Department of Genetics, Blavatnik Institute at Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA, 02115, USA.
Department of Biology, University of Nevada, Reno, 1664 N. Virginia St., Reno, NV, 89557, USA.
BMC Ecol Evol. 2023 Aug 25;23(1):41. doi: 10.1186/s12862-023-02149-3.
The Mexican tetra, Astyanax mexicanus, includes interfertile surface-dwelling and cave-dwelling morphs, enabling powerful studies aimed at uncovering genes involved in the evolution of cave-associated traits. Compared to surface fish, cavefish harbor several extreme traits within their skull, such as a protruding lower jaw, a wider gape, and an increase in tooth number. These features are highly variable between individual cavefish and even across different cavefish populations.
To investigate these traits, we created a novel feeding behavior assay wherein bite impressions could be obtained. We determined that fish with an underbite leave larger bite impressions with an increase in the number of tooth marks. Capitalizing on the ability to produce hybrids from surface and cavefish crosses, we investigated genes underlying these segregating orofacial traits by performing Quantitative Trait Loci (QTL) analysis with F hybrids. We discovered significant QTL for bite (underbite vs. overbite) that mapped to a single region of the Astyanax genome. Within this genomic region, multiple genes exhibit coding region mutations, some with known roles in bone development. Further, we determined that there is evidence that this genomic region is under natural selection.
This work highlights cavefish as a valuable genetic model for orofacial patterning and will provide insight into the genetic regulators of jaw and tooth development.
墨西哥脂鲤（Astyanax mexicanus）包括可杂交的水面栖居和洞穴栖居形态，这使其成为强大的研究工具，能够揭示与洞穴相关特征进化相关的基因。与水面鱼类相比，洞穴鱼类的头骨中存在几种极端特征，例如下颌突出、口裂更宽、牙齿数量增加。这些特征在个体洞穴鱼之间甚至在不同的洞穴鱼种群之间都高度可变。
为了研究这些特征，我们创建了一种新的摄食行为检测方法，可以获得咬痕。我们发现，下颏后缩的鱼在牙齿印记的数量增加时会留下更大的咬痕。利用从水面鱼和洞穴鱼杂交产生杂种的能力，我们通过对 F1 杂种进行数量性状基因座（QTL）分析，研究了这些分离的口面特征的相关基因。我们发现了显著的与咬（下颏后缩与上颏前突）相关的 QTL，其映射到 Astyanax 基因组的一个单一区域。在这个基因组区域内，多个基因存在编码区突变，其中一些与骨骼发育有关。此外，我们确定有证据表明该基因组区域受到自然选择的影响。
这项工作强调了洞穴鱼作为口面模式形成的有价值的遗传模型，并将为颌骨和牙齿发育的遗传调控因子提供深入了解。
