Proliferative Layer Research Articles

Ras Mutations and expression in head and neck squamous cell carcinomas

Mutational activation and overexpression of the family of ras proto-oncogenes have been associated with many human tumors. The role of mutations of H-ras, K-ras, and N-ras, as well as expression of the respective protein products (p21s) in normal mucosa, dysplastic mucosa, and squamous cell carcinomas (SCCs) of the head and neck has not been fully described. In our study, 51 tumors (40 paraffin embedded and 11 fresh frozen) were examined to determine if mutational activation of ras is an important molecular event in head and neck SCC. Analyses of codons 12, 13, and 61 of H-ras, K-ras, and N-ras revealed no mutations, suggesting that mutational activation of ras is not important in the majority of head and neck SCCs. Immunocytochemistry (ICC) was used to define the expression of H-ras, K-ras, and N-ras in normal mucosa, dysplastic mucosa, and SCC of the head and neck and to determine if expression of ras family members correlated with early or late events in the development of SCC. Expression of p21N-ras in nine samples of histologically normal head and neck mucosa revealed moderate staining in the basal proliferative layers with progressively less staining as cells matured. The most superficial layers of normal mucosa failed to express p21N-ras. A low level of p21H-ras was expressed in all layers of normal mucosa while K-ras was not expressed. ICC of SCC tumor sections revealed cytoplasmic expression of N-ras in nine of nine tumors, H-ras in five of nine tumors, and K-ras in one of nine tumors. Expression of H-ras, K-ras, and N-ras in head and neck SCC was not related to histologic differentiation or TNM staging; however, p21N-ras was overexpressed in seven of nine tumors. Furthermore, the pattern of N-ras expression in dysplastic lesions revealed expression in all layers of the mucosa in contrast to normal mucosa, which expresses p21N-ras primarily in the basal proliferative layer. The change in p21N-ras expression pattern in dysplastic mucosa and its overexpression in the majority of tumors suggest that loss of control of N-ras expression may be an early step in carcinogenesis of head and neck SCC.

Expression of neuron-specific tubulin defines a novel population in the proliferative layers of the developing telencephalon

We have used a monoclonal antibody against the neuron-specific class III beta-tubulin (TuJ1; Lee et al., 1990b) to study the distribution and morphology of immature neurons in the proliferative ventricular and subventricular zones of the developing telencephalon. Mouse brains from embryonic day 12 (E12) to postnatal day 5 (P5) were fixed either with a non-cross-linking agent, HistoChoice, or with 4% paraformaldehyde, and processed for TuJ1 immunohistochemistry. TuJ1 immunoreactivity first appeared in the proliferative zones of the developing cerebral cortex at E13-E14 as the cortical plate was emerging. After E14, tangentially oriented TuJ1-positive cells were abundant at the interface between the ventricular and subventricular zones. This tangential pattern was less conspicuous in the developing striatum. Within the cortical and striatal ventricular zone TuJ1-positive cells were less numerous and displayed a variety of orientations and morphologies. Postnatally, after the period of neurogenesis has ended, TuJ1 immunoreactivity continued to increase in the subventricular zone and remained high until the last developmental stage examined (P5). Anti-MAP2, another neuron-specific marker, never labeled the cells of the ventricular and subventricular zones, pre- or postnatally. To determine the birthdates of TuJ1-positive cells in the cortical-ventricular and subventricular zones, brains were double labeled with TuJ1 and bromodeoxyuridine according to different pulse-chase schedules. TuJ1-positive cells were postmitotic and generated throughout the period of cortical neurogenesis. Collectively, the results suggest that TuJ1 immunoreactivity distinguishes two neuronal populations: those that remain for an indefinite period of time in the proliferative zones, and those that leave the proliferative zones soon after being generated. Although the fate of the TuJ1-positive cells that reside in the proliferative zones remains unclear, their tangentially aligned orientation and their distribution suggest that they migrate independent of radial glial fibers.

