def collapse_annotations(column):
    """
    Collapse gene annotations among transcripts to a single string.
    
    Parameters
    ----------
    column : pd.Series
        Annotation column from gene annotation dataframe. 
    
    Returns
    -------
    str
        String with unique annotations separated by ';'.
    """

    values = column[~column.isna()]
    if len(values) > 0:
        return ';'.join(values.astype(str).unique())
    return None