Deep RNA sequencing of pectoralis muscle transcriptomes during late-term embryonic to neonatal development in indigenous Chinese duck breeds

Pectoral muscle (PM) comprises an important component of overall meat mass in ducks. However, PM has shown arrested or even reduced growth during late embryonic development, and the molecular mechanisms underlying PM growth during the late embryonic to neonatal period in ducks have not been addressed. In this study, we characterized potential candidate genes and signaling pathways related to PM development using RNA sequencing of PM samples selected at embryonic days (E) 21 and 27 and 5 days post-hatch (dph) in two duck breeds (Gaoyou and Jinding ducks). A total of 393 differentially expressed genes (DEGs) were identified, which showed higher or lower expression levels at E27 compared with E21 and 5 dph, reflecting the pattern of PM growth rates. Among these, 43 DEGs were common to all three time points in both duck breeds. These DEGs may thus be involved in regulating this developmental process. Specifically, KEGG pathway analysis of the 393 DEGs showed that genes involved with different metabolism pathways were highly expressed, while genes involved with cell cycle pathways showed lower expression levels at E27. These DEGs may thus be involved in the mechanisms responsible for the phenomenon of static or decreased breast muscle growth in duck breeds during the late embryonic period. These results increase the available genetic information for ducks and provide valuable resources for analyzing the mechanisms underlying the process of PM development.

Skeletal muscle characterization of Japanese quail line selectively bred for lower body weight as an avian model of delayed muscle growth with hypoplasia

This study was designed to extensively characterize the skeletal muscle development in the low weight (LW) quail selected from random bred control (RBC) Japanese quail in order to provide a new avian model of impaired and delayed growth in physically normal animals. The LW line had smaller embryo and body weights than the RBC line in all age groups (P<0.05). During 3 to 42 d post-hatch, the LW line exhibited approximately 60% smaller weight of pectoralis major muscle (PM), mainly resulting from lower fiber numbers compared to the RBC line (P<0.05). During early post-hatch period when myotubes are still actively forming, the LW line showed impaired PM growth with prolonged expression of Pax7 and lower expression levels of MyoD, Myf-5, and myogenin (P<0.05), likely leading to impairment of myogenic differentiation and consequently, reduced muscle fiber formation. Additionally, the LW line had delayed transition of neonatal to adult myosin heavy chain isoform, suggesting delayed muscle maturation. This is further supported by the finding that the LW line continued to grow unlike the RBC line; difference in the percentages of PMW to body weights between both quail lines diminished with increasing age from 42 to 75 d post-hatch. This delayed muscle growth in the LW line is accompanied by higher levels of myogenin expression at 42 d (P<0.05), higher percentage of centered nuclei at 42 d (P<0.01), and greater rate of increase in fiber size between 42 and 75 d post-hatch (P<0.001) compared to the RBC line. Analysis of physiological, morphological, and developmental parameters during muscle development of the LW quail line provided a well-characterized avian model for future identification of the responsible genes and for studying mechanisms of hypoplasia and delayed muscle growth.

The clavicular part of the pectoralis major: a true entity of the upper limb on anatomical, phylogenetic, ontogenetic, functional and clinical bases. Case report and review of the literature

The pectoralis major consists of three parts: clavicular, sternocostal and abdominal. The first is usually separated from the deltoid by a deltopectoral triangular space, and often from the sternocostal part by another triangular space. The clavicular part is a new acquisition in Anthropoids, to optimize stabilization of the upper limb to the thorax thus permitting an increased limb mobility in Primates. It is synergetic with the deltoid in arm flexion and even more in adduction. This action is important in Humans, as the coracobrachialis becomes smaller in Mammals. Among non human Primates, those having cranially displaced shoulder joint show a significant clavicular origin of the pectoralis major. The clavicular origin might be necessary in flexion of the forelimb, when the humeral insertion of the muscle is on the same transverse plane as, or cranial to, the sternal manubrium. As to the blood and nerve supply, occurrence in Humans of a neuro-vascular pedicle for the clavicular part, shared with the deltoid, indicates a relatively morpho-functional independence of this part from the rest of the muscle. Under this regard, the width of the lateral pectoral nerve, which supplies the clavicular part of the muscle, may be related to a greater functional ability. Many manoeuvres for plastic and reconstructive surgery are performed by isolating the clavicular part of the pectoralis major. Indeed, this part may be considered as a true, self-standing anatomical entity. In fact, it has morphological individuality, peculiar bony attachments and functional autonomy, so that it is simply adjacent to the sternocostal part. Moreover, according to phylogenesis, this topographic relation develops secondarily, in parallel with the development of the clavicle. Therefore, it may be regarded not only as a simple part of an extrinsic muscle of the thorax, but also as an intrinsic muscle of the upper limb.

