Tissue Growth Patterns Research Articles

Expression of parathyroid hormone-related peptide in human thyroid tumours.

The purpose of this study was to evaluate the distribution of parathyroid hormone-related peptide (PTHrP) in human thyroid tissues. The presence of PTHrP was studied immunohistochemically in 107 consecutive patients with human thyroid tumours. PTHrP expression was revealed in 97.6 per cent of carcinomas, but not in paranodal normal thyroid epithelial cells. Although there were no differences in the incidence of PTHrP positivity among papillary, follicular, and anaplastic carcinoma cases, PTHrP expression levels were correlated with the growth pattern of thyroid cancer. Strong immunopositivity was detected in 67.3 per cent of papillary growth tissues in papillary carcinomas. A tissue growth pattern consisting of colloid-absent follicles had a high incidence of strong immunopositivity irrespective of the histological type of tumour. Anaplastic carcinoma without colloid production also showed strong immunoreactivity in all cases. In contrast, a growth pattern of colloid-rich follicles did not show strong immunopositivity in either papillary or follicular carcinomas. Follicular adenomas showed positive immunostaining in only one case, and no adenomatous goitres showed PTHrP antigens. In situ hybridization and reverse transcription-polymerase chain reaction (RT-PCR) revealed strong PTHrP mRNA in thyroid cancer tissues, but not in normal thyroid tissues. PTHrP expression was not associated with metastasis, calcification, or hypercalcaemia in thyroid cancers. These results suggest that the expression of PTHrP in human thyroids is closely related to the malignant alteration of normal thyroid epithelial cells, especially in the growth pattern of thyroid carcinoma tissues.

Histomorphometric analysis of the repair of a segmental diaphyseal defect with ceramic and titanium fibermetal implants: effects of bone marrow.

We used a rat femoral diaphyseal defect/implant model to quantify the ingrowth of bone, cartilage, and fibrous connective tissue in a comparative study of woven sintered titanium fibermetal and porous hydroxyapatite/tricalcium phosphate ceramic implanted with and without the addition of syngeneic bone marrow cells. The patterns of tissue growth into the implants were analyzed with respect to time, type of implant, and the presence or absence of syngeneic marrow. Significantly more bone was found in ceramic implants than in fibermetal implants, with the addition of syngeneic marrow than without it, and at 4 months than at 2 months. Significantly more bone was found at both time periods in ceramic implants with bone marrow than in any other combination studied. We hypothesize that these findings resulted from interactions between the implanted material and its surroundings, specifically its ability to serve as a substratum for cell attachment, and cells in and around the defect, whether surgically implanted or arising from the soft-tissue bed.

A MATHEMATICAL MODEL OF TUMOR GROWTH WITH SPATIALLY DECREASING DIFFUSION COEFFICIENT OF MITOTIC INHIBITOR

Intercellular diffusion of mitosis inhibiting factors, maintained by proper intercellular contact, is one of the means of transferring “positional information”—a message to peripheral cells of a growing normal tissue instructing them where (at what size of the tissue) to stop their further proliferation by mitotic cell division. This property is commonly known as “contact cell inhibition of mitosis” in biology. In a growing tumor tissue, this regulatory mechanism is absent and as a result, peripheral cells of a tumor tissue, being devoid of any “positional information”, go on dividing successively, increasing the size of the tumor (uncontrolled growth). In this paper, the above idea has been captured in a reaction-diffusion model of tumor tissue growth with a spatially decreasing diffusion coefficient, D(r), of the mitotic inhibitor. This model merely provides an alternative explanation of certain observations on normal and tumor tissue growth. The solutions of the simple model (with (i) D=constant for normal tissue growth and (ii) D=D(r) for tumor tissue growth), discussed in this paper, quite reasonably agree with the characteristic patterns of normal and tumor tissue growth.

The Esthetic Impact of Orthodontics: Planning Treatment to Meet Patients’ Needs

Successful orthodontic therapy in the growing patient involves the coordination of mechanotherapy, growth modification techniques, knowledge of hard and soft tissue growth patterns and patient motivational techniques. These cases represent differing types of Class II malocclusions in which the causes and treatment solutions were quite varied. The differing esthetic needs used treatment plans designed after a careful, problem-oriented assessment of the patient's needs. In each case, the success involved appropriate timing, differential diagnosis, excellent patient cooperation and the design of treatment plans to satisfy occlusal and esthetic goals. Teamwork between general practitioners and orthodontists is critical in meeting patients' needs.

