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Small GTPases of the recently discovered Ras-dva family are specific to the Vertebrate phylum. In Xenopus laevis, Ras-dva-1 is expressed during gastrulation and neurulation in the anteriorectoderm where it regulates the early development of the forebrain and cranial placodes (Tereshina et al., 2006). In the present work, we studied the expression of Ras-dva-1 at later developmental stages. As a result, the Ras-dva-1 expression was revealed in the eyeretina, epiphysis (pineal gland), hypophysis (pituitary), branchial arches, pharynx, oesophagus, stomach and gall bladder of swimming tadpoles. Additionally, we investigated for the first time the expression pattern of Ras-dva-2. This gene encodes a protein belonging to a novel sub-group of Ras-dva GTPases that we identified by phylogenetic analysis within Ras-dva family. In contrast to Ras-dva-1, Ras-dva-2 is not expressed before the swimming tadpole stage. At the swimming tadpole stage, however, Ras-dva-2 transcripts can be detected in the eyeretina and brain. Later in development, the expression of Ras-dva-2 can also be revealed in the mesonephros and stomach.
Fig. 1. Expression pattern of Ras-dva-1 in Xenopus laevis tadpoles. (A and B) In situ hybridisation of the whole tadpole at stage 46. The tadpole is shown from the dorsal (A) and right (B) sides. Ras-dva-1 positive cells are localised in the epiphysis, hypophysis, eye, branchial arches (gills), cement gland, pharynx, oesophagus, stomach and gall bladder. The dotted lines indicate the positions of the sagittal sections shown in D and E. (C) The in situ hybridisation on the whole brain extirpated from a tadpole at stage 45 demonstrates that Ras-dva-1 is specifically expressed in the epiphysis and hypophysis. Dorsal side up, anterior to the left (see scheme of the brain units on Fig. 4E). (D) Ras-dva-1 expression in the cement gland, pharynx and epiphysis as it is seen on the medial sagittal section (see position of the section in A). (E) Para-sagittal section of the tadpole (see position of the section in A) shows that Ras-dva-1 is expressed only in the anterior and posterior regions of the stomach and not in the small intestine. In the anteriorstomach region, the strongest Ras-dva-1 expression can be detected in the areas of acinar glands (arrowheads), which are typical for that part of the gut where they secret different proteolytic enzymes and mucous. Additionally, in the posteriorstomach region Ras-dva-1 expression is stronger in the mucous epithelium (arrow), which lines the stomach cavity and secretes different compounds of the defensive mucous layer. (F) The transverse section of the eye shows that Ras-dva-1 expression is localised in the retina. (G) After staining by haematoxylin, the Ras-dva-1 expressing region can be identified as the Outer Plexiform Layer (OPL) of the retina. Ba – branchial arches (gills), Cg – cement gland, Epiph – epiphysis, Gb – gall bladder, GCL – ganglion cell layer, Hyp – hypophysis, In – intestine, INL – inner nuclear layer, Oe – oesophagus, ONL – outer nuclear layer, Ph – pharynx, PRL – photoreceptor layer, RPE – retinal pigment epithelium, Si – small intestine, St – stomach (aSt – anteriorstomach region, pSt – posteriorstomach region).
Fig. 2. Expression of Ras-dva-1 and Sox2 in guts extirpated from tadpoles at stage 42 and stage 46. (A and B) In contrast to the early marker of the anteriorgutSox2, Ras-dva-1 is not expressed in the gut until it completes differentiation by stage 45–46. (C and D) Like the expression of Sox2, Ras-dva-1 expression can be seen in the oesophagus, stomach and also in the gall bladder. Abbreviations as in Fig. 1. Additionally: Pa – pancreas, Pr – proctodeum.
Fig. 4. Expression pattern of Ras-dva-2 in Xenopus laevis tadpoles. (A and B) In situ hybridisation of the whole tadpole at stage 46. The tadpole is shown from the dorsal (A) and right (B) sides. Ras-dva-2 expressing cells are localised to the brain, eyes and mesonephros. Additionally, weak expression can also be detected in the stomach. (C and D) The dorsal and lateral views of the dissected brain (stage 45) after the in situ hybridisation. The red asterisk indicates the rostral end of the brain. Ras-dva-2 is expressed in the diencephalon – in thalamic nucleus, preoptic nucleus and in pretectumnucleus, in the mesencephalon – within the optic tectum; and also in some cell clusters located in the hindbrain (arrowheads). The lines in D indicate the positions of transverse sections shown in F, G and H. (E) The scheme of the brain units at stage 45. Dorsal side up, the red asterisk indicates the rostral end of the brain. (F) The transverse section of the diencephalon shows Ras-dva-2 expression in the ventromedial thalamic nucleus, posteroventral division of lateral thalamic nucleus and preoptic nucleus. (G) On the transverse section of the mesencephalon Ras-dva-2 positive cells mark the optic tectum, anterodorsal and anteroventral tegmental nuclei. (H) The transverse section of the hindbrain shows Ras-dva-2 expression in nucleus descendens and nucleus motorius nervi trigemini. (I) On the transverse section of the eye Ras-dva-2 expression can be detected in some layers of the retina. (K) Nuclei staining by haematoxylin shows that the Ras-dva-2 expressing layers correspond to the inner nuclear and inner plexiform layers (INL and IPL) of the retina. Abbreviations as in Fig. 1. Additionally: Ad – anterodorsal tegmental nucleus, Av – anteroventral tegmental nucleus, Lpv – lateral thalamic nucleus, pars posteroventralis, Mn – mesonephros, Ot – optic tectum, Pon – preoptic nucleus, Ptn – pretectumnucleus, Tn – thalamic nucleus, VM – ventromedial thalamic nucleus, Vd – nucleus descendens nervi trigemini, Vm – nucleus motorius nervi trigemini.