[Blood flow in skeletal muscles of chicken in the embryonic and early postembryonic periods]

In chicken Leghorn, blood flow volume speed in pectoralis and gastrocnemius muscles was measured on 15 and 19 day-old embryos and at the 1st and the 10th days alter hatching. It was revealed that in the last quarter of embryogenesis BF in muscles did not vary remaining in both muscles in identical limits. Similar BF parameters in pectoralis and gastrocnemius muscles and their age-dependent dynamics were observed at embryos with the detained development (with the body weight 2-fold less than the norm). After hatching, the blood flow in both muscles was grown, on the average, 2.4-fold and remained high by the 10th day, a little decreasing in the pectoralis muscle. It was shown, that increase of a muscular blood flow after hatching was accompanied by different changes of anatomic lumen of the arteries addressed in pectoralis and gastrocnemius muscles: in the former it decreased, in the latter--increased.

Muscle specific differences in the regulation of myogenic differentiation in chickens genetically selected for divergent growth rates

With the human population predicted to reach 9 billion by 2050, increasing food supplies while maintaining adequate standards of animal welfare has become a global priority. In the poultry industry, broilers are genetically selected for greater pectoral but not leg muscularity yield leading to leg disorders and thereby welfare issues. It is known that the pectoralis major of broilers contains more muscle fibres of larger diameters than egg-layers but little is known about the leg gastrocnemius muscle cellular characteristics. As muscle fibre numbers are set by hatch, the molecular regulation of myogenesis was investigated in pectoral (selected) and gastrocnemius (unselected) muscles of chick embryos to help explain diverging post-hatch phenotypes. Results showed that broilers were more active from embryonic day (ED) 8 and heavier from ED12 to 18 than layers. The pectoral muscle of broilers exhibited increased myoblast proliferation on ED15 (raised myonuclei, MyoD and PCNA) followed by increased differentiation from ED16 (raised myogenin, IGF-I) leading to increased muscle fibre hyperplasia and mass by ED18 compared to layers. In the gastrocnemius muscle of broilers, cell proliferation was also raised up to ED15 accompanied by increased PCNA, MyoD and IGF-I mRNAs. However, from ED16, myogenin and IGF-I mRNAs were similar to that of layers and PCNA was reduced leading to similar fibre area, nuclei numbers and muscle mass at ED18. We conclude that genetic selection for enhanced post-hatch pectoral muscle growth has altered the temporal expression of IGF-I and thereby myogenin transcription affecting cellular characteristics and mass by hatch in a muscle specific manner. These observations should help develop intervention strategies aimed at improving leg muscle strength and thereby animal welfare to meet growing consumer demand.

Phosphatase PTEN in chicken muscle is regulated during ontogenesis

The phosphatase and TENsin homolog deleted on chromosome 10 (PTEN) is a lipid and protein phosphatase able to inhibit significant actors of cell signaling (i.e. phosphatidylinositol-3'kinase and mitogen-activated protein kinase pathways). The aim of this study was to characterize PTEN and to investigate its regulation during ontogenesis in chicken muscle. Pectoralis major muscle was sampled on day 18 of the embryonic period (E18), at hatching (d0) and in fed chickens at 2, 7 and 43 days after hatching (d2, d7 and d43). We first cloned the totality of chicken PTEN cDNA; its translation into a putative protein showed more than 95% sequence identity with that characterized in mammals (humans, mice). PTEN was expressed under two major transcripts in the majority of tissues, including muscles where the expression of PTEN mRNA increased with age (P < 0.05). Surprisingly, the protein levels of PTEN (protein characterized with an apparent molecular weight of 55kDa) and its activity were considerably decreased between the E18 and d43 stages (approximately 8-10-fold reduction, P < 0.001). An association between these decreases and higher phosphorylation levels of two potential indirect downstream targets of phosphatase (i.e. AKT and ERK) was observed only in the early growth phases. It was concluded that phosphatase PTEN was expressed in chicken muscle and that its expression was regulated during ontogenesis.