The effect of breed-type and castration on tissue growth patterns and carcass composition in cattle

Records from 210 cattle (119 bulls and 91 steers) of four breed-types slaughtered from approximately 200 to 800 kg live weight, were used to test the hypothesis of similar gender dimorphism among breed in relation to tissue growth patterns and carcass composition. The propensity for muscle growth decreased and that of fat accretion increased with the increase in carcass weight. Compositional differences among breed-types arose from differential growth rates of muscle, bone and fat. Differences in the proportion of fat among breed-types was a result of differences in onset of fattening coupled with nonsignificant differences in relative growth rate of fat. Compositional differences between bulls and steers resulted mostly from earlier and more rapid fattening in steers plus a high and more pronounced impetus for muscle growth in bulls. Differences between genders in carcass composition became more pronounced with increasing weight. Breed-type by gender interactions in composition resulted from a greater gender dimorphism in the later fattening breed-types, the effect of castration being more marked in these types.

Transmural distribution of myocardial tissue growth induced by volume-overload hypertrophy in the dog.

Although chronic volume overload is thought to induce uniform cardiac enlargement, the stimulus for tissue growth has not been defined. Changes in diastolic and systolic stress or strain have been proposed as mechanical factors that may stimulate hypertrophy. Since there are thought to be transmural variations in these stresses and strains, three-dimensional patterns of myocardial tissue growth may provide insight into the role of these factors. To assess the transmural variation in tissue growth after volume overload, the configurations of three columns of four to six gold beads (1-mm diameter) implanted in the left ventricular anterior free wall were recorded in five dogs before and after cardiac enlargement induced by creating a systemic arteriovenous fistula. Data were obtained with end-diastolic pressures adjusted to the same level in the control and hypertrophic states. End-diastolic wall thickness remained constant, whereas left ventricular diameter increased. Small increases in transmural systolic strain were seen. The volumes defined by four beads (a tetrahedron) at end diastole showed increases in myocardial mass of 20-27% after 3.6 (mean) weeks of hypertrophy and were uniform across the wall of the left ventricle. The edges of single bilinear-quadratic finite elements were fitted to the three columns of the bead set at end diastole in control and at end diastole after hypertrophy at equal end-diastolic pressures. Thus, continuous transmural strain distribution were obtained at the hypertrophic state with respect to the control state. The transmural distributions of these end-diastolic growth strains were uniform and positive for both the circumferential and longitudinal components measured in a cardiac coordinate system, with small radial growth strain indicating that growth was predominantly parallel to the epicardial tangent plane. Moreover, when strains were transformed (rotated) to fiber coordinates, in-plane fiber and cross-fiber growth strains were both positive at all locations across the wall and approximately equal in magnitude, indicating considerable growth in the cross-fiber direction. These results indicate that the stimulus for volume-overload hypertrophy may be constant across the wall and that substantial cross-fiber growth occurs during volume-overload hypertrophy.

Growth characteristics and carcass composition of pigs with known genotypes for stress susceptibility over a weight range of 70 to 120 Kg

ABSTRACTA total of 805 Lacombe pigs of different genotype with respect to halothane sensitivity (halothane positive, nn = 205; heterozygote, Nn = 214; halothane negative, NN = 386) were slaughtered over a range in live weight (70 to 120 kg) to assess tissue growth patterns using the allometric equation (y = aXh). The nn genotype was older at slaughter than the NN genotype, but pigs from each genotype were killed over a similar weight range. The relative growth of the primal cuts was influenced by genotype, with nn pigs having a lower coefficient for the bottom shoulder (picnic) and a higher coefficient for the belly. The relative growth of bone was similar for genotypes (P > 0·05) but the relative growth of lean was lower and the relative growth of total fat and depot fat (subcutaneous and intermuscular) was higher for the nn genotype compared with the Nn and NN genotypes. On a within-tissue basis, the relative growth of the tissues in each primal was similar, except for the ham, where the relative growth of lean was higher for nn pigs compared with the two other genotypes. Small differences in tissue distribution were evident, but seldom exceeded 30 g/kg. Although nn pigs had a higher lean content and higher lean: bone ratio than Nn or NN pigs at similar live weights, their relative advantage in composition decreased with increasing live weight.

