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Osteoblasts are derived from mesenchymal stem cells (MSC). The commitment of MSC towards the osteoprogenitor lineage requires the expression of specific genes, following timely programmed steps, including the synthesis of bone morphogenetic proteins (BMPs) and members of the Wingless (Wnt) pathways . The expressions of Runt-related transcription factors 2, Distal-less homeobox 5 (Dlx5), and osterix (Osx) are crucial for osteoblast differentiation [22, 26]. Additionally, Runx2 is a master gene of osteoblast differentiation, as demonstrated by the fact that Runx2-null mice are devoid of osteoblasts [26, 27]. Runx2 has demonstrated to upregulate osteoblast-related genes such as ColIA1, ALP, BSP, BGLAP, and OCN .
Osteocytes are derived from MSCs lineage through osteoblast differentiation. In this process, four recognizable stages have been proposed: osteoid-osteocyte, preosteocyte, young osteocyte, and mature osteocyte . At the end of a bone formation cycle, a subpopulation of osteoblasts becomes osteocytes incorporated into the bone matrix. This process is accompanied by conspicuous morphological and ultrastructural changes, including the reduction of the round osteoblast size. The number of organelles such as rough endoplasmic reticulum and Golgi apparatus decreases, and the nucleus-to-cytoplasm ratio increases, which correspond to a decrease in the protein synthesis and secretion .
During osteoblast/osteocyte transition, cytoplasmic process starts to emerge before the osteocytes have been encased into the bone matrix . The mechanisms involved in the development of osteocyte cytoplasmic processes are not well understood. However, the protein E11/gp38, also called podoplanin may have an important role. E11/gp38 is highly expressed in embedding or recently embedded osteocytes, similarly to other cell types with dendritic morphology such as podocytes, type II lung alveolar cells, and cells of the choroid plexus . It has been suggested that E11/gp38 uses energy from GTPase activity to interact with cytoskeletal components and molecules involved in cell motility, whereby regulate actin cytoskeleton dynamics [60, 61]. Accordingly, inhibition of E11/gp38 expression in osteocyte-like MLO-Y4 cells has been shown to block dendrite elongation, suggesting that E11/gp38 is implicated in dendrite formation in osteocytes .
Sacculina carcini is member of a highly-specialized group of parasitic cirripeds (Rhizocephala) that use crabs (Carcinus maenas) as hosts to carry out the reproductive phase of their life cycle. We describe the naupliar development of S. carcini Thompson, 1836 from a very precise monitoring of three different broods from three specimens. Nauplii were sampled every 4 h, from the release of the larvae until the cypris stage. Larval development, from naupliar instar 1 to the cypris stage, lasts 108 h at 18 °C. A rigorous sampling allowed us to describe an additional intermediate naupliar instar, not described previously. Naupliar instars are renumbered from 1 to 5. Nauplius 1 (N1) larvae hatch in the interna; N2 are released from the interna and last between 12 and 16 h; N3 appear between 12 and 16 h after release; N4 appear between 28 and 32 h; and N5 appear between 44 and 48 h. The cypris stage appears between 108 and 112 h. The redescribed morphologies allowed us to identify new characters. Antennular setation discriminates naupliar instars 3, 4 and 5. Telson and furca morphologies discriminate all naupliar instars. Furthermore, we demonstrate that the speed of larval development is similar within a single brood and between broods from different specimens, suggesting synchronization of larval development. From precise monitoring of broods every 4 h, we demonstrate that the life cycle of S. carcini includes five instars of naupliar larvae instead of four. The morphological characters of the larvae discriminate these naupliar instars and allow the identification of S. carcini from other Rhizocephala species. S. carcini larvae develop synchronously. Consequently, they might be an informative model to study larval development in crustaceans.
Sacculina carcini is a highly specialized barnacle parasite of several Brachyura crabs including the green crab Carcinus maenas . It belongs to the Rhizocephala, all of which present a highly altered morpho-anatomy at the adult stage, related to their endoparasitic lifestyle. The female adult consists of a root system that colonizes the crab cavity and is connected by a stalk running through the integument of the pleon to an external reproductive sac, the externa. One or two males take up residence inside the externa and develop into testes enclosed in the sac. Nauplius larvae are released by contractions of the externa and develop after several molts into a cypris larval stage, which metamorphoses into an adult after fixation on a suitable host crab.
For seven broods, live cypris larvae were relaxed for 10 min in seawater containing tricaine mesylate (MS-222)  before fixation in order to extend the antennules and thus determine the sex of the larva by the morphology of their antennular aesthetascs [14, 15].
