Calcitonin is expressed in gonadotropes of the anterior pituitary gland: its possible role in paracrine regulation of lactotrope function

Previous studies from this laboratory have shown that salmon (S) calcitonin (CT)-like immunoreactive peptide (CTI) is synthesized and secreted by the anterior pituitary (AP) gland. These studies also co-localized CTI to gonadotropes, and demonstrated that SCT is a potent inhibitor of lactotrope function. However, the molecular structure of putative gonadotrope-derived CTI that inhibits lactotrope function has not been defined. The present studies cloned CT cDNA (pit-CT cDNA) from a mouse gonadotrope L beta T2 cell line using RT-PCR and rapid amplification of cDNA ends (RACE) techniques. Alignment of nucleotide sequences of pit-CT and mouse CT revealed greater than 99% homology between the sequences. The pit-CT cDNA was ligated into a mammalian expression vector, and the construct was transfected into L beta T2 cells. Two stable transfectant cell lines (CT.U6/A and B) were obtained by selection in G418. Subsequent S1-nuclease protection assay and immunocytochemistry results have shown that: (1) pit-CT peptide expressed by CT.U6 cell lines immunoreacted with GCT1-anti-SCT serum; (2) secretions of CT.U6 cells inhibited prolactin (PRL) release, PRL mRNA abundance and DNA synthesis of PRL-secreting GGH3 cells; and (3) CT.U6-induced inhibition was abolished by GCT1-anti-SCT serum. The studies also generated a riboprobe from the cloned pit-CT cDNA, and localized CT mRNA expression in gonadotropes of rat AP gland by in situ hybridization histochemistry. These results demonstrate that pit-CT mRNA is closely homologous to mouse CT mRNA; it is expressed by gonadotropes of the rat AP gland, and the peptide may significantly affect lactotrope function by inhibiting PRL release and cell proliferation.

Generation of a constitutively active fragment of PKN in microglia/macrophages after middle cerebral artery occlusion in rats

PKN is a fatty acid- and Rho-activated serine/threonine kinase, which has a catalytic domain highly homologous to that of protein kinase C (PKC). Recent studies have demonstrated that PKN is proteolytically cleaved after apoptotic stimulation and then a constitutively active 55-kDa fragment is generated. However, the role of the 55-kDa fragment are poorly understood. Adult Sprague-Dawley (SD) rats underwent middle cerebral artery occlusion (MCAO), and the temporal and spatial changes in the fragmentation of PKN and of PKC delta were examined by immunoblotting. No proteolytic fragment of PKC delta (about 40 kDa) was detected. The 55-kDa fragment of PKN appeared transiently from 3 days after MCAO at the ipsilateral normal cortex. At the boundary zone of infarction, the 55-kDa fragment was markedly induced from day 5 then peaked on day 21 and persisted until day 28. Analysis of anti-phosphoserine immunoprecipitates with an anti-PKN antibody revealed phosphorylation of the 55-kDa band. Double staining for PKN and Ox42 was used to examine the source of the 55-kDa fragment. PKN immunoreactivity was significantly increased in Ox42-positive cells (microglia/hematogenous macrophages). No DNA laddering and only a few terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells were observed on day 14 in despite of the high level appearance of the 55-kDa band. These results suggest that the constitutively active 55-kDa fragment of PKN does not contribute to apoptosis, but may contribute to a function of microglia/macrophages.

Molecular arrangement in water: random but not quite

Water defines life on Earth from the cellular to the terrestrial level. Yet the molecular level arrangement in water is not well understood, posing problems in comprehending its very special chemical, physical and biological properties. Here we present high-resolution x-ray diffraction data for water clearly showing that its molecular arrangement exhibits specific correlations that are consistent with the presence of rings of H(2)O molecules linked together by hydrogen bonds into tetrahedral-like units from a continuous network. This level of molecular arrangement complexity is beyond what a simple 'two-state' model of water (Bernal and Fowler 1933 J. Chem. Phys.1 515-48) could explain. It may not be explained by the recently put forward 'chains-clusters of completely uncorrelated molecules' model (Wernet et al 2004 Science 304 995-9) either. Rather it indicates that water is homogeneous down to the molecular level where different water molecules form tetrahedral units of different perfection and/or participate in rings of different sizes, thus experiencing different local environments. The local diversity of this tetrahedral network coupled to the flexibility of the hydrogen bonds that hold it together may explain well the rich phase diagram of water and why it responds non-uniformly to external stimuli such as, for example, temperature and pressure.