REDUCED RATE OF ADIPOSE TISSUE GROWTH AND LIPID ACCUMULATION IN MICE SELECTED FOR HIGH BODY WEIGHT

To elucidate the influence of high body weight selection on tissue growth patterns, adipose tissue growth and lipid accumulation were investigated in both a line of mice selected for high 42-day body weight (High line; HL-3) and an unselected (Foundation; FP-3) population. All comparisons between the two lines were performed on a within-sex basis. Logistic growth curve analysis revealed that HL-3 mice exhibited an accelerated growth rate, and reached a higher mature body weight, than FP-3 mice. Employing the allometric equation, Y = aXb, this investigation further revealed that, relative to both body weight and nonadipose tissue weight, adipose tissue and extractable lipid increased slower in HL-3 mice than in FP-3 mice. Only at fixed body and nonadipose tissue weights, which exceeded the maximum weights achieved by the FP-3, did HL-3 adipose tissue and lipid weights exceed those of FP-3 mice. HL-3 mice have previously been demonstrated to exhibit an increased appetite. Therefore, the existing model of selection-mediated compositional changes should be expanded to allow the coupling of an increased appetite with an enhanced relative rate of nonfat tissue growth. Key words: Growth-selected mice, adipose tissue growth, lipid accumulation

Growth responses in a mutant dwarf rat to human growth hormone and recombinant human insulin-like growth factor I.

A new mutant GH-deficient dwarf rat has been used to study the effects of iv infusions of human GH (hGH) and recombinant human insulin-like growth factor I (hIGF-I). This animal has only about 5% of normal pituitary GH content, low circulating GH levels, and no regular GH surges. The defect seems to be specific for GH. Infusions of hIGF-I at 180 micrograms/day for 9 days elevated serum IGF-I concentrations significantly over those in the saline-infused controls (713 +/- 20 ng/ml vs. 395 +/- 31 ng/ml); hGH infusions did not raise IGF-I levels significantly (435 +/- 20 ng/ml). Gel filtration of serum samples showed that the high-dose hIGF-I infusions increased free IGF concentrations, without apparently altering the pattern of IGF-I binding whereas hGH infusions increased the amount of high mol wt IGF-I binding protein. Neither IGF-I nor hGH infusions affected the small amounts of rat GH present in the dwarf rat pituitary glands. Continuous iv infusions of hGH (200 mU/day for 9 days) stimulated body wt gain (2.1 +/- 0.2 g/day) and bone growth (96 +/- 9 microns/day) significantly compared to saline-infused dwarf rats (1.2 +/- 0.3 g/day and 43 +/- 3 microns/day). Infusions of hIGF-I at 180 micrograms/day produced a body wt gain (2.1 +/- 0.5 g/day) similar to that seen in the hGH-infused group but a significantly smaller stimulation of bone growth (63 +/- 3 microns/day). Infusion of a 5-fold lower dose of hIGF-I (36 micrograms/day for 9 days) had no effect on body wt or bone growth. Food intake was unaffected by either hGH or hIGF-I infusions. The pattern of tissue growth was affected differentially by hGH and IGF-I infusions that produced the same overall body wt gain. hGH induced a relatively proportional growth in most of the organs studied, whereas hIGF-I infusion at 180 micrograms/day stimulated a disproportionately greater growth of the kidney, adrenals, and spleen. In some of the animals, tissues were extracted for RIA of IGF-I; the amounts of IGF-I in the liver were similar in control, hGH, or IGF-I-infused animals, whereas kidney and adrenals from IGF-I infused animals contained larger amounts of immunoreactive IGF-I than did those tissues from hGH-treated rats. Thus, both hGH and hIGF-I can promote growth in the mutant dwarf rat, but they differ both quantitatively and qualitatively in their pattern of actions.

