Tapio Heino - Genetics

Drosophila as model organism in developmental biology

Univeristy lecturer Tapio Heino >> Group and contact

Research | Actin binding proteins in development | Selected Publications | Other projects

The fruit fly, Drosophila melanogaster, is one of the most studied eukaryotic organisms After its introduction as an experimental organism at the beginning of the last century, the powerful genetics of Drosophila has placed it in the forefront of many areas of research, notably in developmental biology.

Several genes and gene families which were first found to be important for the development of the fly have turned out to perform analogous functions in mammalian development. An integral part of the human genome project is computational cross-referencing to well-studied model organisms, such as Drosophila, which offer a huge amount of information such as mutant phenotypes and associated sequence data. All the genes which the members of our group are working on have clear human homologues.

Research

Recently Drosophila has become a popular model to understand the biology of human neurodegenerative diseases. Despite substantial amount of similarities between the human and insect central nervous systems, neurotrophic factors (factors which promote and maintain neuronal growth) have remained unidentified in Drosophila. Our project on this field deals with the first fruit fly protein showing high homology to the vertebrate neurotrophic factor, MANF. It has been shown by Petrova et al. (J Mol Neurosci 20:173-187, 2003) that human MANF specifically supports the survival of dopaminergic neurons in vitro. We have characterized Drosophila MANF expression both by in situ hybridisation and immunocytochemistry using an antiserum raised by us.

To analyse the function of the Drosophila MANF gene, we have generated MANF null mutants. These mutants were larval lethal and were rescued using ectopically expressed Drosophila MANF. The goal of our research is to solve the function of Drosophila MANF. By using genetic and biochemical methods, our first task is to identify the as yet unknown receptor. We are also taking advantage of Drosophila cultured cells to find out the MANF mode of action. This part of our research is conducted in close collaboration with the group of Prof. Mart Saarma (Institute of Biotechnology).

Drosophila nervous system

 

 

Drosophila nervous system visualised with monoclonal antibody 22C10.

 

 

Actin binding proteins in development

The actin cytoskeleton is essential for cellular remodeling as well as many developmental and morphological processes. One of our research topics is to use Drosophila as a model to understand the role of actin-binding proteins in the development of multicellular animals. Our aim is to analyze the functions of actin and actin-regulatory proteins in the context of an intact metazoan animal. Using the Drosophila model we have shown (in collaboration with Dr. Pekka Lappalainen, Institute of Biotechnology) for the first time the essential developmental role of the novel actin-monomer-binding protein twinfilin in animal development.

Twinfilin is a ubiquitous actin monomer–binding protein whose biological function has remained unclear. We discovered and cloned the Drosophila twinfilin homologue, and showed that this protein is ubiquitously expressed in different tissues and developmental stages. A mutation in the Drosophila twinfilin gene leads to a number of developmental defects, including aberrant bristle morphology. This results from uncontrolled polymerization of actin filaments and misorientation of actin bundles in developing bristles. In wild type bristles, twinfilin localizes diffusively to cytoplasm and to the ends of actin bundles, and may therefore be involved in localization of actin monomers in cells.

Our studies have also shown that twinfilin and the ADF/cofilin encoding gene twinstar interact genetically in bristle morphogenesis. These results demonstrate that the accurate regulation of size and dynamics of the actin monomer pool by twinfilin is essential for a number of actin-dependent developmental processes in multicellular eukaryotes.

Scanning electron micrographs of bristles in the thorax of adult Drosophila.

Scanning electron micrographs of bristles in the thorax of adult Drosophila. Surface of a wild-type bristle (top) showing straight longitudinal ridges.

Twinfilin mutant bristles have highly irregular ridges (bottom) due to uncontrolled polymerization of actin filaments and misorientation of actin bundles.

Another actin-binding protein we are studying (in collaboration with Dr. Christophe Roos, MediCel Ltd., Helsinki) is alpha-actinin which is an actin cross-linking protein belonging to the spectrin superfamily of proteins. Contrary to mammalian genomes, only a single alpha-actinin gene exists in Drosophila, which is alternatively spliced to generate three different isoforms that are expressed in larval muscle, adult muscle and non-muscle cells, respectively. We have generated novel alpha-actinin alleles, which specifically remove the non-muscle isoform. Surprisingly, the homozygous mutant flies are viable and fertile with no obvious defects. Using a monoclonal antibody that recognizes all three splice variants, we have compared alpha-actinin distribution in wild type and mutant ovaries. The non-muscle alpha-actinin is localized in the nurse cell subcortical cytoskeleton, cytoplasmic actin cables and ring canals. Our studies have also shown that ectopically expressed adult muscle-specific alpha-actinin localizes to all F-actin containing structures in the nurse cells in the absence of endogenous non-muscle alpha-actinin.

Other projects

Until now, attempts at gene targeting in Drosophila have been limited to transposable P elements, which insert genes randomly into the genome. Recently an effective RNAi method was presented that is based on the generation of transgenic flies expressing a hybrid construct of genomic and cDNA sequences. This can be applied to the UAS-GAL4 system to effectively knock-down genes in a tissue-specific manner. Our laboratory, together with Dr. Mikko Frilander (Institute of Biotechnology), has succesfully used this conditional RNAi methodology in vivo. With this tool we can use it to knock-down any Drosophila gene of interest.

Selected publications

Tselykh TV, Roos C and Heino TI. The mitochondrial ribosome-specific MrpL55 protein is essential in Drosophila and dynamically required during development.
Experimental Cell Research 307:354-66, 2005. [PubMed]

Ivanov KI, Tselykh TV, Heino TI and Mäkinen K. The RISC component VIG is a target for dsRNA-independent protein kinase activity in Drosophila S2 cells. Journal of RNAi and Gene Silencing 1:12-20, 2005.

Wahlström G, Lahti V-P, Pispa J, Roos C and Heino TI. Drosophila non-muscle alpha-actinin localizes in ovarian ring canals and actin bundles, but is not required for fertility. Mechanisms of Development, 121:137-1391, 2004. [PubMed]

Meng X, Wahlström G, Immonen T, Kolmer M, Tirronen M, Predel R, Kalkkinen N, Heino TI, Sariola H, Roos C. The Drosophila hugin gene codes for myostimulatory and ecdysis modifying neuropeptides. Mechanisms of Development 117: 5-13, 2002. [PubMed]

Wahlström G, Vartiainen M, Yamamoto L, Mattila PK, Lappalainen P, Heino TI. Twinfilin is required for actin-dependent processes in Drosophila. Journal of Cell Biology 155: 787-796, 2001. [PubMed]

Heino TI, Kärpänen T, Wahlström G, Pulkkinen M, Eriksson U, Alitalo K, Roos C. Drosophila VEGF receptor homologue is specifically expressed in haemocytes. Mechanisms of Development 109: 69-77, 2001. [PubMed]

Group

Group Leader: Tapio Heino, PhD, Docent, Senior lecturer
Tel. +358 (0)2 941 59590
Fax +358 (0)2 941 59366
Tapio dot Heino -at- Helsinki dot Fi

PhD students:

Mari Palgi, M.Sc.
Neurotrophic factors
Mari dot Palgi -at- Helsinki dot Fi

Gudrun Wahlström, M.Sc.
Actin binding proteins
Gudrun dot Wahlstrom -at- Helsinki dot Fi

MSc Student:

Riitta Lindström
Neurotrophic factors
Riitta dot Lindstrom -at- Helsinki dot Fi

Alumni:

Timofei Tselykh, MSc