Poisson Analysis of Streptococcal Bond-strengthening on Saliva-coated Enamel

The forces responsible for bond-strengthening in initial oral bacterial adhesion are unknown. Since Lifshitz-Van der Waals and electrostatic forces work instantaneously upon approach, it is hypothesized that bond-strengthening is governed by hydrogen bonding. Poisson analysis of adhesion forces observed during the retraction of bacterial probes from surfaces in atomic force microscopy can be used to analyze the nature of the adhesion forces. Streptococcal adhesion forces increased from about −0.7 to −10.3 nN when the contact time between cell surfaces and salivary films on enamel was increased from 0 to 120 sec. Initial and final adhesion forces were stronger for initial colonizers of tooth surfaces ( S. mitis, S. sanguinis) than for later, more cariogenic, strains ( S. sobrinus, S. mutans). Retraction curves after increased contact times showed minor peaks, representative of hydrogen bonds, and Poisson analyses indicated repulsive non-specific forces of around +0.3 nN and slightly more attractive hydrogen-bonding forces (−1.0 nN) for initial than for late colonizers (−0.8 nN).

Evaluation of Packable and Conventional Hybrid Resin Composites in Class I Restorations: Three-year Results of a Randomized, Double-blind and Controlled Clinical Trial

Long-term randomized, controlled, clinical trials of treatment outcomes are clearly needed to evaluate the long-term performance of composites in posterior teeth.

Genomic organization and promoter function of the human thyrotropin-releasing hormone receptor gene

We isolated and characterized the gene for the human thyrotropin-releasing hormone receptor. The gene spanned more than 30 kilobases and contained three exons and two introns. Intron 1 exists in the 5'-untranslated region, and intron 2 is more than 25 kilobases in length which interrupts the coding region before the beginning of the putative sixth transmembrane domain. Exon 3 encodes the rest of the coding region and the entire 3'-untranslated region. The 3'-flanking region contains four potential polyadenylation signals, and 3'-rapid amplification of cDNA ends studies showed that only a signal at 2076 base pairs downstream of the stop codon was functional in the anterior pituitary. Primer extension and anchor-polymerase chain reaction studies indicated a transcriptional start site at 344 base pairs upstream of the translational start site. The promoter region does not contain either a TATA box or a CAAT box in the appropriate location. Transient transfection study revealed significant activity of the promoter in GH4C1 cells, and the region between -338 and -933 bp from the transcriptional start site worked as a negative regulator. Knowledge of the genomic organization and the promoter region of thyrotropin-releasing hormone (TRH) receptor gene will allow further studies of possible disorders of the TRH receptor, as well as facilitate elucidation of transcriptional control of the human TRH receptor gene.

CCK-B/Gastrin receptor transmembrane domain mutations selectively alter synthetic agonist efficacy without affecting the activity of endogenous peptides

Recent efforts have focused on identifying small nonpeptide molecules that can mimic the activity of endogenous peptide hormones. Understanding the molecular basis of ligand-induced receptor activation by these divergent classes of ligands should expedite the process of drug development. Using the cholecystokinin-B/gastrin receptor (CCK-BR) as a model system, we have recently shown that both affinity and efficacy of nonpeptide ligands are markedly affected by amino acid alterations within a putative transmembrane domain (TMD) ligand pocket. In this report, we examine whether residues projecting into the TMD pocket determine the pharmacologic properties of structurally diverse CCK-BR ligands, including peptides and synthetic peptide-derived partial agonists (peptoids). Nineteen mutant human CCK-BRs, each including a single TMD amino acid substitution, were transiently expressed in COS-7 cells and characterized. Binding affinities as well as ligand-induced inositol phosphate production at the mutant CCK-BRs were assessed for peptides (CCK-8 and CCK-4) and for peptoids (PD-135,158 and PD-136, 450). Distinct as well as overlapping determinants of peptide and peptoid binding affinity were identified, supporting that both classes of ligands, at least in part, interact with the CCK-BR TMD ligand pocket. Eight point mutations resulted in marked increases or decreases in the functional activity of the synthetic peptoid ligands. In contrast, the functional activity of both peptides, CCK-8 and CCK-4, was not affected by any of the CCK-BR mutations. These findings suggest that the mechanisms underlying activation of G-protein-coupled receptors by endogenous peptide hormones versus synthetic ligands may markedly differ.