Odor deprivation leads to reduced neurogenesis and reduced neuronal survival in the olfactory bulb of the adult mouse

Neurogenesis persists in the olfactory bulbs of adult mice, with new cells being generated in the proliferative subependymal layer. Our previous work has shown that unilateral odor deprivation through naris closure leads to a net loss of granule neurons in the ipsilateral (odor-deprived) olfactory bulb, while not affecting the contralateral bulb. Here we used several experimental approaches to determine if this loss of neurons results from reduced neurogenesis, reduced neuronal survival, or both. First, bromodeoxyuridine immunohistochemistry was used to determine the number of S-phase cells in the subependymal layer eight weeks after naris closure. Proliferation was reduced within and just caudal to the odor-deprived bulb compared to the open-side (control) bulb. Second, counts of pyknotic nuclei four weeks after naris closure were used to document a higher rate of cell death on the deprived side. Third, 3H-thymidine autoradiography was used to assess differences in granule cell survival on the two sides. Granule cell precursors were labeled by a single injection of 3H-thymidine eight weeks after naris closure, and the number of surviving labeled granule cells assessed four and 16 weeks later. Granule cell survival was significantly reduced within the odor-deprived bulbs. These data indicate that the loss of granule cells which follows odor deprivation is caused, at least in part, by reduced neurogenesis and reduced survival of these adult-generated neurons.

Induction of a new metallothionein isoform (MT-IV) occurs during differentiation of stratified squamous epithelia.

A new member of the metallothionein (MT) gene family was discovered that lies about 20 kb 5' of the MT-III gene in both mouse and human. The MT-IV proteins are highly conserved in both species and have a glutamate insertion at position 5 relative to the classical MT-I and MT-II proteins. Murine MT-IV mRNA appears to be expressed exclusively in stratified squamous epithelia associated with oral epithelia, esophagus, upper stomach, tail, footpads, and neonatal skin. The MT derived from tongue epithelium contains both zinc and copper. Many of these epithelia develop parakeratosis during zinc deficiency in the rat. In situ hybridization reveals intense labeling of MT-IV mRNA in the differentiating spinous layer of cornified epithelia, whereas MT-I is expressed predominantly in the basal, proliferative layer; thus, there is a switch in MT isoform synthesis during differentiation of these epithelia. We suggest that MT-IV plays a special role in regulating zinc metabolism during the differentiation of stratified epithelia.

Articular disc and eminence modeling after experimental relocation of the glenoid fossa in growing rabbits.

The articular surface of the glenoid fossa shows some analogy to the mandibular condyle, since the surface is covered by secondary cartilage, which makes the process more elastic than purely bony structures. The condylar cartilage has been shown to be responsive to alterations in load pressures, and this secondary type of cartilage is also able to increase its proliferative activity to a limited extent when the load pressure is altered. The aim here was to measure changes in proliferative activity and type II collagen secretion in the articular surface of the glenoid fossa after steady experimental posterior relocation of the fossa in the rabbit without actively interfering with normal masticatory action. The shape of the articular disc and interrelations of the joint components were measured macroscopically. Twenty-four five-day-old rabbits underwent gluing of the interparietal, temporoparietal, and lambdoidal sutures. Three experimental and 3 control rabbits were injected with tritiated thymidine at 10, 15, 20, and 30 days and were killed after 2 h for histological, autoradiographic, and immunohistochemical examination. The total number of labeled cells in the proliferative layer near the articular eminence was higher in the experimental group, the difference being greatest in the 15- and 20-day-old rabbits. Immunohistochemical examination revealed less staining for type II collagen on the postero-inferior side of the eminence in the experimental group. The articular disc was flattened in the experimental group, and the elastic tissue bundle connecting the articular eminence and the anterior border of the disc was significantly narrower and longer.

