Date of Degree

9-2022

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biochemistry

Advisor

Patrizia Casaccia

Committee Members

Carmen Melendez

Anne Schaefer

Mark Emerson

Peter Cannol

Subject Categories

Biochemistry | Developmental Neuroscience | Molecular and Cellular Neuroscience

Keywords

Oligodendrocytes, Myelin, Nuclear lamins, Laimin associated domains

Abstract

Differentiation of oligodendrocytes from progenitor cells is a highly regulated process characterized by a series of molecular changes, resulting in nuclear and morphological features unique to the mature oligodendrocyte state. Heterochromatin formation starting at the nuclear periphery, as well as increased nuclear rigidity are characteristically observed. The nuclear periphery is characterized by the presence of the nuclear lamina and it has been implicated in higher-order genome organization in cells. Lamins are the protein components of the nuclear lamina, and their expression is dependent upon the cell differentiation stage of the cells. While Lamin B1 (LMNB1) expression is high in progenitors and then progressively declines, Lamin A (LMNA) has an opposite behavior, with levels increasing as progenitors differentiate into oligodendrocytes. This dissertation focuses on the role of the nuclear lamins A and B1 at different stages of oligodendrocyte progenitor differentiation.In my Dissertation, I first address the importance of downregulation of LMNB1 levels during oligodendrocyte progenitor differentiation in vitro. Using overexpression of LMNB1 tethered to a bacterial enzyme responsible for adenosine methylation, I was able to define the genomic regions associated to LMNB1 at each stage of differentiation. Importantly, I identified a gene encoding for a key enzyme in the cholesterol synthesis, to remain associated to the nuclear lamina in differentiated OL overexpressing LMNB1. This suggested that decreased levels of LMNB1 during differentiation, allow the release from the periphery of genes important for myelin synthesis, which can be actively transcribed. It also provided a molecular mechanism for the lipid dysregulation associated with autosomal dominant adrenoleukodystrophies characterized by LMNB1 overexpression.

In the second part of my Dissertation, I contributed to the characterization of the role of LMNA in oligodendrocytes, using lineage specific conditional knockout mouse models, transcriptional and genome accessibility profiling, and studies in cultured primary cells. The study defines LMNA as required for the nuclear sequestration of genomic regions that are normally silenced and located in chromatin regions that are not accessible to transcription factors or enzymes in OL. I propose that LMNA is therefore critical to maintain the stability of the OL transcriptome and prevent inappropriate transcriptional responses to extracellular stimuli which could challenge the mature phenotype.Taken together, these results identify LMNB1 and LMNA as critical components in maintaining the unique transcriptional profile of oligodendrocyte lineage cells at distinct stages of differentiation.

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