Atomic-scale structure of biogenic materials by total X-ray diffraction: a study of bacterial and fungal MnOx

Biogenic materials are produced by microorganisms and are typically found in a nanophase state. As such, they are difficult to characterize structurally. In this report, we demonstrate how high-energy X-ray diffraction and atomic pair distribution function analysis can be used to determine the atomic-scale structures of MnO(x) produced by bacteria and fungi. These structures are well-defined, periodic, and species-specific, built of Mn-O(6) octahedra forming birnessite-type layers and todorokite-type tunnels, respectively. The inherent structural diversity of biogenic material may offer opportunities for practical applications.

BMP1 and TLL1 Are Required for Maintaining Periodontal Homeostasis

Mutations in bone morphogenetic protein 1 (BMP1) in humans or deletion of BMP1 and related protease tolloid like 1 (TLL1) in mice lead to osteogenesis imperfecta (OI). Here, we show progressive periodontal defects in mice in which both BMP1 and TLL1 have been conditionally ablated, including malformed periodontal ligament (PDL) (recently shown to play key roles in normal alveolar bone formation), significant loss in alveolar bone mass ( P < 0.01), and a sharp reduction in cellular cementum. Molecular mechanism studies revealed a dramatic increase in the uncleaved precursor of type I collagen (procollagen I) and a reduction in dentin matrix protein 1 (DMP1), which is partially responsible for defects in extracellular matrix (ECM) formation and mineralization. We also showed a marked increase in the expression of matrix metallopeptidase 13 (MMP13) and tartrate-resistant acid phosphatase (TRAP), leading to an acceleration in periodontal breakdown. Finally, we demonstrated that systemic application of antibiotics significantly improved the alveolar bone and PDL damage of the knockdown phenotype, which are thus shown to be partially secondary to pathogen-induced inflammation. Together, identification of the novel roles of BMP1 and TLL1 in maintaining homeostasis of periodontal formation, partly via biosynthetic processing of procollagen I and DMP1, provides novel insights into key contributions of the extracellular matrix environment to periodontal homeostasis and contributes toward understanding of the pathology of periodontitis.

Nystatin and valinomycin induce tubuloglomerular feedback

The macula densa expresses a luminal Na(+)-K(+)-2Cl(-) cotransporter and a basolateral Cl(-) conductance. Although it is known that cotransport of Na(+), K(+), and Cl(-) is the first step in tubuloglomerular feedback (TGF), subsequent steps are unclear. We hypothesized that Na(+)-K(+)-2Cl(-) entry via the luminal Na(+)-K(+)-2Cl(-) cotransporter elevates intracellular Cl(-), increases electrogenic Cl(-) efflux across the basolateral membrane, and depolarizes the macula densa, initiating TGF. We perfused afferent arterioles with macula densa attached. The macula densa was perfused with solutions containing either 5 mM Na(+) and 3 mM Cl(-) (low NaCl) or 80 mM Na(+) and 77 mM Cl(-) (high NaCl). When the macula densa perfusate was changed from low to high NaCl, afferent arteriole diameter decreased from 15.8 +/- 0.8 to 13.1 +/- 0.7 mm (P < 0.05). Adding 10 microM furosemide to the macula densa lumen blocked TGF. When nystatin, a group I cation ionophore, was added to the macula densa lumen together with furosemide in the presence of low NaCl, it induced TGF (from 18.0 +/- 1.5 to 15.6 +/- 1.6 mm; P = 0.003). When valinomycin, a K(+)-selective ionophore, was added to the macula densa lumen together with furosemide in the presence of low NaCl containing 5 mM K(+), it did not induce TGF. Subsequent addition of 50 mM KCl to the macula densa perfusate induced TGF (from 21.7 +/- 0.8 to 17.5 +/- 1.3 mm; P = 0.0047; n = 6). Adding 50 mM KCl without valinomycin did not induce TGF. When 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB; 1 microM), a Cl(-) channel blocker, was added to the bath, it blocked TGF induced by high NaCl, but did not block TGF induced by valinomycin plus 50 mM KCl. NPPB did not alter afferent arteriole constriction induced by norepinephrine. We concluded that increased NaCl in the lumen of the macula densa leads to influx of Cl(-) via the Na(+)-K(+)-2Cl(-) cotransporter. The accelerated transport increases intracellular Cl(-). The subsequent exit of Cl(-) across the basolateral membrane via Cl( -) channels in turn leads to depolarization of the macula densa and thereby induces TGF.