An assessment of the relationship between tissue growth patterns and selected hormone profiles among sex phenotypes in cattle

ABSTRACTThe four sex phenotypes were used to study the relationship between carcass composition and serum profiles of hormones thought to affect growth. Forty calves (10 bulls, 10 steers, 10 heifers and 10 ovariectomized heifers) from Hereford dams crossed with Simmental-Hereford bulls (¾ Simmental-¼ Hereford) were given a high energy diet from 10 to 16 months of age. Sequential blood samples (20-min intervals) representing 6-h windows were obtained from each animal at the outset of the experiment and at 28-day intervals thereafter. Samples were assayed for growth hormone (GH), insulin, triiodothyronine, cortisol, testosterone, oestradiol-17β, urea and albumin. The 9-10-llth rib was dissected into fat, lean and bone, and chemical analysis was performed on the dissected soft tissue. Bulls accumulated more lean tissue and less fat than any other group. Heifers and ovariectomized heifers accumulated the least lean and most fat while steers were intermediate between bulls and the two heifer groups. Bulls may have accumulated more lean and less fat than the heifers due to higher GH and testosterone concentrations, and lower circulating concentrations of cortisol and insulin. The known function of these four hormones and their relative concentrations between bulls and the two female groups were consistent with their suggested role in the relative carcass compositions. The intermediate composition of the steer carcass may have resulted from an interplay between the proteogenic influence of higher GH concentrations, the proteolytic influence of elevated cortisol, the absence of testosterone and the lipogenic influence of higher insulin.

Breed and sex effects on the development and proportions of muscle, fat and bone in pigs

SummaryThe development and proportions of muscle, fat and bone were studied in 341 entire male and female Iron Age (European Wild Pig × Tamworth), Pietrain and Large White pigs ranging in live weight from 12 to 370 kg. The number of pigs was: Large White, 138 entire males and 112 females; Pietrain, 41 entire males and 31 females; Iron Age, eight entire males and 11 females. The breeds and sexes were compared in terms of the allometric growth coefficients of tissues (b) and of tissue weights at constant side weight and constant weight of total side bone.At the geometric mean for side weight (26·5 kg), Pietrain carcasses had the most muscle (16 kg), followed by Large White (15kg) and Iron Age (11 kg), but the least fat (6 kg). Large White and Iron Age carcasses had 7 and 12 kg of fat, respectively. Relative to side weight, the earliest maturing tissue, bone, was particularly slow growing in Iron Age pigs (b = 0·627) and relatively fast growing in Large Whites (b = 0·801). The opposite was true for fat, the latest maturing tissue, and consequently Iron Age (b = 1·345) and Large White (b = 1·164) pigs were identified as early and late maturing, respectively. Pietrains had a higher growth coefficient for fat relative to side weight (b = 1·249) and lower growth coefficient for bone (b = 0·713) than Large Whites. The difference in percentage fat between Pietrains and Large Whites decreased slightly between 65 and 120 kg live weight. In terms of tissue growth patterns, Pietrains therefore demonstrated early maturing characteristics compared with Large Whites, and it is possible that a low voluntary feed intake under ad libitum feeding conditions prevents them from expressing these characteristics in terms of percentage of fat in the side. Pietrains had a particularly high muscle:bone ratio (6·2 at the mean side weight) compared with Large White (5·2) and Iron Age pigs (5·3).The difference in carcass composition between entire males and females was breeddependent. Entire male carcasses were slightly leaner overall and had a lower muscle: bone ratio than those of females, but tissue allometric growth patterns were similar in the two sexes.

Ultrastructural studies in the preoperative cytologic diagnosis of soft tissue tumors.

A consecutive series of 100 patients operated on for lesions that were assumed to be soft tissue tumors, all of whom had been the subject of fine-needle aspiration in the preoperative investigation, is described. A correlative study of smears and the light- and electron-microscopic findings of embedded fine-needle aspirates and the histopathology of the surgical specimens was performed. Eighty of the lesions were found to be genuine soft tissue tumors, of which 51 were sarcomas. The other 20 cases were either metastatic carcinoma, malignant melanoma, or malignant lymphoma. The embedding technique produced additional light-microscopic information about tissue structure and growth pattern, and electron-microscopic information about tissue and cell differentiation of importance to the diagnosis. In the case of certain types of soft tissue tumor, such as lipoma, neurilemmoma, liposarcoma, and malignant fibrous histiocytoma, and for well-differentiated metastatic carcinoma and pigmented malignant melanoma, the diagnosis may be strongly suggested by the appearance of the smears; the embedding technique serves to further support the diagnosis. In the case of small round-cell malignancies, the ultrastructural examination proved to be of special value, ie, in the distinction of rhabdomyosarcoma, poorly differentiated metastatic small cell carcinoma and malignant melanoma, and occasional cases of malignant lymphoma. Spindle cell sarcomas, such as leiomyosarcoma when well differentiated, biphasic synovial sarcoma when it includes glandular structures, and malignant hemangiopericytoma, could be recognized ultrastructurally, although electron-microscopy generally failed to reach a definite diagnosis as to the subtype in most cases of poorly differentiated spindle-cell sarcoma.

