CAG repeats was present between the two copies of the gene) and could be analyzed in an automatic sequencer using the fluorescent primers. Bone marrow mononuclear cells from all patients with acute myeloid leukemia (AML) showed a clonal or oligoclonal pattern at diagnosis whereas a polyclonal pattern was seen when remission was obtained. Similarly, out of 21 patients with a diagnosis of myelodysplastic syndrome (MDS), a clonal pattern was demonstrated in 10 whereas an oligoclonal or non-clonal pattern was shown in 11. These results show that this non-radioactive and safe technology can now be used on a large scale to evaluate the clonality of highly purified hematopoietic stem cells and their progenitors in hematopoietic malignancies and this might allow new insights into the targets of clonal amplification.

Acute Disease↗
PubMed1998

Clonal analysis of hematopoietic cells using a novel polymorphic site of the X chromosome.

Clonality of hematopoietic cells on a smale scale (nanogram amounts of DNA) can be detected by X-chromosome inactivation using the polymerase chain reaction (PCR). The human androgen-receptor gene (HUMARA) has a polymorphic short tandem repeat (STR), and has generally been used for clonality analysis since heterozygosity for the gene occurs in 90% of caucasian females. We examined heterozygosity of the STR on HUMARA in 110 Japanese females and found heterozygosity in 74 of 110 (67%). To examine for hematologic clonality in females with HUMARA homozygosity, we used a primer specific for a novel polymorphic STR site between DXS15 and DXS134 (DXS15-134) on Xq28. Heterozygosity for this site was found in 50 of 110 females (46%). Clonality of the hematopoietic cells was detected in 91 of 110 females (83%) using PCR of either the STR sites on HUMARA or DXS15-134. The X-inactivation patterns using PCR of DXS15-134 corresponded exactly with those obtained using PCR of HUMARA in 18 females who were heterozygous for both DXS15-134 and HUMARA. Using PCR of DXS15-134, we examined the clonality of bone marrow cells separated by flow cytometry in a patient with erythroleukemia (M6). Clonality was found not only in myeloid lineage cells but also in B lymphocytes. The clonality assay for DXS15-134 may be useful to assess for clonality of hematopoietic cells in the Japanese population, when combined with the HUMARA assay.

Base Sequence↗
PubMed1994

Clonal analysis of the origin of primordial germ cells in the mouse.

Qualitative and quantitative clonal analysis has been used to answer three basic questions about the establishment of the germ cell lineage in the mouse. Where do primordial germ cells originate? What is the size of the founding population at the time of lineage restriction? When and where does lineage restriction occur? Single epiblast cells of 6.0 dpc and 6.5 dpc mouse embryos were injected with a short-term lineage label (lysinated rhodamine dextran, LRDX) and their descendants traced after 40 h embryo culture at neural plate and early somite stages, respectively. An objective matching technique was used to detect the lineage marker in primordial germ cells identified by their characteristic alkaline phosphatase staining. Precursors of the primordial germ cells were found in the proximal epiblast close to the extraembryonic ectoderm in both pregastrulation and early-streak stage embryos. They form part of the presumptive extraembryonic mesoderm and are not lineage restricted while in the epiblast. Quantitative analysis gives a best fit to a model of a founding population of 45 at the time of lineage restriction. The data indicate that the generation time lengthens at the time of allocation. Calculation of clonal histories gives a best fit of 16 h generation time after allocation compared with < 7 h before allocation, with lineage restriction occurring at the early midstreak stage, presumably in the region posterior to the streak in which primordial germ cells are first identifiable. Therefore primordial germ cells are probably allocated early during gastrulation in a group of > 40 cells already segregated in the extraembryonic mesoderm.

Animals↗
PubMed2000

Clonality analysis of various hematopoietic disorders in cats naturally infected with feline leukemia virus.

The clonality analysis of the bone marrow cells was carried out by detecting the integrated proviruses of feline leukemia virus (FeLV) to understand the pathogenesis of FeLV-associated hematopoietic disorders in cats. Bone marrow cells from 4 cases with acute myeloid leukemia (AML), 9 cases with myelodysplastic syndromes (MDS), 2 cases with pure red cell aplasia (PRCA) and 3 healthy carriers infected with FeLV were subjected to Southern blot analyses using an exogenous FeLV probe. Clonal hematopoiesis was found in all the cases with AML and in 6 of the 9 cases with MDS, but not in the cases with both PRCA and healthy carriers infected with FeLV. In the 2 cases with MDS, it was thought that the same clones of the hematopoietic cells might proliferate before and after the progression of the disease irrespective of the changes of the hematological diagnoses by cytological examination. This study indicates that MDS in cats is a disease manifestation as a result of clonal proliferation of hematopoietic cells and can be recognized as a pre-leukemic state of AML.