Breed difference and regulation of the porcine Sirtuin 1 by insulin

Sirtuin 1 (Sirt1) plays an important role in fat metabolism. In the current study, we examined the breed differences in Sirt1 between Jinhua pigs (a fatty breed of China) and Landrace pigs (a leaner breed). In addition, the effect of insulin on the gene expression of Sirt1 and the major lipase, adipose triglyceride lipase (ATGL), and hormone-sensitive lipase (HSL) in fat metabolism was also studied in vitro. Compared with the Landrace pigs, the BW of Jinhua pigs was less (P < 0.01), whereas the body fat content were greater (P < 0.01). The protein content and the mRNA abundance of Sirt1 in Jinhua pigs were less (P < 0.01) in subcutaneous adipose tissues compared with the Landrace pigs. Likewise, the mRNA abundance of ATGL and HSL were also less (P < 0.01) in Jinhua pigs. In vitro, treatment with a different dose of insulin (10, 50 and 100 nM) decreased (P < 0.01) glycerol release and the mRNA abundance of Sirt1, ATGL, and HSL in porcine adipocytes. Likewise, treatment with 50 nM insulin for 24 and 48 h also decreased (P < 0.05) glycerol release and the expression of Sirt1, ATGL, and HSL in porcine adipocytes. Furthermore, insulin and Sirt1-specific small interfering RNA treatment decreased (P < 0.01) the expression of Sirt1, ATGL, and HSL compared with the control or insulin treatment. These results indicate that insulin may regulate transcription of Sirt1, ATGL, and HSL in porcine adipocytes and provide information for manipulating these gene expressions in regulating fat metabolism in pigs.

Comparative analysis of lifestyle factors, screening test use, and clinicopathologic features in association with survival among Asian Americans with colorectal cancer

Background:

Colorectal cancer (CRC) diagnoses and disease-specific survival (DSS) vary between ethnic groups in the United States. However, few studies have assessed differences among Asian subgroups.

Methods:

The Surveillance, Epidemiology, and End Results (SEER) database was used to identify patients with invasive CRC between 1988 and 2008. Differences in clinicopathologic features, and DSS rates were compared among Asian subgroups. The California Health Interview Survey was used to examine risk factors and screening patterns for CRC.

Results:

The study included 359 374 patients with 8.4% Asian. Patients in all Asian subgroups were younger (median: 68 years) at diagnosis than non-Hispanic white (NHW) patients (median: 72 years). Most Asian subgroups, except Hawaiians, had better DSS than NHW patients although Asian subgroups had more advanced disease than NHW. Indian/Pakistani patients had a higher 5-year DSS than other Asian subgroups. Obesity proportions were lower in Asian subgroups (<50.2%) than in NHW (59.8%). Vietnamese men and Korean women had the lowest proportions of CRC screening. Advance tumour stages were highly associated with worse DSS in each ethnicity group. High tumour grades were associated with worse DSS in NHW, Filipino, and Chinese. Older age at diagnosis was associated with worse DSS in most ethnicity groups except Hawaiian and Vietnamese.

Conclusion:

Disparities exist between Asians and NHW with CRC, and among various Asian subgroups. Differences in cancer clinicopathologic features, patients' behavioural habits, lifestyle, and screening patterns may explain some differences in CRC survival observed among ethnic groups.

Zero thermal expansion in a nanostructured inorganic-organic hybrid crystal

There are very few materials that exhibit zero thermal expansion (ZTE), and of these even fewer are appropriate for electronic and optoelectronic applications. We find that a multifunctional crystalline hybrid inorganic-organic semiconductor, beta-ZnTe(en)(0.5) (en denotes ethylenediamine), shows uniaxial ZTE in a very broad temperature range of 4-400 K, and concurrently possesses superior electronic and optical properties. The ZTE behavior is a result of compensation of contraction and expansion of different segments along the inorganic-organic stacking axis. This work suggests an alternative route to designing materials in a nanoscopic scale with ZTE or any desired positive or negative thermal expansion (PTE or NTE), which is supported by preliminary data for ZnTe(pda)(0.5) (pda denotes 1,3-propanediamine) with a larger molecule.

