Gene Networks Database

Strongylocentrotus purpuratus Genes in Development: Cell type specific genes; Actins

Cytoskeletal actin IIIa


CyIIIa codes for cytoskeletal actin. Actin represents one of the most abundunt and best characterized structural components in eucaryotic cells, involved in a wide variety of cytoskeletal, locomotive, and tension-generating functions. Five functional cytoskeletal actin genes are organized in two linkage groups within the genome: CyI-CyIIa-CyIIb and CyIIIa-CyIIIb.
CyIIIa serves as a marker of the earliest known lineage-specific gene expression (Davidson, 1989).


Cytoskeletal actin

Subcellular location


Expression Pattern

Developmental studies of actin mRNA prevalence have been caried out using several sensitive methods including in situ hybridization (Cox et al., 1986), molecular titration with single-strand RNA probes (Lee et al., 1986), RNA gel blot hybridization, and cDNA analysis (Shott et al., 1984; Crain et al., 1981; Garcia et al., 1984).
All of the S. purpuratus cytoskeletal actin genes are activated at 8-9 hr of development, a time when 64-128 cell embryos are predominant in large cultures.
CyIIIa message accumulation is transcriptionally regulated (Lee et al., 1992). The egg and early cleavage embryo contain a relatively small amount of CyIIIa maternal RNA, 1-2 % of the ultimate level of accumulation of each message. The accumulation of the transcripts of zygotic origin of CyIIIa is first observed at 10 hr post fertilization (Lee et al., 1992). For the short period (9-15 hr) following activation CyIIIa is transcribed at dramatically higher rate than observed in late embryo.
At the earliest stages at which CyIIIa expression can be detected , the newly synthesized transcripts are confined to the cells of the prospective aboral ectoderm (Cox et al., 1986; Hardin et al., 1988). Activation of the CyIIIa gene probably occurs in these cells at the 7th-8th cleavage, i.e. only one or two cleavage divisions past the last divisions required for clonal segregation of all of the aboral ectoderm founder cells (Davidson, 1989).

mRNA level

Temporal accumulation

Method 1: in vivo labeling
Reference: Lee et al., 1992
Method 2: molecular titration
Reference: Lee et al., 1986

Developmental time interval (hr) 8-20 20-36 36-65
Average number of cells expressing CyIIIa gene 120 225 315
Amount of actin mRNA as measured by 1 (transcripts/embryo) 6,0 x 10^3 1,5 x 10^4 4,0 x 10^4
Amount of actin mRNA as measured by 2 (transcripts/embryo) 8,5 x 10^4 (-2,8 x 10^4)^* 3,0 x 10^4
^* The minus sign indicates that during this time interval the steady-state prevalence level of CyIIIa transcripts has decreased.

Spatial localization

Method: in situ hybridization
Reference: Cox et al., 1986

Stage 20 hr late gastrula pluteus
Tissue Aboral ectoderm Aboral ectoderm Aboral ectoderm



Regulatory Regions

CyIIIa actin gene regulatory domain.

Regulatory Connections

Upstream Genes



Downstream Genes

Evolutionary Homologues


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Comments are welcome to Kate G. Savostyanova
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