Expression of Sox family genes in early lamprey development

Abstract

Members of the Sox (Sry-related high mobility group box) family of transcription factors play a variety of roles during development of both vertebrates and invertebrates. A marked expansion in gene number occurred during the emergence of vertebrates, apparently via gene duplication events that are thought to have facilitated new functions. By screening a macroarrayed library as well as the lamprey genome, we have isolated genes of the Sox B, D, E and F subfamilies in the basal jawless vertebrate, lamprey. The expression patterns of all identified Sox genes were examined from gastrulation through early organogenesis (embryonic day 4-14), with particular emphasis on the neural crest, a vertebrate innovation. Coupled with phylogenetic analysis of these Sox genes, the results provide insight into gene duplication and di-vergence in paralog deployment occurring during early vertebrate evolution.

Figure 1. Phylogenetic Analysis of lamprey Sox genes

Unrooted phylogenetic tree of Sox genes obtained from a neighbor joining analysis performed on ClustalX. The HMG box protein sequences were used in the construction of the tree. Boxes highlight the families of Sox genes. Abbreviations are Dr, Danio rerio; Gg, Gallus gallus; Mm, Mus musculus; Pm, Petromyzon marinus; Xl, Xenopus laevis.

Figure 2. Expression pattern of SoxB genes

The SoxB genes are expressed within the neural plate, neural tube and branchial arches. SoxB1a, 4–14 days (A): SoxB1a is not expressed in pre-migratory neural crest at E5, with expression initiating at E6 at the onset of neural crest emigration. SoxB1b: 4–14 day (B) SoxB1b is not expressed at E5 or E6 in pre-migratory neural crest. SoxB2; 4–14 day, (C) and sections (D–H) from 6.5 day, 8 day, 10 day, and 14 day, is expressed throughout the neural tube at E5 and E6. Sections reveal SoxB2’s presence at later stages in the neural tube, cranial ganglia, and ectoderm derived portions of the branchial arches. NP: neural plate, PNC: Pre-migratory neural crest, NT: neural tube, BA: branchial arch

Figure 3. SoxD Expression

SoxD is expressed from 4 – 16 day (A–H), sections (B′–H′) beginning on the boarder of the neural plate (A) and progressing to various neural crest derivatives, optic vesicle (D & D′), branchial arches (E, E′ & E″), and branchial arch cartilage (F–H & F″–H′). Beginning E8 (D) SoxD is expressed in forming branchial arch progenitors, optic vesicle and mandibular arch. From E10–E16 (E–H), expression in the forebrain and heart are down decreased over time while expression of SoxD is consistent with branchial arch cartilage condensation. Np: neural plate, Op: optic vesicle, BA: branchial arch. MA: mandibular arch

Figure 4. SoxE Expression

The SoxE family show low level of early expression with SoxE1 and E2 expression in the neural plate at E4 (A & H). SoxE1 (A–G) begins showing expression in the pre-migratory neural crest (C & C′) then cranial ganglia (D, D′, E, E′, & E″), dorsal root ganglia (F & F′), and the branchial cartilage at late stages (G & G′). SoxE2(H–N) is also expressed heavily in the premigratory neural crest (I & I′) and ultimately in the optic (K, K′, L, L′ and N′), otic vesicles (M&M′), and branchial arches (N–N‴). SoxE3(O–U) is expressed early in the otic vesicle (Q & Q′). It is later expressed heavily in the otic vesicle (S & S′), other crancial ganglia (S–U), neural tube, branchial arches (S–U). Op: optic vesicle, Ot: otic vesicle, BA: branchial arch

Figure 5. SoxF Expression

SoxF is expressed early within the blastopore [(A & B) ventral view; E4.5] and the neural plate (C dorsal view). Beginning from E7 to E14, SoxF is expressed surrounding the notochord and in precursors to the thyroid, heart, and branchial arches (E–M). Beginning at E7, SoxF begins to express in the forming thyroid (L). Ventral view of E8.5 displaying the forming thyroid (G). In addition, SoxF is temporarily expressed in the first and second branchial arch at E14 and 16 (J and K). Bp: blastopore, NP: neural plate Th: thryroid precursors BA: Branchial Arch