Expression and function of the keratinocyte integrins

Human keratinocytes express several adhesive receptors of the integrin family. Expression is normally confined to the basal (proliferative) layer of keratinocytes, both in mature epidermis and during development. Altered expression patterns are observed during wound healing, in psoriasis and in squamous cell carcinomas. Keratinocyte integrins are subject to both transcriptional and post-translational regulation and ligand binding ability can be modulated independently of expression. Studies with cultured keratinocytes suggest a variety of functions for the receptors: adhesion to extracellular matrix proteins, intercellular adhesion, stratification, lateral migration and the regulation of terminal differentiation. Three distinct subpopulations of basal keratinocytes, with characteristics of stem cells, transit amplifying cells and cells committed to differentiate, can be distinguished on the basis of differences in integrin expression and function.

Clonal dispersion in proliferative layers of developing cerebral cortex.

In the adult cerebral cortex, many retrovirally labelled clones are widely dispersed, though the mechanisms of this dispersion are not well understood. Here we investigate the temporal sequence of clonal dispersion after labelling progenitors of rat cortical cells with replication-incompetent retroviruses at early stages of cortical neurogenesis, 14-15 days after conception (E14/15). The location of labelled daughter cells was determined 3, 6 or 10 days later. Labelled sibling cells were radially arrayed three days after infection (E18). In contrast, by six days after infection (E20/21), 43% of cortical clones were dispersed non-radially by at least 500 microns. Four of these widespread clones were dispersed longitudinally by > or = 2 mm, implying sustained rates of dispersion of > 15 microns per hour. Dispersed sibling cells occurred within proliferative zones of the forebrain in 35% of widely dispersed clones, suggesting that some dispersion reflects movement of dividing cells. Some clones dispersed beyond the neocortex into the olfactory bulb. Progenitor cell dispersion represents a previously unrecognized mode of migration by which sibling cells become widely dispersed in the developing forebrain.

Growth hormone induces multiplication of the slowly cycling germinal cells of the rat tibial growth plate.

To study the effect of locally infused growth hormone (GH) or insulin-like growth factor I(IGF-I) on slowly cycling cells in the germinal cell layer of the tibial growth plate, osmotic minipumps delivering 14.3 microCi of [3H]thymidine per day were implanted s.c. into hypophysectomized rats, and GH (1 microgram) or IGF-I (10 micrograms) was injected daily through a cannula implanted in the proximal tibia. The opposite leg served as a control. After 12 days of treatment, the osmotic minipumps were removed, and three rats in each group were given GH (20 micrograms/day, s.c.) for an additional 14 days to chase the labeled cells out of the proliferative layers. Labeled cells remained in the germinal layer, in the perichondrial ring, and on the surface of the articular cartilage close to the epiphyseal plate. GH administered together with labeled thymidine significantly increased the number of labeled cells in the germinal cell layer compared to that in the control leg (ratio = 1.95 +/- 0.13), whereas IGF-I showed no stimulatory effect (ratio = 0.96 +/- 0.04). Therefore GH but not IGF-I stimulates the multiplication of the slowly cycling (label-retaining) cells in the germinal layer of the epiphyseal plate. IGF-I acts only on the proliferation of the resulting chondrocytes.

