Canonical Wnt signalling regulates epithelial patterning by modulating levels of laminins in zebrafish appendages

wnt10a is required for zebrafish median fin fold maintenance and adult unpaired fin metamorphosis

BACKGROUND

Mutations of human WNT10A are associated with odonto-ectodermal dysplasia syndromes. Here, we present analyses of wnt10a loss-of-function mutants in the zebrafish.

RESULTS

wnt10a mutant zebrafish embryos display impaired tooth development and a collapsing median fin fold (MFF). Rescue experiments show that wnt10a is essential for MFF maintenance both during embryogenesis and later metamorphosis. The MFF collapse could not be attributed to increased cell death or altered proliferation rates of MFF cell types. Rather, wnt10a mutants show reduced expression levels of dlx2a in distal-most MFF cells, followed by compromised expression of col1a1a and other extracellular matrix proteins encoding genes. Transmission electron microscopy analysis shows that although dermal MFF compartments of wnt10a mutants initially are of normal morphology, with regular collagenous actinotrichia, positioning of actinotrichia within the cleft of distal MFF cells becomes compromised, coinciding with actinotrichia shrinkage and MFF collapse.

CONCLUSIONS

MFF collapse of wnt10a mutant zebrafish is likely caused by the loss of distal properties in the developing MFF, strikingly similar to the proposed molecular pathomechanisms underlying the teeth defects caused by the loss of Wnt10 in fish and mammals. In addition, it points to thus fur unknown mechanisms controlling the linear growth and stability of actinotrichia and their collagen fibrils.

Downregulation of Smad4 expression confers chemoresistance against imatinib mesylate to chronic myeloid leukemia K562 cells

Objective: Imatinib mesylate (IM), a tyrosine kinase inhibitor, exhibits clinically prominent effects against chronic myeloid leukemia (CML); however, a few patients have shown resistance to IM treatment, resulting in disease progression. Smad4 is a tumor inhibitor that transduces TGF-β signaling and modulates genomic stability. Previous studies have indicated that decreased Smad4 expression played a bidirectional role in chemosensitivity in many types of cancers. Therefore, this study aims to evaluate the association between IM sensitivity and decreased Smad4 expression in human CML K562 cells.Methods: Bone marrow (BM) samples were acquired from the patients prior to treatment. qRT-PCR, Western Blotting (WB), colony formation assay (CFA), and apoptosis assay were used to detect relevant indices.Results: Smad4 expression was downregulated in the bone marrow and plasma of patients with multidrug-resistant CML as well as IM-resistant K562 (K562R) cells compared with samples collected from CML patients and K562 cells. Smad4 overexpression inhibited IM-treated K562R cell proliferation and augmented apoptosis, whereas Smad4 silencing promoted viability and inhibited apoptosis in IM-treated K562 cells. In addition, Smad4 expression was inversely correlated with laminin subunit gamma 1 (LAMC1) expression. The upregulation or downregulation of LAMC1 expression partially abolished the effect of Smad4 overexpression or silencing on the IM resistance of CML cells.Conclusion: The downregulation of Smad4 expression might induce drug resistance in CML cells and displayed a possible mechanism through which Smad4 modulates CML cell survival and apoptosis upon IM treatment.

Congenital sensorineural hearing loss as the initial presentation of PTPN11-associated Noonan syndrome with multiple lentigines or Noonan syndrome: clinical features and underlying mechanisms

BACKGROUND

Germline variants in PTPN11 are the primary cause of Noonan syndrome with multiple lentigines (NSML) and Noonan syndrome (NS), which share common skin and facial symptoms, cardiac anomalies and retardation of growth. Hearing loss is considered an infrequent feature in patients with NSML/NS. However, in our cohort, we identified a group of patients with PTPN11 pathogenic variants that were primarily manifested in congenital sensorineural hearing loss (SNHL). This study evaluated the incidence of PTPN11-related NSML or NS in patients with congenital SNHL and explored the expression of PTPN11 and the underlying mechanisms in the auditory system.