Monochromatic light stimuli during embryogenesis enhance embryo development and posthatch growth

Photostimulation with green light accelerated BW and muscle development of broilers. In experiment 1, temperature sensors were inserted into 50 broiler eggs. The eggs were placed under 5 green light-emitting diode (LED) lamps at an intensity of 0.1 W/m2 at eggshell level for 5, 10, 15, 20, and 25 min (n = 10). Egg temperatures were recorded continuously. A high correlation was found between lighting period and egg temperature elevation, and an intermittent light regimen of 15 min on and 15 min off was found to eliminate light-induced egg overheating. In experiment 2, the effect of in ovo green light photostimulation on embryonic development was studied. Five hundred fertile eggs were divided into 2 groups: the first was photostimulated with green light from 5 d of incubation until hatch (0.1 W/m2 intensity) and the second was incubated in the dark. In ovo green light photostimulation caused a significant elevation in BW and breast muscle weight during embryo development and posthatch until 6 d of age. In experiment 3, 240 fertile broiler eggs were divided into 2 groups as described in experiment 2. At hatch, chicks from each in ovo light treatment were divided into 2 subgroups: the first was reared under green light and the second under white light. In ovo photostimulation with green light enhanced BW and breast muscle weight. However, rearing under green light did not have any synergistic effect on BW. Collectively, the results suggest that stimulation with green light enhances development and growth in chicks and that the best effect is achieved when this stimulus is provided during incubation.

The Influence of Selection for Increased Body Weight and Sex on Pectoralis Major Muscle Weight During the Embryonic and Posthatch Periods

Skeletal muscle development and growth results from a complex series of highly organized processes. To address how myogenesis was influenced by selection for increased BW and by sex, both sexes from a turkey line (F) selected only for increased 16-wk BW and its genetic control line (RBC2) were used. Pectoralis major muscle was isolated and weighed from 15 individuals of each sex of the F and RBC2 lines at 14, 16, 18, 20, and 24 d of embryonic development and at 1, 8, 12, and 16 wk of age posthatch. The F line had significantly heavier p. major muscle weights than the RBC2 line beginning at 16 d of embryonic development, and the magnitude of the line differences generally increased with age through 16 wk posthatch The p. major muscle was consistently heavier in males than in females, but the differences between sexes were significant only at 16, 18, and 24 d of embryonic development and at 8 wk posthatch. There was no significant interaction between line and sex for weight of the p. major muscle at any age. The results indicated that selection for increased 16-wk BW in the F line altered growth of the p. major muscle by 16 d of embryonic development and changes were similar for both sexes.

Developmental expression of skeletal muscle heparan sulfate proteoglycans in turkeys with different growth rates

Heparan sulfate proteoglycans (HSPG) are a group of extracellular matrix molecules that link skeletal muscle cells to their extrinsic environment. To investigate if HSPG expression is affected by muscle growth and gender, a turkey line (F) selected for increased 16-wk BW and its unselected random-bred control line, RBC2, were used in the present study. Heparan sulfate (HS) and HSPG levels were measured in embryonic and posthatch pectoralis major muscle. HS levels plateaued at embryonic day (ED) 16 in both lines. A significant decrease of HS occurred at ED 18 in F males and females, and at ED 20 and 22 in the RBC2 males and females, respectively. Embryonic HSPG levels peaked at ED 18, and were significantly higher from ED 14 through 18 in F males and females compared with those of the RBC2 line. Male pectoralis major muscle had more HSPG at early embryonic stages than female muscle in both lines. During 1 to 16 wk posthatch, F male and female pectoralis major muscle contained more HSPG than the RBC2 samples, and HSPG levels in F males were higher than those of the females. Myogenic satellite cells derived from F and RBC2 male and female pectoralis major muscle were cultured to measure HSPG expression during proliferation and differentiation. No significant difference in HSPG level was found between the RBC2 and F line cells. However, in both lines, male-derived satellite cells had more HSPG than the female cells during proliferation and differentiation. These data show that HS and HSPG expression are affected by muscle growth properties and sex.

Development of components of the extracellular matrix, basal lamina and sarcomere in chick quadriceps and pectoralis muscles

1. The purpose of this study was to investigate differences in the development of components of the cell/matrix linkage in two functionally different muscle types: the pectoralis muscle, a major locomotory muscle in birds but not particularly functional in chickens, and the quadriceps muscle, a smaller and more functionally active muscle in the chicken. 2. The development of the extracellular matrix, basal lamina and sarcomere in the pectoralis and quadriceps muscles in chick embryos was examined biochemically to determine differences in the rate of development between these two muscles. Samples of these muscle types were dissected out from chick embryos from embryonic day 10 until 8 weeks post hatch. 3. Using SDS-PAGE electrophoresis and western blotting with antibodies against sarcomeric actin, laminin and collagens I, III and IV, it was apparent that muscle development begins earlier in the quadriceps muscle than in the pectoralis, and that late in the developmental process (d 18) both muscle types were well differentiated. The final concentration of collagens in the mature muscle remained higher in the quadriceps than in the pectoralis muscle. 4. The onset of development of the extracellular matrix, basal lamina and sarcomere was earlier in the quadriceps than the pectoralis, which could have functional implications for these muscles as a whole.