Prenatal development of GABA-immunoreactive neurons in the human striate cortex

The prenatal development of neurons immunoreactive to γ-aminobutyric acid (GABA) in the striate cortex (area 17) of human foetuses aged from 14 weeks to term was studied immunocytochemically. In the 14 week foetus GABA-immunoreactive cells occurred in all layers of area 17 with the highest density in the marginal zone (MZ), subplate (SP), deep intermediate zone (IZ) and ventricular zone (VZ). The cortical plate (CP), which gives rise to most of the definitive adult cortical layers, had relatively low concentrations of GABAergic cells. By 17 weeks the density in the proliferative VZ had declined. At 20 weeks some of the adult layers were recognisable; the density of GABA-positive neurons was now highest in the definitive cortex, especially the deep layers (layers VI and V), was lower in the superficial cortical plate, and was lowest in IZ, where the white matter would form. The peak of GABA-immunoreactive neuronal density continued to move superficially during development, and was in layer IVc by 30 weeks. The laminar distribution stabilised from 30 weeks with three dense bands: in layer IVc and superficial V, layer IVa, and layers II and superficial III. The tangential distribution of GABAergic neurons was determined in two older brains (32 and 39 weeks) and no unequivocal spatial periodicity was observed in this plane. The mean cross-sectional area of GABAergic neurons in area 17 increased with foetal age, and also increased from superficial to deep layers at each age. Most GABA-immunoreactive neurons in younger brains contained immunonegative or weakly positive nuclei and had few visible processes, while in the older brains most neurons contained positive nuclei and had more visible processes. The proportion of GABA-immunoreactive bipolar cells declined during development while that of multipolar cells increased. GABAergic neurons thus differentiate early in human foetal striate cortex. They are initially most numerous in the proliferative layers deep to the developing definitive cortex; from 20 weeks of gestation, their peak moves superficially into the maturing deep layers (VI and V) and a stable laminar distribution is attained by 30 weeks, with peaks in layers II/IIIm, IVa and IVc/V. There is no obvious horizontal periodic distribution before term.

Visual Demonstration of Growth Hormone Receptors on Human Growth Plate Chondrocytes*

The sites of action of GH in the human infant remain unclear; recent evidence in animals suggests direct actions on growth plate and other tissues. We have used a monoclonal antibody recognizing the human GH receptor to visually identify and localize GH receptors in the human infant growth plate. Sternochondral cartilage was obtained at postmortem from infants dying of sudden infant death (n = 20), and either decalcified, fixed, and cut into longitudinal sections or digested with collagenase for monolayer culture of chondrocytes. Sections of cultured chondrocytes were stained immunocytochemically with a monoclonal antibody recognizing human GH receptor (MAb 263), using an avidin-biotin system. Sternochondral cartilage was also obtained at operation from adolescents undergoing sternochondroplasty. In infant tissue, GH receptor was identified in sections in chondrocytes of the proliferative and hypertrophic layers, in perichondrium, in osteocytes in new bone, and in hemopoietic precursor cells in marrow. Cultured chondrocytes showed heterogeneous staining for GH receptor. With prolonged culture from 5-8 days, the pattern of staining changed from individual cells to groups of cells. [125I]Human (h)GH showed specific binding to chondrocyte monolayer (0.6 +/- 0.3%), confirmed visually on emulsion autoradiography. In support of specificity of MAb263, it was able to displace [125I]hGH from monolayers by 35%. Adolescent cultured chondrocytes failed to demonstrate specific binding of [125I]hGH. We conclude that GH receptors are widely distributed in a range of mesenchyme cells in the human infant growth plate, including bone and hemopoietic precursors. The expression of these receptors appears to be maturation dependent in both intact tissue and culture, while they may no longer be expressed after the peak growth phase of puberty.

An immunohistochemical study of localization of type I and type II collagens in mandibular condylar cartilage compared with tibial growth plate

Immunohistochemical localization of type I and type II collagens was examined in the rat mandibular condylar cartilage (as the secondary cartilage) and compared with that in the tibial growth plate (as the primary cartilage) using plastic embedded tissues. In the condylar cartilage, type I collagen was present not only in the extracellular matrix (ECM) of the fibrous, proliferative, and transitional cell layers, but also in the ECM of the maturative and hypertrophic cell layers. Type II collagen was present in the ECM of the maturative and hypertrophic cell layers. In the growth plate, type II collagen was present in the ECM of whole cartilaginous layers; type I collagen was not present in the cartilage but in the perichondrium and the bone matrices. These results indicate that differences exist in the components of the ECM between the primary and secondary cartilages. It is suggested that these two tissues differ in the developmental processes and/or in the reactions to their own local functional needs.

