Identification and developmental expression of Xenopus hmga2β

HMGA Genes and Proteins in Development and Evolution

HMGA (high mobility group A) (HMGA1 and HMGA2) are small non-histone proteins that can bind DNA and modify chromatin state, thus modulating the accessibility of regulatory factors to the DNA and contributing to the overall panorama of gene expression tuning. In general, they are abundantly expressed during embryogenesis, but are downregulated in the adult differentiated tissues. In the present review, we summarize some aspects of their role during development, also dealing with relevant studies that have shed light on their functioning in cell biology and with emerging possible involvement of HMGA1 and HMGA2 in evolutionary biology.

Hmga2 is required for neural crest cell specification in Xenopus laevis

HMGA proteins are small nuclear proteins that bind DNA by conserved AT-hook motifs, modify chromatin architecture and assist in gene expression. Two HMGAs (HMGA1 and HMGA2), encoded by distinct genes, exist in mammals and are highly expressed during embryogenesis or reactivated in tumour progression. We here addressed the in vivo role of Xenopus hmga2 in the neural crest cells (NCCs). We show that hmga2 is required for normal NCC specification and development. hmga2 knockdown leads to severe disruption of major skeletal derivatives of anterior NCCs. We show that, within the NCC genetic network, hmga2 acts downstream of msx1, and is required for msx1, pax3 and snail2 activities, thus participating at different levels of the network. Because of hmga2 early effects in NCC specification, the subsequent epithelial-mesenchymal transition (EMT) and migration of NCCs towards the branchial pouches are also compromised. Strictly paralleling results on embryos, interfering with Hmga2 in a breast cancer cell model for EMT leads to molecular effects largely consistent with those observed on NCCs. These data indicate that Hmga2 is recruited in key molecular events that are shared by both NCCs and tumour cells.

Expression and functional characterization of Xhmg-at-hook genes in Xenopus laevis

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.