Benini F et al. (2006), Identification and developmental expression of ...

XB-ART-34785

Biochem Biophys Res Commun 2006 Dec 15;3512:392-7. doi: 10.1016/j.bbrc.2006.10.074.

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Identification and developmental expression of Xenopus hmga2beta.

Benini F , Onorati M , Altamura S , Manfioletti G , Vignali R .

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HMGA proteins are "architectural modifiers" of the chromatin, characterized by three conserved "AT-hook" motifs, with which they bind AT-rich regions of the DNA, to assist in gene transcription. We report the identification and developmental expression of Xenopus laevis hmga2beta (Xlhmga2beta). We provide evidence of two forms of hmga2 (Xlhmga2alpha and Xlhmga2beta) and of a splicing variant for Xlhmga2beta with an additional AT-hook. By comparing X. laevis and X. tropicalis hmga2 DNA sequences to those of other organisms we show a high conservation of the Xlhmga2beta variant. By RT-PCR, Xlhmga2beta transcripts are first detected before the midblastula transition (MBT), and then become more abundant. By in situ hybridization, localized transcripts are first detected at neurula stages, in the presumptive central nervous system (CNS). At tailbud and tadpole stages, Xlhmga2beta mRNA is detected in the CNS, in the otic vesicles, in neural crest cell derivatives, in the notochord, and in the medio-lateral mesoderm.

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Species referenced: Xenopus laevis
Genes referenced: hmga2 odc1

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	Fig. 1. ClustalW alignment of HMGA2 amino acid sequences found in database search. Conserved AT-hooks are shaded. Amino acid identities are represented by (*), conservative amino acid substitutions by (:), and semi-conservative substitutions by (.).
	Fig. 2. (A) RT-PCR analysis of Xlhmga2b and ODC transcription during development. Developmental stages numbered as in [28]. (B–K) Expression of Xlhmga2b transcripts as detected by WISH during neurula stages. (B) stage 15, dorsal view: arrows show faint labelling in the anterior region of the neural plate; arrowheads show staining around the blastopore; (C) stage 15, posterior view; (D) stage 18, dorsal–lateral view; (E) stage 18, posterior view; (F) stage 18, anterior view; (G) stage 18 embryo hybridized with a sense probe, in dorsal view; (H) stage 20, dorsal view; (I) stage 20, posterior view; (J) stage 20, anterior view: arrowheads show more intensely labelled stripes in the presumptive brain region; (K) stage 20, sense probe, dorsal–lateral view.
	Fig. 3. Expression of Xlhmga2b transcripts at tailbud stages, as detected by WISH. (A) Expression at stage 25; labelling is clearly visible in the head region, and in the dorsal trunk region. (B) Expression at stage 29: strong labelling is detected in the neural tube (nt), especially in transversal stripes (black arrowheads), in the intermediate mesoderm (im, black arrowhead), and in the pharyngeal arches (pa, white arrowheads). (C) Expression at stage 33/34: arrowheads indicate expression in the pharyngeal arches, intermediate mesoderm, and in the notochord (no). (D) Detail of the head region of a stage 25 Xenopus embryo showing distribution of Xlhmga2b transcripts in the neural tube (arrowheads), and in the otic vesicle (arrows). (E) Horizontal section of a stage 29 embryo following in situ hybridization with a Xlhmga2b probe, showing intense labelling in the neural crest derivatives of the pharyngeal arches (from I to IV), but not in the endoderm. (F) Transversal section at an anterior level of a stage 33/34 embryo showing Xlhmga2b expression in neural crest cells (ncc) and in the pharyngeal arches (pa). (G) Transversal section of a stage 33/34 embryo at the level of the otic vesicles, showing Xlhmga2b transcript localization in the otic vesicles (ov), as well as in the heart-forming region (my, myocardium; ec, endocardium). (H) Transversal section of a stage 33/34 embryo at the trunk level, showing Xlhmga2b transcript localization in the neural crest cells (ncc) close to the dorsal neural tube and in the splanchnic layer of the intermediate mesoderm (im); the notochord is only slightly positive. (K) Transversal section of a stage 33/34 embryo at the posterior trunk level, showing Xlhmga2b transcript localization in the notochord (no) and intermediate mesoderm (im).
	Fig. 4. Expression of Xlhmga2b transcripts at tadpole stage 39 as detected by WISH. (A) Distribution of Xlhmga2b transcripts at stage 39. (B,C,D) Sections of stage 39 embryos following WISH to Xlhmga2b probe show transcript distribution in the head region, in the ventricular zone (vz, arrowheads) of the neural tube, in the condensing cartilaginous cells of the first pharyngeal (maxillary) arch (m), and in the condensing ceratohyal originating from the second pharyngeal arch (ch, arrowheads). (E) Horizontal section of a stage 39 embryo reveals strong staining of the notochord by the Xlhmga2b probe; somites (so) are only faintly stained. (F,G) Sections of the developing eye at stage 29 and 33/34, respectively, may be compared to those in section (D), at stage 39, showing initial limited expression of Xlhmga2b in the developing lens and in the surrounding neural retina territory (F, stage 29), that increases later at stage 33/34 to decline by stage 40. Picture shown in (D) was obtained by juxtaposition of two separate pictures of the same section.