Differentiation potential of a monoclonal antibody-defined neural progenitor cell population isolated from prenatal rat brain by fluorescence-activated cell sorting

We have studied the differentiation potential in vitro of a subpopulation of neural progenitor cells from BDIX-rat brain. These cells transiently express a cell surface determinant (CSD) specified by monoclonal antibody (Mab) RB13-2 (Kindler-Röhrborn, A. et al., Differentiation 30 (1985) 53–60), and recently identified as a set of 0-acetylated gangliosides (Reinhardt-Maelicke, S. et al., submitted) also recognized by Mab D1.1 (Levine, J.M. et al., J. Neurosci., 4 (1984) 826–831) and partly by Mab JONES (Schlosshauer, B. et al., J. Neurosci., 8 (1988) 580–592), respectively. As analyzed by immunofluorescence, Mab RB13-2 binding brain cells (prenatal days 11–22; postnatal days 7 and 89) were localized in different areas of the proliferative ventricular layer of the prenatal cerebrum and in the external granular layer of the early postnatal cerebellum. No Mab RB13-2 positive brain cells were found in adult brain. Following their isolation by fluorescence activated cell sorting on prenatal day 18, the differentiation potential of Mab RB13-2 binding brain cells was studied by double-immunofluorescence analysis under different conditions of monolayer culture. In the presence of 10% fetal calf serum (FCS), these cells differentiated into glial fibrillary acidic protein (GFAP) positive flat astrocytes, whereas neurons (neurofilament-positive) and a smaller number of stellate astrocytes (GFAP-positive) developed in a chemically defined medium containing 0.5% FCS. Neural progenitor cells binding Mab RB13-2 may thus either retain more than one option for differentiation into specific cell types, or the expression of the CSD specified by Mab RB13-2 may be common to more than one subset of neural progenitor cells (with or without predetermined unidirectional differentiation pathways) whose survival and/or proliferative behavior could be differentially affected by microenvironmental conditions.

Early appearance of tyrosine hydroxylase immunoreactive cells in the mesencephalon of mouse embryos

The development of mesencephalic catecholaminergic neurons in the embryonic and fetal mouse was analysed in tissues fixed with 5% acrolein using polyclonal rabbit antibodies against tyrosine hydroxylase (TH), the first enzyme in catecholamine synthesis. The first TH positive cells were identified as early as day 8.5–9 of gestation and some expressed TH while apparently still migrating from the proliferative layer. The number of catecholamine cells increased dramatically by embryonic day 9.5–10; at gestation days 10.5–11 numerous TH positive cells bearing many neurites were localized in the ventral part of the mesencephalon but they were not yet separated into two different groups (A9 and A10). After 13 days of gestation two separate catecholaminergic groups could be visualized, although many TH positive cells with long neurites (putative dopaminergic neurons) could still be seen at the edges of the ventricle, and appeared to be moving towards the ventral mesencephalon.On the basis of these results the possibility that catecholamine cells that are produced early during the development of the midbrain may have neurotrophic and/or morphogenetic roles is discussed.

Regulation of Protein Adenosine Diphosphate Ribosylation in Bovine Lens during Aging

Adenosine diphosphate-ribosyltransferase (ADPRT) and poly-ADP-ribose glycohydrolase (poly-ADPRG) activities were investigated in the different structures of bovine lenses. These activities and protein ADP ribosylation were detected only in the lens epithelium proliferative layer. The poly-ADPR glycohydrolase activity decreased, but the poly-ADPR polymerase activity increased during aging. In lens epithelial cells of older animals, the poly-ADP-ribose level and average chain length decreased but the chain number increased. Involvement of DNA break accumulation during aging in the increase of ADPRT activity of lens epithelial cells is discussed.

