One of four peptides (tal-1A, tal-2A, tal-3A and tal-AA) produced from a polycistronic gene that function redundantly in several developmental processes (PubMed:17439302, PubMed:17486114, PubMed:25344753, PubMed:21527259). Required in early stages of leg development for the intercalation of the tarsal segments during the mid-third instar stage and later for tarsal joint formation (PubMed:17439302, PubMed:18801356, PubMed:21527259). Promotes the post-translational modification of ovo isoform B (svb) into its active form which in turn initiates trichome development and promotes tarsal joint development (PubMed:21527259, PubMed:20647469, PubMed:26383956). This is likely due to recruitment of the E3 ubiquitin-protein ligase Ubr3 to svb for ubiquitination of its N-terminus, converting svb into a transcriptional activator (PubMed:26383956). Also enhances interaction of Ubr3 with Diap1 (PubMed:26383956). Required for correct wing and leg formation through its regulation of several genes including those in the Notch signaling pathway (PubMed:18801356, PubMed:21527259, PubMed:21682860). Essential for denticle formation and may have a role in the developmental timing of trichome differentiation (PubMed:17486114, PubMed:25344753). Essential for the development of taenidial folds in the trachea (PubMed:17486114). At early stages of embryogenesis, the polycistronic RNA is expressed in seven segmentally separated blastoderm stripes and in a cluster of cells in the anterior part of the embryo (PubMed:17439302). By stage 13 to the end of embryo development, it is expressed in the dorsal trunks, posterior spiracles, pharynx, hindgut and the area which forms the denticle belts (PubMed:17439302). In the leg disk, it is expressed in a ring pattern presumed to be developing tarsal region around 80 to 96 h after egg laying (AEL) and then in the tarsal furrow at the mid-third instar larval stage (PubMed:17439302, PubMed:18801356). Not detected in the tarsal primordium after 100h AEL but is still expressed in a dorsal chordotonal organ of the leg disk (PubMed:17439302). In pupae, expressed broadly throughout the leg disk 0-3 h after puparium formation (APF) but is not detected in this region 6h APF (PubMed:25344753). High expression 4-8 h APF in the presumptive joints between tarsal segments (PubMed:21682860). In the noctum expressed from 40 to 44 h APF (PubMed:25344753). In wing disks of third stage larvae, expressed in two anterior stripes and later in the precursors for chemosensory organs (PubMed:21682860). From late third stage instar larvae to early pupal stages, it is also expressed in the wing provein cells that develop into longitudinal veins L2-L5 (PubMed:21682860). In eye disks, expressed in preclusters for presumptive R8 photoreceptors and in a stripe of cells in the posterior region of the disk (PubMed:21682860). Polycistronic RNA up-regulated by ecdysone. Simultaneous knockout of tal-1A, tal-2A, tal-3A and tal-AA is embryonic lethal (PubMed:17439302, PubMed:17486114). In embryos chitin secretion and formation of the cuticular exoskeleton appears to be normal (PubMed:17439302, PubMed:17486114). However embryos display a loss of denticle belts and dorsal hairs (PubMed:17439302, PubMed:17486114). Segment-specific epidermal sensory organs are present and segments form normally (PubMed:17439302). The cephalopharyngeal skeleton is lost, and the head skeleton and posterior spiracles are deformed (PubMed:17439302). In the developing leg, tarsal constriction occurs but the tarsal fold does not form (PubMed:17439302). The tracheal system is abnormal displaying a loss of network integrity, an irregular tube diameter and the absence of taenidial folds (PubMed:17439302, PubMed:17486114). Cell packing is not affected, but there is no accumulation of F-actin at the sites of denticle differentiation or formation of F-actin bundles during taenidial development and tracheal tube dilation (stages 14 and 16) (PubMed:17486114). Other F-actin based developmental processes such as filopodia formation of tracheal tip cells, dorsal closure, mitosis or tight packing of denticle cells are unaffected (PubMed:17486114). Denticle and tracheal defects can be rescued by ectopic expression of any one of the four tal peptides (tal-1A, tal-2A, tal-3A and tal-AA) (PubMed:17486114). This protein is produced by a polycistronic gene which also produces tal-1A, tal-2A and tal-3A from non-overlapping reading frames (PubMed:17486114, PubMed:17439302). tal-1A and tal-2A produce the same protein from different reading frames (PubMed:17486114, PubMed:17439302).