An all-round talent: the protein Nulp1 is involved in many developmental processes in men and mice
Martina Saar
The development of single cells to a functional organ and finally a complete organism is an amazing interplay of numerous factors. Since their identification, a class of proteins called basic helix-loop-helix (bHLH) proteins has been found to be involved in various developmental processes. Generally, proteins are classified according to certain patterns or motifs in their basic components, the amino acids, or structures that are formed due to specific interactions between the amino acids. Characteristically, the bHLH proteins feature a stretch of basic amino acids (which can be charged positively) and two sections that are organized as helices and are connected by a flexible loop region. In the HLH region, one of the helices is typically smaller than the other and allows either two identical proteins to connect to form a homodimer, or two different proteins to build a heterodimer. The basicregionis found in most but not all HLH proteins and specifically binds to variations of certain DNA sequences.Many bHLH protein dimers work as activators of transcription (the first step in decoding DNA to make proteins). Nuclear localized protein-1 (Nulp1) is a recently identified protein foundin organs such as heart, kidney and brainduring mouse embryonic development. It contains anHLH domain as well as a stretch of basic residues that closely resembles the transcriptional activation domain of some bHLH proteins. Nulp1 has beenfound in the cell nucleus,indicating its probable involvement in transcriptional processes. The human form hNulp1 also contains a bHLH domain and has been found to be particularly abundant in adult heart. Nulp1 is also expressed in tumor cells, in mouse and human alike. Interestingly, a smaller variant of the Nulp1 protein was found in tumors in addition to the protein in regular cells, suggesting a tumor specific variant that may be linked to cell malignancy.
The aim of this project was to investigate more closely the expression of Nulp1 in mouse brain and other organs and to analyze the truncated form that is found in tumor cells. This was done via a visualization of the protein with a fluorescent color in tissue sections. Furthermore, the amount of protein in several areas of the brain as well as liver, kidney and muscle was quantified. The intended analysis of the tumor variant could not be performed successfully due to methodical problems. Nevertheless, I confirmed that Nulp1 is expressed at notably higher levels in embryonic mouse brain, liver, kidney, lung and several other organs. In very young mice and also adults I measured a particularly high expression in brain and especially within the cerebellum, the part of the brain mainly responsible for orientation and movement. In the other above mentioned adult organs Nulp1 could not be identified indisputably. The fluorescence pictures that were taken further revealed that the area within the cerebellum where the highest expression was observed shifted postnatally. While the outermost cell layers showed the strongest signals for Nulp1 in very young mice, in adult mice the most intense signals were seen within an inner layer. This finding suggests a role of Nulp1 in the maturation of cerebellar neurons that takes place postnatally and involves the inner-directed migration of developing cells. In addition to these developmental functions that Nulp1 seems to have, thre future will show if there is a further involvement in programmed cell death and/or cell malignancy.
Degree project in Biology, winter 2006
Examensarbete i biologi, 10p, winter 2006
Department of Biology Education and
Department of Cell Neurosciences, Neurobiology, Uppsala University
Supervisor: Prof. Dan Lindholm and PhD student Hakan Steen