The evolution of the pectoral girdle

The pectoral girdle articulates the forelimb with the axial skeleton in all vertebrates with paired anterior appendages. The structure of the pectoral girdle and its position along the axial skeleton has changed significantly during vertebrate evolution. These morphological changes have been well described, but there is little comparative embryology to indicate how these changes may have occurred. It is equally obscure how the muscles that connect the head with the pectoral girdle have maintained appropriate attachments even though these 2 structures have become separated. Here I review the changes in the pectoral girdle across different vertebrate taxa, indicating, where known, the developmental mechanisms underlying these changes. I also suggest how the muscular connections between the head and pectoral girdle have been maintained between these once adjacent bones, displaced during vertebrate evolution.

Protein and mRNA analysis of myosin heavy chains in the developing avian pectoralis major muscle

While the existence of post-hatch and adult myosin heavy chain isoforms in the large, avian type IIB pectoralis major muscle has been clearly established, the number and nature of fast myosin heavy chains during in ovo development and the perihatch period have not been resolved. In the present study, developmental fast heavy chain proteins purified by high resolution anion-exchange have been characterized by sequence analysis of a unique CNBr peptide and by complementary mRNA analysis. The four proteins present at 15/16 days in ovo are shown to differ uniquely in primary structure. They correlate with heavy chains II, IV, VI and VII, characterized recently as major or minor species in adult fast muscles using similar methods. These four heavy chains are expressed in a time-dependent fashion from 8 to 16 days in ovo. At the mRNA level, heavy chain VI predominates until 12 days in ovo. Heavy chain IV mRNA is upregulated dramatically at 16 days in ovo preparatory to its protein's predominance in the peri-hatch period. Heavy chains II, IV and V (the post-hatch isoform which replaces heavy chain IV) have major roles in adult fast muscles.

Desmin-lacZ transgene expression and regeneration within skeletal muscle transplants

The purpose of this study was to investigate the initiation and time course of the regeneration process in fragments of skeletal muscle transplants as a function of muscle tissue age at implantation. The appearance of desmin occurs at the very beginning of myogenesis. The transgenic desmin nls lacZ mice used in the study bear a transgene in which the 1 kb DNA 5' regulatory sequence of the desmin gene is linked to a reporter gene coding for Escherichia coli beta-galactosidase. The desmin lacZ transgene labels muscle cells in which the desmin synthesis programme has commenced. We implanted pectoralis muscle fragments from fetal transgenic embryos and mature and old transgenic mice into mature non-transgenic mice. Early events of myogenesis occurring during regeneration started sooner in transplants from 4-month-old (day 3 post-implantation) muscle than in those from 24-month-old (day 5-6 post-implantation) muscle, and they lasted longer in those from young (day 17 post-implantation) than in those from old (day 14 post-implantation) muscle fragments. In adult muscle, transgene activation proceeded from the periphery toward the centre of the transplant. In transplants from fetal 18-day-old pectoralis, myotubes with transgene activity were observed from day 1 to day 19. Desmin immunoreactivity, which appeared about one day after transgene activation, was followed by myosin expression. In adult transplants, the continuity of laminin labelling was disrupted around degenerative fibres, illustrating alteration of the extracellular matrix. Our data suggest that satellite cells from old muscle tissue have lower proliferative capacity and/or less access to trophic substances released by the host (damaged fibres, vascularization) than those from fetal or young adult muscle.

Decorin and collagen type I gene expression in avian low score normal pectoral muscle

The avian Low Score Normal (LSN) genetic muscle weakness is phenotypically characterized by a reduction in the ability of the birds to right themselves from a supine position. Compared to normal skeletal muscle, LSN muscle has normal myosin isoform switching and cell-cell recognition, elevated glycosaminoglycan and decorin levels at embryonic Day 20, and a large increase in collagen crosslinking at 6 wk posthatch. To begin to determine the biological mechanism involved in the elevated decorin protein concentration at embryonic Day 20, the steady-state levels of transcripts encoding both decorin and collagen Type I at embryonic Days 14, 19, and 20, and at 1 d and 6 wk posthatch were measured. On embryonic Day 20, collagen Type I transcripts were not different from the control but there was a significant elevation in decorin transcript levels. At 1 d and 6 wk posthatch, transcript levels of decorin and collagen Type I were not different between LSN and controls. The change in decorin transcript steady-state levels is limited to late embryonic development and suggests an alteration in a signal transduction pathway regulating decorin transcription.