Compared to previous morphological observations , the two spines of the frontal horns in our observations are located anteriorly and posteriorly rather than dorsally and ventrally. In our observations, the second antennular portion of S. carcini swells progressively from N2 to N5, whereas Collis and Walker  found a swelling only in N3 and N4. Our N1 is identical to their N1 and our N4 is similar to their N3, except that we observe lateral spines only in N5. Our N5 is clearly the same larva as their N4. In addition, we found two previously undescribed N5 characters on the antennules. First, the postaxial seta (S5) is reduced compared to its size in N4 (Fig. 2b). Second, the insertion of S5 changes between the N4 and N5 instars from the second to the third antennular portion. S5 needs to be traced through the cuticle during molts, to ensure that it is the same seta from N1 to N5. Moreover, the red pigments in posterior region are useful for identifying late N5 larvae. By comparison, we can conclude that our N2 is similar to their N2. In both N2 descriptions, the preaxial seta (S1) is not reduced. In previous drawings of N2 (Figs. 1B and 24B in ), the second portion of the antennules is not swollen. Also, the furcal rami of their N2 are slightly thicker and shorter than in their N3 and present long and numerous setules. Thus, their N2 corresponds to our N2. From these comparisons, we conclude that our N3 is a previously undescribed naupliar instar.
The morphology of the telson (lateral spines in notches and tubercle) can also be used to discriminate the other naupliar instars (N1, N4 and N5) of S. carcini (Figs. 2c, 3d, p, t). Lateral spines on the telson are visible only in our N5 (Fig. 3t). These spines are present earlier at N4 in P. sulcata and P. gracilis , and in S. pilosella .
From precise monitoring of broods every 4 h, we demonstrate that the life cycle of S. carcini includes five instars of nauplius larvae. The second and third naupliar instars were probably previously identified as a single instar either because their morphologies are similar or because they only last about 16 h each. We also describe these larval instars and present the morphological characters, such as the furca, the fronto-lateral horns, and the setation of the antennules that together discriminate these naupliar instars and identify S. carcini from other Rhizocephala species. Finally, we demonstrate that S. carcini larva development is reproducibly synchronized across different broods.
We compared here the suitability and efficacy of traditional morphological approach and DNA barcoding to distinguish filarioid nematodes species (Nematoda, Spirurida). A reliable and rapid taxonomic identification of these parasites is the basis for a correct diagnosis of important and widespread parasitic diseases. The performance of DNA barcoding with different parameters was compared measuring the strength of correlation between morphological and molecular identification approaches. Molecular distance estimation was performed with two different mitochondrial markers (coxI and 12S rDNA) and different combinations of data handling were compared in order to provide a stronger tool for easy identification of filarioid worms.
DNA barcoding and morphology based identification of filarioid nematodes revealed high coherence. Despite both coxI and 12S rDNA allow to reach high-quality performances, only coxI revealed to be manageable. Both alignment algorithm, gaps treatment, and the criteria used to define the threshold value were found to affect the performance of DNA barcoding with 12S rDNA marker. Using coxI and a defined level of nucleotide divergence to delimit species boundaries, DNA barcoding can also be used to infer potential new species.
An integrated approach allows to reach a higher discrimination power. The results clearly show where DNA-based and morphological identifications are consistent, and where they are not. The coherence between DNA-based and morphological identification for almost all the species examined in our work is very strong. We propose DNA barcoding as a reliable, consistent, and democratic tool for species discrimination in routine identification of parasitic nematodes.
The identification of filarioid and related nematodes via DNA barcoding is an ambitious and desirable goal for many reasons: 1) a fast identification engine, available not only for taxonomists, but validated by them, is useful for quicker diagnoses of filariasis; 2) filarioids cause diseases of high relevance in medical and veterinary fields throughout the world; 3) DNA barcoding can be useful for those cases of difficult or impossible identification by traditional procedures, such as co-infections with more than one filarioid species (e.g. Onchocerca volvulus and Loa loa; see ); 4) parasites conferred to diagnostic laboratories are often of poor quality due to the difficult of sampling adults and undamaged organisms; 5) the model of filarioid nematodes being based on a very good classical taxonomy (starting from ) allow to avoid (as much as possible) problems of 'bad taxonomy' (see discussion in ); 6) DNA barcoding can offer a reliable method for the identification of filarioid nematodes in vectors, allowing widespread campaigns of epidemiological surveys; 7) nematode biodiversity is still highly underestimated both at the morphological and molecular level , and a molecular approach will speed up the estimation of this taxonomic diversity . 2b1af7f3a8