Passamaneck Yale J, Hejnol Andreas, Martindale Mark Q
Kewalo Marine Laboratory, PBRC, University of Hawaii, 41 Ahui Street, Honolulu, HI 96813 USA ; The Whitney Laboratory for Marine Bioscience, University of Florida, St. Augustine, FL 32080 USA.
Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate, 55, 5008 Bergen, Norway.
Evodevo. 2015 Apr 11;6:10. doi: 10.1186/s13227-015-0004-8. eCollection 2015.
Brachiopods undergo radial cleavage, which is distinct from the stereotyped development of closely related spiralian taxa. The mesoderm has been inferred to derive from the archenteron walls following gastrulation, and the primary mesoderm derivative in the larva is a complex musculature. To investigate the specification and differentiation of the mesoderm in the articulate brachiopod Terebratalia transversa, we have identified orthologs of genes involved in mesoderm development in other taxa and investigated their spatial and temporal expression during the embryonic and larval development of T. transversa.
Orthologs of 17 developmental regulatory genes with roles in the development of the mesoderm in other bilaterian animals were found to be expressed in the developing mesoderm of T. transversa. Five genes, Tt.twist, Tt.GATA456, Tt.dachshund, Tt.mPrx, and Tt.NK1, were found to have expression throughout the archenteron wall at the radial gastrula stage, shortly after the initiation of gastrulation. Three additional genes, Tt.Pax1/9, Tt.MyoD, and Tt.Six1/2, showed expression at this stage in only a portion of the archenteron wall. Tt.eya, Tt.FoxC, Tt.FoxF, Tt.Mox, Tt.paraxis, Tt.Limpet, and Tt.Mef2 all showed initial mesodermal expression during later gastrula or early larval stages. At the late larval stage, Tt.dachshund, Tt.Limpet, and Tt.Mef2 showed expression in nearly all mesoderm cells, while all other genes were localized to specific regions of the mesoderm. Tt.FoxD and Tt.noggin both showed expression in the ventral mesoderm at the larval stages, with gastrula expression patterns in the archenteron roof and blastopore lip, respectively.
Expression analyses support conserved roles for developmental regulators in the specification and differentiation of the mesoderm during the development of T. transversa. Expression of multiple mesodermal factors in the archenteron wall during gastrulation supports previous morphological observations that this region gives rise to larval mesoderm. Localized expression domains during gastrulation and larval development evidence early regionalization of the mesoderm and provide a basis for hypotheses regarding the molecular regulation underlying the complex system of musculature observed in the larva.
腕足动物进行辐射卵裂，这与亲缘关系较近的螺旋类群的模式化发育不同。中胚层被推断在原肠胚形成后源自原肠壁，幼虫中的初级中胚层衍生物是一个复杂的肌肉组织。为了研究有铰腕足动物横裂贝中胚层的特化和分化，我们鉴定了其他类群中参与中胚层发育的基因的直系同源基因，并研究了它们在横裂贝胚胎和幼虫发育过程中的时空表达。
发现17个在其他两侧对称动物中参与中胚层发育的发育调控基因的直系同源基因在横裂贝发育中的中胚层中表达。五个基因，即Tt.twist、Tt.GATA456、Tt.dachshund、Tt.mPrx和Tt.NK1，在原肠胚形成开始后不久的辐射状原肠胚阶段，在整个原肠壁中都有表达。另外三个基因，Tt.Pax1/9、Tt.MyoD和Tt.Six1/2，在这个阶段仅在原肠壁的一部分中有表达。Tt.eya、Tt.FoxC、Tt.FoxF、Tt.Mox、Tt.paraxis、Tt.Limpet和Tt.Mef2在原肠胚后期或幼虫早期阶段都显示出最初的中胚层表达。在幼虫后期阶段，Tt.dachshund、Tt.Limpet和Tt.Mef2在几乎所有中胚层细胞中都有表达，而所有其他基因都定位于中胚层的特定区域。Tt.FoxD和Tt.noggin在幼虫阶段都在腹侧中胚层中有表达，原肠胚期分别在原肠顶和胚孔唇中有表达模式。
表达分析支持发育调控因子在横裂贝发育过程中中胚层特化和分化中发挥保守作用。原肠胚形成期间多个中胚层因子在原肠壁中的表达支持了之前的形态学观察结果，即该区域产生幼虫中胚层。原肠胚形成和幼虫发育期间的局部表达域证明了中胚层的早期区域化，并为关于幼虫中观察到的复杂肌肉系统的分子调控的假设提供了基础。