Animals↗
PubMed1995

Clonal analysis of benign and malignant human breast tumors by means of polymerase chain reaction.

Clonal analysis was conduced on a variety of benign and malignant human breast tumors using the method based on restriction fragment length polymorphism (RFLP) of the X 120 chromosome-linked phosphoglycerokinase gene and on random inactivation of the gene by methylation. Breast carcinoma was shown to be monoclonal in origin, consistent with a somatic mutational theory. Precancerous lesions such as atypical ductal hyperplasia and multiple intraductal papilloma were also found to be monoclonal, indicating that certain genetic changes had been accumulated in these lesions. Solitary intraductal papilloma was found to be monoclonal. Since this tumor is composed of two types of cells, luminal epithelial cells and myoepithelial cells, it was suggested that the origin of solitary intraductal papilloma is a precursor cell which is capable of differentiating into both luminal and myoepithelial cells. The fact that fibroadenoma is polyclonal indicates that this tumor is not neoplasia but hyperplasia of a lobule. Epithelial component of phyllodes tumor was found to be polyclonal but stromal component was found to be monoclonal. Thus, phyllodes tumor is considered to be a neoplasm of stromal cells but not of epithelial cells.

Base Sequence↗
PubMed1997

Clonality in nevocellular nevus and melanoma: an expression-based clonality analysis at the X-linked genes by polymerase chain reaction.

The true nature of nevocellular nevus is still unknown and it has been ambiguously classified as a neoplasm or a hamartoma. We studied the clonality of nevocellular nevus and melanoma (malignant melanoma), using an expression-based clonality analysis at the X-linked genes by means of polymerase chain reaction. DNA was extracted from cryostat sections of 20 nevocellular nevi (10 compound and 10 intradermal type) and five melanomas from female patients. A polymorphic portion of the inactivated X-linked gene was amplified after selective digestion of the active X-chromosome with a methylation-sensitive restriction enzyme, Hpa II. Paternal- and maternal-derived fragments were resolved with electrophoresis using the polymorphic restriction endonuclease (BstX I) site for the phosphoglycerate kinase assay, and using the difference of CAG repeats for the human androgen-receptor gene assay. Both assays revealed that all informative nevocellular nevi were polyclonal in origin and all melanomas were monoclonal. Results of the clonality were independent of either the histologic type of nevocellular nevus or whether the nevocellular nevus was of congenital or acquired origin. Thus, nevocellular nevus, congenital or acquired, may be a hamartomatous rather than a neoplastic lesion. The analysis of clonality could be applied to the differential diagnosis of benign melanocytic disease and melanomas.

Adolescent↗
PubMed1986

Developmental origins of skeletal muscle fibers: clonal analysis of myogenic cell lineages based on expression of fast and slow myosin heavy chains.

A clonal analysis was used to show that skeletal muscle myoblasts are committed to distinct cell lineages during development. Myoblasts taken from embryonic chicken hindlimb muscles of different ages were cultured at clonal density. The content of fast and slow classes of the myosin heavy chain isoforms in the myotubes of the resulting muscle colonies was determined immunocytochemically with specific monoclonal antibodies that served as markers for the different fiber types. The muscle colonies formed by cloning myoblasts from early hindlimbs (days 4-6 in ovo) were of three types: the most numerous type, in which all myotubes in a colony contained only the fast class of myosin heavy chain; a less numerous type, in which all myotubes in a colony contained both the fast and slow classes of myosin heavy chain isoforms; and a rare type, in which all myotubes in a colony contained only the slow class of myosin heavy chain. The muscle colonies formed by cloning myoblasts from later hindlimbs (days 10-12 in ovo) were, however, all of one type, in which every myotube in a colony contained only fast myosin heavy chain. Thus, myoblasts in the early embryo (days 4-6 in ovo) were a heterogeneous population committed to three myogenic lineages: fast, mixed fast/slow, and slow, whereas myoblasts from the later embryo (days 10-12 in ovo) were only in the fast myogenic lineage. These results suggest that muscle fiber formation is rooted in two developmental phases--an early phase in which diverse fiber types are formed from intrinsically diverse populations of myoblasts and a later phase in which fibers are formed from a single population of myoblasts.

Age Factors↗