Get the genpred format string representation of the mapping

    :param transcript_name:
    :param gene_name:
    :param strand:
    :type transcript_name: string
    :type gene_name: string
    :type strand: string
    :return: GPD line
    :rtype: string

def transcript_to_gpd_line(tx,transcript_name=None,gene_name=None,direction=None):
    """Get the genpred format string representation of the mapping

    :param transcript_name:
    :param gene_name:
    :param strand:
    :type transcript_name: string
    :type gene_name: string
    :type strand: string
    :return: GPD line
    :rtype: string
    """
    tname = tx._options.name
    if transcript_name: tname = transcript_name
    gname = tx._options.gene_name
    if gene_name: gname = gene_name
    dir = tx._options.direction
    if direction: dir = direction
    # check for if we just have a single name
    if not tname: tname = str(uuid.uuid4())
    if not gname:
        gname = tname
    out = ''
    out += gname + "\t"
    out += tname + "\t"
    out += tx.exons[0].chr + "\t"
    out += dir + "\t"
    out += str(tx.exons[0].start-1) + "\t"
    out += str(tx.exons[-1].end) + "\t"
    out += str(tx.exons[0].start-1) + "\t"
    out += str(tx.exons[-1].end) + "\t"
    out += str(len(tx.exons)) + "\t"
    out += str(','.join([str(x.start-1) for x in tx.exons]))+','+"\t"
    out += str(','.join([str(x.end) for x in tx.exons]))+','
    return out