Effects of neonatal methylmercury exposure on adrenergic receptor binding sites in peripheral tissues of the developing rat

Neonatal exposure to methylmercury produces changes in patterns of tissue growth and function, in part, due to alterations in adrenergic neuronal input. To explore the mechanisms by which these changes come about, newborn rats were exposed to methylmercury (1 or 2.5 mg/kg per day) throughout the preweaning stage and the ontogeny of adrenergic receptor binding sites evaluated in liver, kidney, heart and lung, using [ 3H]prazosin ( α 1-receptors), [ 3H]rauwolscine ( α 2-receptors) and [ 125I]pindolol (β-receptors). In the kidney, methylmercury caused decreases in β- and α 1-receptor binding and increases in α 2-binding; previous work has shown that β-receptor-mediated responses are generally enhanced in methylmercury-exposed pups, and the down-regulation of β-receptor binding thus probably represents a compensatory action secondary to alterations in post-receptor coupling mechanisms. The effects of methylmercury on hepatic adrenergic receptors were different from those seen in the kidney, with substantial elevations in β- and α 1-receptor binding apparent in the preweaning stage; this agrees also with the differences in effects of the mercurial on trophic reactivity and growth in the 2 tissues. Despite the fact that methylmercury causes activation of neonatal cardiac sympathetic nerves, β-receptor binding sites in the heart were unaffected by methylmercury exposure; the failure to down-regulate cardiac postsynaptic receptors in the face of increased nerve activity again represents an anomaly of synaptic regulatory function. These results indicate that methylmercury alters adrenergic responsiveness, in part, through actions on the development of receptor binding sites, and further, that the organ-specificity and receptor subtype-selectivity are consistent with subsequent effects of the organomercurial on adrenergic participationin target organ growth; however, changes in receptor binding alone do not account for all of the effects of methylmercury on synaptic activity or trophic responses.

GROWTH PATTERNS OF MUSCLE, FAT AND BONE, AND CARCASS COMPOSITION OF DOUBLE MUSCLED AND NORMAL CATTLE

Eighteen Double Muscled (DM), 18 Beef Synthetic (SY) and 18 Hereford (HE) bulls were serially slaughtered from approximately 250 to 800 kg liveweight to determine the influence of maturity type and "double muscling" on tissue growth patterns and compositional differences which were examined by using the allometric equation Y = aXb after transformation to common logarithms (log10). As liveweight (LW) increased, the proportions of total side fat (TSF) and subcutaneous fat (SCF) increased, the proportions of total side muscle (TSM) and intermuscular fat (IMF) remained relatively constant and the proportion of total side bone (TSB) decreased. Relative to LW, DM had a similar growth rate for TSM and lower growth rates for TSF, SCF and IMF than HE and SY. All breed types had similar growth rates for TSB on LW. Relative to dissected side weight (DSW) and TSB, the DM bulls had a higher growth rate for TSM than did the HE and S Y bulls. Differences existed between DM and the more normal genotypes in carcass composition. DM was characterized by a high muscle:liveweight ratio, a high proportion of muscle in the carcass, high muscle:bone and muscle:fat ratios and a low proportion of fat compared to the more normal genotypes. Objective criteria to discriminate between HE and DM were SCF, muscle:bone and TSMTMF ratios, and between SY and DM were TSB and muscle:bone ratio. Key words: Beef bulls (young), growth patterns, carcass composition, double muscling, breed type

Acinic cell adenocarcinoma. A clinicopathologic analysis of 294 cases.