METHODS

A total of 1502 patients with congenital SNHL were enrolled. Detailed phenotype-genotype correlations were analysed in patients with PTPN11 variants. Immunolabelling of Ptpn11 was performed in P35 mice. Zebrafish with Ptpn11 knockdown/mutant overexpression were constructed to further explore mechanism underlying the phenotypes.

RESULTS

Ten NSML/NS probands were diagnosed via the identification of pathogenic variants of PTPN11, which accounted for ~0.67% of the congenital SNHL cases. In mice cochlea, Shp2, which is encoded by Ptpn11, is distributed in the spiral ganglion neurons, hair cells and supporting cells of the inner ear. In zebrafish, knockdown of ptpn11a and overexpression of mutant PTPN11 were associated with a significant decrease in hair cells and supporting cells. We concluded that congenital SNHL could be a major symptom in PTPN11-associated NSML or NS. Other features may be mild, especially in children.

CONCLUSION

Screening for PTPN11 in patients with congenital hearing loss and variant-based diagnoses are recommended.

Localization of β-Catenin and Islet in the Pelvic Fin Field in Zebrafish

In zebrafish, pelvic fin buds appear at 3 weeks post fertilization (wpf) during the larval to juvenile transition (metamorphosis), but their fate is already determined during embryogenesis. Thus, presumptive pelvic fin cells appear to memorize their positional information for three weeks, but no factors expressed in the pelvic fin field from the embryonic to the metamorphic stages have been identified. In mice, Islet1 is proposed to promote nuclear accumulation of β-catenin in the hindlimb field, which leads to the initiation of hindlimb bud outgrowth through activation of the Wnt/βcatenin pathway. Here, we examined the distribution of β-catenin and islet proteins in the pelvic fin field of zebrafish from the embryonic to the metamorphic stages. We found that transcripts of islet2a, but not islet1, are detected in the posterior lateral plate mesoderm, including the presumptive pelvic fin field, at the embryonic stage as well as in the pelvic fin bud at the metamorphic stage. Immunolocalization revealed that β-catenin and islet proteins, which are synthesized during the embryonic stage, remain in the cytoplasm of the presumptive pelvic fin cells during the larval stage, and are then translocated into the nuclei of the pelvic fin bud at the metamorphic stage. We propose that cytoplasmic localization of these proteins in the presumptive pelvic fin cells that remained during the larval stage may underlie the mechanism by which pelvic fin cells memorize their positional information from the embryonic stage to the metamorphic stage.

High LAMC1 expression in glioma is associated with poor prognosis

Purpose: Glioma is the most common malignant brain tumor. The molecular mechanisms underlying its malignancy are not fully understood. LAMC1, which encodes extracellular matrix protein laminin γ1, has been implicated in some malignant tumors but has not been systematically evaluated in glioma. The aim of this study was to evaluate the expression of LAMC1 and its clinical significance.

Patients and methods: LAMC1 protein expression in 52 fresh-frozen specimens of different pathological grade gliomas and 5 normal brain tissues was detected by Western blotting. Immunohistochemistry was used to detect LAMC1 protein expression in another set of 76 glioma tissues and 8 normal brain tissues. The associations between clinicopathological factors and LAMC1 expression were analyzed. A log-rank test and a multivariate Cox proportional hazards model were used to determine the relationship between LAMC1 expression and patient prognosis. The expression of LAMC1 at the mRNA level was analyzed in the TCGA database.

Results: LAMC1 was highly expressed in high-grade glioma tissues, with moderate expression in low-grade gliomas, and weak or no expression in normal brain tissues, as detected by Western blotting and immunohistochemistry. A chi-square test indicated that LAMC1 expression was associated with pathological grade but not with other clinicopathological factors, such as age, sex, and tumor size. LAMC1 expression at the mRNA level was upregulated in high-grade gliomas compared with low-grade gliomas and normal brain tissue in the TCGA database. The Kaplan–Meier plot and log-rank test in our patient series showed that high LAMC1 expression was significantly associated with shorter survival, which was consistent with the TCGA database analysis. A multivariate Cox proportional hazards model revealed that LAMC1 expression, WHO grade, and surgery procedure were significantly correlated with overall survival and progression-free survival.