Growth hormone receptors

The receptor for rabbit liver growth hormone (GH) has recently been purified and cloned. Sequencing data demonstrates that this site represents a new class of transmembrane receptor proteins containing covalently linked ubiquitin and N-linked obligosaccharides. Homology with the human GH liver receptor is estimated to be 84%. GH receptors are also present on non-liver cells, however, their function is poorly understood, and it is not yet known if there is homology with the liver site. Direct stimulation of differentiation of preadipocytes to adipocytes by GH has been demonstrated. In bone, binding of GH to the resting cell zone, but not the proliferative layers has been reported. Taken together, these data support the hypothesis of Green and colleagues that GH has a dual mechanism of action which includes direct stimulation of differentiation of precursor cells and a secondary effect of enhancing the clonal proliferative response.

Effects of growth hormone and insulin-like growth factor-I on colony formation of rabbit epiphyseal chondrocytes at different stages of maturation.

The effect of human GH (hGH) and insulin-like growth factor-I (IGF-I) on colony formation of rabbit epiphyseal tibial chondrocytes at different stages of maturation was studied in suspension culture. The epiphyseal growth plate from the proximal tibia of 8-week-old male rabbits was dissected and divided into three different (proximal, intermediate and distal) zones, each zone representing an enrichment of chondrocytes from the germinative, proliferative and hypertrophic cell layers respectively. Chondrocytes from these three zones were isolated by collagenase digestion and cultured in the presence of 10% (v/v) newborn calf serum in suspension stabilized with 0.5% (w/v) agarose for 14 days. The colonies were classified according to diameter and the number of colonies was estimated as a function of colony size (distribution of cloning efficiency). Cell clusters with a diameter of 56 micron or more were classified as colonies. The cloning efficiency (number of colonies formed per 1000 seeded cells) was 10.1 +/- 0.7 and 6.0 +/- 0.8 for chondrocytes isolated from the proximal and intermediate zones respectively. Insulin-like growth factor-I (25-200 ng/ml) increased the number of colonies in chondrocytes isolated from the proximal zone (122 +/- 9.0-156 +/- 8.4%; control value, 100%) and from the intermediate zone (136 +/- 14.0-191 +/- 29%). Low concentrations of hGH (10-40 ng/ml) stimulated colony formation in chondrocytes isolated from the proximal zone (125 +/- 6.4-137 +/- 7.9%) whereas a high concentration of hGH (160 ng/ml) was ineffective. Chondrocytes isolated from the intermediate zone showed no response to low concentrations of hGH (10-20 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in histones H2A and H3 variant composition in differentiating and mature rat brain cortical neurons

Rat brain cortical neurons originate from germinal cells during a period of 6 days immediately before birth. Upon leaving the proliferative layer neurons become irreversibly quiescent. We have previously reported the presence of core histone nonallelic variants in terminally differentiated rat brain cortical neurons. Although the functional significance of core histone variants is unknown, several lines of evidence suggest that the processes of variant replacement could be involved in the structural and functional differentiation of chromatin. Here we describe the changes in core histone composition that occur during postnatal development. The changes in chromatin composition are already apparent at birth, suggesting that the change in synthesis patterns is related to the arrest of cell proliferation and neuron commitment. During postnatal development H2A.2, H2A.x, and H3.3 accumulate, whereas H2A.1, H3.1, and H3.2 decrease. H2A.z is the only variant that remains constant. The time courses of replacement and the observed variant proportions when the variant composition approaches the equilibrium suggest that all H2A variants are synthesized either in germinal cells or in neurons, whereas H3.1 and H3.2 seem to be synthesized only in germinal cells. The extent of the replacement of H3.1 and H3.2 by H3.3 shows that the exchange process affects most of the chromatin. The half-life times of H2A.1 and H3.2 were calculated from their respective exponential decays. Values of 65 days or less and 142 days were found for H2A.1 and H3.2, respectively. The preferential replacement of H2A.1 over H3.2 reinforces the view that the histone core does not degrade as a single unit.

