Matthew I. Goldsmith, M.D.

Assistant Professor
Pediatric Critical Care Medicine

Developmental, Regenerative and Stem Cell Biology Program
Molecular Genetics and Genomics Program

Research Abstract:

General Area of Interest
My lab is interested in skeletal biology and growth control, including growth during normal ontogeny and during the regeneration of tissues/organs. We’re using the zebrafish as a model system to dissect these processes. We’re particularly interested in the relationship between nutrition, metabolism and growth.

Normal Growth and Development
We previously have shown that growth of the adult zebrafish caudal fin is saltatory (Goldsmith et al., 2003). That is, growth proceeds through discreet episodes of growth and rest. Interestingly, growth in other vertebrates, including humans, has also been shown to be saltatory in nature. Caudal fin growth in zebrafish is also isometric. That is, the fin grows in proportion to the rest of the fish. Isometric growth is interesting because we have mutants (see below) that disrupt isometric fin growth. Unlike adult zebrafish, juvenile caudal fin growth is continuous and allometric (Goldsmith et al., 2006). Interestingly, while growth of the adult fin is exquisitely sensitive to nutritional status (fin growth stops within days of initiating a fast), the juvenile fin continues to grow during fasting until the adult fin form is achieved. In addition, growth of the adult, but not the juvenile fin is abrogated by the drug rapamycin. Rapamycin blocks the TOR signaling pathway that is important in sending nutritional status in all eukaryotes, from yeast to humans. We are currently further investigating the role of TOR signaling in juvenile and adult fin growth. Rapunzel (rap) and long fin (lof) are two zebrafish fin overgrowth mutants wherein isometric control of fin growth is lost. Interestingly, fasting rapidly abrogates fin growth in the lof, but not the rap mutant. We have mapped the rap mutation and are nearing completion of the positional cloning project. All of the candidate genes encode for novel, previously unidentified proteins. Therefore, rap provides a novel segue for dissecting the biology of nutrition and growth control.

We are exploring the link between regeneration, nutrition and metabolism. Unlike adult fin growth, fasting does not abrogate regenerative fin growth. In other words, nutrients must be reallocated from other tissues in the starving animal to support the regenerating fin. We would like to understand how this occurs. The Target of Rapamycin (TOR) pathway is an ancient signaling pathway thought to link a cell/organisms nutritional status with growth signals. However, rapamycin (a TOR inhibitor) does not block fin regeneration (it does abrogate normal fin growth in adult zebrafish). We are proposing to knock down components of the TOR signaling pathway during regeneration to further dissect this observation. In addition, we’re beginning to explore the link between nutrition/energy homeostasis in the fish in general and regenerative growth. We are using respirometry to study metabolism/O2 consumption during regeneration. In addition, we are looking at the activity of particular enzymes involved in carbohydrate, protein and fat metabolism during regeneration in fed or fasted conditions. Finally, microRNA’s have recently been implicated as being important in metabolic homeostasis. We are exploring the role of microRNA’s in maintaining metabolic homeostasis during regeneration. We have recently (~ 6 months ago) undertaken a forward genetic mutagenesis screen. Wild type male zebrafish are mutagenized (ENU) and then crossed to wild type females to generate families of fish (F1’s) that are carriers for random mutations (ENU-induced alleles tend to be point mutations, although not all are). We obtain eggs from the F1 females and use early pressure parthenogenesis to generate homozygous F2 lines. These fish are grown up and then screened for fin regeneration mutants. We screen for temperature-sensitive alleles so as to try and capture mutations in genes that might be essential early in development and therefore otherwise lethal. Because we’re screening for an adult phenotype, it’s a somewhat laborious screen. We’ve screened approximately 400 F1 families thus far and we have identified 10-15 putative mutants (not all will turn out to be real). My goal is to screen 1500-2000 F1 families. Fin regeneration mutants will be screened in secondary screens to identify genes involved in the regeneration of other structures (liver, heart, embryonic fin fold, scales). We’re using forward genetics as an unbiased approach to identify novel genes and pathways important in tissue regeneration. Finally, my lab is investigating the origins of the cells that form the new fin during regeneration. That is, where do the cells of the regeneration blastema come from and what do they become? Are all of the cells derived locally, or do some arise from distant locations (e.g. circulating stem cells)? Do a limited pool of precursors (i.e. stem cells) contribute to the regenerating structure or do all classes of differentiated cells (e.g. bone, endothelium, mesenchyme, skin, nerve) dedifferentiate, populate the blastema, an divide and differentiate into the new structure? We are currently using lineage tracing of chimeric clones of labeled cells (GFP) to begin to answer these questions.

Selected Publications:

Oppedal D and Goldsmith MI. A chemical screen to identify novel inhibitors of fin regeneration in zebrafish. Zebrafish 2010 7(1):53-60.

Green J, Taylor J, Hindes A, Johnson SL and Goldsmith MI. A gain of function mutation causing skeletal overgrowth in the rapunzel mutant. Dev Biol. 2009 334(1):224-234.

Schuettpelz L, Behrens D, Goldsmith MI and Druley T. Survival following severe ceftriaxone-induced hemolytic anemia. Journal of Pediatric Hematology and Oncology. 2009 11:870-872.

Goldsmith MI, Iovine MK, O’Reilly-Pol T and Johnson SL. A developmental transition in growth control during zebrafish caudal fin development. Dev Biol. 2006 296:450-457.

Goldsmith MI, Fisher S, Waterman R and Johnson SL. Saltatory control of isometric growth in the zebrafish caudal fin is disrupted in long fin and rapunzel mutants. Dev Biol. 2003 259:303-317.

Last Updated: 7/30/2013 10:12:20 AM

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