Supplementary Material for: Molecular Characterization of Xp Chromosome Deletion in a Fertile Cow

A young cow of the Marchigiana breed (central Italy) with normal body conformation and external genitalia underwent routine cytogenetic analyses prior to its use for reproduction. After normal chromosome staining, only one X chromosome was observed with a normal diploid number (2n = 60) in all 200 studied cells. Subsequent cytogenetic analyses by using both CBA- and RBA-banding techniques evidenced that almost all the p arms of the other X chromosome was lacking. Detailed FISH-mapping analyses with BAC covering this Xp arm region demonstrated that this large chromosome region was deleted. RBA-banding showed that the deleted X was late replicating. CGH array analysis evidenced that deletion involves the Xp arm from the telomere to around 39.5 Mb, referring to the BosTau6 cattle genome assembly. This abnormality deletes about 40 Mb of the X chromosome sequence, but, despite the large number of genes deleted, none of them are programmed to escape from inactivation. This can explain the normal phenotype of the female which is actually pregnant. Finally, we evidenced, by analysis of an SNP mapped to the deleted region (SNP rs29024121), that the only normal (e.g. nondeleted) X chromosome present derives from the father. Hence, the deletion has a maternal origin.

一头来自意大利中部马尔恰诺（Marchigiana）牛品种的青年母牛，其体貌结构与外生殖器均表现正常，在投入繁殖使用前接受了常规细胞遗传学分析。常规染色体染色后，在全部200个被检测细胞中均观察到正常二倍体核型（2n = 60），且仅存在一条X染色体。后续采用CBA-显带（CBA-banding）与RBA-显带（RBA-banding）技术开展的细胞遗传学分析显示，另一条X染色体的几乎全部短臂均发生缺失。针对覆盖该Xp臂区域的细菌人工染色体（BAC）探针开展的详细荧光原位杂交（FISH）定位分析证实，该大片段染色体区域确实存在缺失。RBA-显带结果显示，发生缺失的X染色体为晚复制型。比较基因组杂交芯片（CGH array）分析结果证实，参照牛基因组组装版本BosTau6，该缺失覆盖了X染色体短臂从端粒至约39.5 Mb的区域。该染色体异常缺失了X染色体上约40 Mb的序列，尽管缺失区域包含大量基因，但所有这些基因均未出现逃逸X染色体失活的情况。这一现象可解释该怀孕雌性个体的正常表型。最后，通过对定位至该缺失区域的单核苷酸多态性（SNP）位点rs29024121进行分析，我们证实该个体仅存的正常（未发生缺失）X染色体源自父本，因此该染色体缺失的起源为母本。