Two hundred and ninety-four cases of acinic cell adenocarcinoma were reviewed for the purpose of defining the clinical parameters and determining the distribution of the four histomorphologic tissue patterns and five cell types for correlation to biologic behavior. The vast majority occurred in the parotid gland. There was a male predominance and a peak incidence in the third decade of life. The tumors were usually less than 3 cm in diameter and were slow growing. Pain was a common symptom, but was not indicative of prognosis. Nearly one half of the neoplasms exhibited multiple tissue growth patterns, and three fourths of the tumors displayed more than one cell type. The microcystic pattern was seen most frequently, regardless of the biological behavior of the tumors. The well-differentiated acinic cell was the most prevalent cell type except in cases with metastases, where the intercalated-duct cell type was slightly more frequent. Follow-up of 244 cases revealed a recurrence rate of 12%, a metastatic rate of 7.8%, and death rate of 6.1%. Since all histomorphologic patterns and cell types were manifest in tumors which recurred, metastasized, or caused the death of the patients, it seems appropriate to consider these neoplasms as low-grade adenocarcinomas rather than essentially benign with occasional unpredictable malignant behavior.

Tissue growth patterns in the carcasses of water buffalo and Friesian crossbred cattle—part 1: Individual muscles and anatomical muscle groups

The left sides of the carcasses of twelve Egyptian buffalo, nine half Friesian (♂ Friesian x ♀ Egyptian Baladi) and nine three-quarter Friesian (♂ x ♀ half-Friesian) bulls, serially slaughtered between 161 and 560 kg for buffaloes and between 176 and 448 kg for cattle, were used to describe the growth and distribution of individual muscles and muscle groups. Genotype-group differences in the relative rate of growth were not significant in 85 of 89 muscles and in 8 of 9 muscle groups. The pooled within-group growth coefficients of individual muscles revealed different increasing growth gradients, i.e. disto-proximal in both limbs, mediolateral in the proximal pelvic limb, from elbow flexors to shoulder flexors in the proximal thoracic limb, caudo-cranial in the trunk and from hypaxial to epaxial muscles around the spinal column. The relative growth was lowest in the distal part of the limbs and highest in the anterior part of the carcass (SMG 7 and 8), with the loin and abdominal muscle groups growing at a rate similar to that of the total muscle. The neck and thorax muscle group grew at a higher rate in Friesian crosses than in buffaloes. Genotype-group differences in the weight of each muscle relative to total side muscle (TSM) were significant in 50 of 89 muscles. Of the 50 muscles (constituting around 59% of TSM), 24 (approximately 44% of TSM) were from the expensive muscle groups. As compared with the most different Friesian cross (base = 100) at equal TSM, buffaloes had higher weight of muscle in the hindlimb (107·5% proximally; 106·3% distally) and forelimb (120·0% proximally: 104·6% distally) and significantly less weight of the muscle groups forming the abdominal wall (79·8%) and connecting the forelimb to the thorax (89·1%) and to the neck (90·7%). The weight of the combined expensive groups was significantly greater in buffaloes than in cattle (maximum difference = 1·8 kg) with a tendency for buffaloes to have relatively less of the tender muscles surrounding the spinal column.

Tissue growth patterns in the carcasses of water buffalo and friesian crossbred cattle: Part 2—individual bones and anatomical bone groups

Twelve Egyptian buffalo, nine ♂ Friesian × ♀ Egyptian native Baladi (half Friesian) and nine ♂ Friesian × ♀ half Friesian (three-quarter Friesian) bulls were serially slaughtered between 161 and 560 kg for buffaloes and between 176 and 448 kg for cattle. Anatomical dissection data from the left sides of the carcasses were used to examine the growth of individual bones and bone groups. No significant genetic differences with respect to the growth patterns of bones relative to total side bone were reported, indicating that bones followed similar patterns in buffaloes and cattle. Differential growth of bones occurred following an increase of impetus from cervical vertebrae to os sacrum and with growth coefficients for bones of the forelimb correspondingly higher than for the hindlimb and the entire axial and appendicular skeletons following, respectively, late- and early-maturing patterns. Some significant, though minor, differences between buffaloes and cattle were found when weights of individual bones were adjusted to constant side bone weight. As compared with Friesian crosses, buffaloes had more weight of the ribs and less weight of the vertebral column in the axial skeleton, and more weight of radius-and-ulna and less weight of scapula in the forelimb at equal total bone. There were no significant differences between buffaloes and Friesian crossbreds in the proportion of total bone occurring in the entire hindlimbs and forelimbs and in the distribution of total bone between axial and appendicular skeletons.