In vitro characterization of chondrogenic cells isolated from chick embryonic muscle using peanut agglutinin affinity chromatography

Specific binding to the lectin, peanut agglutinin (PNA), has been reported in embryonic precartilage tissues, including the condensing limb bud blastema and the caudal half of the developing somite. The present study aimed to test the hypothesis that PNA-binding may be a surface characteristic of chondroprogenitor cells residing within noncartilage tissues, such as muscle, which have the potential of being induced to form cartilage, e.g., in the presence of bone matrix-derived factors. Day-14 chick embryonic pectoral muscle, which contained histochemically detectable PNA-binding cells, was dissociated into single cells (TM cells) and fractionated by PNA affinity chromatography into PNA-binding (PNA+) and nonbinding (PNA-) cells by PNA-Sepharose 6 MB affinity chromatography. The differentiation potential of the PNA-affinity fractionated cells in vitro was analyzed as a function of culture plating cell density. Immunohistochemistry of a number of cell-type-specific differentiation markers, including sarcomeric actin, collagen type II, and aggrecan core protein, demonstrated that PNA+ cells, when cultured as a micromass at high density (20 x 10(6) cells/ml), exhibited a chondrocyte-like phenotype, whereas the PNA-cells remained myogenic; however, both PNA+ and PNA- monolayer cultures (4 x 10(4) cells/ml) behaved as myoblastic cells. The expression of collagen type II mRNA was also confirmed by coupled reverse transcription/polymerase chain reaction analysis. These observations suggest that PNA binding, i.e., the presence of specific galactose-containing cell surface moieties, is likely to be one of the characteristics of chondrogenic cells residing in mesenchymally derived embryonic tissues.

Does the nerve supply to both the superficial and deep surfaces of pectoralis major imply two separate developmental origins?

The nature of the nerve supply to the "pocket' of pectoralis major was examined on 7 randomly selected sides of 5 embalmed cadavers. The pocket was a U-shaped muscular fold, opening cranially. The anterior limb and inner surface of the fold were supplied by nerve branches that originated from the middle segment of the pectoral nerve loop and penetrated pectoralis minor. The outer surface of the posterior limb was supplied by one or two branches that extended from the caudal segment of the pectoral nerve loop. If the muscular U-shaped fold is unfolded, it becomes obvious that the posterior wall of the pocket forms the most caudal part of pectoralis major and is supplied from both the superficial (anterior) and deep (posterior) surfaces. This dual surface supply does not suggest any aspect of the developmental origin of the pocket but may simply be due to the relative positions of the pectoralis major and its nerve.

Heterogeneity of myosin heavy-chain expression in fast-twitch fiber types of mature avian pectoralis muscle

The aims of this study are to investigate the diversity of myosin heavy-chain (MyHC) expression among avian fast-twitch fibers, and to test the hypothesis that dissimilar MyHC isoforms are found in each of the principal avian fast-twitch fiber types. MyHCs within the muscle fibers of the pectoralis of 31 species of bird are characterized using immunocytochemical methods. A library of 11 monoclonal antibodies previously produced against chicken MyHCs is used. The specificity of these antibodies for MyHCs in each of the muscles studied is confirmed by Western blots. The results show that avian fast-twitch glycolytic fibers and fast-twitch oxidative-glycolytic fibers can contain different MyHCs. Among the species studied, there is also a conspicuous variety of MyHC isoforms expressed. In addition, the results suggest that two epitopes are restricted to chickens and closely allied gallinaceous birds. There are no apparent correlations between between MyHC epitope and presupposed contractile properties. However, the presence of different isoforms in different fast-twitch fiber types suggests a correlation between isoform and contractile function.

