Biomedical subjects

L Amaravadi

Publications and source records attributed to L Amaravadi.

5 recordsLinked to original sources

PubMed1999

Functional and structural diversity of the human Dickkopf gene family.

Wnt proteins influence many aspects of embryonic development, and their activity is regulated by several secreted antagonists, including the Xenopus Dickkopf-1 (xDkk-1) protein. xDkk-1 inhibits Wnt activities in Xenopus embryos and may play a role in induction of head structures. Here, we characterize a family of human Dkk-related genes composed of Dkk-1, Dkk-2, Dkk-3, and Dkk-4, together with a unique Dkk-3 related protein termed Soggy (Sgy). hDkks 1-4 contain two distinct cysteine-rich domains in which the positions of 10 cysteine residues are highly conserved between family members. Sgy is a novel secreted protein related to Dkk-3 but which lacks the cysteine-rich domains. Members of the Dkk-related family display unique patterns of mRNA expression in human and mouse tissues, and are secreted when expressed in 293T cells. Furthermore, secreted hDkk-2 and hDkk-4 undergo proteolytic processing which results in cleavage of the second cysteine-rich domain from the full-length protein. Members of the human Dkk-related family differ not only in their structures and expression patterns, but also in their abilities to inhibit Wnt signaling. hDkk-1 and hDkk-4, but not hDkk-2, hDkk-3 or Sgy, suppress Wnt-induced secondary axis induction in Xenopus embryos. hDkk-1 and hDkk-4 do not block axis induction triggered either by Xenopus Dishevelled (Xdsh) or Xenopus Frizzled-8 (Xfz8), both of which function to transduce signals from Wnt ligands. Thus, hDkks 1 and 4 may inhibit Wnt activity by a mechanism upstream of Frizzled. Our findings highlight the structural and functional heterogeneity of human Dkk-related proteins.

Amino Acid Sequence↗

PubMed1999

DNA methylation and chromatin structure regulate PU.1 expression.

Knockout studies have shown that PU.1 is required for the normal development of many blood cell lineages, yet overexpression of this transcription factor in erythroid cells can lead to erythroleukemia. Thus, how the tissue-specific expression of PU.1 is regulated is important to our understanding of hematopoiesis. In this study, we showed that B and macrophage cell lines expressing PU.1 contained DNase I-hypersensitive sites in intron 1 and were hypomethylated at three MspI sites flanking exon 1. Results from studies using several T-cell lines suggested that the pattern of methylation changed as these cells matured. A pre-T cell line that expresses PU.1 contained DNase I-hypersensitive sites in intron 1 and was also hypomethylated at both MspI sites. Other immature T-cell lines had methylated at least one of the MspI sites and displayed no hypersensitive sites. Mature T-cell lines had a methylation pattern more similar to that of fibroblasts. Treatment of an immature T-cell line with 5-azacytidine resulted in the expression of PU.1 transcripts. These data suggest that the tissue-specific expression of PU.1 is controlled by chromatin structure and DNA methylation and that this may be a mechanism used to shut off PU.1 expression in specific cell lineages during hematopoiesis.

Animals↗

PubMed1994

Drosophila Forkhead homologues are expressed in CD34+/HLA-DR- primitive human hematopoietic progenitors.

The Forkhead gene (FKH) regulates morphogenesis in Drosophila. It is the prototype of a new family of transcriptional activators. We used the polymerase chain reaction (PCR) to analyze the expression pattern of this new transcriptional regulatory gene family in primitive hematopoeitic progenitors. Partially degenerate oligonucleotides to two conserved amino acid sequences of this family were used to prime a PCR amplification of cDNA synthesized from CD34+/HLA-DR- hematopoietic cells. Known and novel FKH genes were found to be expressed in these cells.

Animals↗

PubMed1994

Characterization and expression of the Xenopus c-Myb homolog.

The c-Myb protein is a sequence specific DNA-binding transcriptional regulator that is critically involved in the regulation of hematopoietic differentiation. Its role in these processes suggests that the function of c-Myb may be important early in the establishment of the hematopoietic lineage. We have isolated cDNA and partial genomic clones representing the Xenopus c-Myb homolog (Xc-Myb) in order to examine the role this gene plays in early mesodermal patterning in the frog embryo. The establishment of these clones as c-Myb homologs, as opposed to Myb-related sequences, is based upon both predicted amino acid sequences and the location of the exon-intron boundaries within the Xc-Myb gene. Maternally derived Xc-Myb RNA is degraded following fertilization then, beginning at midblastula, re-accumulates throughout early development. Xc-Myb RNA is localized to the animal cap region of the early blastula. Following the onset of gastrulation expression predominates in the ventral half of the embryo. During neurulation expression of Xc-Myb is observed in both the anterior dorsal and ventral vegetal regions of the embryo. Expression of Xc-Myb occurs in several adult tissues, the highest levels of which are in the intestine, heart, liver, lung and ovary. Xc-Myb encodes a protein of 624 amino acids and exhibits a mobility in SDS-PAGE of approximately 75 kDa, identical with that of the murine c-Myb protein. Xc-Myb protein exhibits 70% identity with avian and 67% identity with mammalian c-Myb proteins.

Amino Acid Sequence↗

PubMed1994

A rapid and efficient, nonradioactive method for screening recombinant DNA libraries.

In this report we present a rapid and inexpensive PCR-based method to screen recombinant DNA libraries. The efficiency of this method was demonstrated by the isolation of clones of interest from three different libraries using different vector systems. This method is nonradioactive and makes it easier to handle a large number of samples since there is no need for DNA extraction. The advantages and applications of the method are discussed.

Animals↗