Regulation of osteoprotegerin gene expression in dental follicle cells

Colony-stimulating factor-one (CSF-1) and parathyroid-hormone-related protein (PTHrP) down-regulate osteoprotegerin (OPG) gene expression in the dental follicle of the rat first mandibular molar. To examine this regulation at the signal transduction level, we treated cultured dental follicle cells with either phorbolmyristate acetate (PMA) or dibutyryl cyclic AMP (dbcAMP) to activate either protein kinase C (PKC) or protein kinase A (PKA). Our results demonstrate that PMA up-regulates OPG gene expression and down-regulates the expression of CSF-1 and the PTHrP receptor (PTHrP-R). Conversely, dbcAMP down-regulates OPG expression and up-regulates CSF-1 and PTHrP-R expression. Immunostaining shows that PMA also increases the steady-state levels of protein. Thus, treatment with agents that affect protein kinase activity also enhance the steady-state mRNA and protein levels of OPG, as well as decreasing the mRNA levels of CSF-1 and PTHrP-R. The PKC-alpha isoform may be critical in OPG regulation because PKC-alpha gene expression is enhanced by PMA and reduced by either CSF-1 or PTHrP.

A comparative study of thoracoscopic and open surgery of congenital diaphragmatic hernia in neonates

Background

An increasing number of hospitals have carried out neonatal thoracoscopic assisted repair of congenital diaphragmatic hernia (CDH).

Methods

The 26 cases received thoracoscopic-assisted repair (observation group) and 44 cases open repair (control group). General anesthesia was performed with endotracheal intubation using a trachea cannula without cuff. The general preoperative data, intraoperative hemodynamic parameters, intraoperative surgical conditions, postoperative complications, postoperative recovery condition, postoperative survival rate and recurrence rate were recorded.

Results

The intraoperative mean arterial pressure and heart rate at each time point in observation group were more stable and effective than those in control group (all P <  0.001). The number of manual ventilation, SpO₂ < 90% and hypercapnia cases were significantly lower than those in control group (all P <  0.05). Intraoperative bleeding, incision length and operation duration were significantly lower in observation group compared with control group (all P <  0.001). No significant differences were seen between the two groups in postoperative complications including pulmonary infection, incision infection, pulmonary hypertension, hemorrhage, and scleredema (all P > 0.05). The duration of postoperative mechanical ventilation, antibiotic use and hospitalization in observation group was significantly shorter than those in control group (all P < 0.05). There was no significant difference in postoperative survival rate and recurrence rate between the two groups (both P > 0.05).

Conclusion

The intraoperative hemodynamic parameters of CDH repair under thoracoscopy were more stable, the duration of postoperative mechanical ventilation, antibiotic use and hospitalization were shortened, and the therapeutic effect was better.

Application of ultrasound-based radiomics technology in fetal-lung-texture analysis in pregnancies complicated by gestational diabetes and/or pre-eclampsia

OBJECTIVES

To analyze and compare, using ultrasound-based radiomics technology, fetal-lung texture in pregnancies affected by gestational diabetes mellitus (GDM) and/or pre-eclampsia (PE) and in normal pregnancies, overall and at different gestational ages.

METHODS

In this retrospective study, 430 high-throughput features per fetal-lung image were extracted from 548 fetal-lung ultrasound images (obtained at the level of the four-chamber view of the heart) in 548 pregnant women who delivered between July 2018 and August 2019 at the Obstetrics and Gynecology Hospital of Fudan University. Images had been obtained during ultrasound examinations between 28 and 41 weeks of gestation. The data were divided randomly into training set (80% of fetal-lung images) and independent test set (20% of images), and 20% of the images in the training set were then selected as the validation set. A standard machine-learning model based on ultrasound-based radiomics technology was created using features of fetal-lung texture extracted from the images, and a regression model was used to evaluate the relationship between lung-texture features, GDM and/or PE and gestational age.