The avian low score normal muscle weakness alters decorin expression and collagen crosslinking

Extracellular matrix development of chicken pectoral muscle was examined in the Low Score Normal (LSN) genetic muscle weakness and compared to both normal and avian muscular dystrophy (MD). At 20 days of embryonic development significant elevations were noted in LSN total glycosaminoglycan concentration and decorin, while at 14 days, LSN glycosaminoglycan and decorin levels were indistinguishable from the controls. Levels of a large skeletal muscle chondroitin sulfate proteoglycan (M-CSPG) appear to be unaffected. Morphologically, at 20 days, the extracellular matrix space between muscle fibers increased to a level characteristic to that observed in avian muscular dystrophy. At six weeks posthatch a marked increase in LSN collagen crosslinking relative to MD or control tissues was observed, while collagen concentration was not altered. By one year posthatch LSN collagen crosslink levels did not significantly differ from normal tissue. These data support the concept that the LSN muscle weakness is associated with changes in both proteoglycan and collagen characteristics.

Stimulation of avian myoblast differentiation by triiodothyronine: possible involvement of the cAMP pathway

In a previous work, we have shown that T3 induces a potent stimulation of avian myoblast differentiation. In this study, we demonstrated that this hormone did not affect MyoD and myogenin expression. As numerous data suggest that T3 could affect the cAMP pathway, we have studied its involvement in the myogenic activity of triiodothyronine on quail myoblast. In agreement with Zalin and Montagues (Cell 2, 103-108 (1974)), we observed a transient rise in myoblast intracellular cAMP level some hours before the onset of terminal differentiation. Interestingly, this rise occurred earlier in T3-treated than in control myoblasts, and cAMP production was significantly increased by the hormone. Moreover, T3 increased CREB transcriptional activity, thus suggesting that the entire cAMP signaling pathway was stimulated by this hormone. In addition, we observed that addition of an inhibitor of adenylate cyclase activity prior to the cAMP rise dramatically inhibited myoblast differentiation. Last, we showed that cAMP mimicked all T3 actions upon myoblast differentiation: (1) T3 and cAMP reduced myoblast proliferation by increasing the number of postmitotic myoblasts at cell confluence; (2) T3 and cAMP increased BTG1 nuclear accumulation; (3) T3 and cAMP stimulated terminal differentiation only when added during the proliferative phasis. These data strongly suggest that the transient rise in cAMP production could be essential for myoblast terminal differentiation. In addition, it appears that, at least in avian myoblasts, T3 stimulation of terminal differentiation involves the cAMP pathway.

Ontogeny of the pectoralis muscle in the little brown bat, Myotis lucifugus

The ontogeny of a primary flight muscle, the pectoralis, in the little brown bat (Myotis lucifugus: Vespertilionidae) was studied using histochemical, immunocytochemical, and electrophoretic techniques. In fetal and early neonatal (postnatal age 1-6 days) Myotis, histochemical techniques for myofibrillar ATPase (mATPase) and antibodies for slow and fast myosins demonstrated the presence of two fiber types, here called types I and IIa. These data correlated with multiple transitional myosin heavy chain isoforms and native myosin isoforms demonstrated with SDS-PAGE and 4% pyrophosphate PAGE. There was a decrease in the distribution and number of type I fibers with increasing postnatal age. At postnatal age 8-9 days, the adult phenotype was observed with regard to muscle fiber type (100% type IIa fibers) and myosin isoform profile (single adult MHC and native myosin isoforms). This "adult" fiber type profile and myosin isoform composition preceded adult function by about 2 weeks. For example, little brown bats were incapable of sustained flight until approximately postnatal day 24, and myofiber size did not achieve adult size until approximately postnatal day 25. Although Myotis pectoralis is unique in being composed of 100% type IIa fibers, transitional fiber types and isoforms were present. These transitional forms had been observed previously in other mammals bearing mixed adult muscle fibers and which undergo transitional stages in muscle ontogeny. However, in Myotis pectoralis, this transition transpires relatively early in development.

Temporal appearance of satellite cells during myogenesis

In this study, differences between fetal and adult myoblasts in clonal and high density culture have been used to determine when adult myoblasts can first be detected during avian development. The results indicate that avian adult myoblasts are apparent as a distinct population of myoblasts during the midfetal stage of development. Three different criteria were used to differentiate fetal and adult myoblasts and demonstrate when adult myoblasts become a major proportion of the myoblast population: (1) differences in slow myosin heavy chain 1 (MHC1) isoform expression, (2) initiation of DNA synthetic activity, and (3) average myoblast length. Fetal chicken (ED10-12) pectoralis muscle (PM) myoblasts form myotubes that express slow MHC1 after prolonged culture, while adult chicken PM myoblasts do not. Fetal avian myoblasts were active in DNA synthesis and large when first isolated, reaching peak rates of synthesis by 24 hr in culture, while adult myoblasts were inactive in DNA synthesis and small when first isolated, only reaching peak rates of DNA synthesis and size at 3 days of incubation. A dramatic decrease in the percentage of muscle colonies with fibers that expressed slow MHC1 was observed between the midfetal stage and hatching in the chicken, along with a corresponding decrease in myoblast DNA synthetic activity and average length during this same period in both the chicken and the quail. Myoblast activity and average length increased again 3-4 days posthatch and a small transient increase in the number of slow MHC1-expressing clones was also associated with the massive growth of muscle that occurs in the neonatal bird. We conclude that adult myoblasts are present as a distinct population of myoblasts at least as early as the midfetal stages of avian development.

