Expression and Functional Characterization of Xhmg-at-hook Genes in Xenopus laevis

Abstract

High Mobility Group A proteins (HMGA1 and HMGA2) are architectural nuclear factors involved in development, cell differentiation, and cancer formation and progression. Here we report the cloning, developmental expression and functional analysis of a new multi-AT-hook factor in Xenopus laevis (XHMG-AT-hook) that exists in three different isoforms. Xhmg-at-hook1 and 3 isoforms, but not isoform 2, are expressed throughout the entire development of Xenopus, both in the maternal and zygotic phase. Localized transcripts are present in the animal pole in the early maternal phase; during the zygotic phase, mRNA can be detected in the developing central nervous system (CNS), including the eye, and in the neural crest. We show evidence that XHMG-AT-hook proteins differ from typical HMGA proteins in terms of their properties in DNA binding and in protein/protein interaction. Finally, we provide evidence that they are involved in early CNS development and in neural crest differentiation.

HMGA Genes and Proteins in Development and Evolution

“…Consistent with these different features, Hmg-at-h1 protein showed quite distinct biochemical properties compared to HMGA1 and HMGA2 [139]. Hmg-at-h1, 2 and 3 cDNAs are all potentially encoded in the single locus existing in Xenopus tropicalis, as well as in the duplicated loci of Xenopus laevis [139]. The expression of these cDNAs was analyzed during embryogenesis; basically, hmg-at-h2 is undetectable, hmg-at-h1 is more abundant as a maternal transcript and then levels off, hmg-at-h3 is expressed at low levels initially and then becomes upregulated during the neurula stages.…”

“…hmg-at-hook1, 2 and 3 (hmg-at-h1, hmg-at-h2 and hmg-at-h3) code for proteins containing 8, 8, or 6 AT-hook domains, respectively; differently from HMGA, none of these cDNAs encode a terminal acidic tail. Consistent with these different features, Hmg-at-h1 protein showed quite distinct biochemical properties compared to HMGA1 and HMGA2 [139]. Hmg-at-h1, 2 and 3 cDNAs are all potentially encoded in the single locus existing in Xenopus tropicalis, as well as in the duplicated loci of Xenopus laevis [139].…”

“…The functional role of these proteins was studied by morpholino (MO) antisense injections targeting all the three potential mRNAs, for single or combined ablation. Effects were very mild or absent when MOs for each transcript were injected separately; when MOs against the two most expressed mRNAs, hmg-at-h1 and hmg-at-h3, where combined together, a small, but detectable, disturbance was observed on the cranio-skeletal derivatives of the branchial arches and on the dimensions of the eye vesicle, and was accompanied by reduced expression of relevant neural crest markers [139].…”

“…The expression of these cDNAs was analyzed during embryogenesis; basically, hmg-at-h2 is undetectable, hmg-at-h1 is more abundant as a maternal transcript and then levels off, hmg-at-h3 is expressed at low levels initially and then becomes upregulated during the neurula stages. Localized transcripts are detectable at early tailbud stage in the developing CNS (including the eye) and in the neural crest and its derivatives [139]. The functional role of these proteins was studied by morpholino (MO) antisense injections targeting all the three potential mRNAs, for single or combined ablation.…”

HMGA1 zebrafish co-orthologue hmga1b can modulate p53-dependent cellular responses but is unable to control the alternative splicing of psen1

“…HMGA1 orthologous genes are expressed during vertebrate embryogenesis 3,[33][34][35] and are also commonly upregulated during cancer progression 28 . They are upregulated in response to hypoxia via a mechanism dependent on reactive oxygen species 9,27 .…”