Healing of laser and scalpel incision wounds of rat tongue mucosa as studied with cytokeratin antibodies

The healing process of laser- and scalpel-incision wounds of rat tongue mucosa was investigated by the indirect immunofluorescence technique using a monoclonal cytokeratin antibody (PKK2) binding to low molecular weight keratins of basal keratinocytes, two antibodies reacting with suprabasal keratins and a monoclonal antibody reacting with desmosomes. The wounds were made parallel on both sides of the tongue in thirty animals. In normal tongue only the basal cell layer and the cells at the base of the rete ridges showed PKK2-positivity. In both types of wounds at the same healing phase the whole proliferative cell layer showed a bright PKK2-positivity. The cell proliferation appeared to be confined to all cells of the mucosa. The disturbance in the keratin expression of the healing mucosa could also be revealed with another monoclonal (58CH8) antibody, which reacted only with the suprabasal cells in normal tongue mucosa but lacked reactivity with the healing keratinocytes, whereas polyclonal antibodies to callus keratins showed a bright reactivity also in the healing keratinocytes. Monoclonal antibodies to desmoplakins indicated that the keratinocytes in both types of wounds had normal desmosomal cell-to-cell junctions. As the healing process advanced, the PKK2-positivity regressed to that seen in normal tongue mucosa.

Histomorphometry of age and sex changes in mandibular condyles of young human adults

Changes in cartilage, subchondral bone and their interface were studied using sagittal (6–8 μm thick) sections from the lateral, central, and medial parts of 21 condyles (11 males and 10 females; aged 18–36 years). The presence of undifferentiated mesenchymal (UM) cells in the proliferative zone of the cartilage was noted. Five condyles were judged to be immature because they had hypertrophic cartilage, cartilage resorption and bone formation at the cartilage-bone interface, no compact bone in their anterior and the superior regions, and the many cartilage rests in subchondral bone. Four of these immature specimens were from males. Immature specimens had quantitatively thicker cartilage ( p < 0.01), thinner subchondral bone ( p < 0.005), and less bone, more vascular spaces and more cartilage rests, both at the cartilage-bone interface and in the subchondral bone ( p < 0.001). Of the 16 mature condyles, the older had fewer UM cells in the proliferative layer, thicker compact bone ( p < 0.05), less vascular spaces at the cartilage-bone interface ( p < 0.05) and more bone and less vascular spaces in the compact bone ( p < 0.05 and p < 0.01 respectively). No significant differences were found between mature condyles of males and females, but females had more UM cells, less hyperplastic cartilage and fewer irregularities at the cartilage-bone interface.

Hormonal regulation of longitudinal bone growth.

The regulation of postnatal somatic growth is complex. Genetic, nutritional factors and hormones exert regulatory functions. Hormones that have an established role in the regulation include growth hormone (GH), thyroid hormone and sex steroids. GH promotes mainly the growth of the long bones in terms of final height, while the action of the sex steroids and thyroid hormone is less well known. Longitudinal bone growth is the result of chondrocyte proliferation and subsequent endochondral ossification in the epiphyseal growth-plates. The growth-plate is a cartilaginous template that is located between the epiphysis and the metaphysis of the long bones. GH and insulin-like growth factor-I (IGF-I) have different target cells in the epiphyseal growth-plate. GH stimulates the slowly dividing prechondrocytes in the germinative cell layer while IGF-I promotes the clonal expansion in the proliferative cell layer of a GH primed cell. Thyroid hormone blocks the clonal expansion and stimulates chondrocyte maturation. IGF-I mRNA is primarily regulated by GH, and IGF-I is produced in several tissues such as the liver, muscle, fat and epiphyseal growth plates. However, IGF-I mRNA is also increased during compensatory growth of heart and kidneys and by estrogen in the Fallopian tube in the rat. Nutrition, i.e. energy from fat and carbohydrates and proteins, also influences the final height, but the cellular mechanism of action is not known. The aim of this article is to review hormonal action on longitudinal bone growth.