Analysis of heterogeneous fluorescence photobleaching by video kinetics imaging: the method of cumulants

The method of cumulants has been applied to digital video fluorescence microscopy. The method is used to reconstruct the distribution of fluorescent molecules before the initiation of fluorescence photobleaching, and to characterize heterogeneous photobleaching by imaging one or more of the cumulants of the bleaching decay rate. Using the pipelined pixel processor of the image analysis system for the bulk of the calculations, rather than the general-purpose host-computer CPU, the video kinetics imaging can be performed in near real-time. The method is applied to chick embryo myotubes labelled with fluorescein-conjugated alpha-bungarotoxin. The pre-bleach fluorescence distribution is derived, and the image of fluorescein fluorescence is separated from glutaraldehyde-induced autofluorescence on the basis of the spatially resolved average photobleaching decay rate.

Temporal and tissue-specific expression of myosin heavy chain isoforms in developing and adult avian muscle

We have raised monoclonal antibodies (Mabs) to myosin heavy chain isoforms (MHCs) that have specific patterns of temporal expression during the development of quail pectoral muscle and that are expressed in very restricted, tissue-specific patterns in adult birds. We find that an early embryonic, a perinatal, and an adult-specific, fast myosin heavy chain are co-expressed at different levels in the pectoral muscle of 8-12 day quail embryos. The early embryonic MHC disappears from the pectoral muscle at approximately 14 days in ovo, whereas the perinatal MHC persists until 26 days post-hatching. The adult-specific MHC accumulates preferentially and eventually completely replaces the other isoforms. These Mabs cross-react with the homologous isoforms of the chick and detect a similar pattern of MHC expression in the pectoral muscle of developing chicks. Although the early embryonic and perinatal MHC isoforms recognized by our Mabs are expressed in the pectoral muscle only during distinct developmental stages, our Mabs also recognize MHC isoforms present in the heart and extraocular muscle of adult quail. Immunofingerprinting using Staphylococcus aureus protease V8 suggests that the early embryonic and perinatal MHC isoforms that we see are strongly homologous with the adult ventricular and extraocular muscle isoforms, respectively. These observations suggest that at least three distinct MHC isoforms, which are normally expressed in adult muscles, are co-expressed during the early development of the pectoral muscle in birds. In this respect, the pattern of expression of the MHCs recognized by our Mabs in developing, fast muscle is very similar to the patterns described for other muscle contractile proteins.

The earliest form of C-protein expressed during striated muscle development is immunologically the same as cardiac-type C-protein

A monoclonal antibody (C-315) specific for cardiac-type C-protein was prepared and, in combination with other antibodies specific for fast and slow skeletal muscle C-proteins, it was used to investigate the expression of C-protein isoforms in developing striated muscle cells in vivo and in vitro. During embryonic development of skeletal muscles, a C-protein recognized by C-315 appeared first but only transiently, it being replaced subsequently by two other isoforms recognized by the antibodies to slow and fast skeletal muscle C-proteins in a fiber-type specific manner as previously demonstrated (Obinata et al. (1984) Develop. Biol. 101, 116-124). In contrast, only cardiac-type C-protein was detected in cardiac muscle throughout the developmental stages. When myogenesis in vitro was monitored using the same antibodies, C-315 binding appeared first in multinucleated myotubes as in vivo which was followed by the sequential expression of two other C-protein variants. The reactivity of C-315 as well as that of anti-slow and anti-fast skeletal C-protein antibodies persisted during muscle development in culture. Thus, this study demonstrates that the earliest form of C-protein expressed in striated muscles may either be a cardiac-type isoform or a unique embryonic protein containing an epitope in common with the adult cardiac-type protein, and that transitions of C-protein isoform expression characteristic of each fiber-type occur during muscle development in vivo but not in vitro.