Conclusion: These results demonstrated that LAMC1 may play an important role in glioma progression and may be used in the diagnosis, prognosis, and targeted therapy of glioma patients.

Functional characterisation of romeharsha and clint1 reaffirms the link between plasma membrane homeostasis, cell size maintenance and tissue homeostasis in developing zebrafish epidermis

In vertebrates, early developing epidermis is a bilayered epithelium consisting of an outer periderm and the underlying basal epidermis. It eventually develops into a multi-layered epithelium. The mechanisms that control the architecture and homeostasis of early developing bilayered epidermis have remained poorly understood. Recently, we have shown that the function of Myosin Vb, an actin based molecular motor, is essential in peridermal cells for maintenance of plasma membrane homeostasis. Furthermore, our analyses of the goosepimples/myosin Vb mutant unravelled a direct link between plasma membrane homeostasis, cell size maintenance and tissue homeostasis in the developing epidermis. However, it remained unclear whether this link is specific to myosin Vb mutant or this is a general principle. Here we have identified two more genetic conditions, romeharsha mutant and clint1 knockdown, in which membrane homeostasis is perturbed, as evident by increased endocytosis and accumulation of lysosomes. As a consequence, peridermal cells exhibit smaller size and increased proliferation. We further show that decreasing endocytosis in romeharsha mutant and clint1 morphants rescues or mitigates the effect on cell size, cell proliferation and morphological phenotype. Our data confirms generality of the principle by reaffirming the causal link between plasma membrane homeostasis, cell size maintenance and tissue homeostasis.

Zebrafish: A Premier Vertebrate Model for Biomedical Research in Indian Scenario

The zebrafish (Danio rerio) is a versatile model organism that has been used in biomedical research for several decades to study a wide range of biological phenomena. There are many technical advantages of using zebrafish over other vertebrate models. They are readily available, hardy, easy, and inexpensive to maintain in the laboratory, have a short life cycle, and have excellent fecundity. Due to its optical clarity and reproducible capabilities, it has become one of the predominant models of human genetic diseases. Zebrafish research has made rapid strides in the United States and Europe, but in India the field is at an early stage and many researchers still remain unaware of the full research potential of this tiny fish. The zebrafish model system was introduced into India in the early 2000s. Up to now, more than 200 scientific referred articles have been published by Indian researchers. This review gives an overview of the current state of knowledge for zebrafish research in India, with the aim of promoting wider utilization of zebrafish for high level biological studies.

The cephalopod arm crown: appendage formation and differentiation in the Hawaiian bobtail squid Euprymna scolopes

BACKGROUND

Cephalopods are a highly derived class of molluscs that adapted their body plan to a more active and predatory lifestyle. One intriguing adaptation is the modification of the ventral foot to form a bilaterally symmetric arm crown, which constitutes a true morphological novelty in evolution. In addition, this structure shows many diversifications within the class of cephalopods and therefore offers an interesting opportunity to study the molecular underpinnings of the emergence of phenotypic novelties and their diversification. Here we use the sepiolid Euprymna scolopes as a model to study the formation and differentiation of the decabrachian arm crown, which consists of four pairs of sessile arms and one pair of retractile tentacles. We provide a detailed description of arm crown formation in order to understand the basic morphology and the developmental dynamics of this structure.

RESULTS

We show that the morphological formation of the cephalopod appendages occurs during distinct phases, including outgrowth, elongation, and tissue differentiation. Early outgrowth is characterized by uniform cell proliferation, while the elongation of the appendages initiates tissue differentiation. The latter progresses in a gradient from proximal to distal, whereas cell proliferation becomes restricted to the distal-most end of the arm. Differences in the formation of arms and tentacles exist, with the tentacles showing an expedite growth rate and higher complexity at younger stages.

CONCLUSION

The early outgrowth and differentiation of the E. scolopes arm crown shows similarities to the related, yet derived cephalopod Octopus vulgaris. Parallels in the growth and differentiation of appendages seem to exist throughout the animal kingdom, raising the question of whether these similarities reflect a recruitment of similar molecular patterning pathways.