The establishment of a somitomeric pattern in the mesoderm of the gastrulating mouse embryo.

Mesoderm formation in the mouse embryo begins at 6.5-6.75 days p.c. (postcoitum) when a primitive streak is formed along the posterior side of the egg cylinder. Epiblast cells in a localized region separate from one another and spread laterally between the primitive endoderm and the rest of the epiblast. The newly formed mesoderm contributes to both embryonic and extraembryonic regions. When the endoderm is removed, a definitive somitomeric pattern is first observed in the lateral sings of mesoderm of the mid-primitive-streak-stage embryo. The sequential appearance and the placement of somitomeres in the gastrulating mouse embryo are closely related to the general changes in physical dimensions and to the pattern of tissue growth which occur during the maturation of the egg cylinder. By the late-primitive-streak stage, about four somitomeres are present in the paraxial mesoderm on either side of the embryonic axis. These somitomeres will undergo morphogenesis and give rise to the cranial segments and head mesenchyme of neurulating embryos (Meier and Tam, 1982). The midline or axial mesoderm, consisting of prechordal plate and notochord, is derived from the head process mesoderm originating from the anterior end of the primitive streak. Cells of the head process are compact and adherent to the endoderm. The early presence of a somitomeric pattern which persists and is added to throughout subsequent phases of mesoderm formation suggests that spreading mesodermal cells have relatively stable neighbor relationships. This morphological evidence supports the idea that the expansion of the mesoderm during gastrulation results from tissue growth and progressive deposition of cells from the primitive streak. Cell migration may be limited principally to nonsomitomeric mesodermal cells found in the leading edge of the spreading lateral wings.

A histological examination of tissue culture initiation from immature embryos of maize

The tissue origin, growth patterns and organization ofin vitro tissue cultures initiated from immature maize (Zea mays L.) embryos were cytologically examined. Examination of thick sections from initiating cultures indicated that the scutellum is the tissue of origin. During culture initiation the scutellum, especially in the region of the epithelium, becomes highly meristematic and proliferates rapidly. These cultures were characterized by a cambial zone which provided for extendedin vitro proliferation and by apical meristems developing on the culture surface. These meristems developed to the two leaf primordia stage under the cultural conditions of this study. Differentiation of root primordia associated with the apical meristems was not observed. The apical meristems appeared to arisede novo at the tissue surface and were probably multicellular in origin. The observations are discussed in relation to their significance concerning mutation and selection.

Growth of bovine tissues 1. Genetic influences on growth patterns of muscle, fat and bone in young bulls

AbstractCarcass composition and growth patterns for muscle, fat and bone were compared among 277 young male progeny of eight sire breeds, serially slaughtered at 300 kg live weight, 12 months and 15 months of age. The sire breeds were Simmental (SIM), Charolais (CHA), Danish Red and White (DRK), Romagnola (ROM), Chianina (CHI), Hereford (HER), Blonde d'Aquitaine (BDA) and Limousin (LIM). Tissue growth patterns among breeds were examined by regression estimates from the allometric growth equation (Y = axb) and compositional differences were estimated from the intercepts. No significant sire breed differences were found in the regression of muscle, fat or bone on various size dimensions. In regressions involving fat, however, the fattest (HER) had higher regressions and the leanest (BDA) fattened more slowly relative to muscle and bone growth. Breeds differed significantly in amount of muscle, fat and bone when compared at standard weights.Sire breed ranking for muscle at common bone weights was LIM, BDA, CHA, SIM, HER, ROM, DRK and CHI, while at common carcass weights the ranking was BDA, CHA, LIM, CHI, ROM, SIM, DRK and HER, reflecting differences in fatness. Minor changes in ranking occurred when comparisons were made at a common live weight reflecting differences in dressing percentage. For fat at standard muscle, carcass or live weight the breeds ranked HER, LIM, DRK, SIM, ROM, CHA, CHI and BDA.