BRIEF REPORT |
Correspondence to: Yuko Ito, MS: 74-157 Life Sciences Div., Lawrence Berkeley National Laboratory, Berkeley, CA 94720. E-mail: yito@lbl.gov
![]() |
Summary |
---|
![]() ![]() ![]() ![]() |
---|
HMGN3 (Trip7) is a member of the high-mobility group N (HMGN) nucleosome-binding protein family, which binds specifically to nucleosomes, reduces the compactness of the chromatin fiber, and enhances transcription from chromatin templates. By Western blotting and Northern blotting analysis, we showed that HMGN3 is expressed in a tissue-specific manner, with the strongest expression in mouse brain. Here we analyzed the expression of HMGN3 in various regions of the mouse brain by histological techniques. Enhanced expression of HMGN3 was observed in the lateral olfactory tract, anterior commissure, corpus callosum, internal capsule, fornix, stria medullans, optic tract, and axon bundles. The expression patterns of HMGN3 in the mouse brain was significantly different from that of the related protein HMGN2 and was very similar to that of the glial fibrillary acidic protein (GFAP). We suggest that HMGN3 might play a role in astrocyte function.
(J Histochem Cytochem 50:12731275, 2002)
Key Words: immunohistochemical, expression, HMG proteins, chromatin, mouse brain, GFAP
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() |
---|
The high-mobility group (HMG) proteins are a class of relatively abundant non-histone nuclear proteins, which function as architectural elements (
The HMG proteins are divided into three subgroups: HMGB (formerly HMG-1/-2), HMGA (formerly HMGI/Y/C), and HMGN (formerly HMG-14/-17/Trip 7) (
HMGN2 (HMG17) is a well-characterized protein that binds specifically to nucleosomes, reduces the compactness of chromatin fiber, and enhances transcription from chromatin templates (
Adult mice (20 weeks of age) were sacrificed by decapitation, the brain was removed, immediately immersed in fresh PBS containing 4% paraformaldehyde for 4 hr and 70% EtOH at 4C overnight, and then embedded in paraffin. For immunohistochemical staining, paraffin sections were first blocked with PBSTmilk (PBS with 0.1% Tween-20 and 2.5% dry milk) solution and then incubated overnight at room temperature (RT) with either polyclonal rabbit anti-hHMGN3 (dilution 1:100; antibody 2752) (
The immunohistochemical data revealed that the expression of HMGN3 was enriched in specific regions of the mouse brain (Fig 1B; Table 1). Relatively high expression levels were detected in fiber bundles including the lateral olfactory tract, anterior commissure, corpus callosum, internal capsule, fornix, stria medullans, optic tract, and axon bundles. Most of these regions are part of the thalamocortical sensory pathway (
|
|
We found that the expression patterns of HMGN3 in mouse brain are similar to that of GFAP (Fig 1C; Table 1). GFAP (glial fibrillary acidic protein) synthesis is considered an important factor in astrocyte differentiation and is part of the reactive response of the CNS to injury (
Thyroid hormones (T3) and thyroid hormone receptors (TRs) also act as chromatin-remodeling factors and are considered to be transcriptional co-activators (
To further study the co-localization of HMGN3 with GFAP at the cellular level, we performed double immunofluorescence (Fig 2) with cerebellum, a region in the brain where the distribution of HMGN3 is similar to that of GFAP (Fig 1). As indicated in Fig 2 (middle), expression of HMGN3 was detected in the purkinje cell layer (PC) and was especially prominent in the granular layer (GL). GFAP was also prominently detected in the GL layer (Fig 2, upper). In the molecular layer (MO), the expression of both proteins was not prominent (Fig 2, upper and middle). A merge of the two images (Fig 2, bottom) indicates that the distribution of GFAP (red) partially overlapped (yellow) with that of HMGN3 (green).
These observations, together with our present findings that the localization of chromosomal protein HMGN3 in the mouse brain is similar to that of GFAP, raise the possibility that the distribution of HMGN3 is related to the expression of GFAP. We find that many of the fiber tracts that are related to sensory pathways are strongly immunoreactive for HMGN3. However, we also observed differences in the expression patterns of HMGN3 and GFAP, especially in that the outer Purkinje cells in the PC layer and fibrous cells in the GL layer were prominently stained by HMGN3 (Fig 2). We speculate that HMGN3 might be expressed not only in astrocytes but also in other cells. Therefore, our results raise the possibility that HMGN3 protein plays a functional role in the astrocytes of mouse brain.
Received for publication February 25, 2002; accepted May 15, 2002.
![]() |
Literature Cited |
---|
![]() ![]() ![]() ![]() |
---|
Alcantara AA, Pfenninger KH, Greenough WT (1992) 5B4-CAM expression parallels neurite outgrowth and synaptogenesis in the developing rat brain. J Comp Neurol 319:337-348[Medline]
Bustin M (1999) Regulation of DNA-dependent activities by the functional motifs of the high-mobility-group chromosomal proteins. Mol Cell Biol 19:5237-5246
Bustin M (2001a) Revised nomenclature for high mobility group (HMG) chromosomal proteins. Trends Biochem Sci 26:152-153[Medline]
Bustin M (2001b) Chromatin unfolding and activation by HMGN(*) chromosomal proteins. Trends Biochem Sci 26:431-437[Medline]
Bustin M, Hopkins RB, Isenberg I (1978) Immunological relatedness of high mobility group proteins from calf thymus. J Biol Chem 253:1694-1699[Abstract]
Bustin M, Reeves R (1996) High mobility group chromosomal proteins: architectural components that facilitate chromatin function. In Cohn WE, Moldave M, eds. Progress in Nucleic Acid Research and Molecular Biology. Vol 54. San Diego, Academic Press, 35-100
Collingwood TN, Urnov FD, Wolffe AP (1999) Nuclear receptors: coactivators, corepressors and chromatin remodeling in the control of transcription. J Mol Endocrinol 23:255-275
Eng LF, Ghirnikar RS, Lee YL (2000) Glial fibrillary acidic protein: GFAP-thirty-one years (1969-2000). Neurochem Res 25:1439-1451[Medline]
Gomes FCA, Paulin D, MouraNeto V (1999) Glial fibrillary acidic protein (GFAP): modulation by growth factors and its implication in astrocyte differentiation. Braz J Med Biol Res 32:619-631[Medline]
Lee JW, Choi H-S, Gyuris J, Brent R, Moore DD (1995) Two classes of proteins dependent on either the presence or absence of thyroid hormone for interaction with the thyroid hormone receptor. Mol Endocrinol 9:243-254[Abstract]
Thompson CC, Potter GB (2000) Thyroid hormone action in neural development. Cereb Cortex 10:939-945
West KL, Ito Y, Birger Y, Postnikov Y, Shirakawa H, Bustin M (2001) HMGN3a and HMGN3b, two protein isoforms with a tissue-specific expression pattern, expand the cellular repertoire of nucleosome binding proteins. J Biol Chem 276:25959-25969
Wolffe AP, Hayes JJ (1999) Chromatin disruption and modification. Nucleic Acids Res 27:711-720
Wolffe AP, Kurumizaka H (1998) The nucleosome: a powerful regulator of transcription. Prog Nucleic Acids Res Mol Biol 61:379-422[Medline]