"Fibrous nests" in human hepatocellular carcinoma express a Wnt-induced gene signature associated with poor clinical outcome

Hepatocellular carcinoma (HCC) is the 3rd cause of cancer-related death worldwide. Most cases arise in a background of chronic inflammation, extracellular matrix (ECM) remodeling, severe fibrosis and stem/progenitor cell amplification. Although HCCs are soft cellular tumors, they may contain fibrous nests within the tumor mass. Thus, the aim of this study was to explore cancer cell phenotypes in fibrous nests. Combined anatomic pathology, tissue microarray and real-time PCR analyses revealed that HCCs (n=82) containing fibrous nests were poorly differentiated, expressed Wnt pathway components and target genes, as well as markers of stem/progenitor cells, such as CD44, LGR5 and SOX9. Consistently, in severe liver fibroses (n=66) and in HCCs containing fibrous nests, weighted correlation analysis revealed a gene network including the myofibroblast marker ACTA2, the basement membrane components COL4A1 and LAMC1, the Wnt pathway members FZD1; FZD7; WNT2; LEF1; DKK1 and the Secreted Frizzled Related Proteins (SFRPs) 1; 2 and 5. Moreover, unbiased random survival forest analysis of a transcriptomic dataset of 247 HCC patients revealed high DKK1, COL4A1, SFRP1 and LAMC1 to be associated with advanced tumor staging as well as with bad overall and disease-free survival. In vitro, these genes were upregulated in liver cancer stem/progenitor cells upon Wnt-induced mesenchymal commitment and myofibroblast differentiation. In conclusion, fibrous nests express Wnt target genes, as well as markers of cancer stem cells and mesenchymal commitment. Fibrous nests embody the specific microenvironment of the cancer stem cell niche and can be detected by routine anatomic pathology analyses.

Transient laminin beta 1a Induction Defines the Wound Epidermis during Zebrafish Fin Regeneration

The first critical stage in salamander or teleost appendage regeneration is creation of a specialized epidermis that instructs growth from underlying stump tissue. Here, we performed a forward genetic screen for mutations that impair this process in amputated zebrafish fins. Positional cloning and complementation assays identified a temperature-sensitive allele of the ECM component laminin beta 1a (lamb1a) that blocks fin regeneration. lamb1a, but not its paralog lamb1b, is sharply induced in a subset of epithelial cells after fin amputation, where it is required to establish and maintain a polarized basal epithelial cell layer. These events facilitate expression of the morphogenetic factors shha and lef1, basolateral positioning of phosphorylated Igf1r, patterning of new osteoblasts, and regeneration of bone. By contrast, lamb1a function is dispensable for juvenile body growth, homeostatic adult tissue maintenance, repair of split fins, or renewal of genetically ablated osteoblasts. fgf20a mutations or transgenic Fgf receptor inhibition disrupt lamb1a expression, linking a central growth factor to epithelial maturation during regeneration. Our findings reveal transient induction of lamb1a in epithelial cells as a key, growth factor-guided step in formation of a signaling-competent regeneration epidermis.

Unlike mammals, adult teleost fish and urodele amphibians can fully regenerate lost appendages. Understanding what initiates regeneration in these vertebrates is of great interest to the scientific community. It has long been known that the epidermis that forms quickly over an amputated limb stump is critical for initiating regenerative programs. Yet, little of understood of the molecular and cellular mechanisms by which a simple adult epithelium transforms into this key signaling source. Here, we performed a large-scale, unbiased genetic screen for epithelial signaling deficiencies during the regeneration of amputated adult zebrafish fins, from which we identified several new mutants. One gene identified from this screen disrupts a specific component of the extracellular matrix material Laminin, Laminin beta 1a, a factor that we find to be dispensable in uninjured adult animals but required for all stages fin regeneration. Transient induction of this component by amputation polarizes the basal layer of the nascent epithelium, and, in turn, facilitates the synthesis of signaling factors, the positioning of ligand receptors, and the patterning of new bone cells. We also find that normal induction of Laminin beta 1a by injury relies on the function of Fibroblast growth factors, secreted polypeptide signals that are released early upon injury. Our results identify key early steps in the endogenous program for vertebrate appendage regeneration.