RESULTS

Of the 548 pregnancies included, 108 were affected by GDM alone, 71 by PE alone and 25 by both GDM and PE, and 344 were normal. The overall performance of the GDM and PE prediction model was superior to that of the gestational-age prediction model, with an area under the receiver-operating-characteristics curve of 0.95-0.99, sensitivity of 78.8-97.1% in the validation set and 74.5-91.3% in the independent test set, specificity of 79.8-94.3% in the validation set and 75.7-88.4% in the independent test set and accuracy of 81.0-95.3% in the validation set and 80.6-86.4% in the independent test set.

CONCLUSIONS

Using ultrasound-based radiomics technology, fetal lungs from pregnancies grouped according to whether they were affected by GDM and/or PE could be distinguished from each other and from fetal lungs of normal pregnancies, and lungs from pregnancies at different gestational ages could be distinguished. These findings support further research to explore the use of this non-invasive technology to predict neonatal respiratory complications in women with PE, GDM or their combination. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Studies on the chitin/chitosan binding properties of six cuticular proteins analogous to peritrophin 3 from Bombyx mori

Chitin deacetylation is required to make the cuticle rigid and compact through chitin chain crosslinking. Thus it is presumed that specialized proteins are required to bind deacetylated chitin chains together. However, deacetylated-chitin binding proteins have not ever been reported. In a previous work, six cuticular proteins analogous to peritrophin 3 (CPAP3s) were found to be abundant in the moulting fluid of Bombyx mori. In this study, these BmCPAP3s (BmCPAP3-A1, BmCPAP3-A2, BmCPAP3-B, BmCPAP3-C, BmCPAP3-D1 and BmCPAP3-D2) were cloned and expressed in Escherichia coli and purified using metal-chelating affinity chromatography. Their binding activities demonstrated that although all of the BmCPAP3s showed similar binding abilities toward crystalline chitin and colloidal chitin, they differed in their affinities toward partially and fully deacetylated chitin. Amongst them, BmCPAP3-D1 exhibited the highest binding activity toward deacetylated chitin. The gene expression pattern of BmCPAP3-D1 was similar to BmCPAP3-A1 and BmCPAP3-C at most stages except that it was dramatically upregulated at the beginning of the pupa to adult transition stage. This work is the first report of a chitin-binding protein, BmCPAP3-D1, which exhibits high binding affinity to deacetylated chitin.

Refractometric discrimination of void-space filling and swelling during vapour sorption in polymer films

Thin polymeric films have been deposited as upper cladding layers on a new integrated optical interferometer fabricated from layers of silicon oxynitride on a silicon wafer. The evanescent field of the probing waveguide mode transduces refractive index changes in the polymer layer into the measured phase changes in the device. Real-time measurement of index change and its sign is obtained. Upon exposure to humid air, we record water sorption by films of poly(vinyl pyrrolidone) by a rapid positive index change for void-space filling followed by a slow negative index change for swelling. Sorption of water vapor into a thin film of the viscous liquid polymer polyethylenimine shows only swelling mode behaviour and a simple constitutive model can be applied to give the fractional water occupied volume.

Melting of polymer single crystals studied by dynamic Monte Carlo simulations

We report dynamic Monte Carlo simulations of lattice polymers melting from a metastable chain-folded lamellar single crystal. The single crystal was raised and then melted in an ultrathin film of polymers wetting on a solid substrate, mimicking the melting observations made by using Atomic Force Microscopy. We observed that the thickness distribution of the single crystal appears quite inhomogeneous and the thickness increases gradually from facetted edges to the center. Therefore, at low melting temperatures, melting stops at a certain crystal thickness, and melting-recrystallization occurs when allowing crystal thickening; at intermediate temperatures, melting maintains the crystal shape and exhibits different speeds in two stages; at high temperatures, fast melting makes a melting hole in the thinnest region, as well as a saw-tooth-like pattern at the crystal edges. In addition, the linear melting rates at low temperatures align on the curve extrapolated from the linear crystal growth rates. The temperature dependence of the melting rates exhibits a regime transition similar to crystal growth. Such kinetic symmetry persists in the melting rates with variable frictional barriers for c -slip diffusion in the crystal as well as with variable chain lengths. Visual inspections revealed highly frequent reversals upon melting of single chains at the wedge-shaped lateral front of the lamellar crystal. We concluded that the melting kinetics is dominated by the reverse process of intramolecular secondary crystal nucleation of polymers.