Biological adhesion of the flatworm Macrostomum lignano relies on a duo-gland system and is mediated by a cell type-specific intermediate filament protein

Abstract

BackgroundFree-living flatworms, in both marine and freshwater environments, are able to adhere to and release from a substrate several times within a second. This reversible adhesion relies on adhesive organs comprised of three cell types: an adhesive gland cell, a releasing gland cell, and an anchor cell, which is a modified epidermal cell responsible for structural support. However, nothing is currently known about the molecules that are involved in this adhesion process.ResultsIn this study we present the detailed morphology of the adhesive organs of the free-living marine flatworm Macrostomum lignano. About 130 adhesive organs are located in a horse-shoe-shaped arc along the ventral side of the tail plate. Each organ consists of exactly three cells, an adhesive gland cell, a releasing gland cell, and an anchor cell. The necks of the two gland cells penetrate the anchor cell through a common pore. Modified microvilli of the anchor cell form a collar surrounding the necks of the adhesive- and releasing glands, jointly forming the papilla, the outer visible part of the adhesive organs. Next, we identified an intermediate filament (IF) gene, macif1, which is expressed in the anchor cells. RNA interference mediated knock-down resulted in the first experimentally induced non-adhesion phenotype in any marine animal. Specifically, the absence of intermediate filaments in the anchor cells led to papillae with open tips, a reduction of the cytoskeleton network, a decline in hemidesmosomal connections, and to shortened microvilli containing less actin.ConclusionOur findings reveal an elaborate biological adhesion system in a free-living flatworm, which permits impressively rapid temporary adhesion-release performance in the marine environment. We demonstrate that the structural integrity of the supportive cell, the anchor cell, is essential for this adhesion process: the knock-down of the anchor cell-specific intermediate filament gene resulted in the inability of the animals to adhere. The RNAi mediated changes of the anchor cell morphology are comparable to situations observed in human gut epithelia. Therefore, our current findings and future investigations using this powerful flatworm model system might contribute to a better understanding of the function of intermediate filaments and their associated human diseases.

Profiling of adhesive-related genes in the freshwater cnidarianHydra magnipapillataby transcriptomics and proteomics

“…However, an anterior-specific transcript might be a member of a larger gene family that exhibit a certain sequence overlap with other transcripts – resulting in cross-mapping of short reads. For example, in M. lignano , a tail-specific intermediate filament related transcript involved in adhesion was identified (Lengerer et al 2014). Intermediate filaments comprise a large protein family with various types and isoforms (eg keratin, desmin, vimentin, lamin, and neurofilaments), which results in a distribution of mapped reads within similar sequence regions.…”

“…Differential transcriptomics permit the in silico subtraction of different samples yielding a quantitative ranking of differentially expressed transcripts. Based on a region-specific transcriptome of the flatworm Macrostomum lignano (Arbore et al 2015), an adhesion-related intermediate filament gene has been identified (Lengerer et al 2014) and potential glue candidates are currently under study (Ladurner, unpublished). Thus far, differential transcriptomic studies are becoming popular in bioadhesion research, primarily to identify candidate adhesive genes for reliable downstream analysis.…”

Mechanical adaptability of sea cucumber Cuvierian tubules involves a mutable collagenous tissue

“…A 1 μg aliquot of total RNA was reverse transcribed using the 1st Strand cDNA Synthesis Kit for RT-PCR (AMV; Roche, Basel, Switzerland). Whole-mount in situ hybridisation was performed according to Lengerer et al (2014) with the following changes: (1) template DNA for producing DIG-labelled probe (501 bp) was made using Q5 High-Fidelity DNA polymerase (New England Biolabs, Ipswich, MA, USA) with the forward primer 5′-CAGTGCTCTGATCATCGATTCTTT-3′ and reverse primer 5′-TCTCTCATTTTGAAGCAATCTTCG-3′. A T7 promoter binding site was added to the reverse strand PCR primer and a Sp6 promoter binding site was added to the forward primer for negative control; (2) the heat fixation step at 80°C was omitted; and (3) colour development was performed in NBT/BCIP plus Suppressor 1-Step Solution (Thermo Fisher Scientific).…”

Genome and transcriptome of the regeneration-competent flatworm, Macrostomum lignano

“…Given its promise as a model for studying mechanisms governing pluripotency, a number of groups have worked to establish M. lignano as a model to study stem cell biology and regeneration (16,19,20), sexual selection and reproductive biology (21,22), bioadhesion (23), and neurobiology (24). Efforts of the M. lignano community have resulted in the development of a number of tools that can be used to study M. lignano biology (15,21,(25)(26)(27).…”