Myomesin and M-protein: expression of two M-band proteins in pectoral muscle and heart during development

The expression of the myofibrillar M-band proteins myomesin and M-protein was studied in chicken pectoral muscle and heart during differentiation using monoclonal antibodies in a double-antibody sandwich enzyme-linked immunosorbent assay, immunoblotting, and immunocytochemistry. In presumptive pectoral muscle, myomesin accumulated first, increasing from 2% of the adult concentration at day 7 to 70% by day 16 in ovo. M-protein accumulation lagged 6-7 d behind that of myomesin attaining only 40% of the adult concentration in ovo. The molecular masses of myomesin (185 kD) and M-protein (165 kD) remained constant during embryogenesis. In cultured myogenic cells the accumulation and M-band localization of myomesin preceded that of M-protein by 1.5 d. Chicken heart was shown, in addition to M-protein, to contain unique isoforms of myomesin. In hearts of 6 d embryos, a 195-kD myomesin isoform was the major species; throughout development, however, a transition to a mixture of 195 and 190 kD was observed, the latter being the major species in the adult tissue. During heart differentiation the initial accumulation of myomesin again preceded that of M-protein, albeit on an earlier time scale than in pectoral muscle with M-protein reaching adult proportions first.

Partial aplasia of the pectoralis major muscle with an anomalous distal insertion: two case reports

Two rare cases of subtotal aplasia of the pectoralis major muscle, a residual anomalous formation inserted abnormally into the medial humeral condyle, are discussed.

Persistence of the expression of beta-tropomyosin in dystrophic avian pectoral muscle

The isotype pattern of tropomyosin was investigated in normal and dystrophic avian pectoral muscle using two-dimensional gel electrophoresis. Previous reports have shown that adult pectoral muscle of chickens contains only the alpha-subunit of tropomyosin and a breast-type troponin-T (TN-T), whereas pectoral fetal muscle contains both alpha-and beta-tropomyosin and leg-type TN-T. The change from the fetal to the adult forms begins shortly after hatching. It has been previously reported that avian dystrophic pectoral muscle contains both the leg- and breast-type TN-T; we show that in avian dystrophic muscle there is also persistent expression of the beta-subunit of tropomyosin.

Immunofluorescent and histochemical localization of AMP deaminase in skeletal muscle

Fluorescent antibody staining experiments with both isolated myofibrils and muscle fibers grown in culture show that AMP deaminase is bound to the myofibril in the A band. The strongest staining occurs at each end of the A band. The approximate width of the fluorescent stripes and their relation to the A band remains constant as a function of sarcomere length. Removal of enzyme from the myofibrils leads to loss of staining, and readdition of purified enzyme restores the original staining pattern. A histoenzymatic method for the detection of AMP deaminase activity in cultured fibers gives comparable localization. The results are consistent with the previous observation (Ashby, B. and C. Frieden. 1977.J. Biol. Chem. 252:1869--1872) that AMP deaminase forms a tight complex in solution with subfragment-2 (S-2) of myosin or with heavy meromyosin (HMM).

Sarcotubular development in dystrophic skeletal muscle cells

Dilations of the sarcotubular system and misaligned myofilaments have been reported as early indicators of muscular dystrophy in skeletal muscle. Since the developing tubular component is believed instrumental in initial myofilament alignment during myogenesis, tubular development is evaluated using normal and dystrophic chick embryo skeletal muscle and cultures of normal and dystrophic embryonic pectoral muscle incubated in the presence of horse spleen ferritin. Comparisons of the findings show that periodic tubules are absent from dystrophic somitic muscle and that invaginating tubules from the sarcolemma are found in fewer, randomly located areas of dystrophic pectoral muscle cells. The results indicate that the tubular component is not involved in the bizarre vesiculations seen in mature dystrophic muscle, however, the malalignment of dystrophic myofilaments is probably the result of the poorer development of the T system in this muscle.

Chimaera studies of the origin and formation of the pectoral musculature of the avian embryo

Cervical, brachial, and thoracic somites and brachial somatopleure were transplanted from quail into 2-day chick embryos to determine their contribution to the formation of the pectoralis major muscle. The results show that the musculature of the pectoralis major and pectoralis minor is derived entirely from brachial somites (16-20) while the brachial somatopleure provides much of the connective tissue of these muscles. Migration of somitic cells into the somatopleure appears to begin before the somites are fully formed. The primordium of the pectoralis muscle forms at the base of the wing bud and extends ventro-caudally into the thoracic area to attach to the sternum.